Physical Study Of A 600 KW Heat Pipe Cooled Space Reactor And Research On Its Start-up Without External Neutron Source

With the advantages of high energy density,wide power coverage,long service life and low environmental impact,space reactor power has broad application prospects in the fields of military,deep space exploration and space resource utilization.Heat pipe cooled space reactor adopts heat pipe as the medium for heat export from the core,which has the advantages of compact structure,inherent safety,and high reliability,and has received wide attention from domestic and foreign research units.Unlike conventional land-based reactors with fixed sites,space reactor power systems have the characteristics of design and assembly on land and start-up and operation in space.Therefore,the design and research must revolve around real application scenarios and take into account the impacts of different reactor states on the design parameters.In this paper,a 600 kW heat pipe cooled space reactor design with core integration and no external neutron source start-up characteristics was proposed,and the physical design and reactivity control of the reactor,the reactivity feedback effects of thermal expansion from cold to full power operation,and the feasibility study of heat pipe space reactor passive start-up without external neutron source have been carried out,based on a thorough study of space reactor designs and researches at home and abroad.Specific studies and important findings include:Physical design and reactivity control study of the 600 kW heat pipe cooled space reactor:Based on the basic scheme of Li-cooled heat pipe and highly enriched UN nuclear fuel,the 600 kW heat pipe cooled space reactor design with core integration and passive start-up characteristics was proposed and a systematic analysis of the key influencing factors were carried out.The paper investigates the response of many parameters on the reactor keff,the fuel Doppler temperature coefficient and the critical safety under submersion accidents,including the dimensions of the reflector,the position and radius of the control drums,the adding of burnable neutron absorbers and the thickness of the outer B4C layer.On this basis,the physical design of the space reactor and the evaluation of the neutron energy spectrum,neutron flux distribution and fuel consumption analysis were completed,and the physical feasibility of the scheme was initially verified.The results show that the heat pipe cooled space reactor design can meet the target of>10 years operation life with a full power 600-kW,and the reactivity control requirements for normal start-up and shutdown.The space reactor can be in subcritical condition as long as more than 2 heat pipes maintained their integrity even under submersion accidents plus water ingress due to heat pipe break.Study of the temperature reactivity feedback effect introduced by thermal expansion from cold state to full power operation:Based on the nuclear-thermalstructural analysis method by OpenMC and ANSYS,the power and the temperature distribution,and the thermal expansion of the reactor from cold state to full power operation and the temperature reactivity feedback effect of the 600 kW heat pipe cooling space reactor were evaluated.The results indicate that during normal operation,the maximum temperature of the reactor core is 1372.4 K;When a non-clustered heat pipe cascade failure scenario occurs,the maximum temperature of the core can rise to over 1600 K,but the core heat can still be exported normally.However,when there is a scenario of>4-5 heat pipe clustered cascading failures,the local core temperature may reach 1700-1900 K or above,exceeding the applicable temperature limit of UN fuel.The thermal expansion of UN fuel introduced-59 pcm of reactivity from cold to full power operation,accounting for 60%of the fuel temperature feedback.Considering the thermal expansion effect of UN fuel and reflector,the temperature reactivity coefficient of the space reactor is-0.638 pcm/K.Feasibility study on the start-up of the heat pipe cooled space reactor without external neutron source:Based on the 600-kW heat pipe cooled space reactor design,the secondary neutron yields and the distributions from the interaction of three types of cosmic rays(GCR),Earth radiation belts(ERB)and solar particle events(SPE)with the space reactor materials were studied,and researches on the transient neutron characteristics during the early start-up stage of the space reactor were also conducted.The results show that under GCR irradiation,the secondary neutron yield can reach to 4.86×106 n/s,and the neutron flux is at the level of 2×103 n/(cm2·s).Under a higher proton flux irradiation of SPE-91 Carrington and ERB-AD2005,the secondary neutron yield can reach 108 n/s,and the neutron flux can be 5×104 to 1×105 n/(cm2·s).The reduction in core nuclear fuel loading due to physical design changes has reduced the secondary neutron yield to the 8.3×105 n/s level,requiring the placement of detectors with higher detection efficiency in the space reactor.After a slow introduction of reactivity of 1000 pcm into the space reactor in the early stage,the reactor can reach a critical state with the adding of the secondary neutron source,and the neutron density of the core reaches stability after about 4000 s.The research results of this thesis can provide references for the physical design of heat pipe cooled space reactors,the reactivity control strategy during the cold to hot state process,and the start-up without external neutron source method under cosmic rays.