VARIABLE MODERATOR METHOD OF EX-CORE NEUTRON FLUX MONITORING SYSTEM FOR NUCLEAR POWER PLANT

摘要

PURPOSE: A variable moderator of an ex-core neutron flux monitoring system for a nuclear power plant is provided to obtain sufficient counting rate in a driving area of a nuclear power plant and to differently operate a moderator in driving and output areas. CONSTITUTION: An ex-core flux monitoring apparatus measures neutrons leaking from a nuclear reactor in proportion to the output of the nuclear reactor to monitor the output of a nuclear plant and a threshold state. The thickness of a moderator is selected using a driving device(430) according to an output area to be measured. The number of thermal neutrons reaching the surface of the ex-core neutron flux monitoring apparatus is regulated according to the thickness of the moderator. A support pipe of the ex-core neutron flux monitoring apparatus is set to a moderator thickness(410) optimally designed in a driving area ranging from 0°to 180°around the ex-core neutron flux monitoring apparatus and to a moderator thickness(420) optimally designed in an output area ranging from 180°to 360°.