A nuclear-reactor control-absorber drive mechanism includes a device for monitoring a potential situation of increase to overspeed of the absorber, configured to measure the number of control steps delivered to at least one of the first, second and third phases of the stator during a time window of preset duration or the number of rotation steps of the rotor during a time window of preset duration. The drive is also configured to compare the number of measured control steps with a preset maximum or the number of measured rotation steps with a preset maximum.

Damper systems selectively reduce coolant fluid flow in nuclear reactor passive cooling systems, including related RVACS. Systems include a damper that blocks the flow in a coolant conduit and is moveable to open, closed, and intermediate positions. The damper blocks the coolant flow when closed to prevent heat loss, vibration, and development of large temperature gradients, and the damper passively opens, to allow full coolant flow, at failure and in transient scenarios. The damper may be moveable by an attachment extending into the coolant channel that holds the damper in a closed position. When a transient occurs, the resulting loss of power and/or overheat causes the attachment to stop holding the damper, which may be driven by gravity, pressure, a spring, or other passive structure into the open position for full coolant flow. A power source and temperature-dependent switch may detect and stop holding the damper closed in such scenarios.

A butterfly valve includes a valve body-side valve seat section, a valve box-side valve seat section, and a valve movement mechanism. The valve movement mechanism includes a cam groove, a cam projection, and a reverse key. The valve movement mechanism moves the valve body in an extending direction of the flow passage along with rotation of the valve shaft between a blocking position and an open position. One of the valve body-side valve seat section and the valve box-side valve seat section is formed of a laminated material composed of alternatingly stacked plates made of metal and plates made of expanded graphite.

A butterfly valve includes a valve body-side valve seat section, a valve box-side valve seat section, and a valve movement mechanism. The valve movement mechanism includes a cam groove, a cam projection, and a reverse key. The valve movement mechanism moves the valve body in an extending direction of the flow passage along with rotation of the valve shaft between a blocking position and an open position. One of the valve body-side valve seat section and the valve box-side valve seat section is formed of a laminated material composed of alternatingly stacked plates made of metal and plates made of expanded graphite.

The present invention relates to a passive nitrogen injecting device for a nuclear reactor coolant pump, the device comprising: a nitrogen supply unit for supplying nitrogen; a pressure control valve for controlling the supply of nitrogen from the nitrogen supply unit according to pressure; an accumulator for filling the nitrogen supplied through the pressure control valve at a set pressure, and supplying the filled nitrogen in the event that an accident involving coolant loss occurs; and an isolation valve for controlling the supply of the nitrogen from the accumulator into a seal housing of a nuclear reactor coolant pump. The present invention uses an accumulator so as to be able to supply nitrogen by using the pressure in the accumulator without the supply of external power in the event of an accident involving coolant loss, and therefore has the effect of being able to improve safety.

The present invention relates to a passive nitrogen injecting device for a nuclear reactor coolant pump, the device comprising: a nitrogen supply unit for supplying nitrogen; a pressure control valve for controlling the supply of nitrogen from the nitrogen supply unit according to pressure; an accumulator for filling the nitrogen supplied through the pressure control valve at a set pressure, and supplying the filled nitrogen in the event that an accident involving coolant loss occurs; and an isolation valve for controlling the supply of the nitrogen from the accumulator into a seal housing of a nuclear reactor coolant pump. The present invention uses an accumulator so as to be able to supply nitrogen by using the pressure in the accumulator without the supply of external power in the event of an accident involving coolant loss, and therefore has the effect of being able to improve safety.

An improved, accident tolerant fuel for use in light water and lead fast reactors is described. The fuel includes a ceramic cladding, such as a multi-layered silicon carbide cladding, and fuel pellets formed from U.sup.15N and from 100 to 10000 ppm of a boron-containing integral fuel burnable absorber, such as UB.sub.2 or ZrB.sub.2.

A method for protecting a nuclear reactor includes reconstructing a maximum linear power density released among the fuel rods of the nuclear fuel assemblies of the core; calculating the thermomechanical state and the burnup fraction of the rods; calculating a mechanical stress or deformation energy density in the cladding of one of the rods by using the said reconstructed maximum linear power density, the calculated thermomechanical states and the calculated burnup fractions, by means of a meta-model of a thermomechanical code; comparing the calculated mechanical stress or the calculated deformation energy density with a respective threshold; and stopping the nuclear reactor if the calculated mechanical stress or the calculated deformation energy density exceeds the respective threshold.

A method for protecting a nuclear reactor includes reconstructing a maximum linear power density released among the fuel rods of the nuclear fuel assemblies of the core; calculating the thermomechanical state and the burnup fraction of the rods; calculating a mechanical stress or deformation energy density in the cladding of one of the rods by using the said reconstructed maximum linear power density, the calculated thermomechanical states and the calculated burnup fractions, by means of a meta-model of a thermomechanical code; comparing the calculated mechanical stress or the calculated deformation energy density with a respective threshold; and stopping the nuclear reactor if the calculated mechanical stress or the calculated deformation energy density exceeds the respective threshold.

A safety method for a reactor including a primary circuit and a secondary circuit fluidly isolated from the primary circuit, and a steam generator, and in the event of a meltdown of the core of the reactor with the formation of a corium bath in a bottom of the vessel and the formation of a liquid metallic layer at the surface of the corium bath, the method includes: a break-up by explosion of the fluidic insulation to set the secondary circuit in fluidic communication with the primary circuit so that the secondary fluid follows the primary circuit to flow inside the vessel over the liquid metallic layer of the corium bath.