One of the challenges utilities face in addressing technical issues associa
ted with the aging of nuclear power plants is the long-term effect of plant
operation on reactor pressure vessels. These vessels are exposed to neutro
ns during the operation of a reactor. For certain plants, this exposure can
cause embrittlement of some of the vessel welds, which can shorten the use
ful life of the vessel. This reactor pressure vessel embrittlement issue ha
s the potential to affect the continued operation of a number of US pressur
ized water reactor plants. However, the properties that are degraded by lon
g-term irradiation can be recovered through a thermal annealing treatment o
f the vessel steel. Although a dozen Russian-designed and several US milita
ry vessels have been successfully annealed, US utilities concluded that an
annealing demonstration using a US reactor pressure vessel was a prerequisi
te before annealing a licensed US nuclear power plant. In May 1995, the Dep
artment of Energy and Sandia National Laboratories initiated a program to e
valuate the feasibility of annealing US licensed plants using two different
heating technologies. One team completed its annealing prototype demonstra
tion in July 1996, using an indirect gas-fired furnace at the uncompleted P
ublic Service of Indiana's Marble Hill nuclear power plant in southern Indi
ana. The second team's annealing prototype demonstration using a direct hea
t electrical furnace at the uncompleted Consumers Power Company's nuclear p
ower plant at Midland, Michigan, was scheduled to be completed in early 199
7, but has now been delayed indefinitely. This paper describes the Departme
nt of Energy's annealing prototype demonstration program and the results to
date for each project. (C) 1999 Elsevier Science S.A. All rights reserved.