Power Uprate Impact Evaluations on Waste Heat of Nuclear Power Plants in Taiwan

Abstract

Power uprate is currently being considered by several nuclear power plant (NPP) utilities as a way to improve plant economy since 1970s. In general there are three types of power uprate: measurement uncertainty recapture (<2%), stretch power uprate (2 to 7%), and extended power uprate (7 to 20%). Prior to the uprate, a thorough evaluation of existing plant equipments and environmental impact must be assessed before a final decision and an optimal selection are made. Upon a power uprate, the power density and thermal release of a nuclear reactor would increase immediately, followed by the impact due to the waste heat from the thermal effluent to the environment. In Taiwan, two BWR NPPs and one PWR NPP are now planning for power uprate. These plants are all located by the side of the seacoast and using marine water as the coolant due to that fact that there is no rivers can supply enough light water near the site of the NPPs in Taiwan. The marine water temperature is high during summer time due to the weather of Taiwan is marine tropical. According to the Effluent Standards of Taiwan’s Environmental Law: for effluents discharged directly into marine waters, the temperature at the discharge point shall not exceed 42 °C; and the temperature difference should not exceed 4 °C for surface water at 500 meters from the discharge point. Therefore, the impact from the waste heat is always a very crucial issue to the power uprate of NPPs in Taiwan. This paper focuses on the environmental impact of power uprate due to waste heat release of NPPs in Taiwan. The evaluations are based on the thermal equilibrium of 100%, 105%, and 110% rated power, respectively. The long term monitor data of marine water temperature are also used to evaluate the impact level from waste heat during normal operation of NPPs. To comply with the Effluent Standards of Taiwan’s Environmental Law, especially in summer, it is needed to solve the thermal effluent’s problem before performing the power uprate of NPP. Adding the dilution pump at each reactor unit is assessed to be a practicable way for resolving such trouble.