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AECL-6787
ATOMIC ENERGY WSFSi L'ENERGIE ATOMIQUEOF CANADA LIMITED Y ^ ^ S j P DU CANADA LIMITEE
THE BEHAVIOUR OF DEFECTED ZIRCALOY-CLAD UO2
FUEL ELEMENTS WITH GRAPHITE COATINGS BETWEENFUEL AND SHEATH IRRADIATED AT LINEAR POWERS OF
48 kW/m IN PRESSURIZED WATER
Comportement d'6l6ments combustibles en UO2
gaine de Zircaloy rendus defectueux, comportant un revetement degraphite entre le combustible et la gaine, a des puissance
lineiques de 48 kW/m dans I'eau pressurised
R.D. MacDONALD and J.J. LiPSETT
Chalk River Nuclear Laboratories Laboratoires nucle'aires de Chalk River
Chalk River, Ontario
May 1980 mai
ATOMIC ENERGY OF CANADA LIMITED
THE BEHAVIOUR OF DEFECTED ZIRCALOY-CLAD UO2 FUEL ELEMENTS
WITH GRAPHITE COATINGS BETWEEN FUEL AND SHEATH
IRRADIATED AT LINEAR POWERS OF 48 kW/m IN PRESSURIZED WATER
by
R.D. MacDonald and J.J. Lipsett
Fuel Engineering BranchChalk River Nuclear Laboratories
Chalk River, Ontario KOJ 1J0
1980 May
AECL-6787
L'ENERGIE ATOMIQUE DU CANADA, LIMITEE
Comportement d'éléments combustibles en UO? gainé de Zircaloy rendus défectueux,
comportant un revêtement de graphite entre le combustible et la gaine,
â des puissance linéiques de 48 kW/m dans l'eau pressurisée
par
R.D. MacDonald et J.J. Lipsett
Trois éléments combustibles en UO2 gainé de Zircaloy rendusintentionellement défectueux, ont été irradiés séparément dans une boucle d'eaupressurisée à une puissance linéique de 48 kW/m pendant des périodes allantjusqu'à 850 heures. La libération, de façon constante ou transitoire, desproduits de fission gazeux dans le caloporteur de la boucle a été mesurée avecun spectromètre à rayons gamma in situ. Au cours de l'irradiation chaqueélément a perdu de l'UC^ de la pastille se trouvant sous le trou constituantle défaut de la gaine; cette perte d'UO2 a été attribuée à l'oxydation deslimites de granulation. La libération fractionnelle de façon constante desproduits de fission variait de 1.4 x 10" L pour les xénons à longue vie à 3.5x 10~5 pour Xe-138 â courte vie, ce qui signifiait un retard entre lanaissance et la libération soit dans l'U02 soit dans l'intervalle entre lecombustible et la gaine. La libération des produits de fission lors destransitoires de puissance du réacteur a été jusqu'à quatre fois plus élevée quecelle survenue de façon constante. Les valeurs de libération calculées par deuxmodèles différents ont été en assez bon accord avec les résultats expérimentaux.
Département de l'ingénierie du combustibleLaboratoires nucléaires de Chalk River
Chalk River, Ontario KOJ 1J0
Mai 1980
AECL-6787
ATOMIC ENERGY OF CANADA T.IMITED
THE BEHAVIOUR OF DEFECTED ZIRCALOY-CLAD UO2 FUEL ELEMENTS
WITH GRAPHITE COATINGS BETWEEN FUEL AND SHEATH
IRRADIATED AT LINEAR POWERS OF 48 kW/m IN PRESSURIZED WATER
by
R.D. MacDonald and J.J. Lipsett
ABSTRACT
Three purposely defected Zircaloy-clad UO2 fuel ele-ments were irradiated separately in a pressurized water loopat linear powers of 48 kW/m for times up to 850 hoars. Thesteady state and transient release of gaseous fission productsto the loop coolant were measured with an on-line Y~r^y spec-trometer. During irradiation each element lost UO2 from thepellet under the defect hole in the sheath; this loss of UO2was attributed to grain boundary oxidation. The fractionalsteady state release of fission products ranged from 1.4 x10-1 for the longer-lived xenons to 3.5 x 10"5 for the shorter-lived Xe-138, indicating a delay between birth and release,either in the UO2 or in the fuel-to-sheath gap. Release offission products on rsactor power transients were up to fourtimes higher than the steady state release. Release valuescalculated by two different models were in reasonable agreementwith experimental results.
Fuel Engineering BranchChalk River Nuclear LaboratoriesChalk River, Ontario KOJ 1JO
1980 May
AECL-6787
THE BEHAVIOUR OF DEFECTED ZIRCALOY-CLAD UO2 FUEL ELEMENTS
WITH GRAPHITE COATINGS BETWEEN FUEL AND SHEATH
IRRADIATED AT LINEAR POWERS OF 48 kW/m IN PRESSURIZED WATER
by
R.D. MacDonald and J.J. Lipsett
A. INTRODUCTION
Activity released into the reactor coolant fromdefected fuel elements can reduce the availability of powerreactors by increasing the length of maintenance periods.Occasionally activity release can exceed licensing thresholds.The quantity of fission products released during steady stateoperation of defected fuel is generally dependent on elementpower and hole size. However, during reactor power transientsthe release of fission products from a defected element maybe several orders of magnitude higher than that at steady state.
This report describes three defect tests (Phases I,II and III of the FDO-681 experiment) designed to study thedefect performance of fuel elements irradiated at linear heatoutput of about 48 kW/m. Concentrations of fission productsin the coolant was measured continuously with an on-lineY-ray spectrometer to investigate both steady state and trans-ient activity release.
B. THE FUEL ELEMENTS
All three of the defected elements were clad withZircaloy-4 sheaths and fuelled with sintered U02 pellets. Pelletand element details and dimensions are listed in Tables 1 and 2.Element identifications and their associated irradiation phaseare:
DEFECTED ELEMENT IRRADIATED IN
RPL
LFZ
RPP
Phase I
Phase II
Phase III
of the FDO-68100experiment
Elements RPL and LFZ had a 0.0075 mm thick CANLUB graphitelayer on the inside surface of their sheaths, while elementKPP had a less dense graphite layer (FURRY graphite) approxi-mately 0.03 mm thick deposited on the circumferential surfacesof the UO2 pellets. The sheaths of the three elements wereeach defected by a small hole drilled at about the mid-pointof the fuel stack. The sizes of the holes and their locationsare given in Table 3. A second hole close to the first wasinadvertently drilled through the sheath of element RPP.
Elements RPL and RPP were irradiated intact for tworeactor cycles in test X-286 previous to the FDO-681 experiment.During the first of these cycles both elements operated at alinear heat output of 60 kW/m to a burnup of 50 MW.h/kg U.During the second cycle the maximum linear heat output was closeto 70 kW/m with a total accumulated burnup for each element of140 MW.h/kg U. Element LFZ was fabricated from fresh UO2 pelletsespecially for the FDO-681 experiment. For irradiation, adefected element was assembled into a trefoil carriage with twosimilar but intact fuel elements. These intact elements pro-vided additional heat to improve the accuracy of the loop cool-ant calorimetry (see Section E).
C. LOOP AND SPECTROMETER FACILITY
All phases of the FDO-681 experiment were irradiatedin the X-2 pressurized water loop of the NRX research reactor.A schematic diagram of this loop is shown in Figure 1. Averagevalues of the loop coolant parameters for the three defecttests are:
Phases I II III
coolant: light water
coolant inlet temperature (K)
coolant inlet pressure (MPa)
coolant flow (kg/s)
coolant pH 9.8 to 10.3 maintained with LiOH
coolant hydrogen 8200 to 30,000 mm3/kg
coolant volume 0.074 m3
coolant recirculation , n. c ,. . 104.5 secondstime
The yray spectrometer was positioned over the looppiping at the outlet from the in-reactor test section. With acoolant flow of 0.62 kg/s, fission products released from the
510
7.55
0.620
510
7.65
0.635
510
7.66
0.620
fuel element passed the spectrometer about 23 seconds later.The detector was fabricated from high-purity germanium andwas 5.0 mm thick with a diameter of 18.5 mm. The spectrometerwas mounted on a movable platform where it could view the looppiping through four separate holes in a concrete slab. Eachhole through the concrete was equipped with a collimator; seeFigure 2. The first of these positions looked at a section ofpiping that contained coolant only and was used to measure theconcentrations of fission products dissolved in the loop water(the GFP position). The next three positions looked at pipingsections each containing a trap of a different material whichwere used to study depositing fission products (the DFP posi-tions). A fifth position, a blind hole in the concrete slab,contained a thorium source used for the spectrum energy cali-bration. A control circuit regulated the time, the frequencyand the sequence of the spectrometer scans for each of the fivepositions.
The mathematical model used to calculate the rate offission product release from the element based on fission productconcentrations in the loop coolant is described in Appendix 1.
E. THE IRRADIATION HISTORY
The times and dates of irradiation, the number and typeof power transients, periods of coolant purification (using ionexchange columns) and degassing, are given in Table 4 for thethree Phases of the FDO-681 experiment. The element power his-tories of the three defected elements are shown in Figure 3.Average values of element power output, surface heat fluxes andaccumulated burnups are listed in Table 5. All element powerdata have been derived from calorimetric measurements of theloop coolant and are believed to be accurate to ±7.0%
F. POST-IRRADIATION EXAMINATIONS OF THE DEFECTEDFUEL ELEMENTS
F.I Visual Inspection and Neutron Radiography
Neutron radiographs of the elements before they weredestructively examined are shown in Figure 4. Although theelements were vacuum dried before being radiographed, somemoisture still remained inside their sheaths. Pellet enddishes and the axial gap between the end plug and the top ofthe fuel stack of element RPL were mostly filled by expandingfuel; all the UO2 pellets were extensively cracked. Some
infilling of dishes and pellet cracking were observed in ele-ment RPP but the extent was less than in RPL. Very little fuelcracking had occurred in element LFZ. Small amounts of U02had disappeared from pellets immediately under the defect holesof all three elements.
Visual inspection of the three defected elements re-vealed white banded stains or deposits on the surfaces of thesheaths starting at the defect holes and spreading to the topend plugs (i.e., in the direction of coolant flow); see Figure 5.These stains may be caused by fission products depositing onthe sheaths while the banding may be either a segregation ofdifferent fission products or a change in deposit thickness.We could not identify the fission products responsible for thestains because the elements were contaminated with fuel debrisin the hot cells. The stains could be removed by wiping thesurfaces of the elements with a damp cloth.
The appearance of the defect holes themselves were un-changed from before the FDO-681 irradiations. The exceptionwas the second hole in element RPP. Before the defect testthe bottom of this hole was mostly covered by a thin layer ofZircaloy; after the irradiation part of this layer had disap-peared exposing the UO2 pellets underneath. Small amounts of ayellow material similar to popcorn were observed on the U02underneath the defect holes; this material may be a uraniumoxide with a composition close to U3O8.
F.2 Dimensional Changes of the FDO-681 Fuel Elements
The diameters and lengths of elements RPL and RPPmeasured after the defect tests had not changed significantlyfrom values measured after completion of the X-286 irradiation.The 0.52% diametral strain of RPL was consistent with a fuelelement operating at a Ad© between 4.5 and 5.5 kW/m (the X-286rating) (1) . The almost negligible sheath strain measured atmid-pellet positions on element RPP is unusual for an elementirradiated at a A d G in excess of 4.5 kW/m during the X-286test. This low strain and the corresponding small circumfer-ential ridges were attributed to the larger diametral clearancefor fuel expansion provided by the crushable FURRY graphitecoating. The 0.23% diametral strain for the fresh element LFZwas similar to strains measured in-reactor on identical intactelements irradiated at f\&6 values of 3.5 to 4.0 kW/m (1).The absence of any substantial increase in the diameters ofelements RPL and RPP and the agreement of the LFZ strain withprevious experience, indicate that no waterlogging damageoccurred during the FDO-681 experiment. The relatively large
drilled defect holes have prevented any large pressure buildupfrom taking place in the fuel-to-sheath gap during rapid reactorstartups.
