Hot Resin Supercompaction - the development through the years

Transcription

1 Hot Resin Supercompaction - the development through the years Henning Fehrmann, Mannheim/ Germany 1. Introduction Address of the Author: Dipl.-Ing. Henning Fehrmann Westinghouse Electric Germany GmbH Dudenstr Mannheim Ion exchange resins are widely used in operational systems of NPPs or other nuclear applications for water make up. Ion exchange is an effective treatment method for radioactive aqueous liquids. Spent ion exchange resins are considered to be a challenging waste stream that requires special attention before and during the conditioning to meet the waste acceptance criteria. Several countries have different concepts concerning nuclear waste disposal which are technically as well as politically driven. These concepts have a strong impact on the waste acceptance criteria and defining waste form properties like free liquids, leaching resistance, form stability etc. In those countries where these acceptance criteria exist appropriate treatment options can be identified. But in some cases the requirements change over time which puts the waste generator in a difficult situation. When choosing the waste treatment method the waste acceptance criteria, the site boundary conditions as well as the spent resins technical parameters like physical, chemical and radiological characteristics must be taken into account. Additionally the waste treatment method should be flexible covering regulatory uncertainties. Basically, 3 main methods for the treatment of spent organic ion exchange resins are available: Direct immobilization with cement, bitumen, polymer or High Integrity Container (HIC) Oxidation of resins by incineration, plasma or wet oxidation Removal of all structural water in the resins by thermal treatment The waste volume is increased by immobilization with cement, bitumen, polymer inside a HIC, which is a disadvantage in regards to the limited space of interim storages and repositories. Oxidation of resins by incineration, plasma or wet oxidation provide a high volume reduction, but also require special off gas treatment, high investment costs and are not licensed in all countries for spent ion exchange resins treatment. The residuals of the oxidation treatment can show very high specific activities and dose rates. A thermal treatment process like Hot Resin Supercompaction (HRSC) combines the advantages: Volume reduction of spent resins Generation of waste forms which meet acceptance criteria Generation of waste forms which are flexible in handling Simple off gas treatment and less secondary waste The nuclear industry is interested in reducing the waste volume because in an environment without final disposal options and limited interim storage capacity, volume reduction is an essential criterion to control the overall costs. Beside the treatment of spent ion exchange resins during the power operation of a NPP, there is a need of spent resin treatment in the post operation phase in order to remove all nuclear inventories including waste and fuel. Thus the volume reduction criterion applies for the power operation as well as during the post operation phase. 2. Hot Resin Supercompaction process and its development through the years The HRSC is a thermal spent resin treatment process which has been developed by Hansa Project Anlagentechnik (now Westinghouse) in the late 1980 s as a conclusion of the so called TN-Scandal (1). The first commercial nuclear application for powder resin treatment was at NPP Philippsburg (Germany) in the mid 1990 s. In 2009 a new HRSC system was installed at NPP Tihange (PWR Belgium) to treat spent bead resins. In 2013 another system was installed at the SRTF (Site radwaste treatment facility) of the AP1000 NPPs in Sanmen (PWR China) for treating spent bead resins. In March 2014 HRSC NextGen development program was finalized to improve the overall volume reduction of bead resin treatment. All plants and systems mentioned represent a milestone in the HRSC development. The above mentioned plants differ from each other in details and are optimized regarding spent resin treatment, volume reduction and meeting waste acceptance criteria. With the experience gained in these projects, the HRSC process and equipment can be tailored to customer needs. In the following the different systems are described. 