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The Columbia River near Hanford's N reactor has high levels of strontium contamination. The N Reactor was the last of Hanford's nine plutonium production reactors and used a newer closed loop design for its cooling system while it operated from 1964 to 1986. The N Reactor's heat-exchange cooling system passed the same water through the reactor approximately 100 times. This differed from the cooling water used in the other reactors which only passed once. This was successful at conserving water but caused there to be higher concentrations of contaminants in the discharges. The cooling waters were often discharged into unlined ditches and trenches near the reactor. These discharges have caused the groundwater under the 100-N area to have strontium-90 levels at 1,500 times the drinking water standard.

In 2005 the Department of Energy (DOE) began testing a chemical barrier that traps radioactive strontium before it can reach the river. Most of the results show that there is a 90 percent reduction in the strontium contamination in ground water. The test area extends 300 feet along the Columbia near Hanford's N reactor. The DOE would like to extend the chemical barrier to 2,500 feet to span the width of the area where strontium exceeds drinking water standards in ground water near the river. The building and maintenance of such a barrier would cost $21 million dollars.

The chemical barrier is created by injecting chemicals to form calcium phosphate, also known as apatite, approximately 40 feet deep near the riverbank. The calcium is mixed with citrate to prevent it from binding with the phosphate before it can spread through the ground into a barrier. After the chemicals are injected into the soil, bacteria consume the citrate, allowing the calcium and phosphate to combine into apatite. When groundwater hits the barrier the strontium chemically binds. The combination forms a crystal with the strontium held within as its radiation naturally decays. Strontium's half life is over 28 years. Since some of the strontium has already been in the ground for 30 years, scientists estimate that it will take another 270 years of decay before the strontium levels meet drinking water standards.

The chemical barrier would replace a pump and treat system that was previously used to protect the Columbia River near N Reactor. The system was used for a decade, but shut down in 2006. At a cost of about $10 million, the pump and treat system was seen as a temporary solution while more effective measures were developed. The system only removed about 10 times fewer curies than what would decay naturally.

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