Investigation of possibility for failed fuel detection by using the neutron measurement in primary cooling circuit of HANARO

From the various analyses, it is confirmed that the failed fuel detection system(FFDS) of HANARO has some difficulties in monitoring the fuel failure because of the N-16. So, the FFDS based on the delayed neutron measurement is suggested, and the possibility for the failed fuel detection by using the neutron measurements is investigated in the present work. In normal operation of the reactor, the neutrons generated at the primary cooling circuit are assumed as the photoneutrons emitted by N-16 gamma rays and delayed neutrons by the fuel surface contamination, and the changes of neutron generations before and after reactor shutdown are calculated. From the comparison of calculations and measurements using BF3 detector, it is confirmed that about 70 % of the measured neutrons are delayed neutrons, and 30 % are photoneutrons. The neutron generation rate is calculated by Monte Carlo method, ard the calculated count rate of the photoneutron is 11 % of the whole measured neutron count rate. The amount of uranium exposed to the coolant in the core is also predicted by the delayed neutron transport calculation, and it is lower than the allowable level of surface contamination of the fuel rods. Conclusively, since the level of delayed neutrons generated from the surface contamination of fuel rods are sensitively monitored by the detection method of neutron in primary cooling circuit, it is confirmed that the detection method of delayed neutron is very useful for the monitoring of fuel failure