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2 December 05
New Plant Aids PFR Pond Clean-out
The decommissioning of Britain's Prototype Fast Reactor has entered a new stage, with the start-up of a new £500,000 plant for cleaning out a pond where fuel and other radioactive components were stored.

The first active run of the PFR ion exchange plant has been successfully completed, proving the technology that will be used to clean radioactive contamination from the water in the pond and make it safe to discharge to sea.

The pond resembles a small swimming pool and has a volume of 128m³. Its purpose was to store radioactive components, with the water providing shielding of the radiation. Over the years, a small amount of radioactive contamination has washed off these components, which is now contained within the pond water. To simplify future work on the removal of components from the pond, it was required to reduce these contamination levels and thus the overall radiation levels near the Pond. The removal of the principal contaminant, radioactive caesium, provides the project team with a greater challenge, as it’s totally soluble in water.

The safe and established means of doing this is to use the ion exchange method. Ion exchange is based on what is known as a resin. This can be a synthetic, or a naturally occurring substance, which has a high affinity for the element that is to be removed, in this case caesium. As the caesium laden water is washed over the resin, the resin absorbs the caesium into its structure and releases another, less hazardous element, in exchange. This other element is hydrogen, which then combines within the water to form a minute extra volume of plain water. The resin in this plant is a synthetic called zeolite, which resembles sand.

On the plant, the resin is contained within a dustbin sized stainless steel pot, known as the ‘column’.
The water from the pond is pumped through this column, it becomes thoroughly mixed with the resin, before being returned, now cleansed, to the pond. Thus, the actual plant is almost like a domestic central heating system; basically a circuit of pipework with a pump, with the ion exchange column acting like a boiler.

When a given ion exchange column has absorbed all the caesium that it can, the plant is shutdown. The residual water is blown out of the column and the column is removed as a unit and replaced by a new one. The caesium, now in a solid form, is much easier to control and store than the liquid form which it started out as when within the pond.

The decommissioning of the PFR pond is a key phase in the overall PFR programme and this initial active run has resulted in the removal of nearly 99% of the radioactive caesium content of the pond.

The project to install the IXP was carried out by local contractors and managed by UKAEA on behalf of the Nuclear Decommissioning Authority. The development and design work was done by RWE Nukem, and the plant was built and installed by Halkirk based engineering company JGC Engineering and Technical Services Ltd. The columns were supplied by the French company, Eurofiltec, and the whole plant was installed earlier this year.