EX-CORE NEUTRON FLUX MONITORING SYSTEM IN GRAPHITE PRISM FOR GEN. IV REACTORS

Abstract

Nowadays Gen. IV reactors are attracting more attention, and so the same attention should be given to the safety and security requirements of these reactors. One of the most critical safety criteria is connected to the control of the chain reaction and thus to the neutron flux monitoring system. The neutron flux monitoring system is an integral part of the instrumentation and control system (I&C) on reactor that has to be able to provide a full monitoring range information throughout the whole operation cycle. Neutron flux can be in general monitored via ex-core or in-core instrumentation. The measurement can be conducted by fission chambers, selfpowered neutron detectors (SPND), proportional counters, ionization chambers and other detectors such as plastic organic scintillators etc. The accurate positioning of neutron flux detectors has to be determined for each type of Gen. IV reactor with respect to all technical and physical aspects. This paper is aimed on ex-core measurement of neutron flux of Gen IV graphite moderated reactors, while discussing the international standards, safety requirements, technical requirements, quality requirements etc. This research will be applied to the molten salt modular reactor. The specification of the neutron flux monitoring system together with possible positioning is discussed with respect to the modular reactor dimensions and power. In the final part, first steps towards to the ex-core measurements for Gen IV are made. In order to be able to determine the correct position of the detector, the model of the reactor, where preliminary test will be made is created in Serpent code and this model is validated.