Research Of Radioactive Products Of 100MWt Small Molten Salt Reactor

As one of the six candidate reactor types for the fourth generation advanced nuclear reactor,molten salt reactor uses liquid molten salt as coolant,moderator and fuel,and is the only reactor system that uses liquid among the six reactor types.Operating at high temperature and atmospheric pressure,the molten salt reactor system has obvious advantages in inherent safety,neutron economy,nuclear proliferation prevention and fuel cycle.The international research status and trend show that the fourth generation advanced reactor has become an important means to solve the world’s new energy and environmental problems.The molten salt reactor has become the focus of current research because of its good technical accumulation and unique advantages,and gradually stands out in the fourth generation reactor.Radioactive source term refers to the actual or potential release information of radioactive substances from a given source to the environment,mainly including the type,form,quantity and other release characteristics that change with time of released nuclides.During the operation of nuclear reactors,fissile nuclides produce a large number of radionuclides under the condition of neutron irradiation.These radionuclides have various types,complex evolution characteristics and strong radioactivity.Radioactive product analysis includes reactor design,safe operation,decommissioning of nuclear facilities,and spent fuel management.An important basis for EIA work.Therefore,it is of great significance to accurately determine the type and yield of radioactivity generated in the reactor and to predict the dynamic evolution and distribution of radionuclides in the reactor system for the safe operation of the reactor and for the safety protection of the environment and human beings.As a new generation of reactors,small reactors have significant advantages in inherent safety,economy,construction and transportation,nuclear proliferation prevention,and nuclear thermal application.Based on the research of molten salt reactor,a design model of a small molten salt reactor is designed as the research object,and a set of radioactive products analysis of the equivalent full power of a small molten salt reactor under normal operating conditions is established,and the radioactive output of a small molten salt reactor under normal operating conditions is calculated.The research content of this paper is mainly divided into three parts,which are the design and optimization of the calculation model of small molten salt reactor and the analysis of radioactive products in the main loop.This paper mainly uses Scale6.1software developed by Oak Ridge National Laboratory in the United States,in which the core physical model is created in the sub-transport computing function module KENO-VI,and the complex core is modeled by using various geometrical bodies in the Scale Generalized Geometry Package(SGGP).The paper optimizes the initial simplified model.The basic steps are as follows: on the basis of fixed core size,control rod and overall arrangement of molten salt fuel pipeline,the fuel pipeline size,reflection layer thickness,initial fuel ratio and loading capacity are optimized from the aspects of effective propagation factor,propagation ratio and temperature coefficient.So as to determine the final research model for the subsequent use of the paper.In this paper,the optimized core was used to calculate the radionuclide changes in the core and the amount of reflective nuclides at the end of life of a small molten salt reactor operating for 700 days at the equivalent full power of 100 MWt.The radioactive products of the main loop system of small molten salt reactor are analyzed,and the influence of the radioactive concentration of key fission product nuclides,the total production and its distribution are analyzed.The calculated results show that the radioactivity during reactor operation is mainly provided by fission products and actinide nuclides,which basically come from the continuous decay of short-lived nuclides.Among them,airborne radionuclides,such as fission products of volatile metals,inert gases and isotopes of iodine,account for more than 43% of the total reflectance.As the main source term released to the environment in the molten salt reactor,they need important protection.In addition,the deposition of tritium in the main loop is also a problem that needs to be paid more attention to.The calculation results provide important references for the physical and shielding design,radioactive waste management,in-service maintenance and decommissioning of molten salt reactors.