Annealing Marble Hill

Thermal annealing is the only remedial measure that can be used to recover material properties lost in PWR pressure vessels through exposure to radiation. A thermal annealing process using gas-fired heaters located outside the containment is being developed. The heaters superheat and blow air through ductwork into a heat exchanger inside the reactor vessel. Heat transfer to the reactor vessel is by thermal radiation from the exchanger. Gas-fired heaters enable temperatures during heat-up and cool down of the reactor vessel to be closely controlled. No air comes into contact with contaminated surfaces since the entire system is enclosed and isolated from the reactor vessel and other components. The heat exchanger is of simple design and can be decontaminated readily, unlike complex electric heaters, and can be reused many times. The gas-heating system is also more economic than electric resistance heating. A demonstration of the system is to be carried out at the Marble Hill power plant in Indiana in late 1995. (Author)