Abstract
The N-13 coincidence method is an effective approach for monitoring the primary loop leakage in pressurized water reactors. The high coincidence efficiency and low background are crucial to achieving a lower limit of measurement for such a monitoring system. In this paper, we proposed four types of geometric designs of the sampling composing NaI(TI) detector. For varying container volumes (V), the detection efficiency (e) of these containers was investigated through the Geant4 simulation and experimental measurement. The value of e•V, which is a key combined parameter, was obtained accordingly. Finally, we obtained the optimal size of the suitable sampling and detection container for the coincidence method.
Highlights
During the operation of nuclear power plants, a series of uncertainties, such as the stress relaxation of material and weld joint pressure corrosion, can cause the leakage of the primary loop radioactive water (D’Auria et al, 2017)
K2 depends on many factors such as coincidence efficiency ε of the gamma ray with an energy of 0.511 MeV, gasification of water leaked from the primary loop, uniform mixing time t1, gas transmission time of gas in the sampling pipe (t2) and sampling container (t3) as follows: εQe−λt1 e−λt2 (1−e−λt3 )
Coincidence efficiency ε and εV are shown in Figures 5, 6
Summary
During the operation of nuclear power plants, a series of uncertainties, such as the stress relaxation of material and weld joint pressure corrosion, can cause the leakage of the primary loop radioactive water (D’Auria et al, 2017). Methods to detect the release of reactor coolant to the containment include the indication and/or monitoring of changes in (a) airborne particulate radioactivity, (b) airborne gaseous radioactivity, (c) containment atmosphere humidity, (d) containment atmosphere pressure and temperature, and (e) condensate flow rate from the air coolers (Dissing and Svansson, 1980; Aoki, 1991; Zheng et al, 2016). Among these methods, a reliable leakage monitor method is to measure the concentration of 13N in the containment vessel, e.g., by using the γ-ray energy spectrum method. Geant simulation and experimental measurements were performed to optimize the detection efficiency of the container for several geometric schemes
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