Patent ID: 8036335

Claim:
A reactor vessel thermal load reducing system comprising: a reactor vessel having a reactor vessel wall and being partially filled with liquid coolant to an operating coolant liquid surface level between a bottom and a top of said reactor vessel wall, wherein said reactor vessel wall has the following vertically defined points: Point A at said bottom of the wall, Point C at said operating coolant liquid surface level, Point E at said top of the wall, Point B between Point A and Point C, and Point D between Point C and Point E; a guard vessel located circumferentially outside and adjacent to said reactor vessel; and a reactor vessel wall temperature difference minimizing means, said means comprising a heat conductive member circumferentially located directly adjacent to said reactor vessel wall; solid heat insulation material distributed on the inside of said reactor vessel wall from point D to point C but not from point B to point A; solid heat insulation material distributed on the outside of said guard vessel from a point horizontally adjacent to point B to a point horizontally adjacent to point D; wherein during steady state operation of said reactor, said heat conductive member receives a net amount of heat radiation from said reactor vessel wall from point B to point C, and said heat conductive member radiates a net amount of heat to said reactor vessel wall from point C to point D; wherein said heat conductive member is a member attached to said guard vessel wall; and wherein said heat conductive member has a higher heat conduction coefficient than said reactor vessel wall; and wherein said heat conductive member reduces the thermal stress on said reactor vessel wall that would otherwise be caused by the rapid increase of the liquid coolant temperature being raised during reactor startup from 200° C. to 550° C.