Overall, the tanks hold every element in the periodic table, including half a ton of plutonium, various uranium isotopes and at least 44 other radionuclides—containing a total of about 176 million curies of radioactivity. This is almost twice the radioactivity released at Chernobyl, according to Plutopia: Nuclear Families, Atomic Cities, and the Great Soviet and American Plutonium Disasters, by Kate Brown, a history professor at the University of Maryland, Baltimore County. The waste is also physically hot as well as laced with numerous toxic and corrosive chemicals and heavy metals that threaten the integrity of the pipes and tanks carrying the waste, risking leakage.
The physical form of the waste causes problems, too. It’s very difficult to get a representative sample from any given tank because the waste has settled into layers, starting with a baked-on “hard heal” at the bottom, a layer of salt cake above that, a layer of gooey sludge, then fluid, and finally gases in the headspace between the fluid and the ceiling. Most of the radioactivity is in the solids and sludge whereas most of the volume is in the liquids and the salt cake.
Going with the flow
All of these considerations contribute to the overall problem, which can be summed up in one word: flow. To get to the glass log stage the waste has to travel through an immense labyrinth of tanks and pipes. It has to move at a fast enough clip to avoid pipe and filter clogs as well as prevent solids from settling. This is quite a challenge given the multiphasic nature of the waste: solids, liquids, sludge and gases all move differently. The waste feed through the system will be in the form of a “non-Newtonian slurry”—a mixture of fluids and solids of many different shapes, sizes and densities. If the solids stop moving, problems ensue.
For one thing, there’s a chance that enough plutonium could congregate to trigger a nuclear chain reaction, or criticality—the self-sustaining cascade of atomic fission that releases massive amounts of energy. That would be a serious event even if an explosion did not breach the concrete containment building. Hot slurry could surge backward through the piping, spreading the problem to other parts of the system. Waste solids could also clog pipes, along with ion-exchange filters designed to grab the most radioactive constituents from the low-level waste for addition to the high-level stream.
Whether the solids pile up in the vessels, the pipes or the filters, says Donna Busche, nuclear and environmental safety manager for Hanford contractor URS Corp., “that’s where I’ve got the problem.” Further construction of the Vit Plant’s flawed components cannot proceed unless Busche issues an operating permit, which she is loath to do. She calls the DoE’s failure to require that Bechtel resolve the safety issues sooner “obscene.”
A second explosive risk could arise because both heat and radiation can disassemble water into oxygen and hydrogen. If there are not places along the piping and in the vessels for hydrogen to exit the flow of waste, enough could build up to explode.
And then there’s the extreme radioactivity of the waste, which is far too high for direct human exposure. Enter the Vit Plant’s notorious “black cells.” These are 18 massive concrete enclosures populated by smaller stainless steel vessels. The idea is to guide the waste through the vessels without any human intervention over the 40 years officials believe it will take to process all the waste. The only way to do this is to ensure that the black cells have no moving parts. But because the waste has to be constantly stirred to prevent settling of the noxious and radioactive solids, the plan calls for pulse jet mixers—described as “turkey basters”—to keep the solids suspended.