F.3 Metallography of the Fuel and Sheaths(A summary is included at the end of this section)
F.3.a The_Fuel:
Polished cross sections of all three defected elementsshowed both columnar and eguiaxed grain growth in the U02; seeFigures 6, 7, 8 and 9. The columnar grains in elements RPL andRPP were longer and better defined than those in element LFZ.A ring of small pores were found near the outer edge of thecolumnar grains in elements RPL. Measurements of the ratio ofgrain growth diameter to pellet diameter (r/a) are given forall elements in Table 6. Although elements RPL and RPP experi-enced linear heat outputs above 60 kW/m during their X-286irradiation the average r/a for all three of the defected ele-ments were similar. An increase in the O/U ratio of the fuelwith its consequent effect on the thermal conductivity and graingrowth characteristics of the UO2 (3) may have acted to equalizethe radii of grain growth between elements. However, othertemperature-sensitive phenomena such as pellet cracking, infil-ling of pellet end dishes and grain morphology suggest thatelement RPL operated at the highest temperature followed byRPP then LFZ. Oxidation of the fuel or localized cooling mayhave been responsible for the distortion of the grain growtharea in element LFZ, Figure 7.
In all three elements some of the UO2 under the defectholes had disappeared. The amount of UO2 eaten away was relatedto the time in the defected condition and to the size of thedefect hole. Element RPP which had the longest defect irradi-ation lost more UO2 than LFZ which in turn lost more fuel thanRPL, the element with the shortest defect irradiation. Theamount of U02 which had disappeared from under the larger holein element RPP was estimated at 0.17 grams corresponding to aloss rate of 0.005 grams of UO2 per day of irradiation. Verylittle UO2 was lost from under the second hole in RPP (Figure 9)possibly because this hole was smaller or because the hole onlyopened up part way through the irradiation. The loss of fuelfrom the pellet was probably gradual with the individual grainsbeing loosened by grain boundary oxidation; see the structureshown in Figure 10. However, as steam could not have easilytransported these particles out of the defect hole most of theUO2 may have come out of the element with the water on reactorstartups.
Adhering to the U0 2 surface under the defect holes wasan unidentified phase transparent to polarized light and con-taining dendritic grains (Figure 11). g -y autoradiographs ofthe pellets indicated that the phase was highly active; seeFigures 6, 7 and 8. This material was not found under thesmaller defect hole in element RPP (Figure 9) again suggestingthat this hole did not open up completely until well on in theirradiation. Samples of the phase were analysed and found toconsist almost entirely of fission products. By far the mostabundant constituent was cesium with smaller amounts of Rh, Ru,Tc, Ce, Zr, Nb and Te present (4). Surprisingly, molybdenum,a common solid fission product found in high burnup U02 was notidentified in the phase. Fission product migration from hot tocooler regions of the U02 pellets or a deposition of the fissionproducts from a saturated coolant solution may have been respons-ible for the formation of this phase.
The U02 adjacent to this fission-product-rich phase hadanother unidentified phase both in the grain boundaries andwithin grains (Figure 10). The same phase was also found alongcracks near the periphery of pellets. Figure 12. This phase isprobably a higher oxide of uranium than UO2 although its exactcomposition is in doubt. A second oxygen-rich phase, similarin appearance to that identified by Schaner as V^0g (5), wasobserved in one or two concentric bands near the periphery ofthe pellet and just inside the limit of equiaxed grain growthin elements RPL and RPP, see Figure 13. Observation of bandingof phases in hyperstoichiometric U02 is not new; elements withUO2.2B5 irradiated at CRNL have exhibited as many as three con-centric rings in pellets on post-irradiation examination (6).The bands or rings in RPL and RPP may be either two separatephases of U02.+x (although metallographically they seemed similar)segregating at two different radii or the same phase reflectingtwo irradiation histories (i.e., a maximum and average temp-erature in the fuel)•
This same phase, tentatively identified as U^C^, wasfound uniformly distributed within the grain growth region ofelement LFZ. Why this oxygen-rich phase did not band in thefresh element LFZ is unknown.
F. 3.b T]}e_§l}eath_and_Interface:
Neither the graphite CANLUB nor the FURRY graphite couldbe found in the fuel-to-sheath gaps after the defect irradiations.Both coatings had disappeared from the entire length of the fuelstacks probably because of oxidation of the graphite by steamor high temperature water to form CO and CO 2.
Continuous zirconium oxide films covered both theinside and outside surfaces of the Zircaloy sheaths; ZrO2film thicknesses are given for all three elements in Table 6.Generally the ZrO 2 films on element LFZ were thinner and moreirregular reflecting its shorter total time in reactor. ZrO2film thicknesses on the outside surface of the sheaths were ofuniform thickness up to 2 ym compared to the inside where filmthickness varied widely from 4 to 80 \im. The maximum ZrO2thicknesses on the inside surfaces occurred remote from thedrilled defect holes.
Larger concentrations of zirconium hydride wereobserved in the sheaths adjacent to the defect holes than ateither end of the elements; see Figures 14 and 15. In elementLFZ many of the hydride platelets were found aligned circum-ferentially on the edges of the drilled hole. Although theZrO2 film on the inside surface of the sheath may act as abarrier to hydrogen pickup by the Zircaloy as suggested byLocke (7) the higher hydride concentrations near the defectsare more likely caused by the larger amounts of hydrogenpresent in the fuel-to-sheath gap at this location. Carefulinspection of the sheaths failed to find any concentrationsof solid zirconium hydride (blisters) that are usually associ-ated with the start of severe sheath deterioration.
F.3.c §ummary_of_the_Most_Significant_MetallO2raphic
1. Oxidation of the UO2 pellets had occurred in all threeelements. A phase tentatively identified as U^Og wasfound in concentric bands just inside and outside theequiaxed grain growth limit in elements RPL and RPPwhile the same phase was found evenly distributed withinthe grain growth area of the fresh element LFZ.
2. UO2 had disappeared from the pellets immediately underthe defect holes; the amount of missing UO2 was diroctlyrelated to time in reactor and to the size of the defecthole. The UO2 appeared to be removed by grain boundaryoxidation•
3. A Y-B active phase was found in the portion of the U02pellet immediately under the defect. The phase con-sisted mostly of cesium along with other solid fissionproducts, but no molybdenum.
4. Both the CANLUB and FURRY graphite interlayers had com-pletely disappeared after the elements were irradiatedin a defected condition.
5. ZrO2 layers were found on the sheath inside and out-side surfaces. No large concentrations of zirconiumhydride were observed in any sheath.
6. The second defect hole in element RPP had enlargedduring the irradiation.
F.4 Sheath Deterioration
The three FDO-681 elements have been plotted on Locke'sgraph (7) of days to failure after defection vs. the elementsurface heat flux; see Figure 16. The points representingelements RPL, RPP and LFZ (based on the total irradiation timein the defected condition) are located well within the regionof safe defect operation. This is confirmed by the lack ofsevere sheath cracking or secondary hydriding in any of thethree elements. However, naturally occurring defective ele-ments have exhibited large holes in the sheaths associated withmany hydride blisters when irradiated at similar surface heatfluxes and for similar times (8). The absence of hydrideblisters in the sheaths of the deliberately defected elementmay have been due to the comparatively large holes which allowedan excess of coolant to enter the element and prevented theoptimum 0:H ratio for hydriding. (Naturally occurring defectsusually start as very small holes.) The thick ZrO2 layer onthe inside surfaces of our sheaths may also have preventedhydrogen pickup. This discrepancy between the FDO-681 elementsand naturally occurring defects suggests that future testsshould investigate the effect on sheath deterioration of failuresthat more closely resemble real defects; i.e., very small holesin the sheath (about 1 to 5 micrometres) and defects that occuron-power.
G. FISSION PRODUCT RELEASE: RESULTS AND DISCUSSION
During the experiment the radioisotopes in the loopcoolant were monitored by the high resolution germanium gamma-ray spectrometry described in Section C. For normal reactoroperation the spectrometer was situated over the GFP positioncollecting spectra every 2000 seconds. At 10-hour intervalsthe DFP pipe sections and the standard source were automaticallyscanned to determine the coolant and surface concentrations ofY-ray emitting depositing fission products. Because releaserates are strongly affected by fuel power transients, and thesechanges are known to be rapid, the spectrum accumulation timewas manually shortened to 200 seconds when reactor transientssuch as shutdowns and startups took place. This report con-siders only the dissolved or gaseous fission products (GFP)
in the coolant; the depositing fission products (DFP) will bedealt with separately in another report.
To aid in the analyses of the experiment the gaseousfission products were divided into three groups:
GROUP 1 - The radioiodines: 1-131, 1-133, 1-134 and 1-135.
GROUP 2 - Isotopes with no long-lived precursors: KR-85m,Kr-87, Kr-88 and Xe-138.
GROUP 3 - Isotopes which are daughters of long-lived iodines:Xr-133, Xe-133m and Xe-135.
The coolant concentrations (curies/cm3)* and releaserates (atoms/s) of the individual fission products were calcu-lated from the fission product spectra and plotted on a commontime base by the computer program SUMRT. (For a description ofthe computational methods and loop coolant models see Appendix1.) A typical SUMRT graphic display for the fission productKr-88 during phase III of the FDO-681 test is shown in Figure17. Included in this figure is a time plot of the reactor powerwhich illustrates the behaviour of fission product concentrationand release rate during normal and transient reactor operation.Because of the obvious differences we have elected to treattransient release behaviour separately from the release duringnormal or steady state reactor operation.
G.I Normal Steady State Release of Fission Productsinto the Coolant
During the experiment, within a day of any major powertransients, the release rates tended towards a stable or normalcondition presumably because the internal conditions of thefuel had reached equilibrium. However, during this normal con-dition the release rates of most fission products exhibited acyclic behaviour about some average value; see Figures 17 and18. This behaviour was most pronounced for the Group 2 fissionproducts (i.e., the kryptons and Xe-138); was evident for theGroup 3 fission products (the xenons) but was not distinguish-able from the data scatter ,for the radioiodines. The period-icity of the cycles varied from 8 to 12 hours and the amplitudeseemed to increase during the latter stages of each irradiation.Also, the release rates of Groups2 and 3 fission products seemedto be in phase (Figure 18).
Correlation of this cyclic behaviour with reactor power,fuel power, moderator height and loop coolant pressure was un-successful. Because release rates were computed from the meas-ured concentrations, several tests were made of the computational
*1 curie = 3 7 GBq
10
methods to ensure that the variations were not being artific-ially generated. Since both approaches were negative we con-cluded that the cyclic behaviour of release rate was real.We can only speculate on the excitation mechanism: Possiblythe pressure within the fuel-to-sheath gap was continuallychanging because the coolant radiolysis products, oxygen andhydrogen, were reacting with the sheath and fuel. Alternately,pockets of fission gases may be building up and then releasedfrom enclosed spaces within the fuel-to-sheath interface.
Because we are unable to account for the fine structureof our experimental results, further analyses of the data usethe average value about which the cyclic release behaviouroccurred, herein defined as the steady state conditions forfission gas release from the defected fuel.
The steady state release of fission products into thecoolant during periods of constant reactor power was obtainedfor a number of time intervals during the FDO-681 irradiations.The criteria for choosing the data sample were:
a) a steady reactor power of 30 MW, and
b) a period remote from transients such as reactorshutdowns, startups and power reductions.
