Internal Initiating Event Level 2 Probabilistic Safety Assessment during Full Power Operation of Xi'an Pulsed Reactor

To quantify and estimate the risk of fission products release from Xi’an Pulsed Reactor(XAPR), the special technical essential of XAPR Level 2 Probabilistic Safety Assessment (PSA) was studied, and accident progression and confinement response were analyzed. Then the source terms analysis of XAPR for internal initial event during 2 MW full power operation condition was performed. The results show that in all release categories (RC), the contribution of confinement intact RC01 which is representative of success sequence is about 97.52%. In all abnormal release categories, the confinement seal failure RC02 gives a high contribution of 75.81%. The results also demonstrate that the highest frequency of all categories is from RC01 which is about 4.80×10^-6/(reactor·year）, but its release quantity is the smallest which is 10⁹~10¹³ Bq. The largest release quantity is about 10¹⁴ Bq from RC06 which is described as confinement seal failure and confinement by-pass sequence, and the release frequency of RC06 is about 1.38×10^-8/(reactor·year）. Based on the results, suggestions are given that the ventilation systems should be shut down to prevent fission products from leaking through the stack and the reactor building.