One of the underground tanks suspected of leaking at the Hanford Nuclear Waste Site has been known as an “assumed leaker” for so long—on and off since 1979—that several studies have been conducted to reveal its contents.
On Friday, a spokeswoman for Washington Gov. Jay Inslee could shed little light on that question:
“It’s nuclear waste,” spokeswoman Jaime Smith told AFP, soon after Inslee met Energy Secretary Steven Chu in Washington DC. ”Different tanks have slightly different kinds of waste that they’re holding. We’re not clear yet on exactly what has been leaking for how long.”
But we can get clear. So far DOE has identified only one of at least six tanks that seem to have dropping levels of liquid waste. The level inside tank T-111 has been dropping by 150-300 gallons per year, DOE revealed last week.
Beginning in 1944, Tank T-111 received wastes from processes used to extract plutonium from spent-nuclear fuel for use in nuclear weapons. In the 1960s, T-111 also received waste from equipment decontamination efforts at the Hanford site. It was removed from active service in 1974.
The contents of T-111 are not radioactive enough to meet the definition of high-level waste, according to the Environmental Protection Agency, and the tank’s low temperature (about 60 degrees Fahrenheit) testifies to relatively low radioactivity in the tank.
Nonetheless, T-111 contains a nasty bisque of chemicals used to extract plutonium from spent nuclear fuel, seasoned with traces of radionuclides, the byproducts of fission that can increase the risk of cancer to anyone exposed.
A 1996 study found the tank contains 456,000 gallons of a dark brown or black sludge, gel-like in consistency, streaked through with grey/white material. An observer of core samples described the sludge as smooth and thick, like “swamp mud.”
Initially, T-111 was the second in a chain of three cascading tanks. When waste flowed into T-110, solids settled there and liquids eventually spilled over into T-111, where remaining solids settled before liquids spilled into T-112. But government officials believe the pipe between tanks 110 and 111 clogged at some point, and T-111 may have received wastes directly at several points during its operating life.
The 1996 core samples suggest that operating life had three distinct phases:
1. The bottom of the tank contains waste from the “bismuth-phosphate process” used by technicians in the 1940s to extract plutonium from spent-nuclear-fuel rods.
2. Above this is a layer of “lanthanum-flouride finishing waste” from a process used to concentrate the extracted plutonium.
3. The tank is topped with a layer of waste from equipment decontamination efforts conducted in Hanford’s T-Plant in the 1960s. T-Plant is a decontamination site that formerly served as a plutonium refinery—the one, in fact, that concentrated plutonium for the “Fat Man” bomb detonated over Nagasaki, Japan in 1945.
In the first of those phases, the bismuth-phosphate process, technicians immersed spent-fuel rods from nuclear reactors in a boiling solution of sodium nitrate and sodium hydroxide. The aluminum coating dissolved, leaving slugs of spent fuel intact.
Technicians then dissolved the spent-fuel slugs in nitric acid. Water and sulfuric acid were added, and then bismuth nitrate and phosphoric acid.
The mixture formed a bismuth-phosphate solid that captured the plutonium from the solution, leaving the uranium behind, along with other products of nuclear fission that I will describe below.
A 1996 DOE diagram showing three levels of waste in Hanford Tank T-111.
Technicians washed and centrifuged the plutonium solids three times. And then, according to EPA:
“The uranium and fission products solution along with the water used to wash the plutonium solids were combined and discharged to specific underground storage tanks.”
Documents indicate T-111 mostly took waste from a later phase of the process. In that later phase, technicians added more chemicals to separate the plutonium from the bismuth phosphate and from any remaining fission products—”primarily strontium, cerium, and zirconium,” according to EPA.
The waste from this process, including those fission products, was discharged to underground tanks, and officials believe the lower layer of T-111 contains this type of waste.
In the 1950s, T-111 primarily received waste from an even later phase of the process, the ”lanthanum-flouride finishing” process in which more chemicals are added and the liquid is centrifuged to produce high purity plutonium nitrate.
From EPA and DOE documents, we know Tank-111 is likely to contain, in addition to uranium and plutonium, traces of the following radionuclides from these processes:
- Cesium-137, half-life about 30 years, collects in the soft tissues of the body, and according to EPA, “exposure to radiation from cesium-137 results in increased risk of cancer. Everyone is exposed to very small amounts of cesium-137 in soil and water as a result of atmospheric fallout. Exposure to waste materials, from contaminated sites, or from nuclear accidents can result in cancer risks much higher than typical environmental exposures.”
- Strontium-90, half-life 29.1 years, “is chemically similar to calcium, and tends to deposit in bone and blood-forming tissue (bone marrow). Thus, strontium-90 is referred to as a ‘bone seeker.’ Internal exposure to Sr-90 is linked to bone cancer, cancer of the soft tissue near the bone, and leukemia.
- Technetium-99, half-life 212,000 years. EPA: “Once in the human body, Tc-99 concentrates in the thyroid gland and the gastrointestinal tract. The body, however, excretes half of the ingested Tc-99 within 60 hours. It continues to excrete half of the remaining Tc-99 every 60 hours that follow. After 120 hours, only one-fourth of the ingested Tc-99 remains in the body. Nearly all of ingested technetium will be excreted from the body within a month.
- Nickel-59, half-life 760,000 years, and Nickel-63, half-life 100 years, are hazardous if inhaled, according to Idaho National Laboratory: “The major radiological concern with these two nuclides is related to limiting the exposure to people who are decommissioning and dismantling reactors, primarily for reactors in service for more than 30 years.”
- Americium-241, half-life 432 years. According to the American Library of Medicine, “in the nuclear fuel cycle the transuranic radionuclides plutonium-239, americium-241 and neptunium-237 would probably present the most serious hazard to human health if released into the environment. The principal late effects of all three radionuclides are the induction of cancers of bone, lung or liver.”
Initially the sludge also contained a number of short-lived radioisotopes—such as Ruthenium-106, Antimony-125, Zirconium-95 and Niobium-95—which have largely decayed by now.
Researchers have found the highest radioactivity in the top layer of sludge, which was added to T-111 in the 1960s from the decontamination processes in the T-Plant. T-111 also contains water, the chemical compounds used for plutonium concentration, some chemicals added to prevent corrosion, and a kerosene-like “hydrostatic fluid of normal paraffin hydrocarbons” that researchers added when they took core samples of the tank contents.
Even after the 1996 core sampling, researchers were uncertain what insoluble solids are in the tank. They named 38 likely suspects, ranging from bismuth phosphate to uranyl sulfate.