Development of Boric Acid Concentration Meter for Advanced Thermal Reactors

A boric acid concentration meter was developed for continuous measurment of the 10B concentration in heavy water in a nuclear reactor. The principle of the meter is based on slowingdown of fast neutrons from a radioisotopic neutron source by heavy water and absorption of slowed-down neutrons by 10B depending on its concentraion. The errors in the measurement are casused by temperature changes, photoneutron generation etc. in sampled heavy water and instrumental instability of a neutron measuring system. Laboratory tests with fresh heavy water containing no γ-emitter and demonstration tests at "FUGEN" power plant were carried out, to evaluate the factors of errors separately, and correction techniques for photoneutrons etc. were developed. The results of the tests showed that the meter developed had a measurement precision better than ±0.1ppm 10B in a range of 0-30ppm 10B.