Influence of the gamma-ray fraction in the reactor radiation on the total signal of a self-powered neutron detector
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uence of the GammaRay Fraction in the Reactor Radiation on the Total Signal of a SelfPowered Neutron Detector A. Yu. Kurchenkov*, A. S. Kulakov, N. I. Alekseev, and A. E. Kalinushkin National Research Center Kurchatov Institute, pl. Kurchatova 1, Moscow, 123182 Russia *email: [email protected] Received March 10, 2011
Abstract—For controlling the linear power density in the reactor core, the KhortitsaM software program as a part of the incore instrumentation system (ICIS) employs only selfpowered neutron detector (SPND) data with the neutronic calculation for the consistent determination of the power density in unmeasurable fuel assemblies (FAs). The confidence of the interpretation of the SPND data essentially determines the safe and efficient operation of a reactor. Previously, it was assumed that the gammaray fraction in the reactor radiation does not exceed one percent and is independent of the fuel enrichment and the FA and SPND burnups. Since it is difficult to estimate the contribution of the reactor gamma radiation to the SPND current experimentally, in this work, we present a calculated estimate using modern software and libraries of constants. On the basis of the results of this study, the question is discussed whether it is appropriate to take into account the reactor gamma radiation in the transfer function from the SPND current to the power density of six fuel elements sur rounding the SPND with allowance for both the type of FA and the FA and SPND burnups. Keywords: SPND, FA, ICISM, reactor gamma radiation. DOI: 10.1134/S1063778813130061
INTRODUCTION Unlike all known program packages for calculating the power density distribution in the reactor core, the KhortitsaM code reconstructs the power density in the core only from the data of selfpowered neutron detectors (SPND) with densemesh and raremesh neutronic calculations for interpolation of the power density fields to cassettes not containing SPND. Therefore, the correct interpretation of the SPND data, in particular, the transfer functions from the SPND current to the linear power density in fuel ele ments, plays a determining role in reconstructing the power density in the reactor core. The operation of SPND is based on nuclear physics processes leading to emission of free electrons and for mation of free charge in the initial neutral material of the SPND owing to electron transport and the elec tron charge redistribution among the detector zones. The main process in SPND with a rhodium emitter is the neutron activation of rhodium. The nuclei formed as a result of a neutron capture are β–active; i.e., they make up a highenergy electron source distributed in the bulk of the emitter. In addition to the main pro cess—the radioactive decay—the electron emission results from the interaction of γ radiation of different origin, which is present in the reactor at operating power, with SPND materials. The existing methods of preparation of the transfer function presumes that the fraction of the reactor γ
radiation in the signal of a rhodiu
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