I. G. Ritchie
Nuclear Fuel Cycle and Materials Section
Division of Nuclear Power and the Fuel Cycle
International Atomic Energy Agency
Wagramer Strasse 5, P. O. Box 100
A-1400 Vienna, Austria

P. C. Ernst
25 Bannisdale Way
Carlisle, Ont., Canada
L0R 1H2

Results compiled in the research reactor spent fuel database are used to assess the status of research reactor spent fuel world-wide. Fuel assemblies, their types, enrichment, origin of enrichment and geological distribution among the industrialised and developed countries of the world are discussed. Fuel management practices in wet and dry storage facilities and the concerns of reactor operators about long-term storage of their spent fuel are presented and some of the activities carried out by the International Atomic Energy Agency to address the issues associated with research reactor spent fuel are outlined. Some projections of spent fuel inventories to the year 2006 are presented and discussed.

Activities in the area of management, interim storage and ultimate disposal of spent nuclear fuel from research and test reactors are dominated at the present time by two important programmes. The first is the Reduced Enrichment for Research and Test Reactors (RERTR) programme, and the second is the take-back of spent research reactor fuel by the country where it was originally enriched. In the minds of most research reactor operators, especially those with fuel enriched in the United States, these two programmes are closely linked because a spent fuel take-back programme is the only tangible benefit to be gained from the conversion of their reactor cores from burning highly enriched uranium (HEU) to low enriched uranium (LEU), other than the altruistic goal of non-proliferation. The RERTR programme has already limited and will, if it becomes global, eventually eliminate all trade in HEU for research reactors to the ultimate benefit of all mankind.

At the time of writing, there is only one take-back programme of spent research reactor fuel by a supplier country in operation. During February 1996, the United States Department of Energy (DOE) issued its Final Environmental Impact Statement (EIS) on a Proposed Nuclear Weapons Non-proliferation Policy Concerning Foreign Research Reactor Spent Nuclear Fuel (the Policy). This was followed on 13 May 1996 by the publication of a favourable Record of Decision on the Policy, which has since allowed the resumption of the take-back programme by one of the world’s two major supplier countries, the United States of America. It is hoped that other supplier countries and partners in RERTR will follow suit and implement their own take-back programmes for foreign research reactor spent fuel.

Although the IAEA has been involved with and has fully supported RERTR since its inception through its Department of Research and Isotopes, it was not until 1993 that the Division of Nuclear Energy, Fuel Cycle and Waste Management extended the scope of its spent fuel management programme to include programmes which focused specifically on spent fuels from research and test reactors. These activities cover the collection, analysis and dissemination of information on storage, management and related experience with spent fuels, formulation of norms and provision of technical assistance to developing Member States. A number of concerns were immediately apparent at the beginning of 1993. Many research reactors were in a crisis situation or rapidly approaching a crisis situation and in every case, this was due to spent fuel storage and management problems and the constraints of national laws. It was clear that the capacity for spent fuel storage had been reached or was close to the limit at many research reactors and there were concerns from a materials’ science point of view about ageing materials in ageing storage facilities. The IAEA’s activities in this area have been formulated to address these concerns, but the first step was to obtain an overall picture of spent fuel management and storage world-wide. This has been attempted by the circulation to research reactor operators of questionnaires specifically designed to form the input to the Research Reactor Spent Fuel Database (RRSFDB). Construction and maintenance of this database is an ongoing activity and this report provides a snapshot at the time of writing of the salient information gleaned from the relatively new RRSFDB supplemented by information from the more established Research Reactor Database (RRDB).

Most of the information presented in this section is taken from the RRDB, specifically from the IAEA publication "Nuclear Research Reactors in the World" December 1996 Edition [1]. The RRDB was first published in 1989 [2] and has been maintained ever since. As of December 1996 there was information on 574 reactors stored in the RRDB. Of these, 273 were operational, 12 under construction, 7 planned, 291 shut-down and 1 for which the information was not completely verified.

The distribution of the number of countries with at least one research reactor vs time peaked for developing countries in 1985 but remained almost constant for industrialised countries from 1965 to the present. The IAEA divides the world into six regions and those countries with at least one research reactor are listed by region in Table I.

The age distribution of operational research reactors in the RRDB peaks in the range of 30 to 40 years. In fact, 24% of the reactors are in the age range of 20 to 29 years and 52% in the range 30 to 39 years.

A large fraction, 46%, of operational research reactors operate at a thermal power of 100 kW or less. Almost all of these 125 reactors have fuel for life and will not have spent fuel problems until they finally shut down.

