Abstract
Abstract Kuosheng Nuclear Power Plant, which is the second nuclear power of Taiwan Power Company, has uprated its power from 2894 MWt to 2943 MWt. Taipower has a plan to uprate the power to 3030 MWt (104.7%). In the present study, the uncertainty analyses of fuel rod performance in overpower transients under the stretch power uprate condition are performed using RELAP5 and FRAPTRAN codes. RELAP5 code is used to simulate the thermal hydraulic response of the system in over pressure transients. The results of RELAP5 simulation are used as boundary conditions of FRAPTRAN code calaculations to assess the performance of fuel rods. The target parameters of the assessment are cladding temperature, cladding hoop strain, and fuel enthalpy. The impact of fuel rod manufactures uncertainty on the uncertainty of target parameters are studied statistically. The parameters included in the assessment are cladding outer diameter, cladding roughness, fuel pellet outer diameter, fuel pellet density, fuel pellet roughness, and rod fill pressure. Based on the Wilk’s formula, 207 cases of FRAPTRAN runs are performed to obtain 95th value of the target parameters with 95th confidence. The output of 207 FRAPTRAN runs are also analyzed using parametric method. The RELAP5 input deck of the plant is initialized to the new steady state conditions under higher power. The steady state conditions are compared with these as predicted by TRACE and as documented in the Final Safety Analysis Report (FSAR). The overpressurization transients considered are main steam line isolation valves closure, turbine stop valves closure and turbine control valves closure. This closure of valves increased dome pressure The pressure of reactor coolant system are controlled by safety relief valves and the dome pressure would not exceed the criteria specified by ASME. The results demonstrate that the responses of target parameters are most serious during the transient of main steam line isolation valves closure event. The results of uncertainty analysis show that the 95/95th values of target parameters are within the regulatory limits for all the transient.