Los Alamos National Plutonium Facility-4 (PF-4) and its dangerous plutonium pits

Safety problems at a Los Alamos laboratory delay U.S. nuclear warhead testing and production A facility that handles the cores of U.S. nuclear weapons has been mostly closed since 2013 over its inability to control worker safety risks, Science,  By The Center for Public IntegrityR. Jeffrey SmithPatrick Malon Jun. 30, 2017 “……..A unique task, unfulfilled for the past four years

Before the work was halted in 2013, those overseeing the U.S. nuclear arsenal typically pulled six or seven warheads from bombers or missiles every year for dismantlement and invasive diagnostic testing. One reason is that the unstable metals that act as spark plugs for the bombs — plutonium and highly-enriched uranium — bathe themselves and nearby electrical components in radiation, with sometimes unpredictable consequences; another is that all the bombs’ metallic components are subject to normal, sometimes fitful corrosion.

Plutonium also slowly decays, with some of its isotopes becoming uranium. And the special high explosives fabricated by nuclear scientists to compress the plutonium cores in a deliberate detonation also have an unstable molecular structure.

Invasive testing provides details vital to the computer modeling and scientifically simulated plutonium behavior that has replaced nuclear testing, said DOE consultant David Overskei. He compared the pit — so named because it is spherical and positioned near the center of a warhead — to the heart of a human being, explaining that destructive testing is like taking a blood sample capable of exposing harmful maladies.

The aim, as Vice President Joe Biden said in a 2010 National Defense University speech, has been to “anticipate potential problems and reduce their impact on our arsenal.” Weapons designers say it’s what anyone would do if they were storing a car for years while still expecting the engine to start and the vehicle to speed down the road at the sudden turn of a key.

Typically, warheads selected for testing are first sent to the Energy Department’s Pantex Plant in Amarillo, Texas. Technicians there gently separate their components — such as the detonators — at that site; they also send the pits — used in a primary nuclear explosion — to Los Alamos, and the highly-enriched uranium — used in a secondary explosion — to Oak Ridge, Tenn. The arming, fusing, and firing mechanisms are tested by Sandia National Laboratories in Albuquerque and other locations.

At Los Alamos, the pits are brought to Plutonium Facility-4 (PF-4), a boxy, two-story, concrete building with a footprint the size of two city blocks.  Inside are hundreds of special “glove boxes” for working with plutonium, a series of individual laboratories, and a special vault, in which containers hold plutonium on racks meant to ensure that escaping neutrons don’t collide too often with other atoms, provoking them to fission uncontrollably. Only a small portion of the building is normally used for pit surveillance, while about a fifth is used for pit fabrication, and another seven percent for analytical chemistry and pit certification. Budget documents indicate that annual federal spending for the work centered there is nearly $200 million.

“The Los Alamos Plutonium Facility is a unique and essential national security capability,” McMillan, the lab’s director, said last September during a visit by then-Defense Secretary Ashton Carter, who watched as technicians — attempting to restart their work after the lengthy hiatus — used pressing machines and other equipment to fabricate a mock pit, rather than a usable one.

The building lies in the middle of a 40-acre campus in the mountains above Santa Fe hastily built during World War II to coordinate the construction of the two nuclear bombs used in Japan. Los Alamos is still considered the foremost U.S. nuclear weapons facility — where six of the nine warheads currently in the U.S. arsenal were designed, and where plutonium-based power supplies for most of the nation’s deep-space probes are fabricated. Hundreds of nuclear physicists work there.

Unfortunately, it also has an active seismic zone beneath the PF-4 building, producing persistent worries among the staff and members of the Defense Nuclear Facilities Safety Board, a congressionally-chartered oversight group, that if it experienced a rare, large earthquake, the roof could collapse and toss chunks of plutonium so closely together a chain reaction would ensue, spewing radioactive, cancer-causing plutonium particles throughout nearby residential communities.

Millions of dollars have already been spent to diminish this risk, which until recently exceeded federal guidelines, and the Trump administration last month proposed spending $14 million in 2018 alone to strengthen the building’s firewalls and sprinkler systems. The government has also sunk more than $450 million into preparations for construction of a modern and more seismically durable pit production facility at Los Alamos, projected to have a total price tag between $1.5 billion and $3 billion.

Making new pits involves melting, casting, and machining the plutonium, while assessing how well or poorly the pits are aging requires using various instruments to withdraw small pieces for detailed chemical and material analysis. These operations are typically done in the glove boxes, by specialists whose hands are inserted into gloves attached to the side of sealed containers meant to keep the plutonium particles from escaping. But the work is messy, requiring constant vigilance to be certain that too much of the metal doesn’t pile up in a compact space. The byproducts include “chunks, shards, and grains of plutonium metal,” all of it radioactive and unstable, according to a 2015 Congressional Research Service report.

