Accident Analysis Of China Helium Cooled Ceramic Breeder Test Blanket System

Breeding blanket is a key component in a fusion reactor with main functions of tritium self-sufficiency,electricity production and radiation shielding.Tritium self-sufficiency breeding blanket is a compulsory key component in fusion power deal with these two challenges:producing tritium with equal tritium consumption rate,meanwhile,extraction of high grade heat from blanket at high pressure high temperature coolant.The Helium cooled Ceramic Breeder(HCCB)Test Blanket Module(TBM)is the primary candidate developed by China for testing in International Thermonuclear Experimental Reactor(ITER)machine which is an opportunity to have experimental data to verify the nuclear fusion science and technology for forthcoming Demonstration Power Station(DEMO).Safety design activities are most important steps toward DEMO.The objective of demonstrating safety features of HCCB during ITER operation is an open issue and it demands to validate it when attempting to determine modification in different designing stages,in order to manage and prevent accidents and post accidents situations with high confidence and ensure that possible consequences are bounded.Since the experimental data for HCCB is not available yet,improved simulation models leads designing proper TBM and doing well safety analysis.This work is devoted to accident study of HCCB Test Blanket System of the latest version by RELAP5/MODE4.0.RELAP is commonly conducted code used for Safety studies of fusion facilities like TBM accident analysis.From the point of view of the safety,vacuum vessel pressurization and the bulk quantity of heat flux produced by the plasma disruption is a matter of concern.To demonstrate that whether HCCB TBS preliminary design data are acceptable from the safety stand point,the thermal-hydraulics analysis on Helium Coolant System(HCS)under the condition is performed to validate the system design from the viewpoint of safety and to see whether the TBM is designed with sufficient capability of heat removal under the accident situation.Many accident analyses of all kinds of TBM with different nodalizations and assumptions have done with RELAP in these years for safety demonstration of TBM,however,still we don't know how much the RELAP results are affected by the code user in the choice of,for instance,the number of thermal hydraulic First wall(FW)channels in a TBM nodalization.The following steps below have been carried:1.Two different nodalizations have been done for the safety analysis based on latest version of HCCB TBS.These two models include all of the major components(TBM set,hot legs,cold legs,pumps,heat exchangers,etc.);the difference between these two nodalization is in TBM,which is nodalized in simple and detailed configurations.Steady state condition is simulated to validate the model.2.The accident analysis on in-vessel and ex-vessel loss of coolant accident(LOCA)caused by a double-ended pipe break of helium coolant system,Loss of Heat Sink Accident(LHSA)and Loss Of Flow Accident(LOFA)are carried out to verify whether the system satisfy the requirement of decay heat removal for these accidents.At the end as result of this thesis,nodalization,methodology,heat structure and the results of LOCA,LOFA and LHSA accidents and preliminary optimization for the system designs are discussed.Thermal-hydraulic parameters were compared and analyzed to investigate and evaluate the effect of nodalization on LOCA,LOFA and LHSA consequences.TheModification of nodalization to reflect design characteristic of the first wall(FW)is essential to predict the temperature of FW in accident situation,however,in the transient analysis,all these RELAP5 models present increasing of the FW temperature under the designed value.For fast and general results,it is more appropriate to use simple nodalization.If it is necessary more detailed analysis of the TBM,the detailed model is more desirable although it is apparent that the increasing number of FW channels has a serious consequence for the time processing calculation respect to the simple nodalization applying the same time step.