Finally, while the number of research reactors in industrialised countries peaked in 1970, the number in developing countries appears to have peaked in 1990. Although the RRDB has a section on fuel, it does not address the details of spent fuel storage and management. For this reason, a questionnaire on spent fuel management and storage was designed and circulated to research reactor operators for the first time in February 1993. Responses to this first questionnaire and subsequent revisions sent to selected research reactors revealed a number of deficiencies in the design of the questionnaire, which have been rectified in the current version. This latest version was circulated to research reactor operators world-wide in April 1997. An overview of the responses received up to date, compiled in the RRSFDB, is presented in the next section.

At the time of preparing this paper, the RRSFDB contains 182 entries. Of these research reactors, 23 are permanently shut down, 6 are temporarily shut down for refurbishment, and the remaining 153 are operational. Spent fuel is usually an ongoing liability after a reactor is shut down and the IAEA would like to include details of spent fuel, if it has not been reprocessed, from all of the known 272 shut-down reactors reported in RRDB. In addition, there is a large discrepancy between the 273 operational reactors in RRDB and the 152 reactors that have so far responded to the questionnaires for RRSFDB. Although most research and test reactors with substantial turnover of fuel and, hence, significant inventories of spent fuel, are included in RRSFDB, clearly, some research reactor operators have lost interest in filling-in questionnaires, especially if they cannot see the usefulness of the end result. Nevertheless, it is essential for the IAEA to get a clear and accurate picture of the problems faced by research reactor operators and their concerns about management, storage and ultimate disposal of spent fuel, in order to be able to address them and to exert pressure internationally for the implementation of spent fuel take-back programmes by supplier countries and to begin a dialogue about possible regional repositories as an ultimate solution for countries with no nuclear power programme.

The remainder of this section is divided into two parts. The first deals with numbers of fuel assemblies, their types, enrichment, origin of enrichment and geographical distribution among the industrialised and developed countries of the world. The second is devoted to fuel management practices in wet and dry storage facilities and the concerns of reactor operators about long-term storage of their spent fuel.

Cross-sections of the main Western research reactor fuel assembly geometries may be found in [3], while the cross-sections of the main Russian types are shown in Figures 1 to 4 of the paper by N.V. Arkhangelsky [4]. The Western assembly types include MTR box-types containing 10-24 fuel plates per assembly, involute core assemblies containing 280 plates (High Flux Reactor, Grenoble France), tubular fuel assemblies with 4-6 fuelled tubes per assembly (BR-2, Belgium and Dido, UK), Triga fuel rod clusters with 1-25 rods per cluster (Triga, Republic of Korea - single rods, Triga, Romania - 25 rods per cluster), and pin assemblies with 1-12 pins per assembly (Slowpoke, Canada - single pins, NRU, Canada - 12 pins). All of these assemblies are about 60-90 cm long, except for NRU (275 cm) and Slowpoke fuel pins (30 cm). In Russian designed research reactors, a large variety of fuel assembly geometries have been used. Four of the more important types are shown in Figures 1 to 4 of reference [4] and can be divided into two groups; multi-tube assemblies (IRT-3M and WWR-M) and multi-rod assemblies (CM-2 and RG-1M). The active parts of these assemblies vary in length from 35-200 cm.

Most research reactor fuels are shipped in assembly form. For this reason, in RRSFDB spent fuel numbers are recorded in assemblies, where a fuel assembly is defined as "the smallest fuel unit that can be moved during normal reactor operation or storage". Even so, questions regarding numbers of fuel assemblies obviously caused confusion to respondents to the questionnaires. Consequently, the data received has been reviewed and corrected by a panel of experts who know the details of the various fuel assembly designs. At any particular facility, several different spent fuel types or spent fuels of different enrichments are usually stored. For example, the store may contain one or more types of HEU from prior to core conversion and one or more types of LEU following conversion.

Several facilities report more than three types of spent fuel and for this reason the records in RRSFDB store up to ten fuel types per facility. Strictly speaking, fuels enriched to ³ 20% ²³⁵U are classified as HEU. Since many facilities with LEU cite a nominal enrichment of 20%, we have modified the definition of LEU to be £ 20% ²³⁵U for the purposes of RRSFDB. Since any fuel with exactly 20% enrichment before irradiation will have <20% enrichment after significant burnup, this does not violate the accepted definition.

