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WM’00 Conference, February 27 – March 2, 2000, Tucson, AZ

COLD DEMONSTRATION OF THE VEK VITRIFICATION TECHNOLOGY

IN A FULL-SCALE MOCK-UP FACILITY

W. Grünewald, G. Roth, W. Tobie, K. Weiß

Forschungszentrum Karlsruhe GmbH Hermann-von-Helmholtz-Platz 1

76344 Eggenstein-Leopoldshafen, Germany ABSTRACT In support of the planning and licensing activities and the later operation of the German VEK (Verglasungseinrichtung Karlsruhe) vitrification plant, a full-scale, nonradioactive test facility has been constructed at the Institut für Nukleare Entsorgungstechnik (INE) of Forschungszentrum Karlsruhe (FZK) from October 1996 until April 1998. The mock-up facility represents the main process technique of VEK in a full-scale, cell-like arrangement. It includes the areas of high-level waste (HLW) reception, HLW and glass frit feeding, waste glass melting by a liquid-fed ceramic melter, wet and dry off-gas treatment and part of the canister handling. The facility is equipped with the complete remote handling installations. The experimental program comprehended several long-term test operations carried out under production-like conditions, starting in May 1998 and terminating in December 1999. Main goal of the test program was the overall demonstration of the functionality and safety of the process technique to be applied in VEK. Additional purposes of the testing were the investigation of the process behavior when vitrifying simulated HLW solutions that deviate from nominal HLW composition, and of process upset conditions and their controllability. Parallel to the vitrification operation an extensive remote handling test program has been performed, demonstrating the feasibility of the remote manipulations including the exchange procedure of the melter. The structure and process technique of the mock-up test facility are described. An overview of the test program is given and some main results are presented. Effects of the operational outcome on VEK are outlined. INTRODUCTION The conditioning of about 70 m3 of high-level waste currently stored at the site of the former German pilot reprocessing plant WAK (Wiederaufarbeitungsanlage Karlsruhe) will be performed in a new vitrification plant named VEK (Verglasungseinrichtung Karlsruhe). Construction of the VEK plant has been started by May of 1999. The plant, owned by Forschungszentrum Karlsruhe (FZK) will apply FZK’s vitrification technology. This technology has been developed at the Institut für Nukleare Entsorgungstechnik (INE) during more than twenty years within the scope of various national and international projects (1). In support of the planing, erection and operation of the VEK plant as well as of the licensing procedure, a nonradioactive mock up facility was constructed and operated at INE parallel to the VEK planning activities. The equipment of the test facility comprehends all the components and installations of the main process technique in a full-scale, cell-like


arrangement including the complete remote handling equipment according to the concept of VEK. Design and construction of the prototype test facility designated PVA (Prototypverglasungs-anlage) took place from 1996 until 1998. Start up of PVA’s test operation was in May 1998. Up to the termination of the experimental program by end of 1999 several long-term vitrifi-cation test runs using simulated waste solution were carried out under representative operation conditions. Additionally to the vitrification tests all remote handling procedures necessary for maintenance were demonstrated within a separate program. After a remaining part of the experimental program planned for the year 2000, PVA will be kept available under idling conditions until the end of VEK operation (2005). DESCRIPTION OF THE PVA TEST FACILITY PVA’s process technique forms the basis for the engineering of the main process area of VEK regarding design and arrangement of components, piping network and remote installations as well. It includes the areas of

HLW simulate reception HLW simulate and glass frit feeding Waste glass melting Melter off-gas cleaning Canister treatment Process control system Auxiliary systems

Figure 1 contains a survey of the complete process installed in PVA in form of a simplified flow sheet. In comparison with VEK, the treatment of the secondary liquid waste arising from the wet off-gas cleaning, and steps of the canister treatment after welding are not realized.

