ICIS power density monitoring in high-power VVER NPP. Calculation and experimental justification of accuracy characteristics.
29th Symposium of AER on VVER Reactor Physics and Reactor Safety (2019, Energoland, Mochovce NPP, Slovakia)
core surveillance and monitoring
N.V. Lipin, N.V. Milto, D.N. Skorokhodov, A.Yu. Kurchenkov
Beta emission type of neutron detectors also called self-powered neutron detectors (SPND) are the basis of the in-core instrumentation system ICIS-M. SPND readings is quickly processed and displayed to the operator as an energy release in the all volume of the reactor core. At present, ICIS-M is used at 20 power units with VVER-1000 reactors, and at 3 power units with VVER-1200 reactors.
Algorithms for the transition from SPND currents to the linear power of the all volume of reactor core were developed on the basis of extensive operational experience and numerous measurements. At present, the coefficients for the transition function from the SPND currents to the linear energy release are prepared using the multi-group spectral program TVS-M for each type of fuel assembly and each set of in-core instrumental detector assembly. At the National Research Center “Kurchatov Institute” conducted series of experiments with the irradiation of the SPND at the critical stand which energy spectrum is very close to the VVER spectrum. It confirmed the correctness of the algorithms and programs for calculating functions of the transition from the SPND currents to linear energy release. An indirect confirmation of the accuracy and reliability of the transition from the SPND current to linear energy release during operation of the VVER reactor core is the coincidence of the core power determined from the SPND readings with the power determined by thermal methods.
The transition from linear energy release in measured prisms of fuel assemblies to linear energy release in all calculated prisms of the reactor core is performed using the “Hortitsa‑M” software package, which consists of a power distribution reconstruction module and pin‑wise power distribution calculation module.
Power distribution reconstruction module based on the neutron‑physical model of project code BIPR‑7A and use cross‑section library of this code. The model implemented solution of the 3D two‑group neutron diffusion equation. Pin‑wise power distribution calculation module based on the neutron‑physical model of project code PERMAK-A and use cross‑section library of this code. The model implemented solution of the four‑group neutron diffusion equation.