Of Carr Shutdown Cooling Measures

The CARR (China Advanced Research Reactor), which is under construction now, is a multi-purpose, high capability and credibility research reactor with a power of 60MW. CARR has many characteristics, such as small core, high power density and heat flux, high coolant flowing rates and so on. How to cool down the reactor core after it is shutdown is one of the important safety problems for CARR. The cooling measure will have a large effect on the safety and construction investment of CARR.With the condition of normal reactor shutdown and abnormal (accident) shutdown, the aim of cooling at shutdown is to maintain the cooling structure in reactor core, to ensure enough cooling ability in several phases posterior to shutdown, and to guarantee the MDNBR is less than the limit value for fuel assembly. According to the course of shutdown, the cooling process was divided into three phases. First is the primary phase. The second is the phase in which ECCS (Emergent core cooling system) was put into action. The third is last cooling phase. The analysis, which is done for the main problem and counter-measure in different phases, testify the cooling measure is safe, economical and advanced.The running inertia of the main coolant pump is the key problem of the primary phase. All factors must be considered comprehensively, such as the safety of reactor, the difficulty of manufacture, the demand for anti-earthquake, the demand of reactor operation, the flow rate of ECCS and so on. When the running inertia of the main coolant pump is 450kg.m2 and the flow rate of ECCS is 150 m3/h, the result proves that the above selected value is suitable and economical. It can meet the cooling demand and can improve the capability of the main coolant pump and reduce its manufacture difficulty.The second phase is the most important one in total cooling process for that it is operated on the most complicated condition and at the longest period. The vital points of this phase are listed as follows: selection of the cooling well for emergency, supplying method of electric power, whether the flow rate is satisfied for the cooling under all conditions, preventing the pumps from gas-eroding, and so on. The preferred conditionsare analyzed in detailed, which are showed as: 700m3 water for the emergent cooling well, two emergent pumps used with UPS are operating while reactor is on operation, the bypass valves of system is always open, the system is connected with the main cooling loop by a check value, the water in the reactor pool is continuously cooled in normal condition, the emergent function will be put into used in accident condition. By the analyzing to above measures and calculating for all systems, it is certificated that the system is stable, and is automatic for the switch from normal mode to emergent mode and for the matching between flowing rates and cooling requirements. These designs, including no manpower interruption and automatic matching, will widen the method and accumulate the experiences for domestic research reactor.The structure of the natural circulation valve is the crucial problem in the third phase. The valve is of without manpower and automatically worked by the pressure of the two sides of the valve, which matched with its weight distribution in valve. It can prove that this design can satisfy the demand of the cooling both in the normal condition and in the emergent condition.It was also discussed here that the related cooling measures are analyzed, mainly focused on commissions.This paper discussed systemically the problems of the cooling posterior to reactor shutdown and evaluated the measures at full length. It argues that the cooling measures are safe, economical and advanced. It is meaningful to construction, equipment purchase, experiment check and accepting, installation, commission and operation for CARR.