Figure 1: Simplified process flow sheet of the PVA prototype vitrification test facility


Waste glass melter RS 150 One of the innovations of the process technique is the melter named RS 150 as the main component. It is a new type of melter, the design of which results from the various requirements which are dictated by the special boundary conditions of VEK plant like the small scale, high standard for safety and functionality, of simplicity and noble metals compatibility (2). The structure of the RS 150 melter is shown in Fig. 2 in form of a vertical cut view. It constitutes a liquid-fed Joule-heated ceramic melter with a design throughput capacity of 9 litres per hour. The melter has a cylindrical outside shape, formed by a stainless steel casing. The outer diameter (1.5 m) and the height (1.7 m) are almost identical. The dimensions along with some other characteristic data are compiled in Table I. The melt pool is heated by one pair of power electrodes, placed on opposite sides in the upper part of the melting tank. Two opposite auxiliary electrodes near the melter bottom, staggered by a rotation angle of about 30 degrees referring to the main electrodes, are installed in case that additional power release for glass pouring would be required. The operational experience, however, proved that the temperature in the lower part of the melt, indicated by thermocouples inside theses electrodes, is always high enough to ensure an easy pouring. A sophisticated bottom drain system serves for glass pouring. It works as a thermal valve with an induction-heated metallic glass discharge channel.

Figure 2: Vertical cut view of the ceramic melter RS 150

The noble metals compatibility of the melting system is achieved by combination of the special shape of the melt tank and a bottom drain pouring system. The slope of the melt tank walls in the lower area causes the segregating and settling noble metals particles to flow


towards the discharge area where they are concentrated and drained preferably during the initial starting phase of glass pouring. The round-shaped metallic (Inconel 690) compartment which forms the entrance of the glass discharge channel, serves for protection against blockage by any solid pieces, also arriving at the deepest point of the melt tank. Twelve openings along its circumference and one central opening ensure an unimpeded outflow of the viscous noble metals sediments into the vertical discharge channel.

Table I: Main features of the RS 150 melter

Parameter Data

Design data

Throughput capacity Glass production rate

9 l/h 4.5 kg/h

Geometrical data Outside dimensions

Weight Average melt tank capacity Glass pool surface

∅ 1.5 m, height 1.7 m 8 metric tons ca. 150 l 0.44 m2

Heating system Glass pool heating 1 pair of air-cooled Inconel 690®

electrodes

Installed electrical power 80 kVA (power electrodes)

Auxiliary heating 1 pair of small Inconel 690® electrodes

Start-up heating 5 external SiC heating elements

Glass pouring system Bottom drain system, induction heated

The capacity of the melt tank is about 400 kg, corresponding to the capacity of the used European standard canister. Thus, in case of need, the melter can be emptied by one pouring into one canister. Due to that limited melt inventory, only 100 kg are poured each batch. This, in turn, means that a canister has to be filled by four times. Based on an experimentally verified throughput capacity of waste simulate with reference composition (see below), the pouring frequency is about every 15 h. The production of a complete canister therefore lasts approximately 2,5 days. Feeding of the melter is performed through a central inlet pipe in the melter ceiling, containing separate lines for HLW simulate and glass frit. Liquid feeding (90 % of HLW simulate + 10 % of recycled scrub solution from the dust scrubber) is performed continuously whereas the glass frit in form of beads is added batchwise. The process off-gas exits the melter through the ceiling entering an off-gas pipe that consists of a vertical first part, followed by a horizontal pipe connecting to the first off-gas cleaning component. Two independent cleaning devices are installed to keep the horizontal and vertical pipe free of deposits. The principle is based on cleaning by air shock wave. Within milliseconds, a few litres of pressurized air are released, generating an extremely effective ultrasonic wave. Pressurization of the melter plenum is avoided by lowering of the melter underpressure from


