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

VITRIFICATION FACILITY KARLSRUHE (VEK) – STEPS FROM PLANNING TO REALIZATION

J. Fleisch, H. Kuttruf, W. Lumpp, S. Weisenburger Forschungszentrum Karlsruhe GmbH

Hermann-von-Helmholtz-Platz 1 76344 Eggenstein-Leopoldshafen

ABSTRACT In the scope of the decommissioning and dismantling activities of the German Pilot Reprocessing Plant Karlsruhe (WAK) approximately 70 m³ of highly radioactive, liquid waste (HLW) actually stored in two tanks on site have to be converted into a stable waste form (borosilicate glass) suitable for disposal in a final repository. The HLW with a gross radioactivity of 7.7 x 1017 Bq resulted from reprocessing of 208 tons of oxide fuel over twenty years of operation until late 1990, when WAK was finally shut down. The initial efforts of transportation by rail and subsequent vitrification in the existing PAMELA vitrification plant at Mol/Belgium were given up in September 1996 and replaced by an on site solution. The site-adjusted new vitrification facility VEK is based on the liquid-fed ceramic melter process and benefits from the R&D progress made in the field of the melter technology. Following a two years basic design and licensing phase and a public hearing in May 1998, the first partial construction approval was granted in December 1998, the second in December 1999. Site preparation and civil work is running since January 1999. Simultaneously full-scale non-radioactive tests were carried out covering the melter, it’s remote-handling and the off-gas technology. The detailed engineering of the active plant’s technical equipment is nearly completed. The process of on-site vitrification is scheduled to be completed in 2005. This paper describes the various steps of planning including the basic design, the safety criteria, the experiences made in licensing, and the progress of realization. INTRODUCTION The major precondition for the dismantling and complete removal of the former Karlsruhe Reprocessing Plant (WAK – Wiederaufarbeitungsanlage Karlsruhe)) is the management of the HWL-concentrate still existing in the plant. The shareholders of the Forschungszentrum Karlsruhe GmbH (FZK - Karlsruhe Research Center) - the Federal Republic of Germany and the State of Baden-Württemberg – decided to construct and operate a plant for the on site vitrification and conversion of waste concentrate into a glass product suitable for safe intermediate storage and final disposal. This decision had been preceded by plannings based on different vitrification concepts. One of these concepts, i.e. the transportation of the HLW in special transport casks by rail to the PAMELA vitrification plant in Mol, Belgium, had even advanced up to a first licensing step. However, this concept was then given up as the public and political acceptance diminished and the cost risk resulting from potential delays of the about 30 transports became unpredictable in comparison with the costs incurred by an on site solution. The FZK-Institute for Nuclear Waste Management (INE – Institut für Nukleare Entsorgungs-technik) was in a position to offer an optimized vitrification technology, which allowed to

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

design a plant directed to the specific boundary conditions of the actual waste problem at predictable costs /1/. A positive statement of the German Reactor Safety Commission and the consent of the regional politicians, which was brought about by the government of the State of Baden-Württemberg, resulted in a positive surrounding field when the project started. With establishing the Nuclear Plant Decommissioning Division of FZK and the integration of INE for providing the necessary know-how, rather favorable preconditions had been generated for an effective planning of the plant and licensing procedure /2/. DESIGN PHASE Boundary Conditions The VEK plant was designed in accordance to the state of the art to prevent environmental damages caused by construction and operation. Safety requirements on the building and the vitrification process are based on the relevant acceptable limits according to the German Atomic Law. The technical regulations to be complied with by the former WAK plant were now applied to the VEK as a plant modification. Changed regulations were permitted only in case of boundary conditions specific to the vitrification plant, provided that the safety goals were met. It also had to be taken into account that the waste volume and thus the plant operation time was limited and that the plant afterwards would have to be subjected to stepwise dismantling together with the WAK plant. The location of the VEK building was planned to be adjacent to the existing LAVA waste storage (Plant for the Storage and Evaporation of HLW), from where the liquid HLW will be transferred into the VEK. Moreover, the existing installations of the WAK plant were to be used to the largest possible extent. This mainly referred to the media supply systems, the analytical laboratory and the stack. The VEK plant was not to be conceived for a long-term intermediate storage. Hence, a buffer store only was envisaged in order to decouple the vitrification process from the immediate removal of the produced glass canisters. The plant was to be designed in such a way that the production of secondary liquid and solid waste was minimized and the main activity flow was directed towards to the glass product. The emission limits that had been specified so far for the WAK plant license were to remain valid during VEK operation. It also had to be taken into consideration that the end of the VEK operation was to be followed by a swift and unrestricted dismantling of the plant. Planning risks were to be avoided in order to realize the short construction and licensing periods envisaged. Process Technology and Civil Engineering The on site vitrification plant VEK is based on the liquid-fed ceramic melter process. A simplified basic flowdiagram of the VEK resulting under the above boundary conditions is shown in Fig. 1.

