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Boiling water reactors generally have negative void coefficients, and in normal operation the negative void coefficient allows reactor power to be adjusted by changing the rate of water flow through the core. The negative void coefficient can cause an unplanned reactor power increase in events (such as sudden closure of a streamline valve ...
Thus the BWR has a negative void coefficient. Reactor pressure in a BWR is controlled by the main turbine or main steam bypass valves. Unlike a PWR, where the turbine steam demand is set manually by the operators, in a BWR, the turbine valves will modulate to maintain reactor pressure at a setpoint.
The prototype fast breeder reactor has a negative void coefficient, thus ensuring a high level of passive nuclear safety. This means that when the reactor overheats (below the boiling point of sodium) the speed of the fission chain reaction decreases, lowering the power level and the temperature. [ 25 ]
Fuel temperature coefficient of reactivity is the change in reactivity of the nuclear fuel per degree change in the fuel temperature. The coefficient quantifies the amount of neutrons that the nuclear fuel (such as uranium-238 ) absorbs from the fission process as the fuel temperature increases.
This is measured by the coolant void coefficient. Most modern nuclear power plants have a negative void coefficient, indicating that as water turns to steam, power instantly decreases. Two exceptions are the Soviet RBMK and the Canadian CANDU. Boiling water reactors, on the other hand, are designed to have steam voids inside the reactor vessel.
The reactor physics design is tuned to maximise the use of thorium based fuel, by achieving a slightly negative void coefficient. Fulfilling these requirements has been possible through the use of PuO 2 -ThO 2 MOX, and ThO 2 - 233 UO 2 MOX in different pins of the same fuel cluster, and the use of a heterogeneous moderator consisting of ...
The integral fast reactor (IFR), originally the advanced liquid-metal reactor (ALMR), is a design for a nuclear reactor using fast neutrons and no neutron moderator (a "fast" reactor). IFRs can breed more fuel and are distinguished by a nuclear fuel cycle that uses reprocessing via electrorefining at the reactor site.
The NMR has a much shorter Reactor Pressure Vessel compared to conventional BWRs. The coolant steam drives the turbines directly, eliminating the need for a steam generator. It uses natural circulation, so there are no coolant pumps. The reactor has both negative void and negative temperature coefficients. It uses a uranium oxide fuel with 235