A minimum of eight spectra (representing a period of5 to 6 hours) were taken as the data sample and fission productrelease rates obtained from SUMRT were averaged over this timeinterval. Average fission rates in the fuel for the same timeperiods were derived from the calorimetric heat output of thedefected element. The systematic error on the release ratesthus calculated is about ±20%.
In determining the fission gas release from UO2 fuelit is common practice to use the_ratio of the release rate RRto the production or birth rate BR of the various isotopes.This is the parameter R/B used by many investigators. In thisreport we have defined RR as the average_release rate of fissionproducts to the coolant in atoms/s and BR as the average fissionrate in the fuel (fission/s) times th^ yield of the individualfission product in atoms/fission. If the release rate is di-rectly proportional_to_the quantity (Q) of the fission productin the fuel, then RR/BR can be corrected to equilibrium by theexpression:
= I ^ ^—\ (1)
equilibrium *
11
where X = the decay constant (s~ )
\i = an escape rate coefficient
t = time interval in seconds between the start of thedefect irradiation and the time the data samplewas taken
The derivation of the relationship is given in Appendix 2.Based on experimental data from the defect tests y is alwaysless than 0.1 X and can be neglected in equation 1. Thisequilibrium corrected value of RR/BR has been designatedthe fractional release (FR). For long irradiations and forfission_products with short half lives_the two release param-eters RR/BR and FR converge. Both RR/BR and FR values forindividual fission products are tabulated in Tables 7A and 7Bfor the three phases of the experiment.
G.I.a Phase_I
Figure 19 shows fractional release values plottedagainst the decay constant* (X) for gaseous fission productsand radioiodines released during Phase I. The data divideinto bands that ce-.n be identified with the three isotope group-ings defined earlier in this section. Inspection of the datapoints within the bands showed a distribution that was changingwith time. This was also evident from the concentration andrelease rate plots vs. time derived from the SUMRT program.The equilibrium fractional releases for different fissionproducts are plotted against irradiation time in Figures 20A,B and C. The release of both Groups 2 and 3 fission productsgenerally decrease with increasing irradiation time. No similartime-dependent behaviour of Fr was apparent for the radio-iodines.
* Because of its high absorption cross section for thermalneutrons the decay constant for Xe-135 was amended by theexpression (10)
AA = A + ad> = 8.9x 10"5 s"1
where X = natural decay constant
a = thermal neutron absorption cross section
d> = thermal neutron flux
12
Phase_II
Values of fractional release for Phase II are plottedagainst A in Figure 21 and against irradiation time in Figures22A, B and C. Unlike Phase I the FR values for Groups 2 and 3fission products increased during the course of the irradiationwith the Group 3 fission products increasing at the faster rate.Although the radioiodines were present in greater concentra-tions than in Phase I their FR values still did not show anydependence on time.
Phase_lll
Fractional release values for the Phase III irradiationare plotted against A in Figure 23 and against time in Figures24A, B and C. The fractional release for Groups 1 and 2 fissionproducts mostly decreased slowly with irradiation time. Themost consistent behaviour was shown by the kryptons and Xe-138while the longer-lived iodines displayed more scatter about thesame downward trend. The dependence of Fr on time was not welldefined for Group 3 fission products; Xe-135 behaved like thekryptons but the fraction releases of the longer-lived Xe-133and Xe-133m either increased slightly with time or remainednearly constant. The reasons for the inconsistency in thexenon results and the apparent time dependence of the iodinesin this phase is unknown but the two holes in the sheath, one ofwhich opened up during the irradiation, may have been partiallyresponsible.
The fractional release (FR) of the krypton and xenonisotopes was approximately the same from all three of the ele-ments after about 400 hours' irradiation in a defected condition.Initially the fission product release from the pre-irradiatedfuel was higher than from the fresh element in Phase II. A moredeveloped network of grain boundary tunnels in the higher burnupfuel probably allowed faster access of the shorter-lived fissionproducts into the fuel-to-sheath gap. The fractional releaseof most Groups 2 and 3 fission products, from the higher burnupfuel, decreased slowly with irradiation time while the releasefrom the fresh fuel increased with time. The fresh fuel wouldhave been expected to show increasing fission gas release asthe gas-filled bubbles on the internal grain boundaries link up.The reason for the slow decrease in fractional release with timefrom the two elements with prior irradiation is unclear. How-ever, the effect may be associated with a difference in the rateof oxidation of old and new fuel since U02 oxidation is known toinfluence fission gas release (10).
13
With the exception of Phase III the fractional releaseof the radioiodines was essentially independent of the irradi-ation time and prior irradiation.
G.1.b Mathematical_Re£resentation_of_the_FDO-681
Many investigators (9)(11) of gaseous fission productand radioiodine release from UO2 fuel have found a relation-ship between the fractional release (FR) of various isotopesand their decay constant \ such that:
(2)
where A and C are constants
However, the FDO-681 tests have shown that FR also is afunction of irradiation time as well as X. The general formof the equation for our results then becomes
A B t
FR = - ^ e (3)
where A, B and C are constants and
t = time of irradiation(s)
Constants to fit all phases of the FDO-681 fractional releasedata are listed in the following table:
14
TABLE A
PhaseFissionProductGroup
Remarks
II
III
1
2
3
1
2
3
1
2
3
1.65x10-13
3.62xlO~7
5.12xl0~6
2.44xlO~ 1 2
1.08xl0~8
3.59xl0~8
1.63xl0"8
5.78xio"7
1.35xl0~5
-5.72x10~
-7.07x10
0
~?
6.07x10~7
8.98x10~7
-9.40x10~8
-1.00x10" 7
6.39x10~8
1.83 i N\ i
0.96
0.77
No correlation with time,includes I131 & I133 only.
,s, {
1.13
0.99
No correlation with time,includes I131 & I133 only.
0.90 Includes
0.87
0.59
I133 S I135
Figure 25 shows fractional release values extrapolatedto time = 0 plotted against \ for all three phases of the FDO-681experiment. For comparison we have shown Groups 2 and 3 fissionproduct data from a fresh UO2 fuel element (CEV) irradiated byAllison and Rae (9) at a linear heat output between 35 and 65kW/m. FR values calculated by the ELESIM computer code basedon the Phase II power history are also included in the figure.The ELESIM release model and the comparison of code with experi-ment results are discussed later in section H. A slope of -0.5on a FR vs. A plot indicates that the fission products are beingreleased from the fuel by diffusion with instantaneous escapeinto the coolant (i.e., no holdup or delay in the fuel-to-sheathgap). Numerical values for slopes larger than 0.5 signify aslower release mechanism than diffusion or delay in the fuel-to-sheath gap. The slopes of the lines for the FDO-681 experimentare tabulated in the preceding table as the constant C.
G.l.c Discussion
Variation of the FDO-681 fractional release FR with A
From a study of the slopes in Figure 25 and"Table A itis apparent that all the fission products are either being re-
15
leased from the PDO-681 elements at rates slower than by simplediffusion or the fission products are being delayed in thefuel-to-sheath gap. This reflects the complexity of an actualfuel element where the fission products can be held up in trap-ping sites such as grain boundary bubbles or the fuel-to-sheathgap. The radioiodr.nes in Phases I and II are released at asignificantly slower rate than the xenons and kryptons. Thissuggests that an additional hold up of the iodines is takingplace within the fuel element. The most likely place for thedelay is inside the fuel-to-sheath gap with the iodine beingtrapped either on the inside surface of the sheath or on theouter surfaces of the fuel pellets. The rate of release of allfission products, from Phase III, especially the iodines, *wasfaster than for Phases I and II. A possible explanation isthat the presence of two defect holes in the Phase III elementhas either allowed coolant to flow through the fuel-to-sheathgap between holes or has exposed additional U0 2 surface to thecoolant.
Higher fractions of the kryptons and possibly thexenons were released by the two elements RPL and RPP, whichhad been irradiated previous to the defect tests as part ofthe X-286 experiment, than from the fresh element LFZ. It isnot certain if this effect was caused by the higher burnup ofthe fuel or by the irradiation during the X-286 test at higherlinear powers. It is possible that a more developed network ofgrain boundary porosity and tunnels in the previously irradiatedfuel has allowed faster access of the shorter-lived fissionproducts to the fuel-to-sheath gap. Since all three elementsin the FDO-681 experiment were irradiated at nearly identicallinear powers, differences in fuel temperatures during thedefect test cannot account for the difference in release. Priorirradiation had no effect on the release of the radioiodines.
Eff e£t_of_graghite_interla.yer_on_f ission_p_roduct
release:
There was no evidence in the FDO-681 data that wouldsuggest any difference in fission product release from elementswith either a CANLUB or a FURRY graphite coating. Since all thegraphite had disappeared from the fuel-to-sheath gap probablyquite early in the defect irradiation this result is not unex-pected.
16
Cgmgarisgn_of_the_FD0-681_steady_state_fission
groduct_release_with_other_experiments
The A dependence for the FDO-681 elements is comparedwith similar values from other defect tests in the table below:
TABLE B
FissionProducts
FDO-681
PhaseII III
Allison CANDUS Rae Power Reactor(9) (12)CEV Pickering Gentilly-1
ChenebaultS Delmas WSGHWR
(13) (14)
Group 1 -1 .83 -1 .53 -0.90 N/A N/A N/A
Group 2 -0 .96 -1 .13 -0.87 -0.70 -0 .75 -1 .0
Group 3 -0.77 -0.99 -0.59 -0.82 -0.75 -1 .0
-1.09 N/A
-1.07 -0.57
-1.07 -0.84
The agreement between our FDO-681 results and other defectirradiations is reasonably good, although some values are incon-sistent. The large fractional releases of Groups 2 and 3 fissionproducts from Allison and Rae's (9) defected element CEV compared toour element LFZ (see Figure 25) can be accounted for by the higherlinear heat power of CEV. Why element CEV released Group 2 fis-sion products at a faster rate {i. e., a shallower slope, see Figure25) than the FDO-681 fuel is not understood. Although no X de-pendence of iodine was available from element CEV in Allison andRae's (9) experiment the iodine release generally correlated to aslope of -1.5.
Data from the power reactors, Pickering (12) and WSGHWR(14), a r e similar to Phase I and III of the present experiment.This may be a result of the burnups Deing higher than in Phase II.The power reactor data probably came from fuel with relativelylarge or numerous splits and holes, but if so it is not clearwhy the Gentilly results (12) do not also fit our data. The noblegas data from Chenebault and Delmas (13) are similar to Gentillyor Phase II.
G.2 Release of Fission Products to the Coolant
During Reactor Power Transients
For the purpose of this report we will define a reactorpower transient as being:
17
(a) A reactor trip shutdown where the reactor power is reducedfrom full to zero very quickly. The shutdown period isgenerally less than one hour with the return to full powerbeing quite rapid.
(b) A scheduled reactor shutdown where the reactor power isreduced to a low level (about 15% of full power) overseveral minutes and then is tripped to zero power. Ascheduled shutdown usually extends for greater than 20hours with the startup to full power taking place overseveral days.
A typical irradiation history with reactor power trans-ients is illustrated in Figure 17. Fission product coolantconcentration and reactor power versus time plots were constructedfor each reactor power transient where sufficient spectra wereavailable. Concentrations were used rather than fission productrelease rates because the SUMRT program gave poor release ratevalues for periods of rapidly changing concentrations. Typicalexamples of the change in fission product concentrations in thecoolant during reactor power transients are given in Figures 26to 30. Concentrations of the fission products 1-131, Xe-133,Xe-135 and Kr-85m are plotted on these figures as representativeof the behaviour for each of the three isotope groups describedearlier.