the normal level of 2 mbar to 10 mbar during the short time of cleaning. Cleaning is applied routinely with a frequency of every 8 hours. Melting process control Process control mainly refers to the control of melt level, extent and consistency of the process area on top of the glass pool (cold cap), melt temperatures and to the correctness of the mass streams of HLW and glass frit. Main measurement installations for process control are four thermocouples, which are arranged in different vertical positions in the upper part of the melter interior. The one placed in the lowest position indicates the melt temperature. It is always immersed in the melt. The upper one is positioned in the melter plenum. It supplies information to the operator about the extent of the cold cap on top of the glass pool. To minimize loss of volatile species to the off-gas a high degree of cold cap coverage (80-90%) is aspired. This corresponds to a plenum temperature of 500-650°C. The pool coverage is adjusted by control of the feeding rate. The two intervening temperature monitoring points mark the minimum and maximum melt level. Another independent level detection system is located below the maximum level. It indicates the start of the glass pouring procedure. When contacting the conductive glass melt, an electrical circuit is closed, generating a distinct voltage signal. The signal again disappears as soon as the detection probe surfaces the melt. A third independent method used is calculating the melt level on the basis of a material balance of the entering and exiting mass streams. Reception and feeding of HLW simulate and glass frit feeding The HLW simulate delivery area includes the simulate reception with two 3 m3 tanks and a melter feeding vessel (300 l). The supply with simulate is performed by a 5 m3 simulate storage tank. Each transfer to one of the receipt tanks consists of 1.6 m3 of simulate, corresponding to around a weekly production. The subsequent batchwise forwarding of HLW simulate to the feeding vessel is achieved by a double-stage vacuum-supported airlift system. The constant transfer volume of around 25 l is controlled by the level of the feeding vessel. The minimum level activates the double-stage airlift system, which again is switched off, as soon as the maximum level is achieved. During the continuous emptying of the feeding vessel from maximum down to the minimum level, an amount of glass frit is added to the melter that corresponds to the feeding vessel batch. By this way of linking the transferred volume of HLW simulate and glass frit, a uniform glass melt composition is obtained. Off-gas treatment system The off-gas undergoes a multistage cleaning procedure, consisting of precleaning, further wet cleaning and final filtering. Precleaning is carried out by an airlift-driven scrubbing circuit in the column of a dust removal wet scrubber. A portion of the scrub solution is periodically recycled to the feeding vessel. In the subsequent step, the condensable gases are removed by cooling in a tube bundle heat exchanger. Downstream of this condenser, the remaining finer particles are trapped in a venturi type jet scrubber. In the final steps of wet treatment, the removal of nitrogen gases is achieved in two identical absorption columns (only one in VEK) equipped with valve plates. The liquids arising from the wet treatment are collected in a secondary waste collecting tank and disposed of. In the active VEK plant, the mix is concentrated in a two-stage evaporation process and the concentrate from the first stage is recycled to one of the reception tanks.


Filtering starts with passing a cleanable glass fibre filter, acting as a prefilter and protecting the subsequent two HEPA filters in series against entrained aerosols. A redundant set of blowers serves for the maintenance of the underpressure in the melter and along the off-gas train. The installation of an Iodine filter placed between the two HEPA filters in case of VEK was not realized. Canister treatment PVA’s canister treatment comprehends the first steps up to the canister welding. After pouring of the last batch into the canister, it is kept in pouring position for 1 h to let the glass surface cool down. Then it is transported by the canister vehicle to the unloading position and lifted up into the canister treatment cell inside an insulated overpack. After a 3-4 days cooling period it is lid-welded by a TIG welding machine. The subsequent procedure of decontamination in ultrasonic pool is not demonstrated. Layout of PVA In order to maximize the information collected from design, construction and operation of PVA, and to enable the direct use of the experience for VEK, the main process equipment has been installed in cells according to the layout of the VEK plant. The cells realized in PVA are: HLW reception cell, vitrification cell, canister treatment cell and two off-gas cleaning cells. The reception cell contains the two receipt tanks and the transfer systems to the feeding vessel The vitrification cell (dimensions: 11.5 m high, 6 m long, 3.1 m deep) contains besides the melter the HLW feeding vessel, the dust scrubber and the condenser. Melter and dust scrubber are remotely exchangeable by means of a power manipulator. The necessary remote handling technique is installed as well. Fig. 3 contains a view into the vitrification cell. In the background behind the cylindrical melter, the feeding vessel can be recognized. On the right side of the melter the dust scrubber and the condenser are visible. The left side of the photograph shows the operating windows with the hand-manipulators. The wet and dry off-gas cleaning is installed in two separate areas. The canister treatment cell contains the cooling stations and the welding equipment. Vitrification cell and canister treatment cell can be served by the same power manipulator.


