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Proceedings of the HTR 2014Weihai, China, October 27-31, 2014

Paper HTR2014-71392

Concept of a Prestressed Cast Iron Pressure Vessel for a ModularHigh Temperature Reactor

Dr. Wolfgang Steinwarz, Dr. Dieter BouninSiempelkamp Nukleartechnik GmbH

Siempelkampstrasse 45, 47803 Krefeld, Germanyphone: +49-2151-894290, [email protected]

Abstract – High Temperature Reactors (HTR) are representing one of the mostinteresting solutions for the upcoming generation of nuclear technology, especiallywith view to their inherent safety characteristics. To complete the safety concept ofsuch plants already in the first phase of the technical development, Prestressed CastIron Pressure Vessels (PCIV) instead of the established forged steel reactor pressurevessels have been considered under the aspect of safety against bursting. A long-term research and development work, mainly performed in Germany, showed theexcellent features of this technical solution. Diverse prototypic vessels were testedand officially proven. Design studies confirmed the feasibility of such a vesselconcept also for Light Water Reactor types, too. The main concept elements of sucha burst-proof vessel are: Strength and tightness functions are structurally separated.The tensile forces are carried by the prestressing systems consisting of a largenumber of independent wires. Compressive forces are applied to the vessel walls andheads. These are segmented into blocks of ductile cast iron. All cast iron blocks areprestressed to high levels of compression. The sealing function is assigned to a steelliner fixed to the cast iron blocks. The prestressing system is designed for anultimate pressure of 2.3 times the design pressure. The prestress of the lids isdesigned for gapping at a much smaller pressure. Therefore, a drop of pressure willalways occur before loss of strength (“leakage before failure”). In addition to thesesafety features further technical as well as economic aspects generate favorableassessment criteria: high design flexibility, feasibility of large vessel diameters;advantageous conditions for transport, assembly and decommissioning due to thesegmented construction; advantage of workshop manufacturing; high-level qualitycontrol of components. Nowadays, considering the globally newly standardizedsafety requirements, especially after the Fukushima accident, as well as the progressof the HTR-technology especially in China, the interest for the PCIV concept hasbeen reactivated.

I. INTRODUCTION

Already 40 years ago the concept of a PrestressedCast Iron Pressure Vessel (PCIV) for nuclear powerplants was developed, primarily with respect to theHigh Temperature Reactor technology [1], [2], [3],[4], [5]. At that time goals like design flexibility,improved transport logistics and optimized safetycharacteristics were positioned in the center of the

discussions between prospective manufacturers andusers. However, after approx. 20 years of intensiveand successful research work with some prototypicaltest vessels (Figs. 1 to 5), the final developmentsteps were not initiated, influenced by the reducedglobal interest in pursuing the HTR concept as wellas by the availability of established standardizedforged steel pressure vessels.


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The increased engagement for the so-called nextgeneration reactor types, the successful developmentof Chinese HTR projects and the situation after theFukushima accident leading to newly standardizedsafety requirements promoted the idea of areactivation of the PCIV technique.

The following paper summarizes the basicdesign elements and major issues of the practicalexperience during the development phase.

II. OVERVIEW OF PCIV DEVELOPMENT

Research on the PCIV started in 1973. Followingup on a feasibility study, a first prototype test vesselwas built (Fig. 1, Table 1). At a scale 1:7.5 to theReactor Pressure Vessel (RPV) of the Thorium HighTemperature Reactor THTR-300 (that was in thedesign stage at that time) it already displayed all themain features of a PCIV.

Fig. 1: The first prestressed cast iron pressurevessel

The full-scale research on the PCIV-HTR startedin 1975. Under the leadership of Siempelkamp therewere diverse partners for reactor design and thedevelopment of major components like prestressingsystems and steel liner. First work on a nucleardesign code for the PCIV was done by independentexperts [6].

To demonstrate the qualification of the PCIVconcept, a helium storage vessel for the scram tankfor the THTR-300 reactor was designed (Fig. 2,Table 1). The design was investigated by competentauthorities who also required extensive material and

component testing. The vessel received its nuclearlicense, was manufactured and went into operation in1980 [7]. The test of the ultimate load behavior ofthe hoop prestressing tendon (that was part of thelicensing requirements [20]) is described in sectionVI.1 of this paper.

