Abstract: A heat pipe stablized specimen container for irradiation of specimens at substantially constant temperature within a liquid metal cooled fast reactor comprises a heat pipe containing a vaporizable substance such as sodium. The container is of double-walled construction with the gap filled with argon and at top of the container a volume of argon is trapped within a cavity of the liquid metal level within the container in such a way that retention of argon in this zone is not dependent on sealing welds in the structure of the container, the argon blanket in this zone affording thermal insulation at the top of the container and also around part of the heat pipe, viz an adiabatic section of the latter.

Abstract: Fluid heating arrangements and methods are provided wherein liquid is caused to flow through a fluid permeable electrical resistance heater body. Prior to the heater body, the liquid passes through a fluid permeable flow control member which offers a uniform resistance to the entire flow of the liquid. Static pressure head of the fluid varies over the entry surface of the flow control member, and the permeability of the combination of the heater body and the flow control member are such as to cause a pressure drop in the fluid greater than the variations in static pressure head of the fluid at the entry surface of the flow control member. This promotes a uniform flow of the fluid through the heater body even in the presence of significant differences in static pressure head over the fluid entry surface of the flow control member.