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This solid low-level radioactive waste continues to be dumped into open trenches at the Savannah River Site, but unlike in previous decades scientists have limited the waste to radioactive materials in which the radiation decays relatively rapidly and would be harmless before it might drift away with ground water. Michael Pronzato/Staff

The remaining mission

Since the Cold War ended in 1991, the Savannah River Site, as it is officially known today, has two main missions:

  • To continue to process tritium, the radioactive form of hydrogen used to enhance the power of the plutonium in the nation’s hydrogen bomb arsenal.  
  • To clean-up and safely contain the vast amount of radioactive waste left from a half-century of nuclear weapons production.

The radioactive clean-up

The plant’s radioactive waste clean-up and containment mission falls into three categories: low-level radioactive material, high-level radioactive material and plutonium.

Most of the solid low-level radioactive material is contained simply by burying it on site where its low-level radiation generally degrades relatively quickly.

Other low-level radioactive material is in liquid form stored in dozens of underground storage tanks, some as large as a million gallons. The waste tanks were filled during the course of nuclear weapons material production at the plant. Low-level radioactive material accounts for more than 90 percent of the liquid. High-level radioactive waste accounts for the rest.

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Lee Hart, supervisor for the Defense Waste Processing Facility, uses a remote manipulator to move radioactive material inside the facility where high-level liquid radioactive waste is converted to a solid and immobilized inside of glass. That waste is then sealed in stainless steel canisters and stored in underground vaults inside a vast warehouse at the plant. The idea is to eventually move most of the waste to a permanent underground facility out west. Michael Pronzato/Staff

To clean-up the liquid radioactive waste the plant separates the liquid into soluble salts, mostly low-level radioactive material, and insoluble sludge, the high-level stuff. The soluble salt is then mixed with stable materials and cement and is poured into large, underground, concrete vaults on site and buried.

The insoluble sludge is mixed with a sand-like form of glass, melted at high heat and poured into 10-foot-tall, 2-foot-wide stainless steel cylinders. The cylinders are sealed shut and temporarily stored in individual underground concrete silos inside a vast warehouse. The cylinders ultimately are expected to be shipped for permanent burial in a deep mine in New Mexico. When the plant finishes they will have filled some 5,000 to 7,500 cylinders.

What to do with plutonium remains a complicated political and cost problem. In 2000, the U.S. and Russia agreed to dispose of 34 metric tons each of plutonium produced in their weapons programs. That agreement was suspended late last year by Russia over political disagreements with the United States.

What had been the preferred method to dispose of the plutonium was to mix it with uranium and convert it to fuel — so-called mixed oxide, or MOX. However, the U.S. MOX facility at the Savannah River Site, begun with much fanfare in 2007, is far behind schedule due to technical and design problems, costly construction mistakes and management issues. It was supposed to cost less than $5 billion and start operating this year. But the estimate has increased to $17 billion. possibly double that.

Now the U.S. is considering a different and cheaper approach to deal with the plutonium. It's called down-blending, which basically dilutes plutonium to a low concentration with inert and non-radioactive material, which opponents derisively call angel dust. It would then be encased and shipped for permanent storage in either a deep salt mine in New Mexico or inside tunnels at Yucca Mountain in Nevada.

However, because no agreement has been reached on where to permanently store and contain the plutonium, the nation’s surplus weapons plutonium, along with some plutonium from Japan, Switzerland and Germany, remains stored inside the decommissioned K Reactor building at the Savannah River Site and other government facilities across the country.

Doug Pardue is a Pulitzer Prize winning investigative reporter and a member of The Post and Courier's projects team. Before joining this newspaper, he served as investigations editor at USA Today, The Tampa Tribune and The State (Columbia, SC)