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

Fig. 1. Simplified flowdiagram of the VEK vitrification process The HLW is transferred in batches of 1.6 m³ from the LAVA storage tanks via a transfer vessel, a transfer channel and a pipe bridge of 2.6 m distance into the redundant 2 m³ receiving tanks of the VEK plant. After control by sampling and analysis to assure the product quality and transfer to a 250 l feeding vessel, the HLW is continuously fed (8-12 l/h) into the ceramic lined melter. Borosilicate glass frit is directly added to the melter via an airlock system. The glass melt is periodically (app. 20 h) poured batch-wise (about 100 kg/batch) into stainless steel canisters through a medium-frequency heated bottom drain freeze valve of the melter, 4 batches each canister. The 150 l glass pool is Joule-heated by one pair of air-cooled power electrodes placed on opposite melter walls. A waste glass loading with nominally 16 wt% oxide residues is maintained. The melter off-gas is cleaned in an off-gas system consisting of a wet part and a dry section. The first component is a dust removal wet scrubber, followed by a condenser, a jet scrubber, and a NOX-column. Whereas the dust scrubber solution is directly recycled into the process, the condensate and the other secondary liquid waste are concentrated by a two step evaporation process and then recycled. The liquid low-level waste will be solidified in the waste processing plants of FZK’s Central Decontamination Department (HDB) and intermediately stored outside until a transfer to a repository will be possible. The dry section of the off-gas system consists of redundant sets of glass fiber filter, heater, Iodine filter, two HEPA filters and off-gas blower. The vessel off-gas is first passing a condenser and then treated in the already existing off-gas line of the LAVA plant. The glass canisters are welded after cooling, decontaminated in a nitric-acid pool equipped with ultra sonic cleaning devices, and checked before loaded into the buffer store. The transport and storage casks of the CASTOR HAW 20/28 VEK type for transport to the Gorleben fuel and waste interim storage facility.

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

The basic design and civil engineering planning phases were completed in 1999. According to this design all systems for HLW vitrification are located in a new building (see Fig. 2) adjacent to the existing buildings of LAVA and ELMA (Extended Store for Medium-level Wastes). The building is founded on the -6.0 m level and is 36 m x 29 m x 22 m in dimension. Outer walls and ceilings have a thickness of 1.80 m, the base plate is 2.40 m thick, the inner walls of the process section are at least 1.10 m in thickness. During construction, the existing buildings are protected by a concrete pile wall in order to exclude impermissible settling of the buildings.

Fig. 2. 3D Cut View of the VEK Process Building

The HLW is passed through a transfer channel from LAVA via ELMA up to the northern side of the VEK into the tank of the receiving cell. The receiving cell comprises the two receiver tanks and the evaporator systems where the secondary wastes from the scrubbers and the vessel off-gas system are concentrated and then recycled into the process. The adjacent vitrification cell contains, besides the melter, the feeding vessel and the first two off-gas cleaning components being the dust scrubber and the condenser. The pre-cleaned off-gas leaves the vitrification cell and passes the off-gas cell 1 accommodating the jet scrubber and NOX absorbers. In off-gas cell 2 the dry filtration takes place for finalizing purification (see also Fig. 3). The purified off-gas is finally discharged via the existing LAVA stack under continuous monitoring of the actual release data.