2.1 General process description of Hot Resin Supercompaction The HRSC process itself is simple, it combines drying with a robust mechanical compaction. It does not require any chemical adjustments to overcome negative effects (e.g. cementation) or any sophisticated process control to meet certain requirements (e.g. ph adjustment, specific incineration temperature, or dosing oxidation agents for wet oxidation). In general the process flow is: Dosing dewatered resins into the dryer vessel (or dosing resin suspension and dewatering inside the dryer vessel) Drying of resins (under atmospheric pressure or vacuum) Dosing into compactable drum Supercompaction The dosing of resins is conducted by volume into the dryer vessel directly or by predosed volumes (e.g. 200 l drums or a separate dosing tank). The dewatering is conducted by means of draining the water by gravity, a pump or a centrifugal system. Normally the dryer vessel is filled with one batch resulting in 2 compacted pellets. The dryer vessel is a conical vessel (in the following called conical dryer) which is heated by thermal oil. Thus the resins are contact dried. The drying process can be conducted under normal pressure as well as under vacuum. The dosing of the dried resin into the compactable drum is carried out by volume. The compactable drum with the hot resins is capped and transferred to the Supercompactor where the drum is compacted in the hot state. The compaction force is adjusted according to the type of resins. The final pellet is put into an overpack of suitable size meeting the country specific requirements. 228 atw Vol. 59 (2014) Issue 4 April

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3 2.2 Hot Resin Supercompaction first application in NPP Philippsburg (Germany) The HRSC process with its first application at NPP Philippsburg (KKP) gives a good insight on the general principle how the process works (see Figure 1). The process is described in general in chapter 2.1, more details can be found in (1). The following generations of HRSC stick to this general process, but do have some adaptions. NPP Philippsburg has a special situation as 2 different types of reactors are located on the site, which generate 2 different types of spent resins: KKP 1 (Boiling water reactor) mainly powdered resins (from condensate polishing) KKP 2 (Pressurized water reactor) mainly bead resins. Approx. 23 m 3 /a of powdered resins and approx. 3 m 3 /a of bead resins were generated during the normal operation phase (1). The HRSC process as realized in NPP Philippsburg is shown on Figure 1. The spent resins are dewatered with centrifuge (separator and decanter) system and are filled into 200 l drums. These 200 l drums contain a specific volume of resins and are used to dose the needed amount of dewatered powdered and bead resins into the conical dryer. NPP Philippsburg uses a specific mixture of powder and bead resins to achieve an optimal volume reduction. The conical dryer operates under atmospheric pressure. The end of the drying process is determined by product temperature. The compaction force applied is 1,000 t (2) which is more than 30 MPa. This means that the product produced meets the requirements for the repository Konrad for waste product group 04 (3). The final pellets after compaction are placed into 200 l drums, but so far no grouting is done. This offers flexibility for possible changing requirements on the final waste form. The HRSC process produces repository qualified waste forms, reduces interim storage volume, but still leaves the option for repacking if future requirements change. Either the pellets can be removed from the 200 l drum or the 200 l drum itself can be placed into a final disposal container. For measuring the volume reduction of the process 2 different scenarios have to be taken into account. The volume reduction factor (VRF) of the HRSC process itself and the VRF (final) the pellets incl. the final package. The VRF of the HRSC process is reported with up to 4 (1).Various authors use different approaches to calculate the volume of the final package. In the case of NPP Philippsburg the effective storage volume of a 200 l overpack drum is given with 270 l (1). The effective volume reduction Fig. 1. HRSC at NPP Philippsburg. for the interim storage is given with approx. 25 to 30 %, which results in a VRF (final) 1.33 to Other authors (2) use the filling volume of the overpack drum itself to calculate the VRF (final). Applying this calculation method for NPP Philippsburg the VRF (final) would be approx. 