Calcium mix may block Hanford seepage

RICHLAND – Hanford Nuclear Reservation scientists will soon begin using a substance found in bones and teeth to stop radioactive contamination from reaching the Columbia River.

After seven years of studies and successful tests last year, workers this spring will begin injecting calcium phosphate into the ground to prevent radioactive strontium from a defunct reactor from seeping into the river, state and federal officials said.

Calcium phosphate is found in bones and teeth. Also called apatite, it binds to strontium and forms a crystal that holds the radioactive element in place until its radioactivity naturally decays.

“It should keep it bound up for hundreds of years while the strontium decays away,” said John Fruchter, Pacific Northwest National Laboratory program manager for the project.

Within 90 years, about 90 percent of the radioactivity is gone, and within 270 years, its radioactivity is within drinking water standards.

Plans are to inject a 300-foot-long chemical barrier about 40 feet underground near the banks of the river where ground water is contaminated with strontium.

When the N Reactor was operating to produce electricity and plutonium for the nation’s nuclear weapons program, water used to cool the reactor was contaminated with strontium. Contamination remains in the soil between the reactor and the river and is carried by ground water.

Radioactive strontium is particularly dangerous to humans. Chemically similar to calcium, it is deposited in the bones, where it can continue to release a dose of radiation for years.

Strontium’s similarity to calcium offered a promising cleanup solution, but only after scientists figured out a way to inject the chemical into the earth through wells without the phosphate and calcium binding up.

If the chemicals were combined in solution, they would bind up in the pipe rather than spreading out 30 feet around each of 10 wells along the river, said Mike Thompson, a ground water geologist.

Instead, the calcium is mixed with citrate, which prevents it from binding with the phosphate immediately. As soon as the mixture is injected into the soil, bacteria go to work consuming the citrate, and the barrier begins to form in place, ready to trap strontium.

It should work better than the technology that had been put in place as a stopgap method near the N Reactor, the plan’s backers said.

Formerly, contaminated water was pumped out of the ground and treated to remove strontium. But in a decade of pumping, less radioactive strontium was removed through treatment than naturally decayed.

In another project planned for the area, coyote willow may be planted between the barrier and the river to clean up more strontium. The willow would absorb strontium through its roots. Twice a year, the willows would be mowed and strontium-contaminated leaves and brush would be incinerated and ashes disposed of in a low-level radioactive waste landfill.