4.1 The Molten Salt Reactor is a nuclear reactor which uses graphite as reflector and structural material, and molten salt as coolant. The graphite components will be submerged in the molten salt during the lifetime of the reactor. The porous structure of graphite may lead to molten salt permeation, which can affect the thermal and mechanical properties of graphite. Consequently, it may be necessary to measure the various strengths of the manufactured graphite materials after impregnation with molten salt and before exposure to the reactor environment in a range of test configurations in order for designers or operators to assess their performance.

4.2 For gas-cooled reactors, the strength of a graphite specimen is usually measured at room temperature. However, for molten salt reactors, the operating temperature of the reactor must be higher than the melting temperature of the salt, and so the salt will be in solid state at room temperature. Consequently, room temperature measurements may not be representative of the performance of the material at its true operating conditions. It is therefore necessary to measure the strength at an elevated temperature where the salt is in liquid form. Users should also be aware that a small increase in graphite strength is expected with increasing temperature, and testing at the plant operating temperature will eliminate this small uncertainty.

4.3 The purpose of this guide is to provide considerations, which should be included in testing graphite specimens impregnated with molten salt at elevated temperature.

4.4 For the test results to be meaningful, the test material must have been impregnated at the reactor operating temperature of interest and the strength measurement conducted at the same temperature following the guide here. The user must consider the effect of interaction between graphite and impregnated salt on the representativeness of the strength test based upon the heating and cooling stages between impregnation and testing.