PRESSURIZED-WATER NUCLEAR REACTOR

1,269,523. Reactors. BABCOCK & WILCOX CO. 25 April, 1969 [25 April, 1968], No. 21213/69. Heading G6C. A pressurized water nuclear reactor includes an upright pressure vessel 10, an annular core shield 13 spaced inwardly of the pressure vessel to define an annular passageway 16, a reactor core 22 positioned within the core shield 13 above a plenum chamber 24 and forming the outlet for the plenum chamber, means whereby water that has flowed through the annular passageway 16 may pass into the plenum chamber, and means for imparting a swirl to water flowing through the chamber 24. The water enters the vessel 10 through four circumferentially spaced inlet nozzles 15 and is directed down the annular passageway 16 by inverted U-shaped baffles 27 positioned on the core shield 13 in alignment with the nozzles 15. A series of inclined vanes 30 are attached to the inner surface of the dome-shaped bottom closure 12 of the vessel 10, causing the water from the annular passageway 16 to swirl in the chamber 24. The upper boundary of the plenum chamber 24 is formed by a dome-shaped perforated baffle 31. A vortex inhibitor 29 is attached to the lower central portion of the baffle 31 to control the rotation of the swirling mass of water entering the perforations of the baffle and to increase the flow to the central portion of the baffle with a minimum of energy dissipation. The swirling movement promotes a substantially uniform water flow and water temperature distribution to and through the core 22. The temperature difference required for safety between the temperature of the water leaving the reactor and the saturation temperature of the water can thus be minimized. A condition of unbalance in the incoming water flowing to the annular passage 16 could be caused by many circumstances, e.g. a pump failure in one of the four lines leading to the inlet nozzles 15, and if means for equalizing the flow and temperature were not provided the maldistribution of water entering the core could have serious consequences.