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

Fig. 3. Horizontal Cut View of the VEK Process Building (+4.20 m) Filled canisters are transferred by a transport vehicle and a crane from the vitrification cell into the canisters handling cell, where the cooling station, the welding station, and the decontamination equipment with check of the surface contamination are foreseen. A buffer storage with a capacity of 42 positions (36 of which for glass canisters) decouples the continuous vitrification process from the subsequent periodical transport to an external interim storage. Because of the short service life required for the facility, remotely replaceable process components are limited to the necessary extent. All components outside the vitrification cell represent fixed installations. Within the vitrification cell the melter and the dust scrubber can be completely replaced by remote handling. In case of a melter failing a storage place is provided between the vitrification cell and the canister handling cell. The melter will be dismantled in the vitrification cell at the end of the operational time. Media are mainly supplied via transfer lines from LAVA. For energy supply an autonomous building (EVZ-3) is required as an extension of the existing WAK energy supply center. This separate building accommodates two redundant emergency generators as well as a switchboard, fire alarm and communication systems. The main characteristic production data of the VEK plant are given in Table I.

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

Table I VEK Production data

HLW volume 70 m³ Gross radioactivity in HLW 7.7 x 1017 Bq Waste form loading 16 wt.% HLW oxide residue Glass production about 50 metric tons Number of canisters 130 (430 mm dia . x 1350 mm) Activity of canisters 6.1 x 1015 Bq Thermal power per canister 0.5 kW Nominal feed throughput 10 l/h Daily production 0.2 m³ HLW; 120 kg vitrified waste form Plant operation time 18 months approximately

Based on a 16 wt.% waste glass loading and a feed throughput of approx. 10l/h, which was verified in inactive test operation /3/, the total HLW inventory will be vitrified in a period of less than one year. Considering real availability and reduced throughput during start-up of the vitrification process, a total plant operation time of eighteen months is assumed to be necessary. SAFETY DESIGN The VEK facility is designed in a way that even under extreme accident conditions nontolerable higher radiation exposure to the operational staff and the environment is excluded. A detailed accident analysis has been carried out, considering external and internal events e.g. aircraft and earthquake impacts, criticality, explosion, loss of power supply, fire and strong chemical reactions. Although an airplane crash with the probability of occurrence of about 10-7/year belongs to the so-called residual risk, the VEK building will be designed against airplane crashes for risk minimization. For the VEK site, an actual seismic evaluation has been performed. Accordingly, a maximum horizontal earth acceleration of 2 m/sec2 was applied as the design basis earthquake for both the VEK building and the building of the EVZ-3. For both construction activities, the ground has been improved down to –10 m. The building is equipped with an outer wall thickness of 1.80 m being resistant against aircraft crashes and preventing any wall penetration with the consequence of a severe activity release. The mechanical as well as the process components are designed in a way that earthquake accelerations do not have any influence on their global stability and integrity. The radioactive emissions with the off-gas caused by the VEK operation amount to about 1 - 2% of the limit values specified in the WAK exhaust air regulations for all nuclides investigated. They yield an effective annual dose of 1.86 µSv for adults and 1.12 µSv for babies. Hence, the calculated radiation exposure is far below the permissible limit value of 300 µSv per calendar year given in the German Radiation Protection Regulation (Strahlen-schutzverordnung). A HLW leakage of 1.6 m³ from the receiving tank into the receiving cell and a sudden break of the melter off-gas pipe to the dust scrubber have been identified as radiological representative accidents. This would result in emission rates of 4 x 108 Bq and 1.8 x 108 Bq, respectively. The effective dose rate to the public has been calculated under very conservative conditions to be in the range of 0.2 mSv, which is more than two orders of magnitude below the relevant acceptable limits according to the German Regulations.

