40 years of plutonium production at Hanford created large amounts of radioactive and chemically hazardous waste.
The most hazardous liquid wastes at Hanford were pumped into underground storage tanks. Safely dealing with the waste in these tanks is the most complex and expensive part of the entire Hanford cleanup.
Hanford's Tank Waste
To create plutonium for our nuclear weapons program, a series of chemical processes were used to separate plutonium from other radioactive elements. Each step in these processes created liquid waste. Workers pumped the most highly radioactive portion of the waste into underground storage tanks. The remaining liquids were dumped into the soil
New reactors and processing facilities were added at Hanford throughout the Cold War. In each case, more underground storage tanks were built. By 1964, Hanford had 149 single-shell tanks, divided among 12 "tank farms." The earliest tanks held between 55,000 to 530,000 gallons of liquid. Newer tanks ranged from 758,000 to one million gallons.
Unfortunately, by the late 1950s, Hanford officials realized that some of the tanks, designed to be used for only 10-20 years, had leaked. To try and prevent future leaks, Hanford began building double-shell tanks in the late 1960s. Twenty-eight double-shell tanks - all at least one million gallons in size - were built.
Hanford has 177 underground storage tanks that hold about 56 million gallons of highly radioactive waste. At least 63 single-shell tanks are suspected of leaking or are known to have leaked about one million gallons of waste into the soil. Most of the liquid waste has been pumped out of the single-shell tanks into double-shell tanks to reduce the likelihood and impact of further leaks from the single-shell tanks.
Tank Waste Treatment Plans
Hanford officials plan to clean up Hanford's tank waste by immobilizing it through a process called vitrification.
Vitrification is a process where glass-forming materials will be added to the radioactive waste at high temperatures to form molten glass. The molten glass will be poured into stainless steel containers, where the glass will harden as it cools. The waste will still be radioactive, but no longer mobile or able to spread into the environment.
The U.S. Department of Energy (USDOE) is building a massive complex of facilities at Hanford to vitrify the tank waste. Construction on the Waste Treatment Plant (WTP) began in 2002. Previous attempts to build vitrification facilities at Hanford have failed; the WTP project has also seen a number of challenges:
- Construction slowed in 2004 and stopped in 2005 when officials determined that seismic requirements for the design had been underestimated by about 40 percent.
- Cost and schedule estimates have been revised several times–Initial estimates of around $5 billion
have since been revised to more than $12 billion, and USDOE has acknowledged
that cost estimate will go up as well. The projected completion date of 2011 was
pushed back to 2019, and now – through a Consent Decree – to 2036. Treatment of
the tank waste will likely continue into the 2060s or 2070s.
- A number of technical issues remain to validate that the plant will run
safely and as designed. These technical issues have resulted in a halt to
construction of one of the WTP’s most crucial facilities.
Ideally, when the WTP is fully operational, tank wastes will be pumped to a pre-treatment facility, the largest and most complex facility in the WTP. The building will be 540 feet in length, 215 feet wide, and 12 stories high. The pre-treatment facility will separate out the most highly radioactive materials from the less radioactive materials, called low-activity waste. The high-level waste stream will make up about 10 percent of the waste stream and contain about 90 percent of the radioactivity. It will be vitrified in the WTP's high-level waste vitrification facility. DOE will store the containers of vitrified waste at Hanford until a national high-level waste repository is sited and constructed.
Some of the low-activity waste, which by volume will make up as much as 90 percent of the waste, will be vitrified through a similar process in the WTP's low-activity vitrification facility. The canisters of low-activity waste will be buried at Hanford.
The pre-treatment facility is facing a number of technical problems, so officials are pursuing a plan to initially bypass the pre-treatment facility in favor of a more simplified pre-treatment process to remove solids and certain radioactive materials, and send that waste feed directly to the low-activity vitrification facility. USDOE estimates it could have this in operation by 2023.