Experimental Investigation Of The PRHRS For Molten Salt Reactor Based On A Single Tube

Molten salt reactor(MSR)was ranked as one of the most promising reactors by Generation IV International Forum(GIF).America,Japan and Europe have already conducted relevant research.Chinese study has a late-starting,but exhibits a rapid development.Shanghai Institute of Applied physics,Chinese Academy of Sciences has been entrusted by Chinese government with carrying out the investigation of Thorium Molten Salt Reactor,which is set to come into service in the next 20 or 30 years.Well,the Passive Residual Heat Removal System is(PRHRS)a vital subsystem to guarantee the safety of MSR.Currently,there is less research of PRHRS for the MSR,most of which concentrates on conceptual design.Therefore,in this situation,this paper conducted some fundamental analyses of the PRHRS,depending on the National Natural Science Foundation of China.Some key problems are summarized in the following by analyzing the structure of the PRHRS and massive research papers: flow boiling in the annulus between the bayonet and the center tube,possible instabilities in the boiling loop and the operation characteristics of the PRHRS.According to the problems needed to be settled,two experimental apparatus,Electric Heating Bayonet system(EHB)and Residual Heat Removal system(RHR),have been built up.The EHB is used to study flow boiling and instabilities,and the RHR is aimed at investigating the running law.The EHB consists of a steam drum,a center tube and a bayonet.The diameter of the center tube is 12.7×1mm,and the diameter of the bayonet is 5.4×1.5mm.The bayonet is divided into two parts,heating section and rising section,along the longitudinal axis.Cooling water is stored in the steam drum.When the EHB starts running,water flows downward from the inlet of the center tube,reverses at the bottom of the bayonet,flows upward in the annulus and finally returns back to the steam drum from the outlet of the bayonet.The heat source is supplied by DC power.On the basis of EHB,a thimble is added in the RHR,therefore the double-layer heat transfer tube become integrated.The thimble transfers heat to the bayonet mainly by radiation and gas conduction in the gap.The heat input leads to flow boiling in the annulus.The heat source in the RHR is supplied by high-temperature tube furnace,while the condensing tank is served as heat sink.Subcooled boiling and saturated boiling are accomplished in the annulus on the EHB apparatus.The effects of some significant parameters including heat flux,inlet subcooling,water level in the steam drum and pressure on boiling heat transfer and natural circulation are analyzed.The experimental results are compared with boiling models proposed by Kandlikar,Gungor-Winterton and other researchers.The effects of convection term and nucleate boiling term are also discussed.On this basis,the boiling model proposed by Liu-Winterton is modified.The new modified model shows an improvement on trending and accuracy.The ONB is obtained under natural circulation at low pressure and compared with prediction models proposed by Sato,Jens and others.Some parameters affecting ONB are also discussed.The dependency of ONB on these parameters is analyzed with the Pearson coefficient.Further more,a new correlation is raised.The new correlation is also validated with experimental data from Ahmadi,which shows a conspicuous increase of pertinence.The instabilities including geysering and Density Wave Oscillation(DWO)are investigated.The mechanism,some important characteristics and fluctuation boundary are presented.In addition,a new oscillation of small flow rate is discovered and why this oscillation arises is discussed.The feasibility of the PRHRS is proved experimentally.The distribution of thermal resistance in the heat transfer tube is studied and the effect of some important system parameters including high temperature heat boundary,initial water inventory,water tank and loop resistance on the system running is also analyzed.Additionally,the transient starting process is discussed.A system model based on RELAP5 is proposed,with which the passive heat removal process of MSR is simulated.The special condition,water injecting,is analyzed.Of course,the accuracy of the model is validated with experimental data.The simulated results show that the PRHRS can operate under 150 kPa for a long time and take the decay heat away from the drain tank.For the PRHRS of MSR,the research presented in the paper can provide technical support of practical application.