A Revision on CEFR Main Vessel Leakage Rate Measurement Based on Argon Chamber Numerical Simulation

China Experimental Fast Reactor (CEFR) is a sodium-cooled pool type fast reactor with primary circuit equipment integrated in the main vessel. The main vessel, which constitutes the primary pressure boundary, is also an essential barrier to contain radioactive gas. In order to further evaluate the radionuclide activity during normal operation and accident conditions, it is necessary to measure the leakage rate accurately, for sake of the operation and the safety requirements. CEFR leakage rate was previously measured based on step-down method. The step-down method requires reactor keeping steady condition for long time which is difficult to maintain. Besides, lack of temperature measuring points in the CEFR main vessel argon chamber add up difficulties to accurately evaluate the influence of the temperature fluctuation on the leakage rate. CFD simulation method is adopted to model argon chamber and essential in-vessel structures to obtain finer temperature field. The main vessel wall temperature and the sodium temperature are taken as boundary conditions to calculate the argon chamber temperature. The maximum deviation between test pressure and simulation pressure is 5.91% in the rapid temperature rise test. The correctness and reliability of the simulation scheme are preliminary verified with uncertainty analysis. Based on the established method, the leakage rate measurement test is inspected and the calculation leakage rate 96.39L is obtained. This method has important application value and practical significance by providing reference for the optimization of main vessel leakage rate measurement.