11-4. Loss of Coolant Accident Mitigation for Liquid Metal Cooled Space Reactors VLADIMIR GEORGEVICH, FREDERICK BEST & CARL ERDMAN Summary A loss of coolant accident (LOCA) in a liquid metal-cooled space reactor system has been considered as a possible accident scenario. Development of new concepts that will prevent core damage by LOCA caused elevated temperatures is the primary motivation of this work. Decay heat generated by the fission products in the reactor core following shutdown is sufficiently high to melt the fuel unless energy can be removed from the pins at a sufficiently rapid rate. There are two major reasons that prevent utilization of traditional emergency cooling methods. One is the absence of gravity and the other is the vacuum condition outside the reactor vessel. A concept that overcomes both problems is the Saturated Wick Evaporation Niethod (SWEM). This method involves placing wicking structures at specific locations in the core to act as energy sinks. One of its properties is the isothermal behaviour of the liquid in the wick. The absorption of energy by the surface at the isothermal temperature will direct the energy into an evaporation process and not in sensible heat addition. The use of this concept enables establishment of isothermal positions within the core. A computer code that evaluates the temperature distribution of the core has been developed and the results show that this design will prevent fuel meltdown. Introduction The current national space program incorporates several power sources as possible suppliers of energy for various missions. One of the possible power sources is a nuclear reactor that converts thermal energy into electricity by imposing a temperature difference across thermoelectric elements. Concern about the safety of a nuclear reactor has prompted new investigations to be initiated into methods of rejecting decay heat from the reactor core for the LOCA scenario. Some of the previously proposed methods of heat removal consist of energy removing ‘bayonets' in the core, allowing the energy to be transferred from the pins to the bayonets by radiation heat transfer. Energy is removed by circulating tertiary coolant through the bayonets. Other proposed methods use diode heat pipes located inside the core which would become operational only if a certain predesigned temperature is exceeded. All of the above methods are based on radiative heat transfer from the pins to a secondary surface. The size of the secondary surface is proportional The authors are in the Nuclear Engineering Department, Texas A&M University, College Station,Texas, USA. Paper number IAF-ICOSP89-11-4.
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