After several days of steady reactor power, the concen-trations of kryptons and xenons decreased when the reactor wasshutdown, and rose rapidly (by factors from 1.2 to 2.5) on thenext reactor startup. In contrast, the iodine concentrationsincreased sharply by factors up to 4.0 after the shutdown(similar results are reported by Belle (10) and Lutz (15)) andincreased again (this time by factors up to 25) after the startup.The decrease of the kryptons after shutdown is apparently causedby decay; however, the xenons show a slight increase in theirconcentrations. This release of xenon is probably a result ofthe increased concentration of iodine precursors during theshutdown. For most transients the change \n Xe-133 and Xe-135concentrations is similar; but, in Figures 27 and 30, for someunexplained reason the concentration of Xe-133 did not increaseon the reactor startup.
During reactor startups the peak in the iodine concen-tration usually occurred when the reactor was first brought upto low power (<1 MW) while the xenon and krypton peaked severalminutes later when the reactor power was raised above 1 MW;see Figure 31.
The inventory of the fission products in the fuel hasan effect on the size of the transient release, as illustrated
18
by Figures 27, 28 and 30, where concentrations are plotted for"back-to-back" reactor shutdowns and startups. The size ofthe startup transient for all the fission products is eithermuch smaller or almost non-existent for the second shutdown-startup cycle. When the gas content of the fuel is reducedfollowing a reactor power cycle, it takes time for the gasesto build up or migrate to a position that would give a sizabletransient release.
The FDO--681 steady-state and transient behaviour sug-gests that significant amounts of the radioiodines are heldwithin the fuel-to-sheath gap, probably in combination withother fission products. The iodine that is released duringsteady state is probably a volatile iodine compound such asHOI that is formed in the fuel-to-sheath gap. The iodine heldin the gap of a defected element appears to be removed by hotwater, but not by steam. Therefore, when the fuel cools afterthe reactor has reached zero power anJ water re-enters theelement, iodine is dissolved by the water and makes its waythrough the water phase into the loop. This would accountfor the increase in iodine concentration observed in the coolantimmediately after reactor shutdown. Most of this water satur-ated with iodine would be expelled from the element through thedefect hole when the reactor starts up to low power giving thesecond step in the iodine concentrations on the plots. Theseobservations are in substantial agreement with iodine behaviourduring reactor transients reported by other investigators (15)(16) (17).
The kryptons and xenons released by thermal crackingof the UO2 on the reactor shutdown apparently remain within thefuel element. The kryptons and xenons may be trapped in fuelcracks by the surface tension of the coolant or more likely thevertical orientation of the element allows the gas to collectat the top of the fuel stack. These gases would then be expelledinto the coolant on reactor startup only after the water has beenremoved and replaced by steam.
Eickelpasch and Hock (18) measured the radioiodinesduring shutdowns of the Gundremmingen boiling water reactorand observed peaks in the release rates up to two days afterthe shutdown had taken place. They commonly observed doubleiodine peaks, with the first peak occurring about 5 hours afterthe shutdown. Lutz in his description of iodine release fromAmerican power reactors reported maximum iodine release ratesdue to power transients approximately 5 hours after reactorshutdown (15). It was impossible to confirm the presence of adouble iodine release peak during the FDO-681 test since ourspectrometer was disconnected approximately 4 to 5 hours after
19
each long-term shutdown. However, after 5 hours iodineconcentrations in the coolant were still increasing but ata very slow rate. Unlike the German experience, iodinerelease from one of the Pickering CANDU reactors operatingwith defected fuel peaked about 15 minutes after the reactorshutdown; this was possibly caused by slight depressurizationof the coolant system.
We have specified a parameter for transient fissionproduct release, T R , defined as the change in concentrationduring a transient divided by the concentration of the isotopebefore the transient. To correlate the transient releasewi h reactor parameters we have plotted the T R values against
(a) total irradiation time,
(b) time at full reactor power before the transient,
(c) shutdown and startup duration, and
(d) the decay constant (X).
These plots are shown in Figures 32 and 33; some points wereso scattered that we have made no attempt to indicate trendson these graphs. There was no strong agreement with any ofthe above parameters although certain trends could be dis-tinguished. The most important of these were:
TRANSIENT RELEASE ON SHUTDOWN
(a) Transient releases of iodine increased with totalreactor operating time and also with the length of timethe reactor was at power before the transient occurred,in agreement with the results of Neeb and Schuster (16).
(b) There was no correlation between the shutdown transientrelease of the kryptons and any of the parametersplotted.
TRANSIENT RELEASE ON STARTUP
(a) For Phases I and II the shorter the time at powerbefore the transient the smaller the transient releasevalues for all fission products on reactor startups.
(b) Startup transient releases from Phase III in partic-ular were insensitive to changes in any of the param-eters.
(c) Within the limits of experimental accuracy, transientreleases from all phases were independent of decayconstant (A) .
20
The FDO-681 experiment has demonstrated that we stillhave an inadequate understanding of the variables that affectfission product release during reactor power transients.
H. MODEL DEVELOPMENT
Allison and Rae (9) have proposed a simple model todescribe the fission product release from defected fuel ele-ments during steady state operation. Their model assumesthat the gaseous fission products are relatively mobile withinthe grain growth area of the fuel and that a small percentageof these escape from the hot core to the defect; the amountof fission products contributed to the coolant from the re-mainder of the UO2 is insignificant. Allison and Rae havegiven three equations (listed in Appendix 3) to describe thefractional release FR of (a) the kryptons and Xe-138, (b) thexenons and (c) the radioiodines. We have used Allison andRae's model to calculate the fractional release of selectedfission products from the FDO-681 element LFZ, because it,like Allison and Rae's elements, was unirradiated at the startof the defect experiment.
A comparison of measured and calculated fractionalrelease values* of fission products from LFZ is shown below:
Fission Product
Kr-85m
Kr-87
Kr-88
Xe-138
Xe-133
Xe-135
1-131
1-133
* WHOT-O f rapf ini
TABLE C
Averaged Measured (FR)Element LFZ
0 . 0 0 2 1
0 . 0 0 0 5
0 . 0 0 0 9
0 . 0 0 0 0 8
0 . 030
0 . 0 0 1 7
0 . 0 03 7
0.00012
-ini -rr.1 i~nii~ i i FT? —
Calculated (FR) from theAllison and Rae Model
0.0016
0.00071
0.0012
0.00020
0.0049
0.0010
0.0091
0.00031
/ I \
21
The agreement between FR values is reasonable except forXe-133. Elements RPL and RPP showed higher fractionalreleases than LFZ and therefore would be in worse agreementwith the Allison and Rae model; this indicates that the effectof burnup should be included in the model. Because the threeelements were irradiated at nearly the same power output andbecause the fuel stack lengths were almost identical, Allisonand Rae's (9) effects of length and power on FR could not be con-firmed.
A more fundamental model than Allison and Rae's forpredicting the fission product release from defected fuelelements is desirable. A start has been made by adapting thestable fission gas release calculations now used in the fuelmodel ELESIM MOD 9 (19). This model assumes the fission gasatoms reach grain boundaries either by simple Booth-type dif-fusion or are collected by grain boundaries that sweep throughthe fuel. Once at the grain boundaries the gas atoms collectin bubbles where they remain until the bubbles grow to a sizewhere they interlink forming grain boundary tunnels. At thispoint the fission gases are released to the free volume ofthe fuel element. The inventory of the radioactive gaseousspecies is corrected for decay both during the diffusion pro-cess and during the residence time in the bubbles. When thegas has reached the free volume Allison and Rae's (9) empiricalequation for axial diffusion is used to calculate the decayduring movement to the defect hole. The radioiodines areassumed to behave similarly to fission gas and fission gasrelease from the fuel surface by "knock out" is included.
The ELESIM model (MOD 10 version) was used to predictthe release of gaseous fission products from the fresh eleir.sntLFZ (Phase II) during its FDO-681 irradiation. The resultsare summarized in the table below and the values are plottedon Figure 25.
22
TABLE D
Fission Product
Kr-85m
Kr-87
Kr-88
Xe-138
Xe-133
Xe-133m
Xe-135
1-131
1-133
Averaged PR MeasuredElement LFZ
0.0021
0 .0005
0.0009
0.00008
0 . 0 3 0
0 . 0 3 7
0.0017
0.0037
0.00012
PR Calculated fromELESIM MOD 10
0 .0005
0.0002
0.0004
0.000009
0. 014
0.004
0.0011
0.004
0.00008
The agreement between the ELESIM model and the experimentalresults, although generally within a factor of 3 for mostisotopes, may be improved by (1) making allowance for pre-cursor diffusion and (2) by modelling diffusion in the fuel-to-sheath interface less empirically.
I. CONCLUSIONS
1. For defected fuel elements irradiated in hot pressurizedwater at average linear heat outputs of 48 kW/m, thefractional release of fission gases ranged from 1.4 x10"1 for the long-lived xenons to 3.5 x 10~5 for theshorter-lived kryptons and Xe-138.
2. The fractional release of gaseous fission products fromthe FDO-681 element with fresh U02 increased during itsirradiation while the fractional releases for the twoelements with prior irradiation mostly decreased withtime. Different rates of oxidation for fresh and highburnup UO2 was thought to be responsible.
3. All gaseous fission products were delayed before releaseeither in the UO2 or in the fuel-to-sheath gap. The holdup of the radioiodines was greater than for the noble
23
gases possibly because of absorption on the inside surfaceof the sheath. There was less hold up of iodine in theelement with two defects than those with one defect, prob-ably due to coolant flow in the fuel-to-sheath gap betweenholes.
4. The two fuel elements with previously irradiated fuelreleased more krypton and possibly more xenon into thecoolant than the element with fresh UO2. There was essen-tially no difference in the amount of radioiodines releasedby the three elements.
5. On reactor power transients radioiodines are released onboth shutdowns and startups while the noble gases arereleased in quantity only on reactor startups. Iodinerelease on reactor startup always precedes the release ofkryptons and xenon.
6. The longer the time the reactor has been at constant powerbefore a transient, the larger the release of fissionproducts to the coolant on shutdowns and startups.
7 •. Both the Allison and Rae and ELESIM models gave reasonablepredictions of the fission product release from the FDO-681 fuel element with fresh UO2.
8. The amount of U02 lost from the pellet immediately underthe defect hole is proportional to the irradiation timeand the size of the defect hole. The UO2 is lost asindividual grains that are broken out of the matrixmaterial by grain boundary oxidation.
9. Both CANLUB and FURRY graphite interlayers between thesheath and fuel disappeared after the elements had operatedin the defected condition. The graphite is probably removedby reaction with high temperature steam.
J. ACKNOWLEDGEMENTS
The authors acknowledge the assistance of M.J.F. Notley,H.E. Sills and I.J. Hastings in the preparation of this report.The information on defected fuel in the Pickering reactors wasgenerously provided by the staff of Ontario Hydro. Thanks arealso due to R.W. Bull, J.C. Irvine, D.D. Semeniuk and W.J.Williams for their conscientious processing of the data tapesand to R.J. Chenier and J.R. Kelm for the post-irradiationexamination of the elements. Finally we are grateful for thehelp of P. Kos of Ontario Hydro and E.E. Perez of the CNEA(Argentina) during time the experiment was in-reactor.
24
K. REFERENCES
1. M.J.F. Notley, M.J. Pettigrew and H. Vidal, "Measurementsof the Circumferential Strains of the Sheathing of U0 2Fuel Elements During Reactor Operation", AECL-4072,January 1972.
2. J.A.L. Robertson, "Concerning the Effects of Excess Oxygenin U02", CRFD-973 (AECL-1123), October 1960.
3. J.R. MacEwan and J. Hayashi, "Grain Growth in UO2 III,Some Factors Influencing Equiaxed Grain Growth", Proc.British Ceramic Soc, No. 7, February 1967, page 245 orAECL-2808.
