Multiple Channel Analysis For Flow Stability Of CSR1000

CSR1000 is a Chinese Supercritical Water Reactor whose research is undergoing.The large temperature change in the SCWR leads to a sharp reduction in water density through the SCWR core and this huge variation of density causes various instabilities in the core.The licensing of SCWR would probably require the stability analysis so that the reactor should operate under safe margin.In this regard,the flow stability is essential to study.Typically,single channel stability analysis has been performed extensively for SCWR which can analyze in-phase mode of oscillation but the objective here is to analyze multiple(parallel)channel by considering the effects of adjacent channels thus giving a more realistic analysis.The analysis is done by developing a thermal hydraulic model and then making a system matrix and consequently obtaining the decay ratios from the eigen values of the system which is intrinsically a frequency domain method.The steady state behavior is analyzed.The criterion of stability in the steady state is kept that decay ratio must be less than 0.5.The results suggest that under normal operating conditions the reactor is completely stable.The parametric study is done for stability.The various trends are found to be consistent with literature.The mass flow rate plays important role in the instability.If mass flow rate is increased,the stability is increased since the heat transfer ability of coolant increases.While,if power is increased keeping all other operating conditions constant,the reactor is pushed towards instability due to excessive heat up.Thus,the power distribution also affects the regional stability so regions having higher power are more susceptible to instability.The mesh size has been found to have insignificant effect on decay ratio.The system pressure is also important to consider in the stability analysis since the system is susceptible to DWO near pseudocritical points.The wall thickness between two adjacent channels is assumed to be 2 mm and the heat transfer is considered to take place.The hot channel factor of 1.3 is assumed while in adjacent channels correspondingly a decreased hot channel factor is taken so that the total channels under consideration should have unit factor accumulatively.The heat transfer from hot channel to adjacent channel tends the system to converge towards a specific value of decay ratio of hot channel lower than that of the hot channel has been taken alone.The decay ratio in each case of different number of channels under consideration comes out to be less than 0.5 which shows that the reactor operates well i.e.below the threshold of instability.