1. Field of the Invention
The invention relates to a safety device protecting a nuclear reactor pressure vessel against overpressure failure in the event of inadequate cooling of the core, including a pressure relief valve being pressure-tightly inserted into a wall of the pressure vessel or into a line passing through the wall, the pressure relief valve having a closure element normally blocking a flow from the interior of the pressure vessel to a pressure relief line and being held by a valve closing spring supported against an abutment.
In a device for temperature-dependent pressure relief of pressure vessels, which is known from German Patent DE 36 17 524 C2, corresponding to Published European Application No. 0 247 518 A2 and U.S. Pat. No. 4,836,443, a shut-off device provided in a pressure vessel blow-off line is opened at a preset temperature. The effect achieved through this temperature-dependent pressure relief is that in the event of an extremely unlikely failure of all of the cooling devices of a nuclear power station, the pressure in the primary circuit is reduced to a low level before the wall of the reactor pressure vessel can be damaged by an excessive temperature. In the known device according to the applications and patent mentioned above, the temperature sensor is disposed outside the reactor pressure vessel. The known device therefore works with a relatively high time constant, as calculated from the beginning of the impermissibly high temperature to the commencement of the pressure relief response.
German Published, Non-Prosecuted Application DE 35 26 377 A1, corresponding to U.S. Pat. No. 4,777,013, describes a high-temperature reactor having a reactor pressure vessel and a safety valve in the form of a spring valve for limiting the pressure in the reactor pressure vessel in the event of core heating incidents. The reactor pressure vessel is lined internally with a liner connected to a liner cooling system. The valve spring of the safety valve is formed of a material having a spring force which decreases with rising temperature. When the safety valve is open the valve spring is acted on by a flow of outgoing gas and for cooling purposes it is connected to the liner cooling system.