1.8 to 1.9. In the following the method described in (2) is used to calculate the VRF (final) because drum dimensions and storage concepts can vary. 2.3 Hot Resin Supercompaction for PWR application NPP Tihange (Belgium) The system of HRSC installed at NPP Tihange (PWR) has been modified for treating bead resins exclusively. This required some adaption especially in terms of integration of the system into the plant. The filling of the conical dryer in Tihange is carried out by means of direct transfer from reservoirs into the conical dryer. The dewatering is done simultaneously to the filling by a sieve and a pump. The drying is carried out in the conical dryer under vacuum instead of atmospheric pressure. But in general the process principal is the same as described in chapter 2.1. The compaction of bead resins only is the major difference compared to the process in NPP Philippsburg. The elastic behavior of the bead resins and the ballshaped particle form restrain the resins forming a stable block. As a result the bead resins show a significant spring back effect which can, in the worst case, damage the compactable drum. It was found that an additive can be applied to minimize the spring back effect. Therefore various tests were conducted to find an optimal additive and its concentration. Nevertheless an alternative method by applying reduced compaction force without an additive was tested successfully. As an additional safety factor to ensure a contamination free pellet a double drum system was developed. The double drum works with placing the compactable drum into a slightly larger outer drum. With the double drum, the additive solution as well as the additive free, low compression force solution is feasible. At the end the additive free solution was selected due to slightly better volume reduction of the final pellet. In Figure 2 and Figure 3: the double drum before and after compaction is shown. Compared to NPP Philippsburg the compacted final pellets are directly put into a 400 l drum with internal shielding. After the pellet has cooled down, the 400 l drum is filled with cement. The resulting VRF (final) is calculated in (2) with 0.95 using the filling volume of a 400 l drum. 2.4 Hot Resin Supercompaction for the AP1000 Sanmen (China) Compared to the HRSC system as described for NPP Philippsburg and Tihange, Westinghouse engineered a fully integrated handling and treatment system for the SRTF Sanmen. The HRSC system in the SRTF of AP1000 is fully integrated into the overall treatment concept and waste flow. The HRSC is part of the so called Spent Resin Processing System (RES). The RES consists of reception systems like tanks and fill heads, a conical dryer, the Supercompactor, Grouting and Cementation Station as well as automatic Transport Units and finally the Radiation Monitoring Station for data tracking of the 200 l drum before entering the local storage. 230 atw Vol. 59 (2014) Issue 4 April

4 Waste Technology Fig. 2. Double drum before compaction. Spent ion exchange resins (bead resins) from the AP1000 are transported by a transport tank to the SRTF. The transport tank is coupled automatically without manual operator interaction and spent resins are sluiced to a buffering tank. From the buffering tank the resins are flushed into a dosing tank and dewatered. The precise amount of dewatered resins is transferred directly from the dosing tank into the conical dryer (see Figure 4). The resins are dried in the conical dryer under vacuum until all moisture has escaped. The end of the drying process is determined by vapor pressure and material temperature. During the drying process the resins shrink up to 60 %. To be in compliance with the contractual and repository requirements an additive is used to apply a compaction force of 30 MPa. The experiences gained from the Tihange equipment in regard to the additive are used. The additive minimizes the elastic properties of the bead resins and forms a solid block. With additive dosing and the minimum compaction force of 30 MPa a volume reduction of approx. 2 is achievable. Similar to the Tihange process the resulting resin pellet is grouted/immobilized with cement, but instead of using a 400 l drum a 200 l drum is used. This optimizes the overall VRF(final) compared to the application at Tihange site from approx to approx This optimization is possible due to the missing requirement of using a shielded 400 l drum as described in (2). 3. Discussion of volume reduction factor When comparing the 3 different HRSC installations it becomes obvious that there are differences in VRF. The volume reduction is affected by several boundary conditions: Repository requirements Type of resins, bead or powder resins Pretreatment of resins atw Vol. 59 (2014) Issue 4 April Fig. 3. Fig. 4. Double drum after compaction. Model of conical dryer (left), temporary installation during factory acceptance test. Process conditions First of all the repository requirements have a significant impact on the volume reduction factor. Comparing the VRF (final) of Tihange and SRTF where the VRF (HRSC) is nearly the same (approx. 2) the VRF (final) shows significant difference of 0.95 (Tihange) to approx. 