Taking account of the spectral sensitivity of detectors in SKALA-Mikro RBMK-1000 system algorithms

Abstract

An algorithm is proposed for reconstructing the radial-azimuthal distribution of the energy release in an RBMK-1000 core and its program implementation is constructed. Calculations of the dependence of the ratio of the sensitivity of a hafnium detector on the integrated current are presented. It is shown that the proposed algorithm will make it possible to increase the reconstruction accuracy of the power of process channels.A great deal of attention has been devoted recently to increasing the power of power-generating units with RBMK-1000 reactors. In this connection, it is necessary to increase the margins to the limits of safe operation, specifically, by using more accurate algorithms to reconstruct the radial-azimuthal distribution of the energy release in the special mathematical computational program Prizma-M, which takes account of the spectral sensitivity of the in-reactor detectors with hafnium-dioxide emitters [1].The existing algorithm for calculating the power of the process channels neglects the spectral sensitivity of in-reactor detectors, even though the ratio between the cell-averaged flux density of the suprathermal and thermal neutrons changes appreciably from one process channel to another and especially with a transition to the periphery of the core. The deviation of this ratio from the average is +82%, −19%, and the rms deviation in the plateau zone is 9%. Since the contribution of the suprathermal neutrons to the detector signal can be 20-30%, this will lead to large errors in the determination of the power of the process channels.One weakness in the existing algorithms of the SKALA-Mikro information-measurement system is that the Prizma-M program uses an empirical relation for calculating the fuel assembly power with an in-reactor detectorwhere J is the detector current, in μA; K cal is a calibration coefficient, in MW/μA; ξ d (I) is the dependence taking account of the sensitivity of the detector on the increase of its integral current with increasing integral current of the detector I; ξ t.d (E) is the dependence taking account of energy production of the fuel assembly.Relation (1) contains a methodological error, since it neglects the spectral sensitivity of the detector. In addition, when a new type of fuel assembly is put into operation the new dependences ξ t.d (E) must be calculated.The main problems of improving the algorithm are separating the contribution of the thermal and suprathermal neutrons and introducing the dependence of their sensitivity ratio to the suprathermal and thermal neutrons on the burnup and establishing the relation between the thermal neutron flux density at the detector's location and the power of the process channel. Obtaining the dependence of the detector's ratio of the sensitivity by a computational method is a difficult problem, so

Development of RBMK in-reactor control

“…The adoption of lag-free in-reactor detectors enabled automatic regulation of the radial-azimuthal distribution of the power release and local emergency protection of the core. At the present time, methods taking account of the spectral sensitivity of detectors with an HfO 2 emitter, which appreciably increase the accuracy of reconstruction, are now being prepared for adoption [14]. A more accurate dependence, taking account of the burnup of in-reactor detectors, is being prepared for adoption.…”