In a recent post I mentioned problems they were having problems with the cleanup at the Hanford Nuclear Reservation. The situation is getting a lot more press recently. There are around fifty four million gallons of highly toxic nuclear waste stored in the tanks buried at Hanford. The older single wall tanks are leaking and they are transferring the contents of some of them to double walled tanks. Now it appears that some of the double walled tanks are also leaking. The tanks are only temporary storage for the waste and the plan is to solidify the waste into a glass material through a process called “vitrification.”
Bechtel began construction of a vitrification plant at Hanford in 2000. The radioactive waste from the underground tanks will be analyzed and then separated into different batches by composition and radioactivity. Then each batch will be mixed into melted sand along with some other elements such as boron and hardened into a glass log which will be encased in steel. Barring severe catastrophes such as earthquakes, volcanoes, explosions, etc, the glass logs should be stable long enough for the radioactivity to decline to a safe level. Even if all goes well, it will take at least until 2062 for all the Hanford waste to be vitrified. All of the glass logs will be kept at Hanford until a permanent geological repository is available and then highly radioactive logs will be move to the repository. Since the cancellation of the Yucca Mountain repository, the soonest that the U.S. will have a permanent storage site is 2048.
Vitrification has been tested and works as expected. However, the tests were done on one type of waste with a standard composition. The Hanford tanks contain waste from different reactors using different processes and the composition of the waste varies widely from tank to tank. Around fifty radioactive isotopes may be present. Every element in the periodic table is represented in some tank. The tanks also contain hot, toxic metals and chemicals which pose their own problems aside from radioactivity. The chemical composition of the waste in the tanks is not the only problem. The waste has settled out into layers in the tanks with the passage of the years. There are solid, gooey, liquid and gaseous layers in the tanks.
In order to process the waste, it must move through pipes and containers in the vitrification facility. Since there are so many different physical forms in different combinations, figuring out how to get the contents of any one tank to flow through the system without clogging pipes and filters is a big challenge. And, if enough plutonium or U-235 accumulated at one point, it might go critical and cause a nuclear explosion. Another concern related to the flow problem is the fact that the heat and radiation in the waste can disassociation water in hydrogen and oxygen. If the hydrogen is not allowed to escape from the piping, enough could build up to risk explosions. The waste is so radioactive that human beings cannot approach it. The plan is to have the waste move through a system of tanks over a period of forty years without human intervention. Since there cannot be any moving parts in the chain of tanks, “pulse jet mixers” have been designed to stir the waste enough to keep it moving. The pulse jets suck in the waste and expel it back into the tanks. While it is uncertain whether the current design of the pulse jets can keep the waste properly mixed, they have been shown to move the gritty waste fast enough to grind away at the interiors of the piping. This, in addition to possible chemical corrosion, increases the probability of leaks.
Unfortunately, they were in such a rush to construct the facility that they began construction before the final details of some of the critical processes and flows were worked out. The safety manager at Hanford refuses to issue a permit to Bechtel for further construction before some of the safety issues are worked out. The Defense Nuclear Safety Board calls these problems a “show stopper”. People have resigned, whistleblowers have come forward and activist groups are lodging protests. Of course, technical advisors for the Vitrification Plant say that these are just technical snags and that they can be resolved. I am unconvinced.
