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

A computational-experimental procedure for reconstructing the axial neutron flux density and powerrelease distributions using the Prizma-M program is described. An approach to reconstructing the axial neutron flux density and power-release distributions in the RBMK-1000 assembly channels by using extended detectors with a hafnium dioxide emitter to scan the core is presented. This approach made it possible to compare the reconstruction accuracy of the semi-empirical and computational-experimental procedures used in Prizma-M. It is shown that the reconstruction error for the axial neutron-flux density distribution does not exceed the attested error of the Prizma-M program.A method of reconstructing the axial neutron flux density and energy release distributions was adopted in 1985 in RBMK-1500 at the Ignalina NPP. Based on a semiempirical method, it uses a harmonic expansion of the flux density distribution without a neutron-physical calculation and signals from eight neutron detectors belonging to the control-and-protection system (CPS) and uniformly distributed over the height of each of 20 assemblies [1]. Ionization chambers placed in (n, γ) converter channels served as fast-response neutron flux density detectors. In 2002, this method was incorporated into RBMK-1000 in the newly introduced program Prizma-M of the SKALA-Mikro information-and-measurement system. A special feature of the Prizma-M program here was that 72 four-section in-reactor height-monitoring detectors were used. Each section with a hafnium dioxide emitter had a sensitive part with length equal to 1/4 the core height. The length of the communication line section located in the core was equal to 3/4 the core height. The top and bottom parts of the communication line were connected to the emitter, which made it possible to decrease the uncertainties related with the background signal of the communication line.For the first nine years, a semiempirical method was used in the Prizma-M program. Subsequently, on the basis of positive experience in reconstructing the radial-azimuthal distribution by means of a neutron-physical calculation, the computational-and-experimental procedure was adopted for reconstructing the axial distribution of the neutron flux density and energy release, retaining the semiempirical method in the auxiliary operations.In the computational-and-experimental method, just as in the semiempirical method, an expansion of the form (1) is used for the axial flux density distribution of thermal neutrons in the jth assembly channel. Here k is an index of a point along the core height, k = 1, 2, ..., 28; h k is the distance to the kth point from the core top, m; B j is a vector of the coefficients in the harmonic expansion of the axial neutron flux density distribution in the jth assembly channel; ϕ T (h k ) = [ϕ 1 (h k ), ϕ 2 (h k ),