Fig. 2: PCIV – scram tank for THTR-300

The PCIV research project culminated in thedesign, manufacturing and extensive testing of thePCIV-HTR test vessel. At a reduced scale it featuredthe major design aspects of a full-size PCIV-HTR.(Figs. 3 to 5, Table 1)The design, manufacturing andassembly were supervised by competent authorities.The assembly and operation of this test vessel undera wide range of loading conditions successfullydemonstrated the suitability of the PCIV as RPV forthe HTR (selected results in section VI.3).

Fig. 3: PCIV-HTR test vessel, section


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Fig. 4: Bottom head of PCIV-HTR test vessel

Fig. 5: PCIV-HTR test vessel

The feasibility of a PCIV-HTR was furtherstudied in a follow-up investigation [8], [9], [10],[11], [12], [13], [24]. Its object was to furthervalidate the technology, its safety features and itssuitability, this time for a HTR module reactor. Inthis context Siempelkamp and multiple partnersinvestigated the feasibility of passive decay heatremoval for a PCIV-HTR. The primary cell wall wasalso designed using Ductile Cast Iron (DCI) blockswith integrated cooling elements instead of thestandard design concrete wall (Figs. 6 and 7). Thesewere components of an inactive and redundantcooling system using the principle of naturalconvection.

A wall and primary cell segment was built. Thisfull scale mock-up included all components of a20°C sector. The extensive tests showed that thisdesign can safely handle a loss of coolant accident(selected results in Section VI.4).

Fig. 6: PCIV for HTR module reactor: 1-vesselwall, 2-primary cell, 4-removable head

Fig. 7: RPV and primary cell of HTR modulereactor. Note contour of 20°-segment offull scale mock-up


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With the research program on the HTR modulereactor and the mock-up for testing decay heatremoval the large publicly supported researchprograms came to an end. In a much smaller follow-up program the design of a PCIV for a Boiling WaterReactor (BWR) was investigated. The designrequirements of a diameter of 6.9 m and a pressureof 8.8 MPa were the largest ever for PCIVs.

Up to the HTR module reactor the design hadalways called for double-walled DCI blocksconnected by ribs. The axial tendon was placed inthe wall center (Figs. 3, 6, 7, 14). With the challengeof the BWR a slimmed-down single wall design wasdeveloped. In addition, the separate DCI anchorblocks for the liner were also eliminated. The linerbolts were anchored directly to the single cast ironwall blocks. The axial tendons were placed outside(Fig. 8). Temperature gradients in the cast iron nowwere much smaller than before, reducing theassociated stresses.

A major question was the stress concentration inthe wall caused by the holes for the liner anchors.Extensive stress analysis for stationary and transientconditions followed [23]. It was found that the stressconcentrations can be kept on an acceptable level.

The last investigation up to date was the designwork for a PCIV-HTR 600 module reactor. This wasdone by Siempelkamp as a sub-contractor in the EUsupported international project RAPHAEL. Thedesign was executed for inside dimensions of 7.3 min diameter by 21.7m in height and a pressure of6.5 MPa. The total weight of DCI blocks,prestressing systems and liner added up to just over4.000 tons. A major element of the design work wasan in-situ cooling and decay heat removal system inthe cast iron wall. This is in extension of the conceptof passive heat removal in the primary cell that wasdesigned and tested in the preceding project (SectionVI.4). With the help of the in-situ wall cooling, thedesign temperature of the wall could be reduced to270°C.

Table 1: Overview PCIV design and testing.

