The surveillance capsule irradiation temperature is important to assure that the data obtained are representative of the reactor vessel beltline materials. Capsules evaluated showed that the temperatures exceed 588°F(309°C) during in-reactor exposure. The monitors melt as the result of normal system operating temperature transients up to 588°F(309°C). The apparent melting of thermal monitors at temperatures greater than 588°F(309°C) is the result of long term exposure to temperatures close to the material melting temperature, causing slumping and the appearance of melting.