4. D.H. Rose, private communication to R.D. MacDonald.
5. B.E. Schaner, "Metallographic Determination of the UO2 -UifO8 Phase Diagram", J. of Nucl. Mat. Vol. 2 No. 2 (1960)110-120.
6. A.S. Bain and R.D. MacDonald, "Examination of UraniumOxide Specimens from the Fourth Charge of the EEC Loop",UKE-CR-704, June 1958.
7. D.H. Locke, "The Behaviour of Defective Reactor Fuel",Nuclear Engineering and Design, Vol. 21, No. 2, (1972)318-330.
8. R.D. Page and G.R. Fanjoy, Fuel for CANDU PressurizedHeavy Water Reactors, AECL-5389, January 1976.
9. G.M. Allison and H.K. Rae, "The Release of Fission Gasesand Iodine from Defected UO2 Fuel Elements of DifferentLengths - Exp-NRX-21406", AECL-2206, June 1965.
10. "Uranium Dioxide: Properties and Nuclear Applications",edited by J. Belle, Naval Reactors, Division of ReactorDevelopment, United States Atomic Energy Commission.
11. S. Jacobi, K. Letz and G. Schmety, "Release and Detectionof Fission Products from Defective Fuel Pins", NuclearEngineering and Design 44", (1977) pages 125-135.
12. G.M. Allison, Private Communication to J.J. Lipsett andand R.D. MacDonald.
25
13. P. Chenebault, A. Harrer, G. Kurka and J.p. Stora,Evaluation of Fission Gases and Halogens Released out ofFailed Fuel Running at Constant Power and in PowerCycling Regime, Paper presented at the IAEA SpecialistsMeeting on The Behaviour of Defected Zirconium Alloy CladCeramic Fuel in Water Cooled Reactors, Chalk River, Ont.,Canada, 17-21 September 1979.
14. D.H. Locke, "Defective Fuel Behaviour in Water Reactors",ANS Topical Meeting, Water Reactor Fuel Performance,May 9 to 11, 1977, St. Charles, Illinois.
15. R.J. Lutz and W. Chubb, "Iodine Spiking - Cause and Effect,Trans. ANS, Vol. 28, June 1978, page 649.
16. K.H. Neeb and E. Schuster, "Iodine Spiking in PWR's:Origin and General Behaviour", Trans. ANS Vol. 28, June1978, page 650.
17. N. Eickelpasch, R. Seepolt and R. Hock, "Iodine ReleaseMechanism and its Verification in Plant Operation",Trans. ANS, Vol. 28, June 1978, page 652.
18. N. Eickelpasch and R. Hock, "Fission Product Release AfterReactor Shutdown", IAEA-SM-178/19 CONF, 731083 STI/PUB-351.
19. M.J.F. Notley, "ELESIM: A Computer Code for Predictingthe Performance of Nuclear Fuel Elements", Nuclear Technology,44, 445-450 (1979).
TABLE 1
ElementPhase. . .Tes t C ;
RPLI
LFZII
RPPIII
PelletDensity(Mg/m3)
10.72
10.72
10.72
UO2 FUEL PARAMETERS • TEST
PelletOutside Diameter
(mm)
13.71
13.61
13.66 (2 )
PelletLength
(mm)
18.0
18.0
18.0
PelletStack Length
(mm)
179.0
168.4
179.5
FDO-68100
TotalUO2 Weight
(g)
278.9
257.1
276.0
Pellet EndLand Width
(mm)
0.56
0.56
0.49
Dishing(3)
Depth(mm)
0.64
0.64
0.64
(1) enrichment 4.52 wt% O235 in U
(2) before coating with FURRY graphite
(3) dish location at one end of each pellet
TABLE 2
ELEMENT PARAMETERS • TEST FDO-68100
Element Sheath Sheath Sheath Overall Clearances (mm) Fuel to Clad& Phase Material Outside Diameter Thickness Element Length Diametral Axial InterfaceNumber (mm) (mm) (mm)
RPLI
Zirc-4 15.22 0.71 184.5 0.08/0.11 1.02 CANLUB layeron sheath ID0.0075 mm thick to
-j
LFZII
Zirc-4 15.16 0.71 184.5 0.11 1.07 CANLUB layeron sheath ID0.0075 mm thick
pprIII
Zirc-4 15.21 0.70 184.5 0.08/0.09 1.02 FURRY graphitecoating 0.035 mmthick on pel lets
TABLE 3
Element& Phase
I RPL
I I LFZ
Defect Shape
Drilled Hole
Drilled Hole
DEFECT PARAMETERS
Defect HoleDiameter
(mm)
1.261
1.196
• TEST FDO-68100
DefectLocation*
(mm)
102.4
101.5
Defect Location in Respectto Pellet Fuel Stack
over middle of 6th pelletfrom top
over middle of 6th pellet
III RPP Two DrilledHoles
1.282 #1
0.435 #2
101.0
110.0
close to pellet interfacebetween 5th & 6th pelletover middle of 6th pellet
* distance in mm from top end plug shoulder
TABLE 4
IRRADIATION HISTORY OF PDO-68100 DEFECTED FUEL ELEMENTS
Irradiation Period Total Hours Reactor TransientsPhase Start End Irradiation Type Number
Coolant CleanupType Tine
Variations in Coolant Parameters fromNominal Values
I 03:30 19:59 367.5 I)July 24/75 Aug 10/75
Ion Exchange 10:15 July 25+12:50 July 25Startups 10 09:15 July 29*12:05 July 28 TemperatureShutdowns 10 18:30 July 31+21:00 July 31
19:00 Aug 5 Pressure
Degassing 16:00 July 23+01:30 July 24 Flow
' No significant changes
1 Loop depxessurized on onereactor shutdown
' Flow increased to 0.635 kg/sfor approx 24 h
11:08 20:00II Aug 28/75 Sept 23/75
Startups 20Ion Exchange 08:00 Sept 9 +19:00 Sept 19
579.1 Shutdowns 20 Degassing 19:00 Aug 26 +03:00 Aug 27
Temperature + No significant changes
Pressure * Pressure at 7.5 MPa from 16:00
Sept 4 to 09:00 Sept 8• Pressure at 7.3 MPa from 08:00Sept 8 to 17:00 Sept 8
Flow + High flows during reactor shutdown
MV0
20:29 22:00Oct 8/75 Nov 16/75
846.9
Startups
Shutdowns
10
10
Ion
De*
Exchange
issing
18:00
13:5023:00
23:3004:00
Oct
OctNov
OctNov
21+14:00
30+21:504 +12:00
7 +07:3017+?
Oct
OctNov
oct
22
305
a
Temperature
Pressure
Flow
' Temperature reduced on threereactor shutdowns
* Pressure reduced on two reactorshutdowns
- High flows during two reactorshutdowns
TABLE 5
ELEMENT HEAT OUTPUTS AND BURNUPS TEST FDO-68100Surface Heat Flux
Element & Heat Output Fission Rate Linear Heat Output (sheath to coolant) /Xd8 Burnup (MWh/kg u) Linear heat outputsPhase (kW) (f/s) (kW/m) "2s (kw/m) S t a r t of End of during i r rad ia t ion
Av. Max. Av. Max. Av. Max. Av. 1KW'm M3X. A v . Max. Test Test pr ior to FDO-681 tes t
RPLI
LFZII
RPPIII
8
8
8
.7
.1
.4
9
9
11
.5
.4
.7
2.7xlO14
2.5xlO14
142.6x10
3.0xl014
2.9xlO14
3.7X1014
48.5
48.0
47.0
53.0
56.1
65.
1015.
945.
980
1110.
1100.
1365.
3
3
3
.5
.5
.4
3
4
4
.8
.1
.7
140
0
141
.0
.2
158
20
173.3
60 -»
60 •*
75
75
kW/m
kW/m
O
(1) During experiment Exp-NRX-28600
TABLE 6
VALUES FOR THE RATIO OF GRAIN GROWTH DIAMETER TO PELLET DIAMETER
AMD ZIRCONIUM OXIDE THICKNESSES ON THE SHEATH SURFACES DERIVED
FROM METALLOGRAPHIC CROSS SECTIONS OF THE FDO-68100 ELEMENTS
Element Locatxon from Top End(mm)
88
122 Defect
174
92
125 Defect
174
87
117 Primary Defect
127 Secondary Defect
180
Ratio of Grain GrowthDiameter to Pellet OD
(r/a)
0.639
0.635
0.645
0.663
0.624
0.640
0.628
0.621
0.606
0.660
Zirconium Oxide Thicknesson Sheath (urn)
Av. r/a Outside Inside
RPL
LFZ
RPP
0.640
0.642
0.629
0.
0.
0.
1
1
1
5
5
5
1
1
1
1
to
to
to
to
to
to
to
to
to
to
2
2
2
2
2
2
2
2
2
2
4 to 30
4 to 24
4 to 72
6 to 56
4 to 30
4 to 64
4 to 44
4 to 34
4 to 12
6 to 80
TABLE 7A
FRACTIONAL RELEASE VALUES <FR> FOR FISSION PRODUCTS RELEASED DURING STEADY REACTOR POKER FOR EXP-FDO-68100, PHASES I , I I AND I I I
Phase Date
t J u l 27/75
Jul 31/75
Aug 4/75
Aug 9/?5
II Aug 31/75
S-p 1/75
Sep 3/75
Sep 4/75
Sep 6/75
Sep 16/75
Sep 19/75
Sep 21/75
Sep 22/75
HI Oot 12/75
Oct 14/75
Oct 16/75
Oct 19/75
Oct 22/75
Oct 27/75
Nov 3/75
Nov 8/75
Nov 13/75
Nov 15/75
AccuMulateo.tineIs)
1.80x105
3.82x105
8.24X105
J.3JX206
2.16X105
2.99x10*
4.75X105
5.69x105
7.52X105
1.46xlO6
1.73X106
1.91X1O6
2.06X106
1.91xlO5
3.71X105
5.87X105
8.46x105
1.13X106
1.49xlO6
2.09X106
2.60x10'
2.95X106
3.20X106
FissionRate(f/s)
2.61X1014
2.88xlo"
2.99xlo"
J.oW*
3.37x10"
3.14x10"
3.14X10"
3.15X101*
3.20X10"
3.16X1014
3.16X10"
3.16X1014
3.2SX1014
2.52X1014
2.52x10"
2.65x10"
2.57xlo"
2.59x10"
2.69X1014
2.46x10"
2.43X1014
2.40x1014
2.52xlo"
DataSanple
1
2
3
4
PlottingSflbol , " - « * • .