Year ProjectInside

diameterTemperatureand medium

Designpressure

MPa

1973 Prototype test vessel 2 m 40°C, water 3.9Shows feasibility of PCIV concept beforestart of extensive research program

1981 Scram tank 2 m 30°C, helium 22.6 Nuclear license and service in THTR-300

1986PCIV-HTRtest vessel

4 m 130°C, water 5.3Production and assembly experience.Wide range of tests of a PCIV

1987Design of PCIV for

HTR Module5.9 m 300°C, helium 7.0

Design extended to a passive heat removalsystem in the primary cell

1989Test facility for

passive heat removal20°

sectormax temp. atheater 610°C -

Wide range of tests of passive decay heatremoval of PCIV-HTR and primary cell

1994Design of PCIV for

BWR-10006.9 m 300°C, water 8.8

PCIV design for boiling water reactors.Liner anchors directly in the DCI wall

2006Design work on

PCIV for HTR-6007.3 m 300°C, helium 6.5

PCIV design for HTR-600, in-situ coolingsystem integrated into DCI wall

III. PCIV DESIGN ELELMENTS

The most important design principles of thePCIV are the separation of the load carryingstructure of wall and heads from the prestressingsystem and the separation of strength and tightnessfunctions. The load carrying structure of the cylinderis a solid wall (at the outset the design had called fordouble-wall blocks). The top and bottom heads arestructures with solid faces connected by ribs.Cylinder and heads are segmented into blocks. Theseblocks are made from DCI material. The wall and

heads are prestressed by straight axial and wire-wound hoop tendons. A liner is anchored to thecastings by bolts (Fig. 8).

Due to high levels of prestress the wall structureoperates in compression under all loadingconditions. Faces between the segments are areas ofzero tensile stress. Shear forces are held to minimumby orientation of segment faces normal to majorcompressive stress. Remaining shear forces aretransmitted by shear keys. Just as for conventionalprestressed concrete structures, the cross sections of


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the DCI blocks are much larger than the crosssections of the prestressing tendons. The loads underall operating conditions therefore are primarilycarried by the cast iron: its level of prestress isreduced.

Fig. 8: Characteristic PCIV wall structure

DCI is a material with very good strength andhigh ductility. There is very much experience in highquality manufacturing. It has a fine grained andferritic microstructure. The pearlite content is small.The graphite nodule count is high (Fig. 9). Theseproperties result in very good fracture toughness.DCI is not sensitive to cracks. There were extensivematerial investigations [14], [15]. Noticeableimprovements of its properties also resulted from thedevelopment of DCI casks for storage and transportof radioactive material (e.g. CASTOR®).

There is a wide range of applications thatincludes highly stressed and heavy walledcomponents as for large press frames and windpower, among others. DCI can be manufactured withlarge wall thicknesses. It is suited to operate atelevated temperatures. In the PCIV the segmentsoperate under compressive mean stresses and thus inits range of maximum fatigue strength.

All standard inspection procedures can beapplied. Siempelkamp is equipped and licensed forthese tests. DCI is a material well suited forultrasonic inspection for internal flaws. Whenrequired the inspection can encompass 100% of thevolume. Inspection for surface flaws is standard,either as dye penetrant or magnetic particle test.

Fig. 9: Microstructure of GJS-400 (DCI)

The hoop and axial prestressing systems consistof a large number of tendons. Each tendon is madeup many independent wires. The new high strengthprestressing wire Ultrafort was developed in thescope of the PCIV-HTR program. It can be operatedat the high temperatures of a PCIV-HTR wall andstill displays little relaxation [16], [17], [18].

Table 2: Material properties of DCI and Ultrafort

ductile cast ironGJS 400

prestressing steelUltrafort 6998

RT 300°C RT 300°C

Rm N/mm2 370 350 1800 1500

Rp0,2 N/mm2 240 220 1740 1400

A5 > 12% > 8% - -

E N/mm2 165000 160000 184000 167000

Relaxation < 10%

System tightness for operation conditions of thePCIV is assigned to a steel liner anchored to the DCIblocks [19]. The liner is prestressed together with theDCI blocks. The bolts are designed to keep the linerfrom buckling. The bolts are designed to transfershear and are closely spaced. They are not subject totension.

Heads of PCIVs can be designed as removablelids. The axial prestress of removable heads isdesigned such that they can be removed while axialprestress of the remaining vessel is upkept. Hoopprestress is not affected.

