The fuel rods linear power rate is one of the most important indicators of safety and operating reliability of fuel assemblies (FA) of VVER, which is defined in the in-core monitoring system (ICMS). Modern methods of modeling neutron-physical processes in the reactor core make it possible to more accurately determine the effect of core parameters on the formation of in-core monitoring signals. The article presents to the comparison of the results of Monte-Carlo numerical simulation with the SERPENT and MCNP codes of an element of the VVER-1000 core. The model consists of seven FA - a central fuel assembly, around which there are six neighboring FA and a self-powered neutron detector (SPND), located in the central channel of the central FA. Determinations and comparisons were made of the contribution of each fuel element from all seven FA to the SPND signal, as well as the local sensitivity of the detector and the effect of changes in the parameters of the VVER-1000 core (boric acid concentration and 1st circuit coolant temperature, fuel burnup, etc.) SPND signal. The results obtained in the MCNP and SERPENT codes show that the SPND signal is ~ 70 % generated by neutrons generated by fuel elements of the FA in which the detector is installed, in particular: when the concentration of the boron absorber in the coolant of the 1st circuit is increased, the contribution of neighboring fuel assemblies decreases, and when the temperature of the coolant increases, the contribution to the SPND signal from neighboring fuel assemblies increases. The simulation results allow calculation of the geometric and spectral factors, which determines the contribution of fuel elements to the SPND signal. Also from our results it follows that the spectral characteristics of a neutron field must be taken into account to precisely account for their influence on in-core detector signal formation.
Keywords: self-powered neutron detector, activation of a rhodium emitter, burnup of a rhodium emitter, restoration of energy distribution, channel of neutron measurements.
1. Tsimbalov S. A. Features rhodium neutron detector DPZ-1M / S. A. Tsimbalov // Preprint IAE-3899/4 - 1984. – 16 p. (Rus)
2. MCNPTM – A General Monte Carlo N-Particle Transport Code, Version 4C. Manual / Ed. by J. F. Briesmeister. – LA-13709-M, 2000. – 898 р. – (Documentation for CCC-700/MCNP4C Data Package, Section 4).
3. Leppänen J. Current Status of the PSG Monte Carlo Neutron Transport Code / J. Leppänen // Proceedings PHSOR- 2006 American Nuclear Society’s Topical Meeting on Reactor Physics Organized and hosted by the Canadian Nuclear Society. Vancouver, BC, Canada, Sept. 10–14, 2006.
4. Serpent – a Continuous-energy Monte Carlo Reactor Physics Burnup Calculation Code, User Manual / Ed. by Jaakko Leppänen, March 6, 2013 – 164 р.
5. NTS NNEGC "Energoatom". Development of a national settlement complex ICMS-M2. Protocol № 3 on 11/16/2016. (Rus)