1.6 for the SRTF. This difference is caused by the different used overpack designs. The VRF(final) at NPP Philipsburg is superior compared to Tihange and SRTF due to the different physical properties of the spent resins. Powdered resins or a mixture of bead and powder have better volume reduction properties as bead resins itself. This is due to the fact that bead resins have a round shape so they do not adhere after compac- tion so the void space between the beads does not change significantly. The void ratio for bead resins ranges between 0.2 for hexagonal close packing, 0.48 for simple cubic packing and 0.35 for random close packing (4). When the resins dry, they shrink and lose weight but their shape does not change. This results in nearly unchanged void ratio. In the case of Tihange this void space remains unfilled whereas in the case of SRTF the void space is filled with an additive. In the case of HRSC in NPP Philippsburg where powdered and bead resins are used, the void ratio in the compacted pellet is reduced as the powder particles can adhere together and voids of the bead resins are filled. The addition of an additive, as done for the SRTF HRSC process, 231

5 follows the same idea as the Philippsburg process. But adding inactive additive results in less waste loading, increases the volume and therefore reduces the overall VRF. Reducing the void space in the compacted resins was the simplest solution to improve the volume reduction of the HRSC process for bead resins. But to maximize the volume reduction it was necessary to develop a suitable pretreatment of resins and optimize the overall process. 4. Hot Resin Supercompaction NextGen It was obvious that the VRF of the HRSC can be optimized for bead resins by removing the voids between the beads. A HRSC NextGen development program was initiated where the VRF of the HRSC is improved by grinding bead resins to powder, optimizing the compaction process as well as the drum design. 4.1 Grinding bead resins to powder and optimize VRF For grinding the resin beads to powder several grinding technologies have been assessed and tested. Dry grinding was excluded due to cleaning issues. A wet grinding system was chosen which is designed as add-on equipment for the HRSC. The system is installed on a skid as shown in Figure 5. The design itself is compact and fits in 2 20 ft. containers. The grinding process works as follows: Dosing and adjustment of water/resin ratio Pre-crushing Grinding and transferring to the drying equipment This process is designed as a single passage, means resins/resin slurry is not circulated but directly transferred to the drying equipment after grinding. Intensive research was conducted to find the optimal settings for the grinding process as well as for the later compaction process. With the single passage design it is possible to dose resins of different particle sizes into the dryer to produce different particle sizes distribution in the mixture to improve compaction properties. In Figure 6 the graph shows the test results of various powder compositions, compaction forces and the resulting VRF s. It demonstrates that the compression force has a significant impact on the VRF, but additionally the powder composition can be optimized to get the best result. These results were derived from testing the resin material itself. In order to take advantage from these improved VRF s results at 2,000 t compaction force, it was mandatory that the compactable drum can resist high force without damage. This validation and verification was done as described in chapter Fig by means of simulation and real tests. Various compaction runs at approx. 2,000 t using the improved compactable drum design (filled with a mixture of powdered resins) have been conducted successfully. Neither the compactable drum showed resin powder contamination on the outside nor damages were visible. With the optimized setting it was possible to achieve a VRF (HRSC) of up to 3. This would result in a VRF (final) 2.3 using a 200 l drum as overpack and VRF (final) 1.6 using a 400 l overpack. 4.2 Improvement of compactable drum design The solution of a double drum system as used at NPP Tihange works well retaining the resins in the pellet. From the handling and cost perspective 2 drums are more complex as well as more expensive. For Fig. 6. Modular grinding equipment. VRF vs. powder composition. that reason intensive research and testing was conducted to develop a single drum design which ensures a contamination free pellet after compaction. At first, various simulation runs were conducted to find the optimal solution. In Figure 7 and Figure 8 the simulation results are compared to the actual results. The results revealed that the risk of a drum failure is raised when compacting bead resins with high pressure. This has been proven by real test situation when using to high compaction force. As a conclusion the simulation works reliable to predict the drum behavior and allows using it for optimization. The drum shapes and the material have been modified to improve the compactable drum