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HANDLING SPENT NUCLEAR FUEL—INTERNATIONAL EXPERIENCE



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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop HANDLING SPENT NUCLEAR FUEL—INTERNATIONAL EXPERIENCE

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop IAEA Activities in Nuclear Spent Fuel Management Fyodor F. Sokolov, Aleksey E. Lebedev, and Kosaku Fukuda* The International Atomic Energy Agency (IAEA) has implemented a subprogram on spent fuel management to assist member states. This subprogram is intended to play a catalytic role in promoting cooperation among member states through, among other things, the collection, evaluation, and dissemination of information on the current status of their national program for spent fuel management, and to assist member states in policy making, strategy planning, and implementation. The subprogram contains two projects: one is technology, strategy, and information on spent fuel management and the other is guidance on best practices for long-term storage of spent fuel. The major activities involved in these two projects are categorized as follows: use of the Regular Advisory Group on Spent Fuel Management resolution of technical and institutional issues on spent fuel storage implementation of burn-up credit support of dry storage technology for spent fuel from the water-moderated water-cooled power reactors (VVER) and high-power channel reactors (RBMK) other activities, such as the development of technical cooperation projects, research in spent fuel treatment, and a symposium on storage of spent fuel received from power reactors *   Fyodor F. Sokolov and Kosaku Fukuda, International Atomic Energy Agency; Aleksey E. Lebedev, Technabexport.

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop REGULAR ADISORY GROUP ON SPENT FUEL MANAGEMENT The IAEA activities on spent fuel management have been based on the work of the Advisory Group on Spent Fuel Management (RAGSFM) that was established in 1984, upon the recommendation of an Expert Group Meeting on International Spent Fuel Management in 1982. It met biennially. In 1990 the group was renamed the Regular Advisory Group to express its recurring nature. The main objective of the RAGSFM was to review the worldwide spent fuel management situation, define the most important directions of national efforts and international cooperation, exchange state-of-the art information on spent fuel management, and elaborate recommendations for future IAEA spent fuel management programs. In 2001, following the recommendation by the Standing Advisory Group on Nuclear Energy (SAGNE) to reduce the number of advisory groups, the RAGSFM and the Technical Working Group on Nuclear Fuel Cycle Options (TWG-NFCO) were merged and a new TWG-NFCO was established. The first meeting of the new TWG-NFCO was held in July 2002, on the topic of Impact on Extended Burn-up of Spent Fuel on Back-end Nuclear Fuel Cycle Management. TECHNICAL AND INSTITUTIONAL ISSUES ON SPENT FUEL STORAGE Long-Term Spent Fuel Storage Facilities Over the past three decades approximately one-third of spent fuel has been reprocessed, and the remaining is currently being held in storage. As a consequence some spent fuel has been stored for quite a long time. In addition, the recent trend of higher fuel burn-up and the use of plutonium in mixed oxide (MOX) fuel led to spent fuel characteristics requiring long-term storage due to high levels of heat emission and radioactive cooling. In several member states storage facilities have been licensed to operate for periods up to 50 years. In many cases periods of 100 years or longer are now anticipated. The IAEA implemented the coordinated research project (CRP) on long-term storage of spent nuclear fuel from 1994 to 1997. After the CRP, two Technical Committee Meetings (TCMs) under a new work program were held to address the trends in extended duration of spent fuel storage and the related technological and regulatory impacts: TCM on Good Practices on Long-Term Storage of Spent Fuel Including Advanced, High Burn-up, and MOX Fuel, November 1999 TCM on Requirements for Extremely Long-Term Storage Facilities, October 2000

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop The results of these TCMs are included in the TECDOC.1 The TCMs formed small working groups to provide information within the context of four general subjects: long-term behavior of spent fuel long-term behavior of dry storage systems wet spent fuel storage facilities regulatory concerns related to long-term spent fuel storage The experience in spent fuel storage accumulated over the past decades is largely based on safe and effective wet storage and the effect of time on structures and materials during this limited period of time. The new challenges are to extend the life of new and existing wet and dry storage facilities, and to guarantee their safe performance for much longer periods of time. Selection Criteria for Away-from-Reactor Storage Facilities The survey of Away-from-Reactor (AFR) technologies has been conducted by a group of international consultants, and was published in a TECDOC on the survey of wet and dry spent fuel storage2 in 1999. Many utilities around the world are currently facing spent fuel storage concerns. The total spent fuel storage capacity for all commercial reactor sites worldwide is estimated to be 185,000 tons (t) heavy metal (HM). Further increases in capacity will be based on the business decisions of utilities as well as fuel cycle companies offering either reprocessing or storage services. Shipments to reprocessing facilities are expected to decrease, as new commitments by commercial utilities for spent fuel reprocessing are currently rare. At the current rate of discharges the total inventory at reactor sites worldwide could reach about 192,000 t HM by 2010. In order to accommodate an increasing volume of spent fuel, an AFR storage facility could be constructed. AFR storage can be considered in two categories. The first is an additional interim storage capacity constructed at the reactor site (RS) but largely and entirely independent of the reactor and its at-reactor (AR) pool. The AFR/RS storage could be wet in the form of secondary or additional pools, but most often it would be a dry storage facility, which would have a capability for offsite transport. It has been suggested that some of these AFR/RS may stay operational well beyond the life of the power plants (up to 50 years or longer). The second category of AFR storage is off the reactor site (OS) at an independent location. A large proportion of this AFR/OS capacity is in the form of pools at reprocessing plants particularly in France, the United Kingdom, and the Russian Federation. AFR/OS interim storage can also be centrally located at a selected power plant complex and receive spent fuel from other power plants.

