Abstract: An enhanced passive containment air cooling system for a nuclear power plant that increases the heat transfer surface on the exterior of the nuclear plant's containment vessel. The increased surface area is created by forming a tortuous path in or on at least a substantial part of the exterior surface of the containment vessel over which a cooling fluid can flow and follow the tortuous path. The tortuous path is formed from a series of indentations and protrusions in or on the exterior surface that form a circuitous path for the cooling fluid.

Abstract: The effects of steam generator tube ruptures in a pressurized water reactor are mitigated by reducing the pressure in the primary loop by diverting reactor coolant through the heat exchanger of a passive heat removal system immersed in the in containment refueling water storage tank in response to a high feed water level in the steam generator. Reactor coolant inventory is maintained by also in response to high steam generator level introducing coolant into the primary loop from core make-up tanks at the pressure in the reactor coolant system pressurizer. The high steam generator level is also used to isolate the start-up feed water system and the chemical and volume control system to prevent flooding into the steam header.

Abstract: A nuclear reactor has a passive system for adjusting the pH of post accident water in the containment vessel. A basic liquid is stored in the containment vessel at an elevation above the maximum post accident water level. When radiation levels in the containment vessel exceed a predetermined, normal level the basic liquid is gravitationally drained into sumps located in the containment vessel below the maximum post accident water level where it mixes with emergency core cooling system water, raising the pH of the water to about 7.

Abstract: The spent fuel pit of a pressured water reactor (PWR) nuclear power plant has sufficient coolant capacity that a safety rated cooling system is not required. A non-safety rated combined cooling and purification system with redundant branches selectively provides simultaneously cooling and purification for the spent fuel pit, the refueling cavity, and the refueling water storage tank, and transfers coolant from the refueling water storage tank to the refueling cavity without it passing through the reactor core. Skimmers on the suction piping of the combined cooling and purification system eliminate the need for separate skimmer circuits with dedicated pumps.

Abstract: A pressurized water nuclear reactor uses its residual heat removal system to make up water in the reactor coolant circuit from an in-containment refueling water supply during staged depressurization leading up to passive emergency cooling by gravity feed from the refueling water storage tank, and flooding of the containment building. When depressurization commences due to inadvertence or a manageable leak, the residual heat removal system is activated manually and prevents flooding of the containment when such action is not necessary. Operation of the passive cooling system is not impaired. A high pressure makeup water storage tank is coupled to the reactor coolant circuit, holding makeup coolant at the operational pressure of the reactor. The staged depressurization system vents the coolant circuit to the containment, thus reducing the supply of makeup coolant. The level of makeup coolant can be sensed to trigger opening of successive depressurization conduits.

Abstract: A water storage tank in the coolant water loop of a nuclear reactor contains a tubular heat exchanger. The heat exchanger has tubesheets mounted to the tank connections so that the tubesheets and tubes may be readily inspected and repaired. Preferably, the tubes extend from the tubesheets on a square pitch and then on a rectangular pitch therebetween. Also, the heat exchanger is supported by a frame so that the tank wall is not required to support all of its weight.

Abstract: A nuclear reactor having a reactor vessel disposed in a containment shell is depressurized in stages using depressurizer valves coupled in fluid communication with the coolant circuit. At least one sparger submerged in the in-containment refueling water storage tank which can be drained into the containment sump communicates between one or more of the valves and an inside of the containment shell. The depressurizer valves are opened in stages, preferably at progressively lower coolant levels and for opening progressively larger flowpaths to effect depressurization through a number of the valves in parallel. The valves can be associated with a pressurizer tank in the containment shell, coupled to a coolant outlet of the reactor. At least one depressurization valve stage openable at a lowest pressure is coupled directly between the coolant circuit and the containment shell.

Abstract: A passive safety injection system relies on differences in water density to induce natural circulatory flow patterns which help maintain prescribed concentrations of boric acid in borated water, and prevents boron from accumulating in the reactor vessel and possibly preventing heat transfer.

Abstract: A ventilating system for an enclosure in a nuclear power plant is provided. The enclosure houses an emergency feedwater pump and its driver steam turbine. An eductor mounted in the enclosure is supplied with steam exhausting from the driver steam turbine. The steam jet formed by the eductor draw hot air out of the enclosure, thereby preventing the excessive build-up of heat in the enclousre. An air inlet formed in another wall of the enclosure supplies the enclosure with cool ambient air. The eductor and air inlet are situated to ensure the incoming air flows over the pump, thereby cooling it. A duct transports the steam/air mixture discharged by the eductor to the atmosphere.

Abstract: A passive safety system for a nuclear reactor is comprised of a first subsystem for circulating water solely by natural convection from a first branch to a second branch of a reactor coolant circuit with the circumvention of a steam generator for removing decay heat from the reactor coolant circuit at any pressure. The first branch guides heated water from the reactor vessel into the steam generator and the second branch guides cooled water from the steam generator into the reactor vessel. The first subsystem includes a heat exchanger for cooling water flowing from the first branch and prior to being introduced into the second branch and a first valve for allowing flow of water from the first branch into the second branch solely in response to a parameter value pertaining to operational safety. There is also provided a second subsystem for introducing stored cold water solely by gravity into the reactor vessel for making up for lost water in the reactor coolant circuit at any pressure.

Abstract: A vent system for controlling hydraulically actuated drive means for selectively moving pluralities of rod clusters respectively connected to the plurality of drive means between fully inserted positions within the lower barrel assembly of the vessel in telescoping relationship with fuel rod assemblies contained therein, and a fully withdrawn position. Each drive means responds to the reactor coolant fluid pressure and includes a leakage passage and an outlet channel through which a leakage flow may pass under control of the vent system, the latter comprising a valve arrangement, flow restrictors and a common orifice through which the outlet channels are selectively connected to essentially ambient pressure, for establishing a pressure differential within each drive means producing a net force for moving the drive rods and associated clusters to the withdrawn position at which the drive means mechanically latch the fully withdrawn clusters for mechanically supporting same in the fully withdrawn position.

Abstract: A pressurized nuclear water reactor has a substantially cylindrical flow liner with a cylindrical wall section and bottom and an open top. A barrel forms a riser chamber that contains the core in the flow liner. A pressure vessel contains the cylindrical flow liner to form a second annular chamber therebetween that contains a supplementary liquid coolant, with insulation means to provide a major portion of the supplementary liquid coolant at a first temperature and a minor portion thereof at a second higher temperature. Upon depressurization in the vessel, fluid communication means enable injection of supplementary liquid coolant from the second annular chamber into the core upon flashing of a minor portion to vapor. A further pool of water outside the pressure vessel, and insulation on the wall, maintain the desired temperature in the supplementary liquid coolant supply. Injection or removal of borated solution, as a chemistry control solution, into or from the supplementary liquid coolant is provided.