Saturday, November 30, 2013

High level problems with high level waste

Bechtel has been working for years and tens of billions of dollars to build a nuclear waste treatment plant for the Hanford waste currently leaking out of its tanks near the Columbia River in Washington state, but observers are pessimistic about its likely success:
Energy Department officials have repeatedly assured the public that they have the advanced technology needed to safely dispose of the waste. An industrial city has been under development here for 24 years, designed to transform the sludge into solid glass and prepare it for permanent burial.
But with $13 billion already spent, there are serious doubts that the highly complex technology will even work or that the current plan can clean up all the waste. Alarmed at warnings raised by outside experts and some of the project's own engineers, Department of Energy officials last year ordered a halt to construction on the most important parts of the waste treatment plant.
The concern centers around the novel technology meant to mix the waste before sending it to be vitrified.
The basic plan is to pump the waste into a pre-treatment plant, a factory larger than a football field and 12 stories tall, that would filter and chemically separate the waste into two streams of high- and low-level radioactivity. Then, two other plants would "vitrify," or glassify, the waste. One would produce highly radioactive glass destined for a future geological repository, and the other a lower radioactive glass that could be buried at Hanford.
But serious questions were raised last year after Walter Tamosaitis, one of the scientific chiefs of the project, disclosed that the innovative technology for mixing the waste in processing tanks could cause dangerous buildups of explosive hydrogen gas and might allow plutonium clumps to form.
The Defense Nuclear Facilities Safety Board, an independent federal agency that oversees nuclear weapons sites, validated Tamosaitis' concerns about the mixing technology and found that the safety culture at the project was flawed. Construction on the project's two most important components, the pre-treatment plant and the high-level vitrification plant, was substantially slowed. Tamosaitis was fired.
The questions concern Bechtel's decision not to use traditional mechanical mixers with paddles driven by electric motors, as have been employed at other nuclear processing plants.
Instead, the company chose pulse jet mixers, which function like giant turkey basters. Powered by vacuum and air pressure, they suck waste into a cylinder within the tanks and then spit it out under high pressure. Such a system has never been used in such large tanks. The decision was based on the concern that mechanical systems could break down in highly radioactive "black cells," as the tanks are known, over the 40-year design life of the plant.
But doubts have grown about whether the pulse jet mixers can adequately agitate the waste and prevent the formation of hydrogen gas and clumps of plutonium at the bottom of the tanks and in pipes.
The safety board has demanded that the Energy Department conduct a full-scale test of the mixing system, using nonradioactive sludge, before going any further. The test facility is under construction near Hanford, but the test completion date is uncertain.
The high level radioactive material is the product of nuclear weapons production from more than half a century ago. It seems likely that people will still be dealing with safely disposing of it half a century from now, or worse---that people, if there still are some, will be suffering the consequences half a hundred millennia hence.

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