The concept of the PCIV shows high flexibilityof design. If required, wall thicknesses of the DCIblocks can be produced with high material quality upto 400 mm. Heights and widths of the segments canbe adapted to any particular design and assemblyrequirements. There is no practical limit on vesselheight. Axial tendons of any length can bemanufactured and assembled. Vessel diameters canbe very large. For all practical reasons there is no


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limit on the amount of hoop prestress. Withappropriate structural design of the vessel heads, thediameters of a PCIV can exceed that of welded steelvessels. The challenges of manufacturing,machining, transport and assembly do not increasewith vessel size. Flexible block shapes, dimensionsand weights are further important advantages forhandling and transport. The logistics of componentproduction are relatively simple. The same holds fortransport, assembly and disassembly. These aspectshave been proven by the two test vessels as well asby the PCIV for the THTR-300 scram tank describedin Section II. All three vessels were dismantled afteruse respectively after decommissioning.

The DCI material required for the vessel is astandard product and readily available. Alldemanding production and inspection steps are donein the shop and not during on-site assembly.

After licensing and completion of all design andfirst-of-its-kind work, a PCIV-HTR would require onthe order of two years for completion. That wouldinclude casting and machining of the segments,transports, assembly of liner and DCI segments andfinally axial prestress and wire-winding.

Despite the segmentation of the vessel wall intoDCI blocks, the PCIV structure can be efficientlypre-computed by finite element analysis. Themachining tolerances of the blocks are very small.The assembled structure responds to prestress like anunsegmented solid structure. This was extensivelymonitored during the prestressing sequence of thePCIV-HTR test vessel. Prestress levels measured bystrain and forge gages and displacements of thevessel due to prestress were in good agreement withpre-computed values. There was no shear movementbetween blocks. This good agreement between pre-computed and measured stresses and displacementsalso held true under internal pressure andtemperature loading. The joints between the blocksdid not gap under design loads.

Experience was gained with the manufacturing ofconventional segmented wire-wound DCI structureslike the press frame shown in Fig. 10.

IV. SAFETY FEATURES

The concept for RPVs requires the exclusion oflarge fractures. By definition a large fracture willlead to loss of coolant. A fracture is also defined asto develop quickly (< 1 s). This may cause anexplosion of the vessel which in turn yields to widedistribution of large amounts of radioactive material.The kind of radioactive isotopes developing in an

accident also depend on the rapidity of vesselfracture and explosion.

Fig. 10: Wire-wound segmented DCI press framefor 200 MN rubber pad press

The separation of load carrying functions intocastings and tendons and the sealing function of theliner allows for optimizing each component. Theprestressing tendons of a PCIV are designed towithstand an ultimate pressure of 2.3 times thedesign pressure. Under overload pressure (at a levelto be determined by the designer) the joints betweenthe DCI segments will lose their prestress. All furtherload increase will then be carried by the prestressingsystem alone. This design feature ensures that thereis always gapping and reduction of pressure beforefailure by bursting. This important property wassuccessfully demonstrated in the PCIV-HTR testvessel (Section VI.3).

The prestressing system is of redundant design.Tendons carry loads independently of each other.Failure of individual wire cross sections cannot anddo not propagate to other sections. Both prestressingsystems are designed for carrying ultimate loads.Under ultimate load the prestressing systems displayyielding and no sudden failure. This was clearlyshown in full scale tests for both hoop and axialtendons (Sections VI.1 and VI.2).

In-service instrumentation can be installed forpermanent surveillance. Cable forces and thereforealso the level of vessel prestress can be monitored byredundant force gages, for axial cables as well ashoop tendons. This concept was used and executedin the PCIVs described in Section II. The tendonsare accessible for in-service inspection.

DCI provides good shielding. The level ofneutron radiation on the prestressing system is muchreduced. This reduces the potential for embrittlementof the wires.


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V. MANUFACTURING AND ASSEMBLY

DCI blocks for PCIVs are produced in the sameway as castings for a wide range of otherapplications. Blocks with weights far exceeding 100tons are standard in every-day production.Siempelkamp is the leading manufacturer of heavysectioned DCI castings. The castings are made withsand molds. The number of castings required for aPCIV could be performed by Siempelkamp by itselfwithin a very reasonable time frame.

