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A reactor vessel head for a pressurized water reactor. This structure is attached to the top of the reactor vessel body. It contains penetrations to allow the control rod driving mechanism to attach to the control rods in the fuel assembly. The coolant level measurement probe also enters the vessel through the reactor vessel head.
In the most severe of such scenarios, if the fuel remains insufficiently cooled for prolonged periods of time, the integrity of the primary system (second barrier) can be threatened as well, for example if a substantial mass of molten fuel reaches the bottom of the reactor pressure vessel and melts through it.
The pressurizer vessel itself may be maintained much hotter than the rest of the reactor plant to ensure pressure control, because in the liquid throughout the reactor plant, pressure applied at any point has an effect on the entire system, whereas the heat transfer is limited by ambient and other losses.
The time required for the molten metal of the core to breach the primary pressure boundary (in light water reactors this is the pressure vessel; in CANDU and RBMK reactors this is the array of pressurized fuel channels; in PHWR reactors like Atucha I, it will be a double barrier of channels and the pressure vessel) will depend on temperatures ...
The High Pressure Coolant Injection (HPCI) System consists of a pump or pumps that have sufficient pressure to inject coolant into the reactor vessel while it is pressurized. It is designed to monitor the level of coolant in the reactor vessel and automatically inject coolant when the level drops below a threshold.
The most severe occurring in March 2002, when maintenance workers discovered corrosion had eaten a football-sized hole into the reactor vessel head. [ 4 ] [ 5 ] The NRC kept Davis–Besse shut down until March 2004, so that FirstEnergy was able to perform all the necessary maintenance for safe operations.
BWR designs operate constantly at about half the primary system pressure of PWR designs while producing the same quantity and quality of steam in a compact system: 1020 psi (7 MPa) reactor vessel pressure, and 288 °C temperature for BWR which is lower than 2240 psi (14.4 MPa) and 326 °C for PWR.
The Indian Pressurized Water Reactor-900 (IPWR-900) is a class of pressurized water reactors being designed by the Bhabha Atomic Research Centre (BARC) in partnership with the Nuclear Power Corporation of India Limited to supplement the Indian three-stage nuclear power programme.