Ratios of average cross sections of a number of fuel nuclides in the low-enrichment zone and uranium-plutonium module of the BN-350 reactor

In addition to the alpha (the ratio of the radiation capture and fission cross sections) of the principal fissile isotopes 235U and 239Pu, in fast reactors uncertainties in the capture and fission cross sections for other fuel isotopes also make an important contribution to computational errors in the breeding ratio and quality of unloaded fuel. Moreover, some aspects of the future conversion of the BN-350 and BN-600 reactors to mixed uranium-plutonium fuel require further experimental verification and refinement of existing data on constants. In 1982 and 1983, a module of seven fuel subassemblies containing mixed uranium-plutonium was operated in the low-enrichment zone of the BN-350 reactor. Before the module was placed in the reactor, activation measurements of the average ratios of cross sections were made for a number of fuel nuclides in the area of the future location of the central fuel subassembly of the module. After the module was installed in the reactor, analogous measurements were made in its central fuel subassembly. Activation detectors were placed in a capillary tube mounted in the central fuel subassembly at the level of the median plane, and were irradiated with the reactor in low-power operation. After the module had been operated in the reactor, the fuel from several fuel elements in the central fuel subassembly was subjected to radiochemical studies to obtain data on the change in its nuclidic composition