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A fuel element failure is a rupture in a nuclear reactor's fuel cladding that allows the nuclear fuel or fission products, either in the form of dissolved radioisotopes or hot particles, to enter the reactor coolant or storage water. [1] The de facto standard nuclear fuel is uranium dioxide or a mixed uranium/plutonium dioxide.
The essential service water system (ESWS) circulates the water that cools the plant's heat exchangers and other components before dissipating the heat into the environment. Because this includes cooling the systems that remove decay heat from both the primary system and the spent fuel rod cooling ponds, the ESWS is a safety-critical system. [7]
The Fukushima Daiichi nuclear disaster in 2011 occurred due to a loss-of-coolant accident. The circuits that provided electrical power to the coolant pumps failed causing a loss-of-core-cooling that was critical for the removal of residual decay heat which is produced even after active reactors are shut down and nuclear fission has ceased.
Pumps circulate water from the spent fuel pool to heat exchangers, then back to the spent fuel pool. The water temperature in normal operating conditions is held below 50 °C (120 °F). [ 8 ] Radiolysis , the dissociation of molecules by radiation, is of particular concern in wet storage, as water may be split by residual radiation and hydrogen ...
The Reactor Protection System (RPS) is a system, computerized in later BWR models, that is designed to automatically, rapidly, and completely shut down and make safe the Nuclear Steam Supply System (NSSS – the reactor pressure vessel, pumps, and water/steam piping within the containment) if some event occurs that could result in inadvertant criticality.
Cladding is the outer layer of the fuel rods, standing between the coolant and the nuclear fuel. It is made of a corrosion-resistant material with low absorption cross section for thermal neutrons, usually Zircaloy or steel in modern constructions, or magnesium with small amount of aluminium and other metals for the now-obsolete Magnox reactors ...
RELAP5-3D is an outgrowth of the one-dimensional RELAP5/MOD3 code developed at Idaho National Laboratory (INL) for the U.S. Nuclear Regulatory Commission (NRC). The U.S. Department of Energy (DOE) began sponsoring additional RELAP5 development in the early 1980s to meet its own reactor safety assessment needs.
Passive nuclear safety is a design approach for safety features, implemented in a nuclear reactor, that does not require any active intervention on the part of the operator or electrical/electronic feedback in order to bring the reactor to a safe shutdown state, in the event of a particular type of emergency (usually overheating resulting from a loss of coolant or loss of coolant flow).