ARay IxevMs"1)
O
•oA
Average
1
2
3
4
5
6
7
a9
OD
oAts.C*Q
Q
aAverage
1
2
3
4
5
6
7
8
9
10
oD
oAb>CsQ
O
a0
Average
. KT-85B1 150
'» 4.30x10"*
5.90x10-3
4.65x10-3
4.13x10-3
2.96x10-3
4.41x10-3
1.16x10-3
9.95x10-4
1.16x10-3
1.32X10"3
2.15x10-3
2.72x10-3
2.69X10"3
3.92x10-3
3.04X10"3
2.13X10"3
3.67X10"3
3.79x10-3
3.79x10-3
4.18x10-3
4.23x10-3
3.79x10-3
3.17x10-3
3.29x10-3
2.37x10-3
3.07x10-3
3.59x10-3
Kr-87403
1.48x10-"
1.97x10-3
1.63x10-3
1.28x10-3
9.00x10-4
1.45X10-3
2.65X10"4
2.72x10-4
3.36X10"4
4.12x10-4
5.10x10-4
8.40x10-4
6.75x10-4
9.35xlo"4
1.01x10-3
5.84x10-4
1.35x10"*
1.46X10-3
1.48x10-3
1.63x10-3
1.53x10-3
1.38X10"3
1.14xlo'3
1.19x10-3
9.65x10-4
1.01x10-3
1.31x10-3
Kr-88I9S6.88x10"*
2.56X10"3
2.22X10"3
1.89X10"3
1.43XW"3
2.03xl0"3
5.10x10"*
5.50X10"4
6.05xl0~*
7.00x10"*
8.90xl0~*
1.17X1O"3
1.05X10"3
1.45xlo"3
1.22X10"3
9.05x10"*
1.72X10"3
1.71X10"3
1.72X10'3
1.98X10"3
1.93xlo"3
1.82X10"3
1.57xlo"3
1.58X10"3
1.45X10"3
l-55xlo"3
1.7OX1O*3
Xe-13B25»
7.97xl0~lt
3.27x10"*
2.27x10"*
2.12X10"*
1.57x10"*
2.31x10"*
3.69xlO~S
4.34X10"5
5.10X10"5
4.7BX10"5
1.14X10"*
8.75X10"5
7.B5X1O"5
1.29x10"*
7.35X10"*
2.24x10"*
2.54xl0~*
2.87x10"*
2.95x10"*
2.62x10"*
2.34x10"*
2.21xlo"*
2.49x10"*
1.84x10"*
1.91x10"*
2.40xl0~*
Xe-13381
1.52X10"*
1.29xl0~*
1.37x10""
7.40xX0"2
6.10X10"2
l.OOxlo"1
1.21xlo"2
1.30X1O"2
1.62xlO"2
1.47X10"2
3.67x10"*
5.90X10"2
6.45xl0"2
3.00X10"2
2.5Bxl0"2
3.02xl0~2
5.30X10"2
4.46X10"2
4.13X10"2
3.26xlo"2
2.49X10"2
5.55xio"2
4.59X10"2
3.84xlo"2
5.25x10""
5.60xl0~2
4.45xio"2
xe-133m233
3.59x10"*
5.20X10"2
5.40X10"2
2.46X10"2
5.15X10"2
4.55xlO~2
1.27X10"2
3.05X10"2
2.87X10"2
S.15xl0"2
3.91X10"2
5.95x10"2
3.7Oxlo"2
2.51X1O"2
3.01xl0"2
2.17xlO"2
2.08xl0"2
3.14xl0"2
2.44xlo"2
2.86X10"2
5.50xl0"2
3.74X10"2
3.05X10"2
xe-1352*o
8.93X10"5
5.10xl0"3
5.95X10"3
3.99X10"3
2.54X1O"3
4.40X10"3
4.11x10"*
5.50x10"*
4.41x10"*
6.05x10"*
9.50x10"*
2.37xlo"3
2.85X10"3
2.85X1Q*3
4.23X10"3
1.70X10'3
2.91X10'3
3.O3xlo"3
3.15X10*3
3.62X1O"3
3-SSxlo'3
3.51X1O"3
2.90X10"3
3.25X10"3
2.56X10"3
2.52x1o"3
3.1OX10"3
1-131365
9-95xlO~"
3.3BX1O"2
2.O7xlo"3
2.B9X1O*2
1.09xl0"3
1.65X10"2
8.2X10"3
3.07xl0"3
1.90X10"3
1.82xl0"3
2.14X10"1
4-BSXIO"3
3.98xlO~3
3.71xlO~3
2.21X1O"3
8.40X10"3
5.60xl0~3
1.84xlO~3
6.05X10"3
4.23X10"3
3.27X1O"3
2.56X1O"3
3.98X10"3
2.29X10"3
4.O4xlo"3
1-133 I -134530 OS*
9.48X10" i.18x10"*
1.27x10**
4.03x10"*
2.65x10"*
1.96x10"*
5.25X10"5
1.43x10"*
7.30xl0~5
1.26x10"*
1.18x10"*
3.53x10"*
5.40x10"*
4.62X10"*
3.96x10"*
3.53x10"*
4.29x10**
3.19x10"*
2.52X10"*
5.35xio~*
4.04X10"*
1-1351261
2.87x10"'
1.70X10**
1.70xl0~*
2.22x10"*
2.57x10"*
2.48x10"*
2.42x10"*
TABLE 7B
R/B VALUES FOR FISSION PRODUCTS RELEASED DURING STEADY REACTOR POWER FOR EXP-FDO-68100, PHASES I , XI AND I I I
Date
Jul 27/75
Jul 31/75
Aug 4/75
Aug 9/75
Aug 31/75
Sep 1/75
Sep 3/75
Sep 4/75
Sep 6/75
Sep 16/75
s .p 19/75
Sep 21/75
Sep 22/75
Oct 12/75
Oct 14/75
Oct 16/75
Oct 19/75
Oct 22/75
Oct 27/75
llov 3/75
Hov 8/75
Hov 13/75
llov 15/75
AccumulatedTime(*)
l.aoxio5
3.82x10*
0.24x10*
1.31x10*
2.16x10*
2.99x10*
4.75x10*
5.69x10*
7.52x10*
1.46x10*
1.73X106
1.91x10*
2.06H06
1.91x10*
3.71x10*
5.87x10*
8.46x10*
1.13x10*
1.49x10*
2.09x10*
2.60x10*
2.95x10*
3.20x10*
FluionRate(f/«)
2.61X1014
2.88xlO14
2.99X1014
3.07X1014
3.37X1014
3.14X1014
3.14X1014
3.15X1014
3.20X1014
3.16X1014
3.16X1014
3.16X1014
3.25X1014
2.52X1014
2.52X1014
2.65X1014
2.57X1014
2.59X1014
2.69X1014
2.46X1014
2.43x10**
2.40X10*4
2.52X1014
DataSample X
1
2
3
4
Average
1
2
3
4
5
6
7
a9
Average
1
2
3
4
5
6
7
8
9
10
Isotope )Ray (kev) >
XtS"1) )
Kr-85»11"4.30x10', - 5
Kr-874031.48x10"'
Kr-BB19fi6.68x10"'
Xe-133811.52x10"
Xe-133n233
3.59x10"'
Xe-13524O8.93x10"
1-131 1-133365 530*.95x10 9.48x10"'
1-13512fil j2.87x10"
5.95X10"3
4.65X1O"3
4.12X1O"3
2.9SX10*3
" 34.42x10'
1.16X1O"3
9.95X10"4
1.16X10"3
1.31X10"3
2.15X10"3
2.71xlO"3
2.69X10"3
3.93xlo"3
3.05X10"3
2.13x10'" 3
3.67x10r3
3.78X10"3
3.78X1O"3
4.19x10*3
4.23x10*"
3.78x10*'0"3
3.17X10(-3
n - 3
1.97X10"3
2.63x20~3
1.28xlO"J
9.00xlo"4
3.28x10 '
2.26x10"'
2.13x10"'
1.57x10"'
1.45X10
2.65X10"4
2.72xlo"4
3.37xlO"4
4.12X10"4
5.10X10"4
8.40X10"4
6.75X10"4
9.30xl0~4
l .Olxlo"3
1.09x10""
6.80x10"*
1.45x10 -
1.22x10"-
5.83xlo"
1.46X10"3
1.4Bxlo"3
1.63X10"3
1.53X10"3
1.38X10"3
1.14X10"3
l .MxlO*3
9.65X10"4
l .Olxlo"3
2.31xlo":
2.26x10"'
2.02xl0";
2.02x10"'
2.24x10 *
2.54X10"4
2.88X10"4
2.95xlo"4
2.63X10"4
2.33xlo"4
2.21X10"4
2.49xlO~4
i .a4xio" 4
1.41X10"4
3.16X10"2 2.49x10 5.10x10
6.05x10"" 4.01x10"' 5.95x10"'—2
0" 2
,"2
_2
5.30x105.25x10'"
2
2.81x10'5.15x10'" 2
f3 2.O2X1O"3 '2.31xlO~4 4.94X10"2
4.00x10"
2.55x10*'
8.30x10 '
8.50x10*:
2.50xl0" :
5.30x10"'
6.05xl0";
2.84x10*'
2.46xlO~'
1.04x10*'
2.65x10*'
2.67xlO*;
1.26X10*2
1.92X10*2
2.43X10*2
2.35x10"
2.05X10
4.38x10"'
3.77xl0" :
S.30x10"'
5.55xlo":
1.84X10"2
2.64xlc"2
2.07X10*2
2.09X10"2
3.13X10"2
2.44X1O*2
2.87X10*2
5.50X10*2
3.74x10"
1.31x10 " 3 2.33X10"' 2.35x10'" 4 3.4Oxlo"Z 2.92x10" 2
3.03xl0~
3.14x10"'
3.63x10"
3.55xlO":
3.51xlO*:
2.91x10"'
2.82xlO~:
5.55x10"'
6.50X10"'
7.95X10"
1.04x10 '
3.91x10"'
1.59x10 ;
7.90x10"^
7.15x10"*
7.90x10"'
1.14xio":
3.74x10"'
3.27xlO~'
1.70x10 "
4.93x10""
1.42x10*'
7.30xl0"!
10*3 1.72x10"' 1.12X10*4
3.83X10"4
2.60X10"3
2.46X10*3
l.OSxlO*3
in" 3
4.60x10 '
1.05xlO*:
4.10xl0~J 3.96x10"'
3.26X10"3
2.85X10"3
2.37xl0"3
3.77X10"3
2.14x10"'
3.53x10 '
4.27x10"'
3.19x10"'
2.51x10*'
5.35x10"'
!0~3 2.50X10"3 4.61xlo"4
2.23x10"'
2.55x10"'
34
Phase Date(1975}
Jul 28
Jul 28
Jul 31
Ang 31
Sep 1
5ep 9
Sep 16
Sep 23
Sep 22
Oct 21
Oct 28
Nov 4
Nov 16
ShutdownType
Trip(Reduction
Trip)
Trip)
Trip
Trip)
Trip)
Trip)
(Reduction* Trip)
Trip)
Trip)(Reduction
Trip)
1 ReductionTrip)
Trip)
Trip)
Trip)
(ReductionTrip)
(ReductionTrip)
(ReductionTrip)
(Reduction*Trip)
(Seduction*Trip)
(Reduction*Trip)
SDJ
Duration(»
4620
* 2040
660
zsao
- 2 e 2 0
-» 2940
•+ 13S0
>7.2xlO*
>7.2xlG4
>7.2xtO*
SU*Duration
(a)
4860
2160
2400
1360
4200
6000
4440
TIM at. Power
1.0
10.5
9.0
3
2 3
9
9
21
0.25
12
168
147
128
TotalOperatingTime (h)
S7.Q
69.0
78.S
14 3.9
66.3
89.4
253.2
sea.3
5S6.1
557.0
12.2
36.0
443.3
590. 4
849.9
Kr-85a
0
0
O
0
0
+ 10
414
+11
0
0
0
+ 2
0
0
0
0
Xe-135
+ 30
+ 10
+9
+ 7
+6
+ U
+ 2 9
+2
+8
0
0
0
+8
0
+44
+ 27
+ 28
1-131
• 19
+ 1
+ 3
+ 1
+ 8 7
+6
+ 238
+ 27
+6
+7B
+ 116
+ 764
+ 24
+500
% Tra
Kr-BS*
+52
+ 9
+63
+48
+ 79
+ 30
+ 215
+ 283
+ 191
0
+ 16
+ 51
+ 49
+ 61
niient Bel ease SU
Xe-135
• 32
+25
+ 177
+ 14
+ 29
+17
+125
+ 85
+ 8
0
+ 19
+ 72
+ 33
+ 31
+ 4B
1-131
+ 768
+83
+ 117
+ 44
• IB
+ 131
+9
+ 844
• 42
+ 4 1
+10 3
+ 460
1 T in the fuel element has been at power since tilt, last transient.1 Total irradiation ti-.e fiOM th« start of the experiment.1 SD • shut Down, SO • start up.
