Most of the highly active liquid waste produced from the reprocessing of Material Test Reactor fuel at the UK's Dounreay site has now been transferred from storage tanks and cemented into drums ready for disposal.
|Workers monitor the filling of drums with raffinate and cement (Image: DSRL)
The reprocessing process involved dissolving the fuel in acid and separating the reusable fuel from the waste using solvent extraction. The resulting acidic liquor, or raffinate, was transferred to eleven on-site underground storage tanks.
Phase 1 of the decommissioning of the Dragon prototype gas-cooled reactor at Winfrith has been completed, Research Sites Restoration Ltd recently reported.
This phase involved the removal of all of the reactor plant outside of the reactor pressure vessel. It included the entire primary cooling circuit, the helium coolant purification system, the fuel handling systems, the used fuel storage carousel, the top of the reactor pressure vessel and the top half of the biological shield.
The Dragon reactor operated between 1964 and 1975. Decommissioning began in 2005, but was stopped in 2007 when the funding for Winfrith decommissioning was reduced. The Phase 1 decommissioning project resumed in 2011 when additional funding was secured.
Some 1200 cubic metres of raffinate was generated at Dounreay. It is highly radioactive and accounts for some 80% of the waste inventory at the site in terms of radioactivity.
Dounreay Site Restoration Ltd (DSRL) has announced that all the pumpable raffinate has now been removed from the storage tanks. Since the 1980s, batches of raffinate have been pumped from the tanks, neutralized and mixed with cement powder inside 500-litre drums. Over 4700 drums of cemented raffinate have been produced so far.
The residual non-pumpable raffinate, which contains heavy solids, has already been removed from three of the eleven tanks by dissolving them in nitric acid. This residual raffinate will also be cemented into drums.
Laboratory trials are being conducted to use a decontamination solution of nitric and hydrofluoric acid to clean the empty tanks. Once the tanks have been decontaminated to meet low-level waste (LLW) criteria, they will be removed and disposed of in the new LLW facility.
The MTR was constructed to test the effects of irradiation on metals. It began operating in 1958 and was shut down in 1969. It is now in the final stage of decommissioning.
Researched and written
by World Nuclear News