The Effects Of Tc-99 Transmutation On The PWR Reactivity Control

The rapid development of nuclear power will produce a large amount of radioactive materials inevitably,which will lead to radioactive hazards to the environment,especially the long-lived fission product(LLFP),which still has strong radioactivity in natural conditions after several hundred years.How to deal with these radioactive materials effectively is increasingly received more and more attention.Among nations,a separation-transmutation method has been proposed in order to solve this problem.As the important nuclides of long-lived fission product,Tc-99 has a long half-life and strong environmental migration capacity.Separation-transmutation technology can reduce the radioactivity of Tc-99,while it can be converted into Ru,a necessary industrial essential and a precious metal element.At present,PWRs are the most widely used and most matured technology in devices that can be used as neutron sources.Therefore,it is of great significance and value to study Tc-99 transmutation of PWRs.How to introduce Tc-99 into the core is a key issue.According to the previous researches,most of the researches are about the transmutation of Tc-99 in combination with the fuel rods,which is not conducive to the control of the reactivity.Therefore,this paper innovatively adopts the combination of Tc-99 and burnable poison rods,and study the effect of Tc-99 on reactivity control.This paper mainly uses SCALE code to simulate the BEAVRS model,which is Westinghouse PWR model.Prior to the introduction of Tc-99 into the reactor,a variety of physical parameters,such as refinement modeling based on available reactor parameters,zero power reactivity and excess reactivity,were compared with the standard results to ensure that the simulation results are accurate.Tc-99 was then introduced into the reactor core in two ways,uniformly mixed with burnable poisons and as a coating of burnable poison,the relevant physical parameters were calculated and compared.From the results of the reactivity change,the transmutation rate of Tc-99 and the lifetime of the core,we can see that when Tc-99 is uniformly mixed with burnable poisons,the keff decreases first and then increases with the increase of mass fraction,When the mass fraction is higher than 45%,the keff is higher than that without adding Tc-99;the transmutation rate decreases gradually with the increase of mass fraction from 7.33%to 2.81%;the core life decreases from 400 days to 200 days or so,the change is obvious.When Tc-99 was used as a burnable poisons coating,the keff decreased firstly and then increased with the increase of thickness,which was lower than that without adding Tc-99.The transmutation rate decreased slowly from 5.19%to 3.37%.Lifetime of cores from the beginning of about 400 days down to 350 days or so,which has little effect.Overall,as the mass of Tc-99 introduced into the core increased,the keff basically decreased first and then increased;the transmutation rate gradually decreased and the transmutation quality gradually increased;moreover,Tc-99 was introduced into the reactor as a burnable poisons coating the cores are better than the uniform mixing method.By adjusting the concentration of boron,the number of days with keff greater than 1 is basically equal to the number of days with normal operation.