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

Natural-air cooling of the canister buffer storage ensures an inherently safe heat removal. The central temperatures of the stored glass blocks will be far below 400°C. LICENSING PROCEDURE The expert opinion of the TÜV(Technischer Überwachungsverein Energie- und Systemtechnik GmbH Baden-Württemberg), which entirely confirmed the plant concept, and the expert opinion with regard to the first and second construction step have been submitted. An Environmental Impact Analysis was carried out and received by various involved experts and authorities without any severe objection against the planning concept. In May 1998, a two days' public hearing took place. About 200 objections raised by about 10 individual persons and 5 groups representing citizen initiatives and environmental associations, were discussed. As far as the concept was concerned, no new aspects were brought up. The first partial construction license was granted in 1998 and comprises the preparation of the construction site, the extension of the energy supply center (EVZ-3), the excavation for the foundation of the VEK building and engineering measures for protecting the adjacent buildings (ELMA and LAVA). The second licensing step was granted in December 1999 and comprises the total civil work and mechanical equipment as far as linked to the concrete, e.g. shielding windows, crane systems and the buffer storage. In order to prove that the properties of the glass product will be determined with sufficient accuracy and reliability, a process qualification procedure will be carried out. These properties are based on a set of preliminary relevant parameters for final HLW disposal in Germany. The aim of the process qualification is to make sure that on one hand the process itself is suitable to produce a waste package within well defined limits and on the other hand to prove that the product really meets the required properties for acceptance by a given repository. The waste form qualification includes the definition of the values for several quality parameters of the glass product, and their range of tolerable variation. The license has been applied for in late 1996 by submitting a waste form qualification report /4/. It contains the relevant data of the glass product in respect to the process technique and the intermediate and final disposal, respectively. The process qualification file was reviewed by the Federal Office for Radiation Protection (BfS – Bundesamt für Strahlenschutz) with a positive result. The intention of the basic licensing procedure is to get the license stepwise for both the erection of the plant and for its operation. The partial licenses, which have been applied for within this procedure and their actual status are listed in Table II:

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

Table II Structure of Licensing Procedure Licensing Step Status Partial Erection Licenses 1. Preparation of construction site Granted December 1998 2. Civil work and mechanical equipment Granted December 1999 3. Installation of process and plant

equipment Scheduled December 2000

Operational Licenses 1. Cold test operation of the plant,

establishing of control and safety area Scheduled June 2003

2. Connecting of HLW storage tanks to VEK receiving tanks, hot operation

Scheduled December 2004

For licensing, the Ministry of Economic of the State of Baden-Württemberg in turn cooperates closely with the Ministry of Environment and Traffic as well as with the Ministry of Interior of the state. Some other licensing authorities and state institutions are also involved in the licensing procedure. Examinations of experts based on the FZK/WAK application documents, are prepared by the independent technical control organization TÜV and by others. The result of expert examinations are reported to the state licensing authorities. REALIZATION PHASE Key milestones were the public hearing in May 1998 and the first and second Construction Licenses received in 1998 and 1999, respectively. The total civil work and equipment installation is scheduled for the period between 1999 and the year 2002. Hot vitrification operation is foreseen from 2004 until 2005. The contracts for the total execution of the civil work and component manufacturing are placed with the supplies. The construction and commissioning of the new energy supply center is supposed to be finalized middle of 2000. The civil work related to the excavation for the VEK plant (wall of concrete piles) was completed at the end of 1999. The construction of the VEK building base plate is running since January 2000. Construction of the plant will be finalized under the third partial construction license in 2003. From today's point of view, commissioning will take place in the middle of 2003 within the framework of the first operational license. REFERENCES /1/ G. Roth, W. Grünewald, S. Weisenburger, J. Fleisch; „Verglasung hochaktiver Abfälle“,

atw. 41, Vol. 10, 638-641, 1996 /2/ W. Pfeifer, L. Valencia; “Overview of the Main Decommissioning Activities of the

Karlsruhe Research Center (FZK)”, WM’99, Tucson, Arizona, March 1999 /3/ W. Grünewald, G. Roth, W. Tobie, K. Weiß; “Cold Demonstration of the VEK Vitrification

Technology in a Full-scale Mock-up Facility”, WM’00, Tucson, Arizona, March 2000

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

/4/ R. Gauthier, R. Lamprecht, W. Grünewald, B.-R. Martens; “Qualification of the Karlsruhe Vitrification Plant (VEK) for Conditioning of WAK Reprocessed HLLW”, 3rd Int. Seminar on Rad. Waste Products, Würzburg, June 1997