Full-scale macroscopic reference experiment and calculation of the dose rate of activation γ-radiation in the shielding of a water-cooled water-moderated reactor

Abstract

Interest in reference experiments continues to increase. Such experiments are the basis for verification, validation, improvement, and correction of the computational programs, employed in radiation and transport problems, and libraries of radiation-matter intersection cross sections [1, 2]. Full-scale experiments, performed on real nuclear-power plants, are of special interest.With the further development and improvement of personal computers, reference calculations play an independent role together with experiments. Such calculations, performed with verified and tested programs and constants in good approximations, assessed on experiments, provide specialists more systematic differential data than an expensive experiment.Any description of the reference information should exclude equivocal interpretations of data, it should make it possible to reproduce the results, and its errors should be carefully assessed [3].The present work is devoted to a full-scale macroscopic (integral) reference experiment and calculation, oriented toward determination of the dose rate of activational -r-radiation in the shielding for the example of the first power-generating unit of the Armenian nuclear power plant with a BBER-440 reactor after the plant stopped operating. The reactor was put online in January 1977 and shut down on February 25, 1989.A BBER-440 reactor with a thermal power of 1375 MW (Fig. 1) consists of a 244 cm high cylindrical core with an equivalent radius of 144 cm, a 14 cm thick metal vessel, structures in the vessel (shafts with a bottom, cage with a compartment), and shielding consisting of serpentinite and standard concrete. The last 43.6 cm of the serpentinite concrete are borated (with boron carbide). The serpentinite concrete is poured into a metal structure with a 1.2 cm thick wall. A steel-foil thermally-insulating cylindrical part of the vessel is also secured on the metal structure. The nuclear concentration of the main elements and impurities for different zones of the power-generating unit were taken from the data of [4] and are presented in Table 1. The average monthly thermal power is presented in Table 2. The measurements were performed in a hollow experimental 70 mm in diameter channel with 3 mm thick steel walls, which was arranged in a radial direction in the serpentinite and standard concrete in a vertical plane at the level of the center of the core (see Fig. 1). The channel was provided beforehand during the construction of the power-generating unit. In the scheme represented in the two-dimensional (R, z) geometry of the reactor, the origin of the z-axis is located at the center of the core, the axis R lies in the horizontal plane passing through the center of the core. The average volume intensity of the neutrons in the core in the nominal regime was taken to be equal to 6.8.1012 cm-3-sec -1. The real distribution of the neutron density was chosen along the vertical direction in the core (Fig. 2), and a uniform radial distribution, with an error of several percent, was assumed.The radiation...