Cooling device for reactor container wall of nuclear reactor

In a cooling device for a reactor container wall of a LMFBR type reactor, the reactor container wall is cooled during rising of low temperature sodium between the reactor container wall and a reactor wall cooling liner. Overflowing grooves (recesses for overflow) are disposed each at a predetermined gaps at the upper portion of the reactor wall cooling liner. Upon rated flowrate, sodium after cooling the reactor container wall overflows from the level higher than the upper end of the reactor wall cooling liner. Upon scram flow rate, sodium after cooling the reactor wall overflows from the level higher than the lower end of each of the overflowing grooves into the reactor container. Accordingly, circumferential localized flow sodium after cooling reactor container wall caused by the error for the horizontal degree of the reactor wall cooling liner can be reduced even upon occurrence of scram flow rate, to ensure the cooling performance for the reactor container wall. In addition, fabrication accuracy and installation accuracy of the reactor water cooling liner can be mitigated. (I.N.)