Testing of a system for measuring the nonuniformity of energy release in a BBER-440 core according to indications of detectors located outside the reactor

Abstract

In the development of BBER-440 reactors, stringent requirements were not imposed on the monitoring of the heat release distribution in the core. This was explained by the stability of the heat distribution and the large margins up to critical heat regimes during normal reactor operation. Integrated on-line monitoring of the heating intensiveness of the fuel assemblies was performed by temperature monitoring of each assembly, and in so doing off-line sporadic monitoring of the vertical heat release was provided in the central channels of some fuel assemblies by means of activation measurements. However, the "Volna" system intended for this purpose did not provide the required operational reliability and representativeness of measurements and was taken out of operation as being obsolete. However, the "Volna" system intended for this purpose did not give the required operational reliability and representativeness of measurements and was shut down for reasons of obsolescence.As time passed, the requirements for increasing fuel economy, increasing fuel energy intensiveness, and more stringent national and international requirements for safety of nuclear power plant operation as a whole and nuclear fuel in particular made it necessary to monitor on-line the nonuniformity of the distribution of energy release in the core. The spatial distribution of energy release was first implemented in the BBER--440 reactor at the Lovis nuclear power plant by means of in-reactor 3-emission detectors. Later, assemblies of such detectors were included in the V-213 reactor plant (Roven nuclear power plant --power-generating units 1 and 2; "Paksh" nuclear power plant, Kola nuclear power plant --power-generating units 3 and 4, and so on). In the V-230 type BBER-440 there is no such monitoring of the energy-release distribution, though such monitoring is now required for reactors of this type. Thus, according to the technological operating regulations, during reactor operation at power it is necessary to make sure that the coefficient of nonuniformity of energy release over the volume of the core does not exceed an established value, which is impossible to do without monitoring the nonuniformity of energy release over the height of the core. Specifically, at the Kola nuclear power plant (power-generating units 1 and 2) assemblies of inreactor detectors were installed in some fuel assemblies. However, this expensive re-equipping of the reactors is not always justified.Computer systems employing indications of extrareactor neutron detectors are widely used to monitor the distribution of energy release in the cores of high-power pressurized-water reactors [ 1 ]. In Russia a prototype of such a system was installed and tested at the Novovoronezh nuclear power plant (power-generating unit 5) [2]. Extrareactor monitoring of the distribution of energy release, as compared with purely in-reactor monitoring, has the advantage that there are fewer detectors in the core and therefore fewer locations where the reactor vessel is more dense, the dose lo...