Criticality experiments: analysis, evaluation, and programs. 7. Program of Experimental Investigations on Critical Facilities at IPPE

In general, the BFS-1, BFS-2, MATR, and RF-GS critical facilities remain in operation at the Institute of Physics and Power Engineering (IPPE). BFS-1 and BFS-2 are universal facilities primarily intended for use with solid component elements; however, the license allows the use of water in central sub-zones. The BFS-1 and BFS-2 facilities are used for simulation of fast systems as well as systems with intermediate and thermal spectra. The MATR critical facility is intended for research of temperature effects on water-moderated cores over a wide range of temperatures (up to 250 deg. C) and pressures. The RF-GS critical facility is designed (with adaptable opportunities) for the simulation of multiplying systems with a water moderator. The experimental programs are being developed in the following directions: 1. use of plutonium released from the military programs as fuel for the BN and VVER reactors as well as for its immobilization in geological formations; 2. based on the perspective of the nuclear fuel cycle (in accordance with the initiative of the President of the Russian Federation), implemented in a new generation of fast reactors; 3. investigations of prospective reactors and accelerator-driven systems and creation of benchmarks for testing of calculational codes and neutron data for nontraditional materials. A considerable part of these investigations is being carried out in cooperation with foreign laboratories (United States, Japan, France, People's Republic of China, Republic of Korea, etc.). These programs are focused in three main directions. The first is concerned with the BN-600 reactor. Investigations into the use of a hybrid zone with this reactor have been carried out since 1999 and include the BFS-62-1 core (BN-600 initial state), BFS-62-2 (uranium core, steel reflector), BFS-62-3 (hybrid core, steel reflector), and BFS-62-4 (hybrid core, radial blanket). These experiments will be finished at the beginning of 2001 and are being carried out in cooperation with the Japan Nuclear Cycle Development Institute and the Commissariat a l'Energie Atomique. Beginning next year, the plan is to study mockups of a fully loaded MOX core in the BN-600 reactor. The second direction of work is focused on the use of weapons-grade plutonium in MOX fuel for VVER reactors. The first batch of 150 fuel pins with vibro-compacted MOX fuel was manufactured and the experiments with uranium and mixed loadings of cores on MATR and RF-GS facilities were started in 2000. The plan is to also use the BFS-1 facility for one series of experiments. This work will be carried out under the scientific super- vision of the Kurchatov Institute-Moscow and is funded by ISTC (Project no.371B). The third direction was initiated in 1999 and 2000 and entailed the creation of benchmarks for highly enriched uranium or plutonium, silicon dioxide, and hydrogen (polyethylene). Eleven benchmarks (BFS-79 and BFS-81 assemblies) were assembled on the BFS-1 facility in cooperation with the Idaho National Engineering and Environmental Laboratory. While additional experiments of this type are not scheduled, the facilities and the materials will remain available for additional work for a few more years. The experiments on mockups of the BREST-300 reactor (lead coolant, mixed nitride fuel) were started in 1999 on the BFS-77 assembly where characteristics of the central sub-zone (breeder parameters, spectral indexes, density, and void reactivity effects of the coolant) were studied. In 2000, a sector mockup of the core and the reflector of BREST-300 (BFS-64 assembly) was created on the BFS-2 facility. The main points of this measurement program are control rod worths in the reflector, distributions of fission rates, spectral indexes, and radial dependence of void effect of the coolant. At present, the manufacture of additional materials for the BFS facilities (plutonium, uranium nitride, lead, etc.) is in progress. The final task is creation of the full-scale (or nearly full-scale) mockup of the BREST-300 reactor. The study of mockups of prospective BN-800 re actor cores with mixed nitride fuel will begin in 2001. One of the key features of this program is the study of the contribution of reaction (n, p) on nitrogen in neutron balance of the core. Future plans include the following work: 1. cores of fast and thermal reactors using fuel in an inert matrix (except earlier experiments on BFS-58). A series of assemblies, BFS-91, is planned in 2001 where the Doppler effect on plutonium will be investigated in addition to other neutron physical characteristics. 2. benchmarks that test neutron data on lead and bismuth (prolongation of a series of experiments on BFS-85 and BFS-87 assemblies carried out in 2000) and a study of accelerator-driven systems mockups with Pb and Pb-Bi targets; 3. experiments in substantiation of the hyper-thermal graphite reactor with plutonium fuel (together with the Kurchatov Institute-Moscow and OKBM-Nizhni Novgorod); 4. critical experiments on RF-GS on nuclear safety in storage of MOX fuel; 5. experiments of a different type on improvement of neutron data for minor actinides; 6. experiments on optimization of targets for the production of 37Ar and other isotopes on BN-800 at BFS-62 and BFS-66 assemblies; 7. study of temperature effects and other characteristics in prospective cores of VVER (MATR facility); 8. simulation of fast neutron reactor cores under the CEFR (China) and KALIMER (South Korea) projects. At present, several experimental programs are being carried out on the critical facilities at IPPE (Obninsk). The analysis of many of these experiments is being performed cooperatively with experts from the United States, Japan, France, the People's Republic of China, and the Republic of Korea. The IPPE critical facilities are open for international cooperation. (authors)