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop Approximately 92 percent of AFR storage capacity is wet and the remaining 8 percent is dry. Both wet and dry storage technologies have to address the following six requirements: Fuel cladding integrity should be maintained during handling and exposure to corrosion effects of the storage environment. Fuel degradation during storage should be prevented by providing adequate cooling in order not to exceed fuel temperature limits. Subcriticality of the spent fuel should be maintained under both normal and emergency conditions. Radiological shielding of the spent fuel should protect plant operators, the public, and the environment from exposure of radiation doses in excess of regulatory limits. Environmental protection should be assured by minimizing the release of radioisotopes. Fuel retrievability should always be available. IMPLEMENTATION OF BURN-UP CREDIT In 1997 the IAEA started to monitor the implementation of burn-up credit in spent fuel management systems, to provide a forum to exchange information and to gather and disseminate information on the status of national practices of burnup credit implementation in the member states. In October 1997 the IAEA organized an Advisory Group Meeting (AGM) to examine and report on the status of burn-up credit for storage, transport, reprocessing, and disposal of pressurized water reactor (PWR), boiling water reactor (BWR), VVER, and MOX spent fuel. Since the proceedings of the AGM were published in 1998,3 significant developments have served to advance the use of burn-up credit throughout the world. The IAEA held several consultancies in July and December 1998, July 1999, and July 2001 to monitor the progress in burn-up credit implementation. In Vienna in July 2000 a TCM evaluated the implementation of burn-up credit in spent fuel management systems to determine the progress of international activities related to the use of the credit. The proceedings of this TCM were published as a TECDOC.4 In October 2001 a training course on the implementation of burn-up credit in spent fuel management systems was held at the U.S. Argonne National Laboratory, with 25 participants from 12 countries. A TCM on the requirements, practices, and developments in burn-up credit application was held in Madrid, Spain, in April 2002.5 The TCM recommended continued acquisition of data to support burn-up credit. In particular, the need for additional chemical assay to benchmark calculation methods was identified. Fur-

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop ther studies of axial effects and verification methods for fuel burn-up values were recommended. A new TECDOC on the Implementation of Burn-up Credit in Spent Fuel Management Systems, which is the result of the CRP on Spent Fuel Performance Assessment and Research (SPAR, 1997–2002), was published in 2001 as IAEA-TECDOC-1241 (see Note 5). SUPPORT FOR DRY STORAGE TECHNOLOGY FOR SPENT FUEL FROM THE VVER AND RBMK REACTORS The government of Japan provided extrabudgetary funds from 1995 to 2001 to increase the safety of spent fuel storage from VVER and RBMK reactors. In the framework of this project, seven TCMs and workshops were held from 1995 to 2002, and a dry storage test was conducted. Beginning in 1997 workshops were held as follows: Prague, Czech Republic, October 1997 Ignalina, Lithuania, October 1998 Balatonfüred, Hungary, October 1999 Prague, Czech Republic, July 2001 St. Petersburg, Russia, June 2002 The dry storage test was performed at the Research Institute for Atomic Reactors (RIAR) in Russia, using spent fuel rods irradiated to 46 MWd/kg U burn-up on average in VVER 440.6 The fuel rod cladding material is a Zr-1 percent Nb alloy. The dry storage tests were performed at 350°C for two months and at 390°C for another two months. Prior to the tests and after the 350°C test and the 390°C test the spent nuclear fuel was inspected by nondestructive methods. The tested fuel rods did not show any detectable changes in optical appearance, eddy current testing, profilometry, length measurement, gamma scanning, or oxide thickness measurement. In parallel, three fuel rods taken from the neighborhood of the tested spent nuclear fuel with practically identical operation performance were inspected by destructive methods to obtain the fission gas content in the fuel, the void volume, and mechanical test data from fuel rods. Detailed statistical investigation of the fuel rod diameter measurements indicated that a diameter increase of 1 to 2 µm had occurred. This value corresponds to the theoretical forecast for the diameter increase during the test. No negative effects on the fuel rods in the test were observed in the course of the test program. An extrapolation of the test data for longer-term storage shows that even under constant storage temperature the total strain at 350°C after 50 years remains at 1 percent. Assuming a pattern of falling temperature over the course of five years, for precooled fuel in a dry storage cask the total hoop strain does not exceed approximately 0.02 percent.

