The feasibility analysis of pipe heating by VVP during hot shutdown

Heating pipe by main stream release system (VVP) is arranged after the zero power experiment, and this operation is in the critical path, so it is necessary to consider the heating during hot shutdown. It will be useful to optimize the overhaul period. In this paper, the feasibility of the pipe heating by VVP during the hot shutdown of the pressurized water reactor (PWR) nuclear power plant is identified. Either engineering judgment or thermal-hydraulic analysis, can show that the wording conditions of pipe heating through VVP can be satisfied under the hot shutdown as long as measures are taken to control the APG discharging flow, water feeding flow, setting value of GCTa and the opening degree of VVP main isolating bypass regulating valve. The engineering judgment which sort the technical standards and carry out the qualitative analysis is used to draw a preliminary conclusion. However, pipe heating has not been finished under such circumstances where the efficiency of pipe heating is sensitive to the parameters of loop 1 and 2. In order to take reasonable control measures, reduce the risk and understand the physical phenomena in advance, it is suggested to carry out a thermal and hydraulic analysis according to the specific parameters before pipe heating. Safety assessment use the thermal hydraulic system code to show the process of heating pipe accurately, and analyze the consequences. Finally the report shows the specific control ways. (authors)