Transmutation Of Neptunium-237 In PWR BEAVRS Model

Spent fuel can produce radiation continuously for a considerable period of time,so special disposal methods are needed to prevent them from harming environment.Neptunium-237 is one of the major sources of spent fuel hazards,accounting for about 50%of the mass of minor actinides(MA)and with a half-life of more than 2 million years.Through Partitioning and Transmutation(P&T)technology,Neptunium-237 will occurs(n,γ)reaction in reactor,then decay into Plutonium-238,a valuable element used in nuclear batteries.At present,most of the reactors in operation in the world are pressurized water reactors(PWR).BEAVRS model is a three-dimensional PWR core model proposed by the Massachusetts Institute of Technology(MIT)based on a commercial PWR in 2013.Therefore,based on BEAVRS model,we select Neptunium-237,a single nuclide,to research its transmutation characteristics in PWR.In our research,benchmarks under Hot Zero Power(HZP)state of BEAVRS are simulated by MCNP5.After comparing with the measured data and other simulation results,the accuracy of the simulation with MCNP5 is proved.Then,based on the analysis of previous studies,the option of partially replacing the original burnable poison with the oxide of Neptunium-237 is selected.Therefore,we introduce three patterns of 237NpO2 partial substitution for burnable poison B2O3 in BEAVRS core:External substitution,Internal substitution and Homogeneous substitution.In our research,NJOY99 code is used to produce ACE format nuclear data of required materials nuclides based on ENDF/B Ⅶ.1 database.Then,MCNP5 and SCALE is used to simulate the core effective multiplication factor(keff),fuel temperature coefficient(FTC),moderator temperature coefficient(MTC),burn-up and transmutation rate of the three patterns.After comparing with the original reactor,the following conclusions are drawn:237NpO2 partial substitution for burnable poison B2O3 will reduce the keff of the core,and the decreasing trend slow down with the increase of the substitution mass.The three patterns have nearly no effect on the core FTC,but can increase the absolute value of the MTC,which is beneficial to the core safety.All three patterns will reduce the core-life and burn-up level.The best one is homogeneous substitution pattern,core-life is 335 days,burn-up is 47.8%,80.7%and 85.5%of the original reactor.At the same time,obtains the highest Neptunium-237 transmutation rate in the three patterns,at 18.3%,consumed 56.8 kg of Neptunium-237,6 times of a 1000 MW PWR Neptunium-237 annual production,then with a 83.3%conversion rate produced 47.3 kg of Plutonium-238,nearly 40 times of the Plutonium-238 annual production of a 1000 MW PWR.