CALCULATION METHODOLOGY ASSESSMENT TO DETECT LOCALISED PERTURBATION IN SODIUM-COOLED FAST REACTOR WITH EX-CORE INSTRUMENTATION

摘要

Safety and reliability are essential requirements for development and operation of Sodium-cooled Fast Reactors. Development of a neutron flux monitoring system (NFMS) for the French SFR is one of the key R&D areas identified. Diverse possibilities of detector system installation should be studied for different locations in the reactor vessel in order to detect any perturbations in the core. In this paper, we aim to explore two calculation routes available for neutron flux monitoring, assess them for their efficiency to detect fission rate variation at Above-core structure (ACS) location and discuss the associated pros and cons. The two calculational approaches we refer here are criticality mode and external source mode. We discuss the feasibility of choosing this location for detecting in-core perturbations and evaluate the methodology needed to achieve it. The paper focuses on the difficulties associated with neutron detection when the detectors are located at far-off distances from the source. We found that for a difficult case such as ours where the detectors are located far-away from the source, criticality mode doesn't work. Variance reduction techniques, employed in the external source mode are indispensable to drive neutrons to areas of interest.