Takehiko Mukaiyama

Review of research and development of accelerator-driven system in Japan for transmutation of long-lived nuclides

Abstract Active and comprehensive studies on an accelerator-driven subcritical system (ADS) for transmutation of long-lived nuclides have been carried out at the Japan Atomic Energy Research Institute (JAERI). In the late 1970s, JAERI started the basic study of this subject and later, comprehensive studies have been performed under the “OMEGA” program of Japan: the long-term program for research and development on partitioning and transmutation (P&T) technology. Based on a design study of a dedicated transmutation system, JAERI decided to concentrate its efforts for transmutation study on the development of ADS. The construction of an experimental facility for the ADS development was proposed as a part of the Neutron Science Project of JAERI, which aimed at the construction of the world most powerful spallation neutron source. Since 1998, JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing a High-Intensity Proton Accelerator Project. An ADS experimental facility composed of a subcritical assembly and a liquid lead-bismuth target/coolant engineering facility will be constructed under this project. In this paper, the development of ADS at JAERI, together with related technologies of P&T, both under the OMEGA program and the joint proposal, is reviewed. Other activities on ADS study in Japan are also reviewed.

Partitioning and transmutation studies at JAERI both under OMEGA program and high-intensity proton accelerator project

Abstract At the Japan Atomic Energy Research Institute (JAERI), active and comprehensive studies on partitioning and transmutation (P&T) of long-lived nuclear waste from the reprocessing processes of spent fuel has been carried out under the OMEGA program. Studies at JAERI include a design study of dedicated transmutation systems both of an MA burner fast reactor (ABR) and an accelerator-driven subcritical system (ADS), and the development of a high intensity proton accelerator as well as the development of partitioning process, nitride fuel fabrication/dry separation process technologies and nuclear data studies. During the course of studies, JAERI developed the concept of the double-strata fuel cycle, in which a dedicated system is used for transmutation. Comparing the various transmutation systems, such as thermal neutron spectrum or fast neutron spectrum systems, power reactors or dedicated systems, from the viewpoints of reactor physics, nuclear fuel cycle and socio-technical issues, it was concluded that the ADS is the best option for transmutation of minor actinide(MA). JAERI, therefore, decided to concentrate its R&D efforts on the development of ADS and related technologies. One of the goals of R&D is to provide a basis for designing demonstration facilities of ADS, aqueous partitioning process and nitride fuel fabrication and dry separation technologies. As the initial step toward this purpose, the construction of an ADS experimental facility is planned under the High-Intensity Proton Accelerator Project which JAERI and the High Energy Accelerator Research Organization (KEK) are jointly proposing since 1998. The paper discusses the some of the results of P&T studies and the outline of the High-Intensity Proton Accelerator Project under which ADS experimental facility will be constructed.

Actinide integral measurements in FCA assemblies

Abstract Integral measurements were conducted in seven FCA assemblies to test the fission and capture cross sections of higher actinides. The assemblies built for this purpose cover the systematic change of the neutron spectrum shape. The integral data measured are (1) the central fission rate ratio of Np-237, Pu-238, Pu-239, Pu-242, Am-241, Am-243 and Cm-244 relative to the fission in U-235, and (2) the central sample worths of Np-237, Pu-238, Pu-240, Am-241 and Am-243. The implications of the comparison between the measured data and the calculated values using the JENDL-2 and the ENDF/B data are discussed.

High temperature Doppler effect experiment for 238U at FCA, (II) : Reaction rate measurement up to 2,000°C with a foil heated by laser exposure

For evaluation and improvement of the accuracy of calculations of the Doppler effect in a temperature range up to 2,000°C, a new experimental device was developed to measure the 238U Doppler effect at the Fast Critical Assembly of Japan Atomic Energy Research Institute. The measurement technique is based on a reaction rate measurement with a heated foil. Components of the device that are subjected to high temperatures are made of tungsten, while the remaining structural parts are made of stainless steel. The measurements were carried out in a mock-up core of an oxide-fueled fast reactor, where the Doppler reactivity worths up to 1,500°C were previously measured. In the analysis, the activation Doppler effect was determined by precise calculation of the effective capture rate in the Doppler foil. A collision probability cell code with ultra-fine group structure, PEACO-X, was used in the resonance energy range and the conventional cell code SLAROM was used in all other energy ranges. When the JENDL-3.2 data...

High temperature Doppler effect experiment for 238U at FCA, (I) Reactivity worth measurement with a small heated sample up to 1,500°C

The experimental device for Doppler effect measurement was developed for the Fast Critical Assembly of Japan Atomic Energy Research Institute. The Doppler effect up to 1,500°C can be measured with this device. The experimental data is to be used for evaluating and improving the calculation method of the Doppler effect in higher temperature range. The measurement technique is based on a reactivity worth measurement with a heated sample. The device is made of tungsten for the high temperature parts and stainless steel for the other structural parts. The measurements were carried out in a mock-up core of an oxide-fueled fast reactor. In the analysis of the experimental data, the Doppler reactivity worth was calculated by a first order perturbation theory and JENDL-3.2 library. A collision probability cell code with ultra-fine group structure, PEACO-X, was used to obtain the precise effective cross sections in a pin cell model of the Doppler sample. The calculation underestimates Doppler effect by about 5% in high temperature range. The Doppler effect above 1,500°C was estimated by the extrapolation of the measured data below this temperature. When the calculated and extrapolated Doppler reactivity worths at 2,000°C were compared, a good agreement between them was obtained. The significant improvement of calculation reliability of the Doppler effect in the higher temperature range was achieved by this experiment.

Reliability of Actinoid Nuclear Data Differential Data and Integral Tests.

The current status of the neutron nuclear data of major and minor actinoid nuclides is reviewed. As to the major actinoids, most of the long standing problems have been resolved, though some problems still remain in the inelastic scattering, fission spectrum etc. On the contrary, the data status is not satisfactory concerning the minor actinoids, particularly those which play the role of main fissile and fertile materials in actinoid burner reactors. To fulfill such requirement JENDL Actinoid File will be provided, which contains 89 actinoid nuclides from Th to Es. In order to validate the minor actinoid nuclear data, two types of integral tests are described. One is the analysis of post-irradiated fuels, where JENDL-3 data give better results than ORIGEN-2 for Pu and Am production. The reaction rates and central reactivity worths have been measured in FCA IX cores, and problems of JENDL-3 have been pointed out. In order to improve the minor actinoid data, much more efforts will be required both on the experimental and theoretical work.