DELAYED NEUTRONMONITOR
SURGETANK
•SCINTILLATION
MONITOR
t
IN-REACTOR
— TESTSECTION
MAKE-UP
FIGURE 1 X -2 LOOP FLOW SCHEMATIC SHOWING LOCATION OF GAMMA RAY SPECTROMETERAND IN-REACTOR TEST SECTION
y-RAY SPECTROMETER
LEAD PLUG WITHCALIBRATION SOURCERECESS (POSITION 4)
SLAB OVER SOUTHRECOMBINATION ROOM
LEAD COLLIMATORS (3)(POSITIONS 1-3)
HEV1MENTCOLLIMATOR(6POSITION)
'Z:?A'Z\V^£li\"yV- •;>•'<
, • "> • -SS.
1" SHED.-80 PIPE (SS)
INSULATION COOLANT FROM X-2TEST SECTION
FLOki
TRAPS 1 - 31 - CARBON STEEL2 - MONEL
Footnote: 1 inch = 25.4 ™ 3 _ S T f l | N L E S S S T E £ L
FIGURE 2 SPECTROMETER AND TRAP LOCATIONS ON X-2 LOOP OUTLET PIPING
O1
37
§a.
suiz
I I I I5b kW/m (MAX)
8 10 12 14TIME OF IRRADIATION (days)
FIGURE 3A LINEAR POWER vs TIME FOR ELEMENT RPLPHASE I FDO-681 TEST
20
38
39
8 12 16 20 24TIME OF IRRADIATION (days)
FIGURE 3C LINEAR POWER vs TIME FOR ELEMENT RPPPHASE III FD0-S81 TEST
40
Top ofelement
Defect Defect
Bottom ofelement
RPL LFZ RPP
Figure 4 Neutron Radiographs of Defected Elements Irradiated inExperiment FDO-68100.
FlowDrilledDefect Holes
Figure 5 Sheath of element RPP (Phase III) showing two defect holes and plume ofmaterial deposited on the surface of the sheath. Material originatesfrom defect holes and seems to be tapered by the coolant flow. Heavywhite deposit around defect holes occurred during post-irradiationexamination in the hot cells.
42
Defect
145 Bl ihx
Defect
786
Figure 6 Fuel element section from element RPL at location of defect.Dark band of U,,09 visible on polished section outside graingrowth resgion. Note band of small pores in columnar grains(arrow). £Y radiograph shows high activity in unidentifiedphase near defect.
43
Defect
145 II
Defect
789
Figure 7
Defect section element LFZ showing well-defined equiaxed graingrowth with UO2 missing from underneath defect hole. 3Y radio-graph shows high activity in fuel near defect.
44
Defect
145 El
Defect
787
Figure 8
Defect cross section from element RPP showing grain growthregion and bond of UuO9 in fuel near sheath; appreciableamount of fuel has disappeared out the defect hole-By radiograph shows high activity in phase adjacent to thedefect.
45
Defect
145 Fl
Defect
738 7J5X
Figure 9Element RPP section through secondary defect hole in sheath,note very little fuel has disappeared compared with Figure 10.UijO9 band is less distinct than under primary defect.By radiograph does not show high activity in the fuel adjacentto the sheath defect.
46
Defect
Defect
145 B3 [B] 500X
Figure 10
[A] Unidentified phase in the grain boundaries of the UO2near the defect hole of element RPL.
[B] Unidentified phase within grains near the defect hole ofelement RPL (note how grains seem to be separating nearedge of UO2) .
Unidentified phase in both photos may be a higher oxidethan UO2.
47
U0 2Unidentified
PhaseMountingPlastic
145 E2 100X
Figure 11
Unidentified phase adjacent to defect hole of elementRPP. Note the dendritic structure on the outer surfaceof the phase. The phase shows high activity on (3y auto-radiographs.
48
151 D4
151 II [B] 200X
Figure 12
[A] Unidentified phase {may be similar to Figure 7). Found alongthe surfaces of cracks near periphery of UO2 pellets fromelement RPP.
[B] Pinkish particle that revealed a structure only under polarizedliaht, element LFZ.
49
U.,0 9 U.,0.3
roCDXI
145 E5 & 145 E6 50X
Figure 13 Cross section of UO2 pellet from element RPP showingtwo bands of Ui,O9 the inner one at the junction of thecolumnar and equiaxed grains and the outer oneapproximately half way between the sheath and thegrain growth region.
50
OD OD
+Jua1
(D
a
145 15 150X 145 14 150X
..[A] [B]
Figure 14 [A] shows typical zirconium hydride concentration insheaths from elements RPL and RPP and most sectionsfrom element LFZ.
[B] shows heavy concentration of hydride in sheath ofelement LPZ adjacent to the drilled defect hole;more hydride platelets are located near the outsidesurface of the sheath.
51
o
o
145 E4 150X
Figure 15 Typical of hydride concentration near defect of elementsRPP and RPL. Compare with Figure 9B.
52
1000
100 _
ccLU
. . . . 1
LF2
—
—
. . . . 1
(D) "
• I I
1 1 '
, 1 .
RPP
RPL
1 ' 1
>(m)
( i )
, , 1
I f 1 ' 1
-681 FUEL Q
\
-
-
—
\-» LOCKE'S\ BOUNDARY FOR\SEVERE HYDRIDING\ OF SHEATHS
\. . 1
10 -
1 —
500 1000 1500 2000
ELEMENT SURFACE HEAT FLUX ( k W / m 2 )
2500
FIGURE 16: BOUNDARY CURVE FOR DEFECT OPERATION FROM LOCKE (7), PLOTTINGDAYS TO FAILURE DUE TO SHEATH HYDRIDING AFTER DEFECTIONAGAINST SURFACE HEAT FLUX FOR THE FDO -681 ELEMENTS.
K r-SB I 196 KiV GAKHA RAY ENERGY PEAK!
{ I I I I I I I 1
\ •
:i2 2 -
18 '
1 1 •
10 '
6 '
2 •
-A-A
II
J
i i i i i i
.A
— A
9 10 11 12 13 l<4 IS IS 17 18 19 20 21 22 23 2 1 25 26 27 28 29 30 31 1 2 3 >4 5 6 7 8 9 10 I I 12 13 14 IS 16 17 18
OCT NOVIRRADIATION TIHE ( d a y s )
FICUPE 17 FISSION PRODUCT RELEASE SATE AND COGLANT CCNCLiTBATION FOR KrBB ALSO THE REACTOR POIF.R
CURING PHASE I I I EXP-FDO-6B100
F o o t n o t e : 1 c u r i e = 3 7 GBq
JO"
io 1 0
(Xe l35)
"*<Xe13B>
FIGURE 18 FISSION PRODUCT RELEASE RATE vs TIUE SHOWING THE CYCLIC RELEASE
BEHAVIOUR OF SIX ISOTOPES DURING PHASE I I I IRRADIATION
10"12:00
NOV 7
12:00
NOV 8
12:00
NOV 9
12:00NOV 10
12:00NOV i l
IRRADIATION TIME
1131 Xe 133 Xe 133m 1133
Kr 88 Kr 87
1135 Kr 85m Xe 135 1134 Xe 138
10"
10- '
I10 •
10-
FIGURE 1 9 : FRACTIONAL RELEASE ( F R ) PLOTTED AGAINST DECAY CONSTANT ( X ) FOR PHASE I .
FOO - 6 8 1 EXPERIMENT
1 0 - 5
DECAY CONSTANT X ( s * 1 )
10-3
56
FIGURE 20A: FRACTIONAL RELEASE ( F R ) VS IRRADIATION TIME FOR
PHASE I GROUP 2 PRODUCTS
10"
10*2
GROUP 2
FISSION PRODUCTS
O Kr - 85 m
D Kr 87
O Kr 86
A Xe 138
10-3
D oa O
a
10 -4 li I100 200 300 400
IRRADIATION TIME (hours)
500 faOO
57
FIGURE 20B: FRACTIONAL RELEASE (FR) VS IRRADIATION TIME FORPHASE I GROUP 3 FISSION PRODUCTS
10-'
O
a
10 -2 GROUP 3
FISSION PRODUCTS
OXe 133
OXe 133 m
Oxe 135
10 -3
10"-4 100 200 300 400
IRRADIATION TIME (hours)
500 600
58
FIGURE 20C: FRACTIONAL RELEASE (FR) VS IRRADIATION TIME FOR
PHASE I GROUP 1 FISSION PRODUCTS
10-'
10 -2
GROUP 1FISSION PRODUCTS
O I 131• I 133
10 -3
I100 200 300 400
IRRADIATION TIME (hours)
500 600
10"
I 131 Xe 133 Xe 133m
Kr 88 Kr B7
I 135 Kr85m Xe135 I 134 Xe 138
—I-
10-2
CJ
FIGURE 21: FRACTIONAL RELEASE (FR) PLOTTED AGAINST DECAY CONSTANT ( X)
FOR PHASE n
1Q-S 10"<
DECAY CONSTANT X (s"')
10-3
60
10-1FIGURE 22A: FRACTIONAL RELEASE (FR) VS IRRADIATION TIME FOR
PHASE D GROUP 2 FISSION PRODUCTS
10-2
GROUP 2FISSION PRODUCTS '
OKrDKrAKr
85 m8788138
10 -3 - o
o
o o
o o
io-5I t i «
100 200 300 400 500
IRRADIATION TIME (hours)
600
10-'
61
oD
DO
10"3
Oo
GROUP 3FISSION PRODUCTS
O Xe 133D Xe 133 mO xe 135
FIGURE 22B: FRACTIONAL RELEASE (FR) VS IRRADIATION TIME FOR
PHASE D GROUP 3 FISSION PRODUCTS
10 -5 t • I i I100 200 300 400
IRRADIATION TIME (hours)
500 600
62
10'FIGURE 22C: FRACTIONAL RELEASE <FR) VS IRRADIATION TIME FOR
PHASE n GROUP 1 FISSION PRODUCTS
10-2
Oo
GROUP 1
FISSION PRODUCTS•is I 131
I 133
10 • 4
a
10-5I . I
100 200 300 400
IRRADIATION TIME (hours)
500 600
10-1
1 131 Xe 133 Xe 133m I 133 I 135 Kr I
Kr 88 Kr 8?
Ke135 Xe 136
10-2
to-»
7 0 " '
FIGURE 2 3 : FRACTIONAL RELEASE (FR) PLOTTED AGAINST DECAY CONSTANT ( X ) FOR PHASE H I
1 0 " 5 10 -
DECAY CONSTANT X ( s - 1 )
10-3
g
n - 10 '
10-2
10'3
i o - «
FIGURE 24A: FRACTIONAL RELEASE (FR) VS
GROUP 2
FISSION
0
0D
A
•
PRODUCTS
O
8
A
I.
O
8
A
(
GROUP
0 Kr 85ra
D Kr 87
O Kr 88
A Xe 138
O
oD
A
1 .
2
O
OD
A
f
FISSION PRODUCTS
O
0D
A
1. 1
IRRADIATION
O
OD
A
. 1
TIME FOR PHASE
O
OD
A
1 .
m
o
O
D
A
1 •
O
O
a
A
.1100 200 300 400 500 600 700 S00 900
IRRADIATION TIME (hours)
10-'
10-2
io-3
io-<
o
-
O
—
o
D
0
ll
FIGURE 248: FRACTIONAL RELEASE (FR) VS
GROUP 3 FISSION PRODUCTS
GROUP 3
FISSIfr -ODUCTS
O
D
o
O
0
O
1 *
O Xe 133
O Xe 133 m
[O Xe 135
O
OO
: ' t'V:... , : ^ , . tffl.
