Vol 122, No 1 (2017)

A passive system for introducing an absorbing material into the core without any mechanical motions is incorporated in the BR-1200 lead-cooled fast reactor. The structural arrangement of the setup and the results of calculations of transient regimes in the BR-1200 reactor are described. A system with such setups included in the core will make it possible to lower the maximum fuel, fuel-element cladding, and coolant temperatures below the design limits, including in the event of accidents with multiple failures, and to completely suppress a fission chain reaction if the efficiency of the system is high enough.

A method of taking account of the maximum temperature of fuel-element cladding and temperature nonuniformity along the perimeter of the fuel elements taking account of interchannel mixing of the coolant in the FA of sodium-cooled fast reactors is described. The calculation of the temperature field using the MIF code with a random distribution of the flow sections of the channels and the energy release of fuel elements using the Monte Carlo method shows that the average maximum temperature of fuel-element cladding lies in the interval determined in the models of tightly packed and maximally open bundles and that the temperature nonuniformity along the perimeter of the fuel elements is higher than in the calculation performed with average parameters of a bundle.

Experimental data on the precipitation of an impurity (sodium oxide) in sodium coolant in a model of a cold trap of a fast reactor are obtained using a specially developed technique. The working model included the zones of filtration, spontaneous cooling, and cooled settling tank, which were intended for collecting the settling impurities. The working cavity was cooled by sodium-potassium alloy melt outside its housing. It is shown that there are two local maxima in the distribution of the sodium oxide deposits along the height of the model; these peaks correspond to the initial and final sections of the cooling zone. The model constants of impurity mass transfer in the model of a cold trap are refined experimentally. The calculations performed with the refined model of mass transfer for the standard variant of a cold trap built into the reactor tank showed that the model constants are optimal.

The spectral-kinetic characteristics of cerium- and chromium-doped samples of BaWF₈ synthesized by the hydrothermal method were investigated. A luminescence band peaking at 490 nm with half-width 150 nm was found. It is shown that in the terms of the conventional luminophore NaI(Tl) the integral light yield of the x-ray luminescence equals 32% for BaWF₈ crystals and 36.5% for BaWF₈:2%CrF₃. No afterglow of the experimental crystals is observed 20 msec after irradiation stops. Analysis shows that undoped and doped BaWF₈ crystals synthesized by the hydrothermal method are promising materials for x-ray tomography.

A comparative analysis of the levels of radioactive contamination of the environment on territories exposed to the accidental emissions from the Chernobyl and Fukushima (Japan) NPP is presented. An integral evaluation of the post-accident radio-ecological conditions based on evaluation of the irradiation dose rate to biota organisms and subsequent environmental risk calculations is presented. It is shown that with the exception of the Red Forest territory near the Chernobyl NPP the highest dose loads on biota in the exclusion zones of both plants are approximately the same taking account of the uncertainty of their evaluations in the first post-accident period. The ecosystems in the exclusion zones remain viable and have retained their species diversity. On most of the radioactive track of the Chernobyl NPP and outside the Fukushima NPP exclusion zone, the radiation risk levels are significantly below environmentally safe values.