Figure 3: View into the vitrification cell of PVA GOALS AND EXPERIMENTAL PROGRAM OF PVA Overall goal of the PVA operation has been the complete, nonradioactive demonstration of the vitrification technology to be installed in VEK and especially the prove of the functioning and noble metals compatibility of the new designed small scale melter. Other goals with respect to VEK have been

Confirmation of the VEK design basis (f.e. HLW throughput capacity, decontamination efficiency)

Collection of operational experience and creation of an operational data basis Clarification of the effect of varying waste compositions on the process behavoir Clarification of the impact of process upsets and their controllability Verification of the remote handling concept Prove of the ability to produce waste glass with specified composition Support of the licensing (participation of licensing authority’s experts in test runs) Pre-training of VEK operational staff

Within a time period of 20 months, 5 long-term vitrification tests were performed with different objectives. The respective tests each lasting about 4 weeks were carried out in a continuous mode in imitation of hot operation. Table II gives a survey of the test runs, their objective and some experimental details.


Table II: Survey of the test program and goals of PVA operation

Test run Simulate Objective Time period

PVA-1 Original HLW refer-ence simulate (7.3 m3), total oxide content 90 g/l,

Overall cold process demonstration

May – June ´98

PVA-2 Actual HLW reference simulate (5.2 m3), total oxide content 120 g/l

Overall cold process demonstration

Nov. – Dec. ´98

PVA-3 HLW simulate (4.7 m3), low total oxide content 80 g/l, low portion of undissolved oxides

Process behaviour with non-nominal HLW composition

April – May ´99

PVA-4 HLW simulate (4.6 m3), extremely high total oxide content 160 g/l, high portion of undis-solved oxides

Process behaviour with non-nominal HLW composition Simulation of process upsets

Sept. – Oct. ´99

PVA-5 Actual HLW reference simulate (3.8 m3), total oxide content 120 g/l,

Process behaviour Simulation of process upsets

Nov. – Dec. ´99

Remote tests

Separate program Demonstration of remote handling concept

Sept. ´98 –March ´00

The first two runs have been directed to the general process demonstration, to the prove of the safe and reliable functioning of the process equipment, to the determination of the decontamination efficiency and of the HLW throughput capacity. The HLW simulate used in both tests only differed by a proportional higher element concentration of the second one, which is regarded as the solution with the actual reference composition (total oxide content 120 g/l). In the third and fourth test, the processing of HLW simulate was tested that distinctly deviated from the nominal case regarding total oxide content and relative composition as well. The simulate used in the third run represented an HLW composition with a very low total oxide content (80 g/l), whereas the one applied in the fourth test showed an extremely high total oxide content of about 160 g/l. The last test run again used a simulate with nominal composition. One main objective of the last two tests was also the generation of simulated process upset situations in order to examine the impact on the process and to prove their safe controllability. HLW simulate, glass frit and glass product Table III contains the comparison of the chemical composition of the reference HLW of WAK to be vitrified in VEK and of the simulate used. The concentrations given refer to the oxides contained in the solution. Except for the actinides and technetium, which only exist as radioisotopes, all elements (or oxides, resp.) were simulated by stable isotopes of the same quantity. The actinides were replaced by Lanthanum, whereas Tc was replaced by Manganese. The noble metals were contained in the total quantity with the reservation, that the portion of


