Preliminary Conceptual Design Of The Radiation Shielding For The2MWt Thorium Molten Salt Reactor With Liquid Fuel

Molten Salt Reactor (MSR), in which the fissile and fertile materials are dissolved in amixture of molten fluorides, was originally proposed by the Oak Ridge National laboratory(ORNL) in1940s. The MSRs have unique characteristics in good neutron economy, hightemperature and low vapor pressure, inherent safety, online refueling and proliferation resistanceand physical protection. In2002, the MSR was selected as one of the recommended R&D for themost promising systems by the Generation IV International Forum (GIF). It can be noted that theMSR was operated at high temperature and low vapor pressure due to the use of molten salt asthe fuel and coolant. The radiation shielding design of the MSR was also different from the solidfuel reactors that the shields of the MSR were support not only to attenuate the radiation doserate but also to separate the high temperature core from the shielding materials. Thatsignificantly challenges the radiation shielding design of the MSR. In this study, the radiationshielding calculations and primary conceptual shielding design were carried out for the2MWtThorium Molten Salt Reactor with liquid fuel (2MWt TMSR-LF) of the TMSR Project, astrategic priority research program lunched by the Chinese Academy of Science (CAS) inShanghai Institute of Applied Physics (SINAP). The main chapters are as follow:Chapter1: Introduction. The history of the MSR was reviewed and the researchesprogresses around the world were introduced. And for the radiation shielding study of the MSR,the developments of the radiation shielding and thermal analysis about nuclear reactor werepresent.Chapter2: Radiation and thermal source analysis of the2MWt TMSR-LF. According to thestructure parameters of the2MWt TMSR-LF, the Monte Carlo code MCNP5was employed tosimulate the particle transport. The power destiny, the neutron and gamma spectra of the2MWtTMSR-LF were calculated. In order to analysis the impacts of online processing on the sourceterms and provide reliable source terms for the radiation protection of MSR, a calculationmethod of the source terms for the MSR with online processing was studied, and the analysiscode PostTRITON was developed. Also the computational fluid dynamics (CFD) analysis of thecore of the2MWt TMSR-LF was performed by using the FLUENT code. The temperaturedistribution and the maximum of the temperature were presented.Chapter3: Shielding design for the2MWt TMSR-LF with U-Pu fuel. With the results ofthe analyses of radiation source and thermal source, requirements of the shielding design wasanalyzed. The objective of radiation shielding design was set up and shielding calculations were carried out. The bulk shielding of the2MWt TMSR-LF should be consist of the thermal shieldand the concrete shields. The thermal shield was designed to be of metal heat pads with coolantcirculating. Stainless steel and cooper were considered for the heat pads, while molten salt, gasesand water were candidates for the coolant. The differences of radiation dose rates and thetemperatures on the internal surface and external surface were calculated and analyzed. Based onthe results, stainless steel was better than cooper for the heat pads. And the plan of water-cooledthermal shield was the best choice for its performance in reducing the radiation dose andtemperature. However, the plan of water-cooled thermal shield was eliminated because of thechemical safety of the contact of water and molten salt. Molten salt has better performance inreducing the radiation dose rate than gas, but worse in bringing down the temperature. To sum up,stainless steel was proposed to be the heat pads and gas as the coolant in the design of thethermal shield. Two layers of concrete shields were still required around the core of the2MWtTMSR-LF, the barite concrete one and the ordinary concrete one. The MCNP5calculations werecarried out to determine the thicknesses needed to decrease the dose rate. The CFD analysis wascarried out to study the temperature distribution of the bulk shielding. All of the results indicatethat the designed bulk shielding satisfies the radiation shielding requirements for the2MWthTMSR-LF.Chapter4: Shielding design for the2MWt TMSR-LF with Th-U fuel. The2MWtTMSR-LF was designed to be loaded with two different fuels, the uranium-plutonium fuelLiF-BeF2-ZrF4-UF4and the thorium-uranium fuel LiF-BeF2-ThF4-UF4. So that the bulk shieldingwas implemented to the2MWt TMSR-LF with the thorium-uranium fuel LiF-BeF2-ThF4-UF4to demonstrate that the shielding complex deigned by this study meets the shielding requirementsin both of the two kinds of load plans.Chapter5: Summary and prospect. The achievements and the insufficient of the presentwork were summarized, and the possible improvements were prospected.