Shutting down gas cooled nuclear reactors

Claim 1

In a gas cooled nuclear reactor having a reactor core with coolant channels therethrough, a material, for introduction into said coolant channels to effect reactor shutdown, said material being normally contained at a region remote from said reactor core and comprising a plurality of coherent, free-flowing pellets each pellet comprising a solid neutron poison material and a solid organic substance, said organic substance remaining solid at a first, relatively low, temperature prevailing in said coolant channel at said region remote from the reactor core to allow free flow of the pellets through the coolant channel, said organic substance melting at a second, relatively high, temperature prevailing in said coolant channel at a region within the reactor core, the molten organic substance being adherent to a coolant channel wall and to the solid neutron poison material and thus capable of adhering the solid neutron poison substance to a coolant channel wall in the reactor core.

Claim 8

A method of shutting down a gas cooled nuclear reactor which method comprises introducing into a coolant channel which extends into the reactor core of a nuclear reactor and coolant channel which has a first, relatively low, temperature at a region remote from said nuclear reactor and a second, relatively high, temperature at the core region of said nuclear reactor, a plurality of coherent, free flowing pellets, said pellets being introduced into said coolant channel at said remote region and flowing freely therethrough to said core region, said pellets each comprising a neutron poison substance and a solid substance which changes in state on rising to a pre-determined temperature prevailing in said core region of said coolant channel, said change in state resulting in disintegration of said pellet and deposition of said neutron poison in said core region of said coolant channel to effect shut-down of the reactor.

Claim 9

A method of shutting down a gas cooled nuclear reactor which method comprises introducing into a coolant channel which extends into the reactor core of a nuclear reactor and coolant channel which has a first, relatively low, temperature at a region remote from said nuclear reactor and a second, relatively high, temperature at the core region of said nuclear reactor, a plurality of coherent, free flowing pellets, said pellets being introduced into said coolant channel at said remote region and flowing freely therethrough to said core region, said pellets each comprising a neutron poison substance and a solid substance which changes in state on rising to a pre-determined temperature prevailing in said core region of said coolant channel, said change in state resulting in disintegration of said pellet and deposition of said neutron poison in said core region of said coolant channel to effect shut-down of the reactor.