performance. The simulation results for the optimized shape and material in Figure 9 demonstrate good correlation to the real test results shown in Figure 10. The new drum design has been simulated and tested successfully with resins for 1,000 t as well as for 2,000 t compaction force. This new drum design is used for the SRTF Sanmen. This new drum design is a real step forward because before that development, powder resin compaction was limited to 1,000 t compaction force. Now it is possible to use the full power of the supercompactor reaching maximum volume reduction as well as eliminating the need for a double drum. 5. Areas of application of HRSC into post operation All NPP s have spent resins on site once they enter the post operation phase and start preparation for decommissioning. These spent resins came from the power operation phase and very often from full system decontamination which is usually carried out before starting decommissioning. In order to remove all nuclear inventory incl. waste and fuel, these wastes have to 232 atw Vol. 59 (2014) Issue 4 April

6 Waste Technology Fig. 7. Simulation results old drum design. Fig. 8. Fig. 9. Simulation results new drum design. Fig. 10. Actual test results new drum design. be treated on or offsite. Some plants have waste treatment equipment available, some do not. In each case it is worth to reconsider the existing waste treatment system if it is suitable to support actual waste treatment tasks as well as future tasks during decommissioning. An integrated waste treatment approach for post operation as well as the decommissioning and dismantling phase can offer cost benefits. Waste treatment tasks in the post operation phase could already be different to the tasks performed in the normal power operation. Especially spent resins coming from full system decontamination can contain chemicals and dissolved metals which are different from the usual waste coming from the power operation. In case of cementation, as the preferred waste treatment method, changing waste composition could lead to significant challenges due to the fact that the resins can interact with the cement. To be sure cementation works for this new spent resin waste stream testing and qualification is recommended. atw Vol. 59 (2014) Issue 4 April The HRSC process is robust towards changing chemical composition of spent resins and does not require additional qualification. Furthermore the waste product is minimized in volume, flexible in handling and packing. Looking into the German requirement, the waste product from HRSC is qualified according to (3) when applying at least 30 MPa compaction force, but still flexible for repacking if required. Grouting/Immobilization with cement can be done without cost intensive cement recipe development efforts. If necessary the HRSC waste product can be adjusted to be packed in MOSAIK containers. With that, the VRF (final) could be significantly enhanced so more treated spent resins would fit into the MOSAIK container. The HRSC waste product can be retrieved from every container, repacked according to future requirements or reclassified in regards to activity. Especially in countries where no final repository site is available or regulatory requirements can change a flexible waste product with minimized volume can offer benefits in the Actual test results old drum design. post operational and decommissioning phase. In addition to the flexible handling of waste product itself the Supercompactor (needed for the HRSC) can be used for other waste streams during post operation and decommissioning phase. This multipurpose property and flexibility of the HRSC process and the Supercompactor fits well into the Westinghouse adapted products for the decommissioning market. 6. Summary The HRSC process looks back into a history of nearly twenty years. The process was first used successfully for powdered and minor amount of bead resins at NPP Philippsburg. In NPP Philippsburg more than 3,800 pellets have been produced since The adaption of the HRSC to the bead resins coming from a PWR was successfully. Currently the HRSC in Tihange is awaiting the demonstration test with the Belgian authorities. 233

