The Short-lived Nuclide Equilibrium Concentration Method Measures Fuel Consumption

The application of the burnup credit technology allows the impact of reactivity reduction after irradiation in the critical safety analysis of spent fuel,thus effectively improving the safety and economy of spent fuel storage and operation.However,no matter what kind of spent fuel management system when applied the burnup credit,we must verify the burnup of spent fuel first,which makes burnup measurement technology become an essential key technology of the burnup credit.So far,people have developed a variety of characteristics and uses of burnup measurement methods,we did some expand the study based on the gamma spectrometry which is the most widely used method to determine burnup.In view of the fact that the method of using long half-life nuclides as the identification nuclide for burnup measurement is affected by the history of irradiation,using short half-life nuclides as the identification nuclides is complicated.This paper presents a burnup measurement method with a wider range of application——based on the equilibrium concentration of short half-life nuclides.This method is carried out by placing the spent fuel in the reactor for a certain period of time or making the fuel to be tested to maintain a constant neutron flux for a period of time before discharge so that the short half-life identification nuclide to establish a concentration balance.In this paper,the contribution of 239Pu to the identification nuclides is considered according to the different enrichment,and the corresponding formula for solving the burnup by identification nuclide is deduced.In order to screen the nuclides that satisfying this burnup measurement method,hundreds of fission nuclides in the ORIGEN simulation results were analyzed and screened based on the half-life duration,the parent nucleus characteristics,the energy of the characteristic gamma and the branch ratio.Six candidate identification nuclides 88Kr(2.84 h)?91Sr(9.63 h)?92Sr(2.66 h)?133I(20.83 h)?135I(6.58 h)?142La(1.52 h)were screened out.To further verify whether it is possible to identify the characteristic gamma peak of the nuclide in the spent fuel gamma measurement spectrum with different fuel consumption depth in the burnup measurement experiment.In this paper,the comparison between the simulated spectrum and the actual y-ray spectrum is carried out,and the rationality of the data processing program and model is verified.Then,the time of cooling of the spent fuel before and after irradiation is simulated.The results show that the cooling time before irradiation of spent fuel does not affect the equilibrium concentration of nuclides,and it can be seen from the simulated? spectrum that when the spent fuel is irradiated for 1-4 times the half-life of the identification nuclide,identification nuclides can present significant observable characteristic peaks,which in turn indicate that this cooling zone is suitable for gamma measurements during the experiment.Finally,the burnup values measured under different experimental conditions obtained by the six kinds of identification nuclides.The calculated burnup values of HEU and LEU spent fuel were in agreement with the theoretical values.And the deviation of the burnup values from the theoretical value is?3%without considering the detection efficiency and self-absorption,thus it verifies the feasibility of using these new identification nuclides to determine burnup.