Machining of the blocks can be performed bySiempelkamp itself and by a host of external shops.For a short production schedule of a PCIV therewould be several shops involved. Machining to verysmall tolerances is routine. Fitting the blockstogether poses no problem. Machining of the blocksfor the PCIV-HTR test vessel was done by threedifferent shops. In pre-assembly and during wire-winding the segments displayed a perfect fit.

The axial tendons for the PCIV follow theestablished design of Bureau BBR. This is a designwith widespread application in civil engineering.There is a parallel arrangement of round wires thatare anchored with button heads (Fig. 11). For thePCIV the tendon forces must be very high. Thisrequires a much bigger number of wires per tendon.Therefore the sizes of the anchor heads must also bemuch larger. As part of the PCIV-HTR developmentsuch anchors and tendons were built and tested bySUSPA and HRB (see Section IX.2). The axialtendons are manufactured completely in the shop andthen transported to the construction site.

On-site construction of the PCIV begins with theassembly of the blocks of the bottom head. Thebottom head is partially prestressed with a few wirelayers in a raised position and lowered onto thevessel supports. The shop-machined liner panels forthe bottom head and the transition to the cylinder areput in place in raised positions so as to permitwelding and inspection from both sides of the welds.After lowering the liner bottom into its final position,work continues with welding together of the full-height panels of the cylinder liner. This includes allforgings for the penetrations. The liner bolts arewelded and inspected starting with the bottom headand continuing with the blocks of the cylinder thatare placed ring by ring and also partially prestressedwith a few wire layers. Bolts with welding defectscan be removed and new bolts placed. A perfect fitand plane surface, for example for the seals of thelids, is achieved by local on-site machining of theliner forgings. Both of these procedures weresuccessfully tested in full-scale mock-up tests and inthe PCIV-HTR test vessel. Finally the axial

prestressing tendons are put in place. Axial prestressis done in sequence with winding morecircumferential wire layers.

Fig. 11: Axial tendon for lid of PCIV-HTR testvessel (design by Bureau BBR)

VI. MAJOR RESULTS OF LARGE-SCALETEST SETUPS

VI.1 Ultimate load behavior of a hoop tendon

The circumferential wire winding was a first-of-its-kind design. The competent authorities in thenuclear licensing of the PCIV scram tank required afull-scale mock-up test of such a hoop tendon up tofailure [20], [21]. For the test, the wires were appliedindirectly onto a large number of stressing shoesspaced uniformly over the circumference of the wallsection (Fig. 12). The stressing shoes were liftedradially by high pressure tension-bars (simulatinginternal pressure). The complex hoop tendonbehaved similar to a standard tensile specimen. Alinear phase was followed by a non-linear phase withtension-bar forces and radial displacements stillincreasing. This was followed by a yielding phase.One by one individual wires in the lowest two layers(subject to the highest increase in stress) ruptured.However, this did not result in a reduction of overalltendon force, since neighboring wires took up thedifference. Testing continued until several dozenwires had failed. The average stress in the total wirepackage at that point hat reached 97% of the nominaltensile strength of an individual wire.

VI.2 Ultimate Load Behavior of an axial tendon

The axial tendons used in all of PVIC-HTRresearch were designed by Bureau BBR ofSwitzerland. The design for the RPV at the time ofthis test called for axial tendons made up of 324round 7 mm wires. Such a tendon was tested understepwise load increase up to ultimate loading. Thetest was terminated under marked yielding and afterseveral wires had ruptured. These ruptures did not


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lead to a drop of total tendon force. The maximumforce corresponded to 104% of the nominal tensilestrength of the 324 wires. The anchor remainedintact. It could be concluded from the performanceof the anchor head that heads with up to 400 wiresare feasible [22].

Fig. 12: Test of wire-wound hoop tendon

VI.3 PCIV-HTR Test Vessel

The test vessel featured the major design aspectsof a full-sized PCIV-HTR. The number of DCIblocks was very large in order to study theperformance of a segmented wall in assembly(machining tolerances, liner, prestress) and underloads. The internal pressure was equal to that of thereference HTR at that time (5.3 MPa). Prestress wasdesigned for an ultimate load of 2.3x5.3 = 12.2 MPa.In order to limit costs, water and not helium wasused as pressure medium. For the same reason ofcosts the temperature was limited to 130°C, allowingwater to be used as pressure medium. Otherwise theexternal peripheral components of the heating andpressurizing circuit would have been demanding andtoo cost intensive.

