Plutonium has been in the news over the past few weeks, and some aspects are worth commenting upon. The first had to do with the collapse of a tunnel storing nuclear waste from Hanford, where the United States produced weapons grade plutonium during the cold war. Secondly, the Trump administration in its fiscal 2018 budget request for the Department of Energy sought to end the National Nuclear Security Administration’s MOX (Mixed Oxide Fuel programme), and the third on the safety of plutonium related work at Los Alamos.
There’s a kind of connection linking these three news items.
Hanford was quite the complex, consisting of multiple plutonium production reactors and plutonium reprocessing plants. By plutonium, in this case, we mean weapons grade plutonium which has very high concentrations of Pu-239. The plutonium was produced in dedicated nuclear reactors, that is their very purpose was to produce plutonium rather than electricity, which irradiate their nuclear fuel rods over relatively short periods to prevent the build up of Pu-240. The spent nuclear fuel is chemically reprocessed in a reprocessing plant, and plutonium reprocessing produces nuclear waste.
Some of the considerable waste that was generated at Hanford was stored in tunnels on site, and in early May one of those tunnels, which contained mixed waste of radioactive and nonradioactive elements from reprocessing, collapsed which put the spot light on maintenance at Hanford and similar cold war era facilitates associated with the US nuclear weapons programme.
Jeff Terry has a great article on this at The Bulletin of the Atomic Scientists. Key quote
After the tunnel collapse at Hanford, it should be clear that decontamination and demolition work needs to go forward—that many of the department’s obsolete facilities need to be removed. But I expect that not enough funds will be available to perform this work as quickly as it should be carried out. Meanwhile, diverting significant funds from the department’s “active” mission to perform legacy waste clean-up is not easy to do. The public, however, would prefer not to hear of any more surprise collapses of radioactive tunnels, so diversion may be necessary
Those plutonium production reactors and chemical reprocessing plants produced a *lot* of plutonium. Both Russia and the US have a considerable amount of weapons grade plutonium left over from the cold war, enough for a significant number of nuclear warheads. If Russia and the US wanted to surge to cold war era overkill stockpiles of nuclear weapons they wouldn’t need to produce plutonium as they have plenty to draw upon. However, fabricating that plutonium into fissile bomb cores would be relatively slower process than it was during the cold war. Some of that plutonium is declared excess, and one programme that was on the cards to dispose of that excess plutonium, in the United States, involved the fabrication of Mixed Oxide Fuel (MOX) at Savannah River, another cold war era site. It should be stressed that most of the excess plutonium at issue doesn’t come from the stockpile produced during the cold war so much as it comes from the plutonium primaries of dismantled nuclear weapons. The MOX fuel would be fabricated at Savannah River and then burned in civilian nuclear reactors to generate electricity.
The 2018 budget request, following on from Obama era policy, asks Congress to cancel this programme. This is a welcome development. One of the problems with MOX is that it’s envisaged to be part of a closed nuclear fuel cycle, the long time goal of the nuclear industry. To be sure, in this instance, the plutonium has already been reprocessed but this programme had the effect of legitimising MOX in the civilian sector and a civilian closed fuel cycle would require plutonium reprocessing. The programme is also costly, and budget savings could be diverted to the programmes that Terry speaks of.
Now that excess plutonium has to be dispensed with. Instead of MOX the idea is to dilute it and then be rid of it
The Department of Energy’s preferred alternative of dilute and dispose is a hands-on process that mixes plutonium with inert material. Plutonium is ground up in a “glove box” by hand with a mortar and pestle. A small amount is then placed inside a canister and shaken with inert materials. The canister is then shipped to the Waste Isolation Pilot Plant for permanent interment at the salt-mine facility in New Mexico
However, a battle looms in Congress so MOX might yet live to see another day.
One of the things that Los Alamos did during the cold war was fabricate plutonium metal for use in the fissile core of nuclear weapons, at a place called Tech Area 55. The Department of Energy wants to expand the capacity of Los Alamos so that it can produce 80 plutonium pits a year by 2027, from the current 20 (which tells us something about the future of nuclear weapons), however an interesting report about safety at the glove boxes at Los Alamos was published at the Los Alamos Monitor. Among other things we read
In April a fire broke out at the facility during “housekeeping day,” when workers attempting to dispose of materials that were capable of igniting through contact with air caught fire when they emptied them into a bag.
“Upon discovery, an operator attempted to place the bag into a metal container when the bag conflagrated (caught fire), causing minor burns to several fingers. He then pushed the cart containing this material to the front of the room away from the glove box line and smothered the fire using an appropriate handheld extinguisher. The operators called 911, exited the room, and made additional notifications in accordance with procedure,” read a statement from the Safety Board’s report on the incident. The material turned out to be lanthanum nickel hydride, which was used in activities at the facility 20 years ago. The material was described as non-radiological
The key issue appears to be the deferment of maintenance and safety upgrades. There’s a definitely a discernible thread here.