Rhodium was substituted by Palladium. The total content of the simulate and expected active HLW is identical (120 g/l). Remarkably high concentrations of sodium (33 g/l) and of noble metals (total 7 g/l) are characteristic for this waste solution. The compositions of the active reference and simulated waste glass products are listed in table IV for the target waste glass loading of 16 wt.% of oxides. The tolerated loading range is 13-19 wt.%. An essential feature of the waste glass composition is the high total concentration of noble metals of almost 1 wt.%, requiring a special noble metals compatible melting technology as indicated above. Table IV also contains the composition of the production glass frit and the startup glass frit. Both are are the same used for the tests and for hot operation. Start up of the melter requires a different glass frit than the production glass frit due to its low content of sodium and the therefore high viscosity. The reduced concentration of sodium is to compensate the high portion that is contributed by the waste solution (see Table III). The chemical composition of the startup glass frit is also shown in Table IV. Furthermore the important glass melt properties are given for the glass frits and product. RESULTS FROM PVA OPERATION Overall results The overall production data of PVA operation are listed in table V. In almost 3000 hours of net feeding time, a total volume of about 26 m3 of HLW simulate containing 2.9 metric tons of waste oxides were converted to 18 metric tons of glass product which was poured into 44 canisters. The simulate volume corresponds to almost 40 % to that of the real waste. This intense operation period ensures a sufficiently hard performance test for the vitrification technology to be applied in VEK. A main prove of the reliable and safe functioning of the technology is the resulting plant availability of 100 %. This means that no interruption of the melter feeding due to any problems concerning equipment failure or misoperations occurred throughout all the tests.


Table III: Composition of reference HLW and Table IV: Composition of the reference HLW glass product, the simulate (as oxides) simulate glass product, of the production glass frit and

the start-up glass frit

Oxide

HLW-Reference Oxide residue

g/l

HLW-Simulate Oxide residue

g/l

Oxide

Reference glass product

wt.-%

Glass product wt.-%

Production glass frit

wt.-%

Start up glass frit

wt.-%

SeO2 Rb2O SrO Y2O3 ZrO2 MoO3 TcO2 RuO2 Rh2O3 PdO Ag2O CdO SnO2 Sb2O3 TeO2 Cs2O BaO La2O3 CeO2 Pr2O3 Nd2O3 Pm2O3 Sm2O3 Eu2O3 Gd2O3

0.12 0.42 1.25 0.97 4.53 7.06 1.81 3.95 0.96 2.08 0.18 0.13 0.11 0.02 0.88 4.46 3.46 3.21 4.94 2.21 7.86 0.01 1.73 0.20 0.59

0.12 0.42 1.25 0.97 4.53 7.06

-1) 3.95

-2) 3.04 0.18 0.13 0.11 0.02 0.88 4.46 3.46

13.82 4.94 2.21 7.86 0.01 1.73 0.20 0.59

SeO2 Rb2O SrO Y2O3 ZrO2 MoO3 TcO2 RuO2 Rh2O3 PdO Ag2O CdO SnO2 Sb2O3 TeO2 Cs2O BaO La2O3 CeO2 Pr2O3 Nd2O3 Pm2O3 Sm2O3 Eu2O3 Gd2O3

0.02 0.06 0.17 0.13 0.60 0.93 0.24 0.52 0.13 0.28 0.02 0.02 0.01 0.00 0.12 0.59 0.46 0.42 0.65 0.29 1.04 0.00 0.23 0.03 0.08

0.02 0.06 0.17 0.13 0.60 0.93 - 0.52 - 0.40 0.02 0.02 0.01 0.00 0.12 0.59 0.46 1.83 0.65 0.29 1.04 0.00 0.23 0.03 0.08

- - - - - - - - - - - - - - - - - - - - - - - - -

- - - -

0.5 0.9 - - - - - - - - - -

0.5 - - - - -

0.2 - -

UO2 ßNp2O3 PuO2 Am2O3 CmO2

9.00 0.67 0.28 0.62 0.03

-3) -3) -3) -3) -3)

