Sellafield seeks solid foundation for cleaner wastewater

London

Persistent discharges of radioactive waste into the Irish Sea could come to an end thanks to a technique that can lift an awkward pollutant out of water.

Chemists at the Sellafield reprocessing plant in northwest England have tested a process aimed at removing technetium-99 from wastewater.

Technetium-99 has a half-life of 213,000 years and is the main radionuclide still being discharged from Sellafield. It has been accumulating in seaweed and lobsters as far afield as the North Sea, leading to angry protests from the Norwegian and Irish governments.

Most of Sellafield's technetium-99 was generated by a now-disused processing plant, and some 1,800 m³ of contaminated wastewater is stored in tanks at the site. The isotope had proved awkward to extract and so the water, once cleaned of other pollutants, is being dumped into the sea at a rate of about 240 m³ per year.

The new cleaning process uses the salt tetraphenylphosphonium bromide (TPP), which is added to the wastewater. TPP binds with technetium-99 to form an insoluble compound that precipitates out as a solid.

The Sellafield chemists completed tests on the technique in December and will release their evaluation in April. If the results are positive — as many observers expect — BNFL, which operates the plant, is set to implement the technology at a cost of £2 million (US$3.7 million).

“The results are very promising but we still have to go through a final assessment,” says Ian Parker, head of nuclear regulation at the UK Environment Agency, which oversees the plant.

Parker adds that the agency had been worried that the precipitate might have been difficult to incorporate in concrete for safe and permanent disposal, but that early test results suggest this can be done.

Technetium-99 is not thought to be harmful in small doses, but Ireland and Norway have complained that traces of the isotope found in marine life have led to cuts in the prices fish merchants will pay for lobsters and other seafood.

The abatement technology could ease a major headache for BNFL, but other problems remain at Sellafield. European courts, for example, have been hearing a plea from the Irish government for the facility to close its mixed oxide fuel plant, which releases small amounts of plutonium into the sea.