The distribution of fuel types among the reactors in the RRSFDB is shown in Table II. Although the majority are of MTR, Triga or standard Russian types, a significant percentage (18%) are classified as other types which underlines the fact that many experimental and exotic fuels exist at research reactors around the world, posing problems for their continued storage, transportation and ultimate disposal.

The regional distribution of spent fuel, with a distinction made between developing and industrialised countries, is shown in Figure 1. As might be expected, the majority of spent fuel assemblies are stored in the industrialised countries. The origins of the enrichments of the RRSFDB spent fuel inventory is broken down into fuel of US, Russian, and other origin in Figure 2. In this case, others include China, France, UK, South Africa, natural uranium fuels and those cases where the origin of enrichment was not known or simply left blank on the questionnaire. As expected, the US supplied all of the enriched fuel in North America and most of that in Asia and the Industrialised Pacific, while Russia (or the former Soviet Union) supplied most of the enriched fuel in Eastern Europe. Somewhat surprisingly, the US was not the major supplier of enrichment in Western Europe, mainly because of the Russian designed reactors in the former eastern Germany.

The regional breakdown of US-origin and Russian-origin fuel, classified as HEU or LEU, is shown in Figure 3. This involves totals of 6,822 HEU and 5,198 LEU assemblies of US-origin and 11,324 HEU and 25,283 LEU assemblies of Russian-origin. Of interest in this Figure is the fact that HEU outweighs LEU in North America, whereas the reverse is true in Western Europe. To some extent this is because more research reactors in Western Europe have undergone core conversion than is the case in North America. HEU also outweighs LEU in Africa and the Middle East, Eastern Europe and Asia and the Industrialised Pacific. It is worth noting that a significant fraction of Russian-origin HEU was originally enriched to only 36%, while most US-origin HEU was originally enriched to ³ 90%.

Overall, there are 56,622 spent fuel assemblies stored in the facilities that have responded to the RRSFDB questionnaires to date and another 22,202 assemblies in the standard cores. Of these 56,622, 47,059 are in industrialised countries and 9563 are in developing countries, while 19,670 are HEU and 36,545 are LEU.

The numbers of US-origin and Russian-origin HEU and LEU spent fuel assemblies at foreign research reactors which might be involved in take-back programmes are compared in Figure 4. At present10,212 spent fuel assemblies of US-origin are located at foreign research reactors, while the equivalent number of Russian-origin is 32,945. As mentioned above, RRSFDB involves only a limited number of the known research reactors in the world, nevertheless these data give an idea of the scope of the problem represented by research reactor fuels. On the basis of these data and a rough knowledge of the numbers of assemblies used each year, it is possible to make projections for the numbers of spent fuel assemblies that will be accumulated in the future. The projections for the total number of assemblies that might be eligible for return to the country of origin by 2006 is also presented in Figure 4

As shown in Table III, by far the most commonly used form of spent fuel storage is the at-reactor pool, pond or basin. Since the average age of these facilities in the RRSFDB is 25 years, the success of wet storage where the water chemistry has been well controlled is remarkable. In fact, many aluminium clad MTR fuels and aluminium pool liners show few, if any, signs of either pitting corrosion or general corrosion after more than 30 years of exposure to research reactor water. Also shown in Table III are the many facilities that also have an auxiliary away-from-reactor pool or dry well. At away-from-reactor facilities, the trend is to transfer fuel from wet storage to dry storage, which avoids some of the expense of water treatment facilities and their maintenance.

The parameters typically monitored at wet storage facilities are shown in Table IV. Details of the frequency of monitoring and/or control of these parameters are contained in RRSFDB. They show a remarkable variation from continuous monitoring to "routine" or "occasional".

Similar results for dry storage are shown in Table V. Clearly, dry storage requires less monitoring and maintenance than wet storage and at most dry storage facilities the operators are content to monitor the activity continuously. Several; however, are recognising the importance of assessing the moisture content of dry storage facilities.

The concerns expressed by reactor operators about their spent fuel are listed in Table VI. The results of the initial questionnaire indicated that often facilities had more than one concern. This was addressed in the latest questionnaire by requesting the facilities to rank their concerns in order of importance. Not surprisingly, the majority are concerned with the final disposal of their fuel. This is followed by concerns about limited storage capacity, and cask availability. Not surprisingly, finances are of less concern now than in the previous responses. This is due, in part, we presume, because of the United States Return of Foreign Research Reactor Spent Fuels programme which is paying for the disposal of spent research reactor fuel from the lower income countries possessing fuel of US origin.

