REMOVAL OF EFFECT OF PHOTONEUTRON ON BORIC ACID CONCENTRATION MEASURING APPARATUS FOR HEAVY WATER REACTOR

摘要

PURPOSE:To remove effect of photoneutron, by arranging a first neutron measuring device and a second neutron measuring device with a filter for a low energy neutron on a measuring container having a neutron source. CONSTITUTION:A measuring container 1 is provided with an additional second neutron measuring device 4a with a filter for a low energy neutron, for example, a Cd filter 6. Neutron np decelerated by heavy water D is mostly converted to a low energy momentarily and hits the Cd filter 6 to be shielded and absorbed and the measuring device 4a detects neutron (n) and the photoneutron np alone (n+np) reaching it 4a being directly irradiated from 252Cf out of the amount of neutron (n+np). On the other hand, the amount (n) of neutron from 252Cf can be measured beforehand as 56Mn and 24Na do not exist when a heavy water reactor is not in operation. Thus, (n+np)-n=np is given thereby enabling removal of effect of neutron in the conversion of the amount of photoneutron to a 10B density.