Most of the nuclear power reactors in the U.S. were built in the 1970s and 1980s. They were licensed for forty years and many have reached that age or will reach it soon. Some operators have applied for permits to operate their reactors for an additional twenty years and most of these applications have been granted. Materials used to build nuclear reactors age and deteriorate over time. The big question that needs to be answered is whether or not it is safe to continue operating reactors well past their original licensed lifespan.
     The Consortium for Advanced Simulation of Light Water Reactors (or CASL, for short) was created during the Obama administration to help extend the life of nuclear power reactors. It is funded by the U.S. Department of Energy (DoE). CASL has been working on the creation and refinement of a reactor modeling program they call Virtual Environment for Reactor Applications (VERA).
      VERA provides a high-resolution computer model of nuclear reactor equipment. It can simulate safety concerns, reactor startups, and fuel-rod behavior, and other processes, equipment and materials. David Kropaczek is the director of CASL. He says that it might be possible to extends commercial power reactor operations to one hundred years but only if we understand how extended lifespans would affect the materials in the reactor. VERA appears to be able to accurately show how reactor materials age.
       It is hoped that VERA will enable nuclear power plant operators to do away with some of the extreme conservatism which was applied in the construction of old nuclear power reactors. By using VERA, plant operators should be able to identify which reactor components need to be replaced in order to keep the reactor in operation safely.
       The development of VERA was supported by real-world data from private companies including Westinghouse which designs reactors and distributes nuclear fuel, the Tennessee Valley Authority and the Electric Power Research Institute.
        Another application for VERA will be to model the affect of grid demand changes on nuclear reactors. When the full output of a reactor is not needed, some reactors can have their output turned down which is called load-following. This stresses the nuclear fuel and there is a question of exactly how much this stress can damage the fuel. As long as the stress can be minimized, more load-following could be available.
       Kropaczek says “Nuclear power plants need to be boring with respect to operations, with respect to the fuel. I don’t want to see any surprises—that’s the goal of a plant: nothing happens. Load-following is no longer steady state and boring. We need to go from 100 percent to 50 percent power and back again. So you’re worried about the fuel and stresses on the fuel and things are changing. VERA can actually… model fuel behavior for load-follow, [reporting] what the fueling is going to do and what is the fuel operating level?… We can look at every fuel rod, every fuel pellet in the core; we can look at those stresses in the fuel.”
      CASL is working on making VERA available to many U.S. utilities. They are installing VERA on a one thousand core computing cluster at the Idaho National Laboratory this month. They will be training twenty-four people from twelve different nuclear power companies.
       The use of VERA should allow existing nuclear reactors to be operated safely for longer periods of time that their original licenses permit. Hopefully, this will allow extra time for the development of advanced nuclear reactors and economical renewable energy installations.