1 May 2002
Nuclear waste meltdown
Lexa McAdams is a nuclear waste expert at Bechtel National Inc. in Richland, Wash., who’s sharing her expertise on a nuclear waste project at Bechtel. As a licensing engineer in the controls and instrumentation group for the project (the River Protection Project Waste Treatment Plant), McAdams and others hope to identify strategies to help control and reduce some types of nuclear hazards.
The hazards involve not only radiation produced during World War II and the Cold War from nuclear weapons but also the nitrous oxide compound (NOx) chemical exposure, which has the potential to asphyxiate, McAdams said. As part of the integrated safety management program, McAdams and her team are identifying control strategies to prevent and mitigate these hazards. It’s similar to the American Institute of Chemical Engineers’ HAZOP process for identifying hazards and strategies, she said. “We have limitations based on radionuclide concerns, in addition to chemical process concerns. We examine both kinds of hazards.”
Sometimes McAdams and her team consider instrumentation as one of the control strategies. “The engineer must make sure it’s appropriate to use an instrument as part of the control strategy. But we may not have an instrument that can survive the radiological environment. Radiation has a tendency to be hard on electronics, so we have to identify where instrumentation would play a role.”
In this case, the project is using the concept of a melter technology called vitrification—melting radioactive waste into glass—to eradicate some types of nuclear waste.
The team is partnering with melter technology expert Washington Group International, along with all design disciplines at the plant. Although it is not a new technology, the team is treating the waste by melting it into glass because “it’s the most stable form of keeping the radioactive components from getting into the environment,” McAdams said. The team is basing the project on a pilot plant in Frederick, Md. “There’s a pilot melter there that Duratech is operating for us to test out the technology,” she said.
The CBS show 60 Minutes highlighted the project in its 17 March 2002 broadcast, mentioning the overwhelming 53 gallons of hazardous waste at the Hanford site in Richland. The show said the melter process won’t actually produce a product until 2007 and warned against the hazards of building facilities on the “fast track” before the equipment is ready. Bechtel is designing three facilities, one each for low-level and high-level waste and a pretreatment facility, by building one layer at a time. “We have to make sure our specifications and procurements are ready so we can lower equipment into the building as each level is set,” McAdams said.
|More on melting nuclear waste|
|Ceramic melter technology is a large-scale system capable of transforming high-level radioactive waste into a stable, glasslike product suitable for long-term disposal. The technology converts the inorganic fractions of waste into a glass product and recoverable metal while transforming organic wastes into hydrogen-rich fuels through the plasma heating process. In Hanford’s vitrification process, operators will pretreat the waste to separate the high-level radioactive waste from the low-activity waste. They’ll add silica and other glass-making materials and heat this mixture to 2,000°F in an electric melter.
They’ll then pour the molten glass into large stainless-steel canisters and cool them for a few days before welding them shut and decontaminating them. The Hanford site has a canister storage building to store the canisters until it ships them to a federal geologic repository for permanent underground disposal.
Another challenge with the project is that in nuclear waste, each batch is slightly different, with a different set of chemicals and processing that came to make it, McAdams said. The team hopes the melter technology will be transferable to different batches. “The problem is, the chemistry of the waste itself will dictate whether you can make glass or not,” she said. “Each waste has its own challenges because they all have different chemical compositions. Often it’s not the radionuclides that cause the problem—it’s the chemistry.”
The waste at the Hanford site is particularly caustic. “It has a tendency to crystallize,” McAdams said. The project precludes using a bubbler-type instrument because the crystallization of the waste in the bubblers blocks the tubes. And because the Bechtel plant is the largest to use the melter technology, “some issues that may not have been safety issues in a smaller system may become issues because of the volume we’re working with, especially in radionuclides,” McAdams said. IT
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