Control of reactor metal temperatures is important to avoid over-stressing the pressure vessel and core support systems on a ‘shutdown’ reactor. The Operat­ing Rules state certain minimum temperatures for the vessel when pressurised. When the reactor is operat­ing there are preset temperature differentials between upper gas duct and vessel which must be maintained. Recorders in the CCR display these metal tempera­tures to aid the operator in complying with the rules. Loss of individual temperature measurements would not cause any problem.

Reactor shield concrete temperatures

The monitoring of reactor concrete temperatures is necessary to maintain the integrity of the biological shield. These temperatures tend not to change very rapidly and under normal operation remain virtually static. There is only one 12-point recorder situated in the annexe of the CCR from which the operator can detect trends and make arrangements for the neces­sary adjustments to cooling air flow via dampers. Loss of any of these measurements would not cause the operator any short term problems as adjustments rare­ly have to be made.