To assess the characteristics of 13N decay, a monitoring method of the
primary loop leakage rate based on the ?-? coincidence method was proposed.
In this work, sampling and measurement devices were designed, in which NaI
(Tl) crystals were used as coincidence detectors. The Geant4 simulation
method was used to study the relationship between the efficiency e and
capacity V change of different devices, and the eV value under the
corresponding capacity was obtained. According to the value of eV, the
optimal sampling and measurement device was determined, and then the
detection efficiency of the device was calibrated experimentally. Taking the
600 000 kW reactor of Qinshan Phase II as the research object, the lower
limit of detection was discussed. When the sampling point was located in the
fume hood of the control rod drive mechanism, the theoretical lower limit of
the coincidence method was 0.756 Lh-1.