Nuclear reactor pressure vessel

Purpose: To prevent the occurrence of thermal shocks in the wall of a pressure vessel during emergency coolant injection in a PWR type reactor and the lowering of material strength. Constitution: A partition plate is provided along a pressure vessel wall in a downcomer region formed by the pressure vessel wall in a downcomer region formed by the pressure vessel wall and a shroud. Furthermore, the region formed by the pressure vessel wall and the partition plate and the upper plenum are connected by a small hole. In such a constitution, a recirculation pump is driven during steady operation to maintain a higher pressure in the downcomer region than in the plenum. In the event of a loss-of-coolant accident, the plenum pressure is higher than the pressure in the downcomer region. Accordingly, high-temperature water coming from the plenum through the aforesaid small hole flows down in contact with the pressure vessel wall, preventing the sudden cooling of the pressure vessel wall likely to be caused by the injection of emergency coolant, the degradation of wall material properties, and the occurrence of thermal shocks. (Kamimura, M.)