1 > M | . • •
* $ * ' - •
' • • ' . $ ,
1. i . i
IRRADIATION
O
D
o
. 1
TIME FOR
oD
o
1 ,
PHASE ELI
§
O
oo
O
.1100 200 300 400 500 600 700 800 900
IRRADIATION TIME (hours)
FIGURE 24C: FRACTIONAL RELEASE (FR) VS IRRADIATION TIME FOR PHASE ED
GROUP I FISSION PRODUCTS
10"' GROUP 1
FISSION PRODUCTS
0 I 131
D I 133
0 1 135
10-2
s
10-3
D
o
10"100 200 300 400 500 600 700 800
IRRADIATION TIME (hours)
900
ID"1 —GROUPFISSION 1PRODUCTS[XENONS!
F I G U R E 25 F R A C T I O N A L RELEASE ( F R ) FOR t = 0 v s
DECAY CONSTANT ( X ) FOR PHASE I , I I ,
AND I I I OF THE F D O - 6 8 1 E X P E R I M E N T
A <•
10"1 — GROUP IFISSIONPRODUCTSlIODTNES
I Q " 1 -
1 0 " ' -
1 0 - ' -
EXPERIMENT FDO-681
ELESIM
ELESIM• ALLISON
AND
RAE ELEMENT CEU
1131 I t 133 Xel33m 1133 1135 Kr85m Kr88 X«135 Kr87 X«138
^ROUP 2• F ISS ION
PRODUCTSURYPTONSJ
i o - 8 ID"5 10"
DECAY CONSTANT X (s"1)
io-
102
10'
10°
- OCT. 17, 1975 PHASE I I I FIGURE 26 CONCENTRATIONS OF Kr-85m, Xe-135, Xe-133
AND 1-131 PLOTTED AGAINST TIME FOR A TRIP
REACTOR SHUTDOWN AND A REACTOR STARTUP
Footnote: 1 curie = 37 GBq
Xe
-133
- 1 3 5
- . . _ /
^ — :• 1-131
— / . Kr-85m
_ REflCTOR POWER
1
: r1 1 1
— 30
- 2 0 REflCTOR
POWER
. 1 0 ( H U )
- n
3 10 ' t
18:00 19:00 20:00 21 :00
TIME (h)
22:00 23:00
g
z
r
WCE
N1
<_>
10*
101
10
SEPT.
—
23, 1975
9:0b :
'"'V
/
PHASE I I
^v
///
\l
J
f/1 /
—
10:55
I
FIGURE 27 CONCENTRATIONS OF Kr-55m, Xe-135.Xe-133 AND 1-131 PLOTTED AGAINST TIMEFOR A SCHEDULED REACTOR SHUTDOWN ANDA REACTOR STARTUP
Footnote: 1 curie = 37 GBq
_ _ _ Xe-135
•-~-..r " * ~ ~ Kr-85m
1-131
REACTOR POWER
1
REACTOR_ 2 Q POWER
(HW)
- 10
- 08:00 9:00 10:00 11:00
TIME (h)
12:00 13:00
SEPT. 2 3 . 1975 PHASE I I FIGURE 28 CONCENTRATIONS OF Kr-55m, Xe-135 , Xe-133 AND 1-133PLOTTED AGAINST TIME FOR A TRIP REACTOR SHUTDOWNAND A REACTOR STARTUP. THE TRIP SHUTDOWN HASOCCURRED ABOUT U HOURS AFTER A SCHEDULED SHUTDOWNOF THE REACTOR Footnote: 1 curie = 37 GBq
- — — Xe-133
Xe-135
101
10'
REACTOR
o
18:00 19:00 20:00 21:00 22:00 23:00
TIME ( h )
71
- S
AND
133
XE-
inm
TOR
REAC
aLU
EDUL
o cc« oLJ a.0=
8
CO
o1—
•—zUICJ
s
CO
zCD<xQUJ1—h -O—1Q_
_ I
CO
£gh-3
u .l
i i i i 11 i i i i
(Eui3/!3i/) N0UBaiN33N03
10*
5- h-
10'
- JULY 3 1 . 1975 PHASE I
—
_
f
i /
13
0
I
32
I
14:34
J
FIGURE 30
REACTOR POWER
I I
CONCENTRATIONS OF K r - 8 5 m ,
PLOTTED AGAINST TIME FOR
SHUTDOWNS AND STARTUPS IN
Footnote: 1 curie - 37 "iBq
#*-
/ • ' . . • • - . . . '
--J
17 :32
— 1
X B - 1 3 5 , Xe-133 AND I -131
TWO SCHEDULED REACTOR
CLOSE PROXIMITY
Xe-133
Xe-135
1-131
Kr-B5m
t-30
2 Q REACTOR
POWER
(HW)
-10
o I12:00 13:00 14:00 15:00 1b:00
TIME (h)
17:00 18:00 19:00
73
2I
1 0 " '
FIGURE 31: PLOT OF THE VARIATION FISSION PRODUCT CONCENTRATION INCOOLANT DURING A REACTOR STARTUP OF PHASE I OF THE
FDO-681 EXPERIMENT SHOWING THE EARLIER RELEASE OF THE RAOIOIOOINESCOMPARED TO THE XENONS AND KRYPTONS. COUNTING TIME DURING THE POWERTRANSIENT WAS 200 SECONDS.
13:05 Xe 135
13:01
13:05
REACTOR POWER
11:00 12:00 13:00
TIME JULY 2 8 / 7 5
F o o t n o t e s 1 c u r i e = 3 7 GBq
I 133
Kr 88
14:03
30
25
20
15
1° Ic
F I G U R E 3 2 : S C H E M A T I C P L O T S OF ( T R ) R E L E A S E V A L U E S FOR K r 8 5 m ; Xe 1 3 5 . AND I 1 3 1 A G A I N S T T I M E V A R I A B L E S
SHUTDOWN TRANSIENT FISSION GAS RELEASE (TR) (5)
FDO-
68100
PHASE
I
(TR)
n(TR)
m(TR)
••
•
w
TOTAL TIME AT POKER BEFORE TRANSIENT(h)
Kr 65 m Xe 135
* \
s
1 131
J1 - *
* I *
•MM
*•
H
•t
TOTAL REACTOR OPERATING TIME(H>
Kr 85m
•
Xe 139
IN
I 131
••
M
••
M
REACTOR SHUTOOIN DURATION(s)
Kr 85 in Xe 135
m
I 131
• • • "
• l*f»
STARTUP TRANSIENT FISSION GAS RELEASE (TR) (%)
FOO •68100PHASE
TOTAL TIME AT POWER BEFORE TRANSIENT( h )
TOTAL REACTOR OPERATING TIME(h)
REACTOR STARTUP DURATION(s)
Kr 85 m Xe 135 I 131 Xe 135 I 131 Xe 135 I 131
I
(TR)
n(TR)
HI
(TR)
75
F I G U R E 3 3 : S C H E M A T I C P L O T S O F I T R I R E L E A S E V A L U E S F O R F I S S I O N G A S E S A G A I N S T D E C A Y C O N S T A N T ( X )
SHUTOOKN TRANSIENT FISSION GAS RELEASE <TR) (X)
FOO-
68100
pmsF
DECAY CONSTANT X (S '< )
Kr 85m. Kr 87. Kr 88, Xe 138 Xt 133, Xi 133 m, Xe 135 1 131, t 133, 1 135
(TR)
n(TR>
En
(TR)KrflSm K t H Kr»T 119ft
STARTUP TRANSIENT FISSION GAS RELEASE (TR) ( * )
FOO -
68100
PHASE
DECAY CONSTANT X
Kr 85m, Kr 87, Kr 88, Xe 138 Xe 133, Xl 133 m, Xe 135 I 131, I 133, I 134, I 135
1
(TR)
n(TR)
HI
(TR)
APPENDIX 1
THE LOOP MODEL
The principal features of the model for determiningthe release of fission gases from the element into the loopcoolant are summarized below:
The change in the inventory of a fission product withtime in the loop is given by the expression:
= Z(t)+R(t)-AQ(t)-6Q(t)-aQ(t)-KQ(t) (A)dt
where Q(t) = the total inventory of an individual fissionproduct in the coolant at any time (atoans) .
Z(t) = the production rate of a fission product fromuranium contamination in the in- reactor sectionof the loop (atoms/s).
R(t) = the fission product release rate from the defectedfuel element (atoms/s).
Ao(t) = amount of inventory lost by radioactive decay(atoms/s) X = decay const. (s~l).
3Q(t) = amount of inventory removed by the loop purificationcircuits (atoms/s) 3 = purification const. (s~l).
aQ(t) = amount of inventory deposited on loop surfaces(atoms/s) a = deposition const. (s~l)•
KQ(t) = amount of inventory lost from the loop by coolantleakage (atoms/s) K = leakage const. (s~^)•
For the FDO-68100 defect tests in the X-2 loop thepurification, deposition, leakage and contamination effects wereso small that they can be neglected in the model. This leavesradioactive decay as the main mechanism for removal of thefission products from the loop.
Thus R(t) = AQ(t) + ^ l i ) (B)
Q(t) is related to the fission product concentration in thecoolant at the element location by the expression
A1.2
O(t) - No(t) v ^ XLe J (C)
/where No(t) = fission product concentration in the coolant
adjacent to the element (atoms/cm3)
v = volume of loop (cm3)
u = coolant velocity (cm/s)
L = length of the loop piping (cm)
Since at equilibrium the disintegration rate equalsthe release rate, the measured fission product concentrationat the spectrometer (N (t)) is equal tc
XNexp(t) = No(t) e u
where X = the piping distance from the element to the spec-trometer (cm). Substituting for No(t) in equation(C)
Q(t) = Nexp ( t ) e " v l 1 ~rB I (D)
Q(t) can now be determined experimentally and by using equation(B) the release rate R(t) of individual fission productscan be calculated at any time during the test.
APPENDIX 2
TIME DEPENDENCE OF RR/BR
let RR be the release rate of an isotope from a defected element
BR be the birth rate of this isotope
Q be the quantity of this isotope in the fuel
y be an escape rate constant
then |2. = B R - AQ - yQ (A)
with RR = yQ . (B)
Now at equilibrium
§ | - 0 = BRg - X Q E - U Q E - BRg - X Q E - RRE (C)
=) = _JL CD)BB.L U + A
however for any t less than infinity, equation A becomes
-U+y)t r (X+p)tQ = e Jt=Q BR(t) e dt (E)
if we assume BR,t» is constant, then equation (E) becomes
A + y
Q(t) = -£5_ (1 - e I (G)
or
Q(t) (A + y) = BR 1̂ - e j
divide equation (H) by RR = yQ 3
A2.2
-(X+uK i (I)
but from equation (D) we know that
BRA, V + X
so equation (I) can be rearranged to give
(K)*X\ = 55 / 1 - e "(UlJ)t\
SRL RR,*., \ /
or
(L)
APPENDIX 3
Equations for calculating the release of fission productsfrom the Allison and Rae release model (9).
Kryptons + Xe-138 Fc = a- In / I + LX\ (A)
Vc
Fc
•51A3/2
In r + LX2i"
LX2a
iodines Fc = -̂S- ^ 7 ^ - <B>V 3 / 2
Xenons Fci = | l n / i T ^ - \ + =2. ' ^ In / " ^ \ (C)
where Fc = fractional release
L = length of fuel stack
A = decay constant
a = grain growth fraction of fuel
S - surface area of grain growth region
V c = volume of grain growth region
ak/e are rate constants, solved graphically
D1 = diffusivity of iodine, solved graphically
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