7 The installation of the HRSC in SRTF Sanmen is under commissioning and the first run is expected for In SRTF Sanmen the new improved drum design will be used. The development of HRSC Next- Gen including the Resin Grinding and the improved drum design has proved its performance in full scale testing successfully. With the HRSC NextGen the achievable VRF is improved up to 40 %. Each installed HRSC system can be upgraded to HRSC NextGen. This provides a great flexibility so each user can chose the configuration of the HRSC process according to his targets and requirements. The HRSC process represents an effective waste treatment technology which can deal with the challenges of volume constraints, political uncertainties and changing requirements. The HRSC process is also a good choice in the post operation and de-commissioning phase as it consists of multipurpose components like the Supercompactor. 7. List of references 1. Schenke, J. and Roth, Andreas: Experiences from over 10 years operation of the Resin Hot High Force Compaction as well as new applications for PWRs. Dresden : s.n., KONTEC 07 Conference Transcript. 2. Johan Braet, David Charpentier, Baudouin Centner, Serge Vanderperre. Radioactive Spent Ion-Exchange Resins Conditioning by the Hot Supercompaction Process at Tihange NPP Early Experience. Phoenix, Arizona, USA : s.n., WM2012 Conference. Comapct Brennecke, Dr. Peter: Anforderungen an endzulagernde radioaktive Abfälle (Endlagerungsbedingungen Stand: Oktober 2010) Endlager Konrad. s.l. : Bundesamt für Strahlenschutz Fachbereich Sicherheit nuklearer Entsorgung, SE-IB-29/08-REV A. Alan Moghissi, Herschel W. Godbee, Sue A. Hobart. Radioactive waste technology. [ed.] Amer Society of Mechanical p Decommissioning and Waste Management Enhanced Productivity in Reactor Decommissioning and Waste Management Karl Wasinger, Offenbach/Germany 1. Introduction As for any industrial facility, the service live of nuclear power plants, fuel cycle facilities, research and test reactors ends. Decision for decommissioning such facilities may be motivated by technical, economical or political reasons or a combination of it. Front-end and back-end facilities are shut down to be replaced by new, more efficient plants, designed in compliance with up to date safety standards and regulatory requirements. As of today, a considerable number of research reactors, fuel cycle facilities and power reactors have been completely decommissioned. Others have already been shut down for decommissioning either because further operation results economically unreasonable or following a change in the national energy generation Address of the Author: Karl Wasinger Areva GmbH Kaiserleistraße Offenbach plan such as decided by the German Federal Government in 2011 and determined by the 13 th Amendment of the German Atomic Energy Act (Atomgesetz AtG). However, the end point of such facilities lifetime is achieved, when the facility is finally removed from regulatory control and the site becomes available for further economical utilization. This process is commonly known as decommissioning and involves detailed planning of all related activities, radiological characterization, dismantling, decontamination, clean-up of the site including treatment and packaging of radioactive and/or contaminated material not released for unrestricted recycling or industrial disposal. Decommissioning requires adequate funding and suitable measures to ensure safety while addressing stakeholders requirements on occupational health, environment, economy, human resources management and the socioeconomic effects to the community and the region. One important aspect in successful management of decommissioning projects and dismantling operation relates to the economical impact of the endeavor, primarily depending on the selected strategy and, as from commencement of dismantling, on total duration until the end point is achieved. Experience gained by Areva in executing numerous decommissioning projects during past 2 decades shows that time injury free execution and optimum productivity turns out crucial to project cost. Areva develops and implements specific performance improvement plans for each of its projects which follow the philosophy of operational excellence based on Lean Manufacturing principles. Means and methods applied in implementation of these plans and improvements achieved are described and examples are given on the way Areva offers to support owners to benefit from this experience. 2. Strategic Approach Determining the right strategic approach to decommissioning is crucial for optimization of works and the resulting economic burden. The variety of constraints and challenges involved with decommissioning requires a systematic approach to define the strategy to be adopted for each individual case for which IAEA (International Atomic Energy Agency) has published related guidance on Policies and Strategies for the Decommissioning of Nuclear and Radiological Facilities [1]. Strategies which may be adopted for decommissioning disused nuclear facilities typically include immediate dismantling or deferred dismantling 1. A third option denominated as entombment is described as to enclose the radioactive inventory of a disused facility for long time until it is decayed to such level permitting unrestricted 1 For more detailed definition see [1] 234 atw Vol. 59 (2014) Issue 4 April