UO2 Np2O3 PuO2 Am2O3 CmO2

1.19 0.09 0.04 0.08 0.00

- - - - -

- - - - -

- - - - -

Cr2O3 MnO2 Fe2O3 NiO CuO ZnO K2O F Cl P2O5

3.34 0.46

12.66 2.32 0.04 0.02 0.35 0.02 0.02 3.42

3.34 2.27

12.66 2.32 0.04 0.02 0.35 0.03 0.02 3.42

Cr2O3 MnO2 Fe2O3 NiO CuO ZnO K2O F Cl P2O5

0.44 0.06 1.68 0.31 0.01 0.00 0.05 0.00 0.00 0.45

0.44 0.30 1.67 0.31 0.01 0.00 0.05 0.00 0.00 0.45

- - - - - - - - - -

0.5 -

1.8 - - - - - - -

Na2O MgO Al2O3 CaO Total

32.84 0.90 0.14 0.66 121

32.84 0.90 0.14 0.66 121

Na2O MgO Al2O3 CaO SiO2 B2O3 TiO2 Li2O

10.30 1.97 2.62 4.54 50.40 14.78 1.01 2.94

10.30 1.97 2.62 4.54 50.40 14.78 1.01 2.94

7.1 2.2 3.1 5.3

60.0 17.6 1.2 3.5

10.9 2.0 2.9 4.8

54.7 16.0 1.1 3.2

HNO3 (mol/l) 2.5 2.5

1) TcO2 replaced by MnO2 2) Rh2O3 replaced by PdO

Total 100 100 100 100

3) Actinide oxides replaced by La2O3, Viscosity and el. resistivity

1150°C 950°C

47.0 dPas 7.0 Ωcm 830 dPas 21.0 Ωcm

101 dPas 9.4 Ωcm

1387 dPas 27.1 Ωcm

44 dPas 6.4 Ωcm 495 dPas 18.9 Ωcm


With respect to glass product, it could be demonstrated by analysis of 930 glass samples that the process is well suitable to generate a glass composition within the specified range of waste oxide loading. The average waste loading obtained during the five test runs varied between 16.1 and 16.4 wt.% compared to the tolerated range of 13-19 wt.%. To investigate the effect of filling a canister by four batches, glass samples were taken from the interfaces between the batches by cutting a canister into half. The result did not reveal any effect of the glass properties (f.e. crystallisation).

Table V: Overall production data of PVA operation

Parameter Data

Melter feeding rate 8 – 12 l/h

Glass production rate Feeding time HLW simulate (feed) volume Waste glass production Simulated waste oxides Number of pourings / canisters Waste glass loading (target 16 ±3 wt.%) Number of glass / liquid samples Plant availability

5 – 7 kg/h 3000 h 26000 l (28800 l) 18 metric tons 2900 kg 187 / 44 16.1 – 16.4 wt.% 930 / 940 100%

Melter performance and noble metals compatibility The new melter proved a good performance with regard to processing behavior, process control, glass pouring and throughput capacity. Depending on the composition of the waste simulate, a melter feeding capacity of 8-12 l/h could be achieved. The corresponding range of the glass production rate was 5-7 kg/h. The design values of 9 l/h and 4.5 kg/h, respectively, based on the processing of the HLW reference simulate, were exceeded by almost 30 %, when vitrifying this simulate. The reliability of the bottom drain system and the simple, safe glass pouring procedure could be demonstrated by totally 187 pouring operations. The achieved accuracy referring to the poured target weight was within a tolerance of ± 2 kg. Additionally, the simulation of an operator’s error with respect to overfilling of a canister when not terminating the pouring resulted in a safe stop of the glass flow after further discharge of less than 5 kg. The switching off was automatically triggered by a weight-controlling signal when arriving at the target weight. Thus, an overfilling can be excluded. One of the primary requirements to the RS 150 melter was the ability to process waste solutions with high concentrations of noble metals as they are contained in the HLW of WAK (see table III). Depending on the used simulate, the total concentration ranged between 3,7 and 9 g/l, leading to concentrations from 0,7 to almost 1 wt.% in the glass melt. In the course of the experiments, a total amount of about 165 kg of noble metals (considered as oxides) was fed to the melter. The discharge efficiency was controlled by analysis of glass samples taken from the pouring stream. Figure 4 shows results from the second test run (PVA-2).


