QUALITY CONTROL OF CONSTRUCTING "DRY" PROTECTION OF BELARUSIAN NPP
Research subject: “dry” protection serves to lower the radiation flow of nuclear reactor core and reduce radiation heat to assure normal operation of biological protection. It guarantees desired operating conditions of neutron flux control equipment by being the element of normal use of the nuclear facility’s system. Goals: uniform distribution of concrete’s density and moisture percentage in “dry” containment shell are requisite conditions for nuclear facility’s successful operation. Control of “dry” protection’s production is performed in two stages. First stage - after concrete’s pouring and concrete strength development. The second one - after the heat treatment. Heat treatment is required for stabilization of physicotechnical characteristics in the volume of “dry” containment shell by being the most expensive and important operation. Materials and research methods: serpentinite concrete is used for “dry” containment shell. At elevated temperatures it saves up to 15 % of chemically bound water which contains hydrogen necessary for lowering fast and intermediate neutron fluxes. Requirements for concrete laying in metal formwork are given. Density and moisture determination was carried out by logging equipment with measurement data recording. Logging probe is used for simultaneous recording of scattered gamma rays (gamma-gamma logging - GGL) to determinate concrete’s density and of secondary scattered fast and intermediate neutron flux, mainly on hydrogen’s atoms (neutron-neutron logging - NNL), to determinate concrete’s moisture. Results: processing of the measurement results was carried out in accordance with the rules of determination and methods of calculating the statistical characteristics from the sample data. The coefficient of variation between all passages of blocks of “dry” protection of GGL before heat treatment is equal to 12.37 %, after heat treatment - 9.5 %, and NNL - 3.42 % and 3.04 % respectively. Conclusions: the above results show that the “dry” protection of the Belarusian NPP after heat treatment satisfies the requirements of uniformity both in density and humidity.