Notably, a 2013 Los Alamos study depicted leaks of glove boxes at PF-4 as frequent — averaging nearly three a month — and said they were often caused by avoidable errors such as inattention, improper maintenance, collisions with rolling storage carts, complacency and degradation from the heat that plutonium constantly emits. It said that sometimes those operating or supervising the equipment “accepted risk” or took a chance, rushed to meet a deadline, or otherwise succumbed to workplace production pressures.

“Operations always wants it yesterday,” the lab’s current criticality safety chief and the lone NNSA expert assigned to that issue in the agency’s Los Alamos oversight office warned in a private briefing for their colleagues at Sandia labs last month. Managers “must shield analysts from demands” from production personnel, they said.

Besides posing a serious health risk to those in PF-4, glove box releases of radioactive material each cost the government $23,000 to clean up, on average, the Los Alamos study said.

An acute shortage of criticality experts

Calculating exactly “how much material can come together before there’s an explosion” — as the Nobel laureate physicist Richard Feynman once put it — is a complex task. While visiting the production site for highly-enriched uranium in

Oak Ridge, Tenn., during the 1940’s, for example, Feynman was surprised to see stocks of that fissionable material deliberately stored in separate rooms, but on an adjoining wall that posed no barrier to collisions involving atoms of uranium and escaping neutrons on both sides. “It was very dangerous and they had not paid any attention to the safety at all,” Feynman wrote years later.

Plutonium work is so fraught with risk that the total mass of that metal allowed to be present in PF-4 is strictly limited. A decade ago, the limit was increased without an appropriate understanding of the risks, according to an NNSA technical bulletin in February. But with pieces of it strewn and stored throughout the normally busy building, partly because the vault is typically full, its managers have labored for years to systematically track down and remove excess stocks. They had some success last year, when they got rid of nearly a quarter of the plutonium on the building’s “main floor,” according to recent budget documents.

Criticality specialists are employed not only to help set these overall mass limits but to guide technicians so they don’t inadvertently trigger chain reactions in their daily work; those specialists are also supposed to be the first-responders when too much dangerous material is found in one place.

“The weird thing about criticality safety is that it’s not intuitive,” Don Nichols, a former chief for defense nuclear safety at the NNSA, said in an interview. He cited an instance in which someone operating a stirring machine noticed that fissionable liquids were forming a “critical” mass, so the operator shut the stirrer off, not immediately realizing that doing so made the problem worse. In other instances, analysts had judged a plutonium operation was safe, but then more workers — whose bodies reflect and slow neutrons — wound up being present nearby, creating unanticipated risks.

Those doing the weapons disassemblies and invasive pit studies are typically under “a big level pressure” to complete a certain number every year, Nichols added. They are expected to do “so many of these in this amount of time,” to allow the labs to certify to the president that the stockpile is viable. Meanwhile, the calculations involved in avoiding criticality — which depend on the shape, size, form, quantity, and geometric configuration of material being used in more than a dozen different industrial operations — are so complex that it takes a year and a half of training for an engineer to become qualified and as many as five years to become proficient, experts say.

“It’s difficult to find people who want to do this job,” particularly at the remote Los Alamos site, said McConnell, the NNSA safety chief. With plutonium use mostly confined to creating the world’s most powerful explosives, “there are…very few public-sector opportunities for people to develop these skills,” he added. As a result, he said, many NNSA sites lack the desired number of experts, which slows down production.

At the time of the 2013 shutdown, after numerous internal warnings about the consequences of its mismanagement, Los Alamos had only “a single junior qualified criticality safety engineer” still in place, according to the February NNSA technical bulletin. Nichols, who was then the NNSA’s associate administrator for safety and health, said McMillan didn’t “realize how serious it was until we took notice and helped him take notice.”

Without having adequate staff on hand to guide their operations safely, technicians at PF-4 were unable to carry out a scheduled destructive surveillance in 2014 of a refurbished plutonium pit meant for a warhead to be fit atop American submarine-launched ballistic missiles. It’s been modernized at a cost of $946 million since 2014, with total expenses predicted to exceed $3.7 billion. Generally, up to 10 of the first pits produced for a new warhead type are set aside for surveillance to assure they’re safely constructed and potent before they’re deployed. But the planned disassembly was cancelled and the NNSA hasn’t scheduled another yet, because of the shutdown.

The lab also hasn’t been able to complete planned invasive studies of the aging of plutonium used in a warhead for an aircraft-delivered nuclear bomb, now being modernized at an estimated cost of $7.4 billion to $10 billion.

Former deputy NNSA director Madelyn Creedon told an industry conference in March that if new funds are given to the agency in President Trump’s new budget, she knows where she’d advise it be spent. “One of the things that doesn’t take a huge amount of money but it’s one that has been cut back over the last couple of years, is surveillance — enhanced surveillance” of existing warheads, Creedon said……..http://www.sciencemag.org/news/2017/06/safety-problems-los-alamos-laboratory-delay-us-nuclear-warhead-testing-and-production

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