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop RELATED ACTIVITIES Technical Cooperation Project on Spent Fuel Management Technical Cooperation (TC) projects aim to provide technical assistance and respond to national or regional needs. In the field of spent fuel management the recent TC projects involved the following countries: Romania on the back end of the nuclear fuel cycle at Cernavoda nuclear power plant, ROM/4/020 (1997–1998) and ROM/4/023 (1999–2000) Bulgaria on reracking the existing AFR spent fuel storage facility at Kozloduy nuclear power plant for increased storage capacity, BUL/4/011 (2001–2002) China on the study of burn-up credit for critical safety analysis in nuclear power plant spent fuel storage and transport, CPR/4/023 (2002–2003) Spent Fuel Treatment Under the heading of spent fuel management, reprocessing activities have been reviewed from time to time using the terminology spent fuel treatment. The activities on spent fuel treatment implemented after 1990 have been an AGM in 1992, a TCM in 1995, an AGM in 1998,7 and an AGM in 2000. After the AGM in 2000, a TECDOC will be drafted covering three major topics: national report, review of current technologies, and a review of emerging technologies. The TECDOC will be completed in 2003. International Conference The IAEA has held an international symposium on the storage of spent fuel from power reactors once every four years since 1987. The objectives of the symposiums are to review recent advances in spent fuel technology exchange information on state-of-the art techniques and prospects of spent fuel storage review and discuss the worldwide situation and the major factors influencing the national policies in this field exchange operating experience on wet and dry storage facilities identify the most important directions that national efforts and international cooperation in this area should take The last symposium, in November 1998, was attended by 130 experts from 32 countries and 3 international organizations, including the IAEA.8 The domi-

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An International Spent Nuclear Fuel Storage Facility: Exploring a Russian Site as a Prototype - Proceedings of an International Workshop nant messages to come out of the symposium were that the primary spent fuel management solution for the next decades will be interim storage, the duration time of interim storage is becoming longer than earlier anticipated, and storage facilities will have to be designated also to receive spent fuel from advanced fuel cycle practices, that is, high burn-up and MOX spent fuel. The next international conference is planned for Vienna on June 2–6, 2003. SUMMARY AND CONCLUSIONS The major emphasis of spent fuel management in the near term program will be placed on continuous review of spent fuel incidents and storage capacity worldwide long-term issues of spent fuel storage covering optimization of cask and container loading and fuel failure classification burn-up credit, including a particular depletion code for burn-up credit using chemical assay extension of the operation of interim storage facilities The IAEA continues various activities associated with spent fuel management by taking into account the General Conference Resolutions, requests from member states, recommendations of major meetings, and the IAEA Medium Term Strategy. NOTES 1.   IAEA-TECDOC-1293, Long term storage of spent nuclear fuel—Survey and recommendations, Final report of a coordinated research project, 1994–1997, (2002). 2.   IAEA-TECDOC-1100, Survey of wet and dry spent fuel storage, (1999). 3.   IAEA-TECDOC-1013, Implementation of burnup credit in spent fuel management systems, Proceedings of an Advisory Group meeting held in Vienna, October 20–24, 1997, (1998). 4.   IAEA-TECDOC-1241, Implementation of burnup credit in spent fuel management systems, Proceedings of a Technical Committee Meeting held in Vienna, July 10–14, 2000, (2001). 5.   H. P. Dyck, Overview on the burnup credit activities at the IAEA, Proceedings of the Technical Committee Meeting on the Requirements, Practices, and Developments in Burnup Credit Applications, Madrid, Spain, April 22–26, (2002). 6.   H. P. Dyck (IAEA), V. P. Smirnov (RIAR), and S. Pavlov (RIAR), Results of VVER-440 FR examination after testing under simulated dry storage conditions, to be published as a TECDOC. 7.   IAEA-TECDOC-1103, Status and trends in spent fuel reprocessing, Proceedings of an Advisory Group Meeting held in Vienna, September 7–10, 1998, (1999). 8.   IAEA-TECDOC-1089, Storage of spent fuel from power reactors, Proceedings of a symposium held in Vienna, November 9–13, 1998, (1999).