Plans for increasing either the number of spent fuel racks, facility size or both are presented in Table VII. These numbers reflect the concerns about storage capacity, interim storage and emergency core unload listed in Table VI.

Finally, 106 facilities (58%) reported the availability of an internal transfer flask.

Besides compiling and maintaining the RRSFDB, which is the subject of this paper, and supporting RERTR, the Agency was involved as an observer in almost all of the meetings of the "ad hoc" group of research reactor operators, known as the Edlow Group, which successfully sought to return US-origin spent fuel from foreign research reactors. Towards this same end, the Director General of the IAEA has written to Secretary O’Leary of the US DOE (1 July 1993) and Mr. Victor Michailov, Minister of Atomic Energy of the Russian Federation, (2 February 1995) suggesting that these major partners in RERTR could facilitate the non-proliferation goal of RERTR by taking back foreign research reactor fuel.

To aid the US take-back programme, especially for developing Member States, the Agency has organized activities to help Member States to prepare their spent fuel for shipment back to its country of origin.. The main activities in this area were a Training Course held at Argonne National Laboratory, USA, from the 13th to the 24th of January 1997 and the preparation of a draft "Guidelines" document entitled "GUIDELINES DOCUMENT ON TECHNICAL AND ADMINISTRATIVE PREPARATIONS REQUIRED FOR SHIPMENT OF RESEARCH REACTOR SPENT FUEL TO ITS COUNTRY OF ORIGIN" given to participants at the Training Course.

A Safety Guide on Design, Operation and Safety Analysis Report for Spent Fuel Storage Facilities at Research Reactors has been submitted for publication. During 1997 the IAEA convened a Technical Committee Meeting to collect and evaluate information on procedures and techniques for the management of failed fuels from research reactors and in 1997 will convene an Advisory Group Meeting on the Management and Storage of Experimental and Exotic Spent Fuels from Research and Test Reactors.. Also, the Agency offers advice through IFMAP, the Irradiated Fuel Management Advisory Programme, to operators of spent fuel storage facilities and more tangible assistance to developing Member States through the IAEA’s Technical Assistance and Co-operation programmes.

Recognising that the degradation of materials, equipment and facilities through ageing is becoming of more concern to many operators, the Agency has organised several activities in the materials’ science field. Prominent among these was the preparation of a document on the durability of nuclear fuels and components in wet storage which has been submitted for publication. This draft document contains information on aluminium clad fuels used in research reactors developed as part of a Co-ordinated Research Programme (CRP) on Irradiation Enhanced Degradation of Materials in Spent Fuel Storage Facilities. Another CRP is devoted specifically to research reactor fuel cladding and focuses on the monitoring and control of corrosion in wet storage. These programmes are supplemented by a series of Regional Workshops organised by the IAEA to deal with all aspects of spent fuel handling, management, storage and preparation for shipment.

In recent years the problems of spent fuel from research reactors have received increasing attention as concerns about ageing fuel storage facilities, their life extension and the ultimate disposal of spent fuel loom larger. The overall scope of these problems can be gauged by examination of the databases compiled and maintained by the IAEA. It is clear that more exposure of the problems and concerns and more international co-operation will be necessary to resolve the outstanding issues. It is also clear that take-back programmes of foreign research reactor fuels, if and when they are implemented, will not continue indefinitely. At some stage in the not too distant future (in 2006 for foreign research reactors with US-origin fuel), research reactor operators will be faced with having to find their own solutions regarding the permanent disposal of their spent fuel. For countries with no nuclear power programme, the construction of geological repositories for the relatively small amounts of spent fuel from one or two research reactors is obviously not practicable. For such countries, access to a regional repository for research reactor fuel would be an ideal solution. The time is ripe for serious discussion of regional repositories and to begin planning for the day when neither take-back programmes nor the reprocessing option might be available.

1. INTERNATIONAL ATOMIC ENERGY AGENCY, Directory of Nuclear Research Reactors, IAEA, Vienna 1995.
2. INTERNATIONAL ATOMIC ENERGY AGENCY Nuclear Research Reactors in the World, IAEA Reference Data Series No. 3, December 1996 Edition.
3. J. E. Matos, Foreign Research Reactor Spent Nuclear Fuel Inventories Containing HEU and LEU of US-origin, Proceedings of RERTR 1994, Williamsburg, USA.
4. N. V. Arkhangelsky, The Problems of Treatment of Irradiated Fuel at Russian Research Reactors, IAEA-TECDOC-900 (1996) 127-138.

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