Low power physics test experience at YGN 3 as the lead unit

YGN 3 is the first power plant (lead unit) having System 80 characteristics with a core rated power of 2815 MWth. The nuclear design of YGN 3 has the features of a 4-batch initial core, low leakage loading pattern, and use of gadolinia burnable poison in the initial core. The YGN 3 low power physics testing (LPPT) program is characterized by the performance of low temperature and normal temperature zero power physics measurements, including measurements of shutdown group worths, net shutdown worth (N-1) at low temperature condition, and the measurements of the reactivity worths of the limiting 'ejected' and 'dropped' control rods. Temperature coefficients of reactivity were also measured at both temperature conditions. This program met all requirements of Regulatory Guide 1.68 and was conducted at YGN 3 to verify the adequacy of the design methods and to confirm the plant operability was in accordance with the design features. During LPPT, the Reactivity Monitoring System (PC based digital reactivity computer) was used to measure isothermal temperature coefficient (ITC), control element assembly (CEA) group worth, and critical boron concentration (CBC). The C-E Reactivity Analyzer (CERA) was utilized for automated data analysis of the ITC and CEA group worth measurements. All test objectives have been satisfied and all measured values are in good agreement with the predictions. Because of the successful LPPT measurement at YGN 3, many tests can be eliminated or reduced in scope by applying more stringent acceptance criteria in YGN 4 and UCN 3 and 4 as follow-on-units. The efficiency of the startup physics test program will be significantly enhanced for YGN 4 and UCN 3 and 4 by reducing the duration and scope of the testing since first-of-a-kind measurements need not to be repeated. Operation at off-normal conditions, especially low temperature criticality and the N-1 worth measurements, will be also reduced or eliminated