A system and method for drying cavities loaded with high level waste (“HLW”) is devised. The invention utilizes a non-intrusive procedure that is based on monitoring the dew point temperature of a non-reactive gas that is circulated through the cavity. In one aspect, the invention is a method comprising: a) flowing a non-reactive gas through the cavity; b) repetitively measuring the dew point temperature of the non-reactive gas exiting the cavity; and c) upon the dew point temperature of the non-reactive gas exiting the cavity reaching and remaining below a predetermined dew point temperature for a predetermined time, discontinuing the flow of the non-reactive gas and sealing the cavity. In another aspect, the invention is a system designed to carry out the method.