700kWe Gas-cooled Space Reactor Characteristics Analysis And System Transient Characteristics Research

Being the only source that can provide large and long-lasting power in the current and near-term future,the nuclear energy plays an important role in the aerospace field.However,since its space application requires a complex interdisciplinary fusion and to solve a series of technology challenges,it has quite limited scale of development all around the world except for Russia and the United States in the cold war period.Most of all,it has serious hazardous accident results.In recent years,the development of aerospace technology,nuclear technology,computer technology,etc.and the growth of need for large space power provide new opportunity for the development of space nuclear reactor.In this thesis,characteristics and safety analysis of the 700 kWe space nuclear system based on the large space power demand were conducted.The 1/12 reactor three dimensional simulation and system characteristics analysis were also conducted using the physics and computational fluid & dynamic software.Firstly,the design goals,constraints and configuration were chosen for the 700 kWe space nuclear system based on the history experience and technology analysis.Then the heat balance algorithm of the system was modeled based on the thermal-dynamic characteristics and the influence of key parameters on the system efficiency,device heat transfer,system total weight,etc.was clarified.At last,the system highest and lowest temperature of 1500 K and 390 K were decided for the 700 kWe space nuclear system according to requirements such as ten-year lifetime,high efficiency,less total weight and well overall performance.Based on the system heat balance parameters,preliminary reactor physics model was established.A Monte Carlo software was used to study the influence that the geometric parameters,fuel enrichment,material temperature,control rod arrangement,etc.have on the reactor physics characteristics.The basic characteristics of the 700 kWe gas-cooled fast space reactor were acquired.Besides,the effects of the insertion of control rod in different positions were analyzed and found out that the outermost control rods have the ability to aggravate the radial power distribution non-uniformity,while the inner control rods have larger worth and the ability to flatten the radial power distribution.Based on the analysis,three preliminary control strategies were proposed.Finally,physics and control stragety optimization were conducted according to the design goals,constraints and high safety requirement.The final design can ensure the sub-criticality requirements for the reactor in the design accidents such as flooding scenarios.Afterwards,a simpled 3-D 700 kWe gas-cooled space reactor geometry model with a reasonable level of details was established,and one twelfth of it was used to conduct comprehensive flow and heat transfer simulations,which adopted the calculated 3-D power distribution as one of the boundary conditions.The influence of the bypass cooling,surface radiation,core internal structure,flow diffuser plate and wire structure was analyzed and further optimization direction was clarified based on the results comparison.At last,by using the optimized reactor structure,the reactor peak temperature was reduced by roughly 200 K and the pressure drop was reduced by roughly 100 kPa.By adopting the optimized power distribution,the reactor peak temperature was further reduced by about 70 K.The 1-D space nuclear system safety analysis was conducted based on the 700 kWe gas-cooled space nuclear reactor system design.The Jave language was used for the 1-D system analysis platform programming.Typical conditions such as the start-up,loss of coolant,loss of heat sink,and reactivity insertion were calculated and the transient characteristics of the key parameters like reactor power,reacitivity,system temperature,pressure,turbine rotating speed and device heat transfer were acquired.It was found out that the gas-cooled space nuclear system has fast transient characteristics with a time scale of minutes.Thus to ensure safety,safety system or emergency disposal strategy should be established.Related results can provide insights for the safety characteristics of the megawatt-class gas-cooled space nuclear system and meaningful for the establishment of the system control,power changing control,and accident emergency response strategy.