Segmentation of the bottom head into 13 blocksrepresented the top head segmentation of thereference PCIV-HTR. A very large opening in thetop slab received a removable lid. It was placedeccentrically in order to cause non-symmetricdeformations for the surfaces at the ring seal underloads. The machining of the DCI blocks was done byseveral subcontractors. There was no problem withthe dimensional tolerances during assembly.

The test vessel was fully instrumented. Besidesstrain and temperature gages, force gages weremeasuring the forces in the axial and hoop tendons.Surface displacements were measured against anoutside frame. Displacement gages also monitoredblock joints. Agreement between measured andcomputed results was good. This shows that the

finite element pre-computations can simulate PCIVbehavior despite its complex structure.

The block joints did not gap under designpressure. Gapping at the lid was specified to occur atan overload pressure of 1.3x5.3 = 7 MPa. In order tomeasure a helium leak rate, the seal was located inbetween two concentric ring areas. The inner ringarea was under helium pressure (equal to waterpressure). In the outer ring the helium leak rate wasmeasured. Up to a pressure of >6.5 MPa the leak ratewas minute. Leakage occurred under the specifiedpressure of 7 MPa. At that point the compression ofthe seal had been reduced by 0.4 mm. Leak-beforefailure was demonstrated.

For the ultimate loading test the axial prestress ofthe lid against the top head had to be increased inorder to avoid gapping at the lid. The PCIV masteredthe pressure of 12.2 MPa. There were marked gapsat a number of joints.

VI.4 Test of passive decay heat removal systemfor a PCIV-HTR Module Reactor

A full-scale mock-up of the RPV wall and primarycell were built as a 20° sector of about 2 m in heightwith original geometry (Fig. 7) and materials. Tosimulate the symmetry conditions in the cylinderwall (no heat flow circumferentially and vertically)there was massive insulation on the respective faces(Fig. 13). One of the test goals was to measure thedetails of the heat flow from the electric heaterthrough the complex structure to the cooling pipesand the primary cell outside surface to improvefuture pre-computation.

Fig. 13: Mock-up of PCIV-HTR RPV wall andprimary cell for testing passive decayheat removal


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The maximum heat flow in a HTR cooling accidentof 5 kW/m2 could be safely handled by the passivecooling system, despite a near doubling of thetemperatures in the structure. The feasibility of aPVIC for a HTR module reactor with passive decayheat removal was confirmed.

VII. CONCLUSIONS

The design of the prestressed cast iron vessel wasinvestigated deeply since the mid 1970’s. Manycompanies and research institutes renowned in thefield of nuclear engineering took part. Materialresearch took place on components like cast iron,prestressing steels and liner. Most of the designfeatures were thoroughly analyzed and extensivelytested in large scale realistic tests and full-scalemock-ups. As a rule this also covered behavior underultimate loads. Much of the work was accompaniedby seasoned experts. In one case a nuclear licensingprocedure was run through for a PCIV that went intoservice in a nuclear power plant. For politicalreasons the research slowed down after theChernobyl accident and came to a halt in Germanyabout twenty years ago. No further work is plannedat this stage. The PCIV is a promising concept for areactor pressure vessel, especially with view totoday’s enhanced safety requirements. The level ofdesign validation is high. Nevertheless, significantwork would remain for advancing from the conceptstage to nuclear licensing.

REFERENCES

[1] D. Bounin, The prestressed cast iron pressurevessel – The new concept for large pressurevessels, Konstruieren + Gießen 12 (1987) Nr. 4(in German)

[2] D. Bounin, E.-P. Warnke, Concept for BWRReactor Pressure Vessel as Prestressed Cast IronVessel, Proc. ICONE 5, Nice, 1997.

