The calculation and measurement of fast neutron reflection in the vver-1000 mock-up model placed in the lr-0 reactor

Abstract

The paper attempts to address the issue of the effect of biological shielding simulator on neutron transport in its vicinity. Neutron reflections from the biological shielding model may worsen the radiation conditions in the end part of the pressure vessel. A similar problem emerges in connection with in the design of transport experiments, where the reflections may distort the effect of transmitted material on transport. The experiments were conducted in the VVER-1000 mock-up placed in the LR-0 reactor whose modular character allows extraction of its central part. The spectra were observed in conditions of full biological shielding as well as of its modification (in which case the central part of the biological shielding on was removed). The neutron spectra were measured with the use of proton recoil method. In neutron energy range below 1MeV the hydrogen spherical proportional counters (diameter of 40 mm) with various pressures of hydrogen were used, while in the case of over 1MeV scintillation detector with 10 x 10 mm cylindrical stilbene detector was employed. The results of the experiment were compared with calculations. The calculations were performed with ENDF/B-VII.0, JEFF-3.1. JENDL-3.3, JENDL-4.0, ROSFOND 2009, and CENDL-3.1 nuclear data libraries. On the basis of the resulting calculations and experiments, we may conclude that neutron reflections from the biological shielding increase the neutron flux density in the vessel. Generally, the calculation overvalues the effect of reflections. In the case of the back concrete reflector addition, the increase in neutron flux density in 0.1-0.2 MeV was measured as 18 % while calculational result is 29 %.