The Effects Of MA Transmutation On AP1000 Safe Operation

Separation-transmutation is to separate useful nuclides and highly radioactive nuclides from the spent fuel, and put the highly radioactive nuclides into reactor and are irradiated by neutrons, then convert them into a low-level radioactive nuclides, stable nuclides or high-level radioactive useful nuclides. This paper studies the effect of MA transmutation in the AP1000 core on the safety performance of the reactor. Firstly, we build the AP1000 reactor core by the MCNP code, and reach criticality by adjusting relevant parameters. We add MA nuclides into the core by coating MA around the fuel pellet, this method will improve the MA transmutation rate. In the paper, we design 11 coating patterns. There are three different fuel assemblies with different fuel enrichment in the first cycle of AP1000 core; we design 7 types of patterns on the three different fuel assemblies. We write these 77 kinds of patterns into the AP1000 core by the MCNP code.We simulate the effective multiplication factor of each loading pattern by MCNP code. In the paper, we select the largest effective multiplication factor in the same adding MA nuclides mass, and that is the minimal impact on the core reactivity. By comparing the various patterns, we select the pattern that adding MA transmutation target in the region of 4.45% fuel enrichment as the optimization program.The adding MA nuclides will play the similar in the core poison on some extent. In this paper, we use MA nuclides to substitute for the boric acid in the coolant. We calculate the reduced boric acid concentration of each pattern on different MA coating thickness. To reduce the impact of the introduction of MA nuclides on core safety performance, we select 0.002 cm MA coating thickness as an optimization pattern.We calculate the neutron flux of the optimization pattern by MCNP code, and by comparing with the normal core we find that the introduction of MA nuclides has no impact on the core neutron flux spectrum. We calculate the power peak factor of core, and by comparing the change before and after adding MA nuclides we found that because the MA nuclides are added into the core, the power peak factor change from 1.5569 to 1.9847, and the power distribution is not flatten as without MA transmutation materials, which indicates that loading of MA nuclides to reactor also introduce slightly negative effects to the safe operation of reactor.The fuel temperature coefficient and moderator temperature coefficient of the optimal pattern were calculated by MCNP and NJOY code. After comparison to the normal reactor which had no MA nuclides, we found that the fuel coefficient of optimal pattern is negative, a negative feedback effect, but the absolute value is smaller than normal core fuel temperature coefficient, which means that will affect the safe operation. The moderator temperature coefficient of selected optimal pattern is also negative, with the negative feedback effects, and the absolute value is larger than the normal core moderator temperature coefficient, which increase the safe operation of reactor in some extent.We calculated the burnup of the optimal pattern by the DRAGON code. After one year’s burnup the MA nuclides transmutation rate is 14.766%, and 44kg MA nuclides we are incinerated per year, which is equal to the twice MA nuclides output of one million kilowatts PWR.