Figure 4: Concentration of noble metals in the pouring glass stream

The diagram contains the concentrations of Rutheniumdioxide and Palladiumoxide as a function of the quantity of glass poured into the canister. The data are given for a complete canister filling (four pouring batches). Additionally the nominal target values are shown. The graphs indicate the expected discharge characteristic, provoked by the special melter design (see above). The shape of the curves confirm the effective collection of the noble metals sediments in the discharge area and the subsequent increased discharge at the beginning of the pouring. Balances based on sample analysis showed a complete discharge efficiency. These findings could be confirmed by inspection of the melter’s interior after the complete emptying at the end of the test runs. Decontamination efficiency The decontamination efficiency of the melter and of the off-gas line was evaluated from mass balances. The balances are based on the analysis results of liquid samples which were taken in a daily frequency from the scrub solutions of all components of the wet off-gas treatment and from the receiving tanks. The results for the melter decontamination efficiency were counterchecked by direct determination from glass product analysis. A good agreement for both methods could be observed. Table VI contains the decontamination factors (DF), calculated for the elements Caesium and Strontium, which together amount to more than 95 % of the radioactivity in the WAK HLW, and for Ruthenium. In this table, the experimental DF values for the melter only and for the melter-to-NOx-absorber I are compared with the design values. The DF values given exemplarily are obtained from the second test run (PVA-2), which was carried out by using the simulate of the HLW reference composition. The DF values found for the melter indicate a high retention efficiency for each of the three elements,


each of them exceeding the design value distinctly. A similar result can be observed for the melter-to-NOx-absorber I DF with the exception of Ruthenium, which achieves the design value. A general assessment from all test runs is, that the required efficiency for decontamination of radioactivity across the melter and the wet cleaning is ensured. The dry cleaning efficiency was not tested during PVA operation. For this part, a sufficient data basis is available.

Table VI: Decontamination factors (DF), obtained from the PVA-2 test run with reference simulate. Comparison with the design data

Element Melter Melter to NOX-absorber I

PVA-2 test Design PVA-2 test Design Cs Sr Ru

42 133 12.5

30 60 5

16300 273000 12400

9000 45000 12500

CONCLUSIONS Prior to its hot application, the vitrification technology to be applied in FZK’s VEK plant has been extensively tested by operation of the PVA prototype test facility. Within almost 3000 hours of HLW simulate feeding distributed over five continuous long-term test runs the safe and reliable functioning of the process under varying conditions could impressively be demonstrated. Additionally to the actual cold process demonstration using a reference HLW simulate, simulates with distinctly deviating compositions and oxide contents were processed. A plant availability of 100 % could be achieved in all test runs. The two final test runs were used for examination of the impact and controllability of various simulated process upset situations. The overall process performance was highly satisfying. The melter showed the expected stable operating behavior. The feeding rate was found to be 20-30 % above the design value. During the production and pouring of around 18 metric tons of highly noble metals containing simulated waste glass the melter proved its noble metals processing compatibility. This result could be gained on the basis of glass sample analysis. The reliable and safe functioning of the pouring system could be demonstrated by almost 200 pouring events. Glass sample analysis also confirmed the melting of glass product within the tolerable range of waste loading. Referring to the decontamination efficiency, the design DF values for Caesium and Strontium as the main activity-carrying elements could be distinctly exceeded across the melter and the wet off-gas cleaning system. Due to the 1:1 scale and the cell-like arrangement of PVA, a direct transfer of operational experience and data is possible to a large extent. This is especially valid for the results obtained from the remote handling test program. PVA’s vitrification concept is applicable in the active VEK plant without any essential modifications. REFERENCES (1) G. Roth; “INE’s HLLW vitrification technology”, Atomwirtschaft 40.Jg. (1995), Heft 3,

pp 174-177


(2) J. Fleisch, W. Grünewald, W. Lumpp, G. Roth, W. Tobie.; ”Status of planing and licensing of the German HLLW vitrification plant”, WM’98 Conference, Tucson, AZ, March 1-5, 1998, Proceedings

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