[3] D. Bounin, E.-P. Warnke, Aspects of burst safetyof prestressed cast iron pressure vessels, ICONE4, USA, 1996

[4] D. Bounin, M. Sappok, W. Steinwarz, E. P.Warnke, PCIV as RPV for BWR, JahrestagungKerntechnik, Aachen, 1997 (in German)

[5] W. Fröhling, D. Bounin, W. Steinwarz, A.Böttcher, M. Geiß, M. Trauth, Prestressed CastIron Pressure Vessels as Burst-Proof PressureVessels for Innovative Nuclear Applications,Research Centre Jülich, 2000, ISSN 1433-5522(in German)

[6] W. Zerna, G. Schnellenbach and Partners, Studyon Design Requirements for PCIV-HTR,Bochum, 1981 (in German)

[7] D. Bounin, B. Beine, The prestressed cast ironvessel for helium storage, Gas Cooled ReactorsToday, BNES, London, 1982

[8] E.-P. Warnke, Qualification of safety propertiesof the PCIV-HTR and the reactor cell of theHTR Module for the inactive heat removal,Siempelkamp, Krefeld,1990 (in German)

[9] K. Kugeler, P.-W. Phlippen, Thermodynamicinvestigation of Passive Heat Removal project,Nuclear Safety Dept., RWTH Aachen, 1991 (inGerman)

[10] M. Geiß, W. Häfner, P. Hejzlar, A. Kneer, R.Schulz, L. Wolf, Experimental and analyticalstudies for the validation of PCIV-HTR andprimary cell passive decay heat removal, FinalReport BF-R 40056-01, Battelle Institute,Frankfurt, 1993 (in German)

[11] N. Kohtz, Final report on Accident and SafetyAnalysis of PVIC-HTR Module, EA no. 18: Pre-and post-computation for tests passive heatremoval for PCIV, Siemens report KWUBT71/93/005, Bergisch Gladbach, 1993 (inGerman)

[12] B. Beine, E.-P. Warnke, W. Voß, Test setup toinvestigate residual heat removal of a PCIVHTR Module Reactor, Final Report,Siempelkamp, Krefeld, 1993 (in German)

[13] E.-P. Warnke, T. Kanzleiter, D. Bounin,Elements for passive heat removal undercontainment loading conditions, ICONE 5,Nice, 1997

[14] G. Buchholz, A. Orlikowski, W. Pittack,Investigation of microstructure and strength andultrasonic inpection of heavy-section DCIblocks, MPA-NW expert’s report no. 31 1000 186-03, Dortmund, 1988 (in German)

[15] M. Rödig, U. Berthold, Investigation of fatiguestrength of DCI under compressive mean stress,Report IWE-IB-10/94, Institute for Materials inPower Engineering, Research Centre Jülich,1994 (in German)

[16] S. Engineer, W. Schmidt, H. Gebel, H.Schaffrath, Testing of manufacturing process forflat and round wire from a new prestressing steelmaterial (Ultrafort 6998) for the PCIV-HTR,Forschungsinstitut Thyssen Edelstahlwerke AG,1985 (in German)

[17] SUSPA, Report on high-temperature relaxationat 300°C, 1984 (in German)

[18] G. Buchholz, Comparative investigations ofhigh-temperature prestressing Steels, MPA-NW-expert’s report no. 31 1000 1 87-02, 1988 (inGerman)

[19] Research project PCIV-HTR, Final report onliner, LCS Steinmüller, Gummersbach, 1990 (inGerman)


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[20] Institute for Structural Engineering Berlin,Administrative ruling on permission to use theprestressing methods for the PCIV-scram tankfor the THTR-300 nuclear reactor, Ref.no. I/12-25.03-24, Berlin, 1978 (in German)

[21] F. Rostasy, Expert review of prestressing systemdevelopment for PCIV-PNP and PCIV-HTR, TUBraunschweig, Inst. for building materials andconcrete structures, 1987 (in German)

[22] SUSPA/BBR, Tensile test on 20 MNprestressing tendons to determine the ultimateloading behavior, Meeting FederationInternationale de Precontrainte, 1982 (inGerman)

[23] M. Geiß, Analytical investigations of PCIV,Contribution of Battelle Institute to Final ReportAGIK, Report no. BF-R-40.075-28, Eschborn,1997 (in German)

[24] H. Reutler, G. H. Lohnert: The HTR-Module, anew reactor concept. Atomwirtschaft-Atomtechnik 27 (1982) 32

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