Preparing for (nuclear) licensing beyond 60 years

[Altair_IV]

2. That's also correct.

Contrary to the scientifically uniformed opinions of some; the Laws of Physics actually *enable* the extension of reactor lifetime.

As with any commercial fossil-fueled electric power plant, the components of the Rankine steam cycle part of the plant are replaceable. As parts age, they can be replaced, just as they do with old airplanes to keep them flying like old Douglas DC-3s. That's why there are fossil fueled plants that are many decades old.

In terms of the nuclear steam supply system; those components can be replaced as well. Even in PWRs, utilities have replaced the large steam generators with new copies of the originals to restore the system to its original state. What many here don't realize, is that the core the reactor which consists of the fuel assemblies is replaced as the reactor is refueled. Basically, the reactor vessel holds the fuel assemblies which spend about 3 years inside the reactor. So the core itself is continually renewed. The only component that can't be readily replaced is the reactor pressure vessel itself.

The pressure vessel doesn't experience wear; but it is susceptible to a type of ageing which is neutron embrittlement. The steel that makes up the reactor vessel is a crystal; the atoms are arranged in a lattice structure. Fast neutrons can dislodge an atom from its proper place in the crystal lattice. When that happens, the steel becomes slightly more brittle. As long as this ageing or embrittlement process is not too severe, the reactor vessel can still perform its function. In fact, extra strength is designed into the reactor vessel to compensate for the effects of embrittlement. As the reactor operates, instruments measure the intensity of the neutrons. Using that information, one can calculate how much embrittlement has occurred from the measured neutron dose; and determine whether that degree of embrittlement is to great for the vessel to continue operating. It's those records that are given to the NRC staff scientists and engineers for their analysis. If the NRC staff agrees that embrittlement is within limits; then they can recommend to the Commission that the re-licensing be approved. If embrittlement were to be too much, the utility has a choice; they can retire the plant, or they can anneal the vessel. If you heat the vessel to the right temperatures, the dislodged atoms have enough energy to move within the lattice and "fall back" into their original lattice positions. That's why metals are annealed after they are worked or forged. We've known how to anneal metals for centuries.

So just as one can keep a vintage aircraft in flight-worthy condition even at an advanced age; one can do the same with a nuclear power plant. Again, the designers of the reactor plants anticipated that they would have service lives beyond the 40 years and 60 years of the original license and first re-license. Therefore, the reactors were designed to have service lives much greater than the 60 years.

Altair_IV