Consequences of 'hot spots' on PCRVs

The concrete walls of the PCRVs shall be protected from the high temperatures of the reactors coolant by means of the heat protection system, i.e. insulation and cooling. For large areas of the inside face of the vessel, the concrete temperatures generally lie thetween 400C to 700C. Should the insulation be damaged, the above temperatures could be greatly exceeded, depending on the extent of the damage and the effectiveness of the cooling system. Although the method of fixing the insulation to the liner is more than adequate, a constant check is to be kept of the insulation effectiveness. The cooling system lends itself to such a check. A deterioration in the insulation would result automatically in an additional rise in temperature of the cooling water. By checking the cooling water at entry and exit with thermometers and feeding this information to a simpe computer, temperature changes in the cooling water of about 10C and above can be detected with certainty. This temperature rise of about 10C corresponds to an area of completely damaged insulation of less than 1 m2 up to a few m2 depending on the prevailing thermal conditions. It can be generally concluded from calculations on the THTR-300 reactor that because of the constant check on the liner cooling system, all damage to the insulation which could impair the PCRV integrity can be detected. (Auth.)