The use of medium enriched uranium fuel for research reactors

This program, concerning the use of the medium enriched uranium fuel in research reactors, is very important to Japan Atomic Research Institute, so called JAERI. First, I will introduce our reactors which use the highly enriched uranium fuel. One of them is Japan Research Reactor-2. JRR-2 is a tank type, highly-enriched uranium 93%) fueled, D2O moderated and cooled reactor. Its maximum operating power is MW thermal. Another reactor is Japan Research Reactor-4, JRR-4. JRR-4 is a swimming pool type, 93% enriched uranium fueled and light water moderated and cooled reactor. The maximum operating power is 35 W thermal. These two reactors are located in Tokai Research Establishment. The third research reactor is Japan Material Testing Reactor, JMTR, which is situated in Oarai Research Establishment. JMTR is a tank type, light water moderated and cooled reactor using the 93% enriched uranium fuel. So JAERI has three research reactors which use the HEU. Second, I want to describe our present situation for use of medium enriched uranium fuel in research reactors which are operated by JAERI. If the use of highly enriched uranium fuel in research reactors will not be allowed by the other than technical reasons, what kind of fuel is acceptable to meet the purposes of research reactors? Many discussions were made in various fields in JAERI. As a result of discussion and analyses, we have concluded that the use of 20% and 30 - 40% enriched uranium fuel replacing the current 93% enriched uranium fuel is not promising for our research reactors, because it reduces the performance of our reactors greatly compared with the currently operated reactors and thus results in the significant increase of fuel cycle cost and the fatal deceleration of various R and D programs, which are important for international collaborations. The alternate fuel must have a high reliability as before, If a sufficient time is available for development of high performance fuel, we could attain these goals. Our present evaluation is based on this implicit optimistic assumption. The feasibility for usage of the medium enriched uranium fuel in our research reactors was studied by analysing the nuclear characteristics and thermo-hydraulic consideration, changing the fuel plate parameters in an appropriate range. It was shown that about 45% enriched uranium could be used for our research reactors under the condition that the technical basis for fabricating such fuel would be established. If we use U-Al alloy, a near term R and D will reach 30 w/o uranium loading density. However, this loading density is not applicable even to JRR-2 fuel. Moreover it should be considered that in Japan we have only one fabricator of research reactor fuel. The specification of fabricated fuel plates there is restricted only one set of parameters as used for research reactors. If there are two different specifications of fuel plates, availability of such small amount (less than 20 kg-U of 45% enriched uranium of fuel is problematic. So we must standardize the specification of research fuel plates. Considering adoptability for JMTR, we must choose 40 w/o loading density as the target of R and D. The cost and time schedule of R and D for the medium enriched fuel are not clear at this moment. This is our present situation