A Numerical Analysis Of Asymmetric Operation On The Small Reactor

A variety of abnormal operation conditions may happen during the nuclear power plant operation changes frequently under the ocean conditions. These abnormal conditions have a great effect on the dynamic behavior of neutron kinetics and the safety of thermal-hydraulics.In order to ensure the vitality of the nuclear power plant and the safety of people, it's extremely important to take some measures to maintain the nuclear power plant operation under abnormal conditions. Therefore, the researches on operating features of the nuclear reactor under abnormal operation conditions need to be carried out.In this paper, thermal-hydraulic calculations and numerical simulations have been conducted to research the operating properties of small nuclear reactor under asymmetric conditions. The RELAP5 has been used to calculate the operation of the primary and the second loop system under asymmetric inlet flow or temperature and the single-loop operation.The calculation results show that the greater the difference of loop-flow is, the stronger fluctuation of the system and equipment's operating status appears. The reduction of feedwater may cause the cyclical fluctuation of generator's circulation flow, which can affect the safety of reactor. And a closed attention should be paid to the state of isolated loop in order to prevent the over-pressure damage the equipments. Overall, attentions must be paid to the dynamic behavior of reactor's power, pressurizer and steam generator under asymmetric operation.For the simulation of flow field and temperature field in reactor pressure vessel under asymmetric operation, the calculation results of CFX show that asymmetric condition has an obvious influence on coolant mixing of pressure vessel and the distribution of flow and temperature in core inlet. Under normal condition, the inhomogeneity of core inlet flow's distribution is within ± 5%, but it reaches to ± 8% when the speed difference of two main coolant pump is 50% or 75%. The more difference of pressure vessel's inlet flow, the more serious of each core channel's flow deviating from the average flow. Moreover, the coolant mixing in the lower plenum is insufficient when inlet temperature of pressure vessel is asymmetric. The distribution of core inlet temperature is also uneven and the local temperature is higher. And the inhomogeneity of flow distribution is within ±6% due to the influence of the difference in inlet temperature. Furthermore, the inhomogeneity of flow distribution in core inlet is more serious under the single-loop operation, which reaches to±9%.