Already struggling to meets its currently scheduled closure date of December 2019 (extended a number of times from its original 2012 closure date) the ‘system blockage’ which forced the B205 magnox reprocessing plant to shut down on 23rd February not only flags up yet another failure by the plant to meet its annual target (for the ninth successive year) but also bears the hallmarks of having more serious implications for the 50-year old plant than Sellafield Ltd or the Regulators are currently prepared to admit.
Reported in the site’s Sellafield Newsletter on the 6th March, the February incident involved a blockage to the feed of the chemical reagent ferrous sulphamate in the plant’s primary separation area where the chemical reagent is used to reductively strip and separate the plutonium from the acid-dissolved uranium fuel from which the fission products have already been removed. That the blockage was located at the plutonium separation stage of the process – rather than elsewhere in the plant – would appear to be confirmed by the Office for Nuclear Regulation (ONR) statement that ‘based on the total amount of material that was in the system the possibility of a criticality incident had been ruled ….’ (ONR FoI response to Dr David Lowry 19th March).
After stating that the plant had been shut down after unsuccessful attempts by workers to return the flow of the chemical reagent to the sustained rate required, ONR further commented that ‘a recovery exercise proved successful’. This is hard to reconcile with the fact that B205 remained closed for reprocessing (Sellafield Ltd to CORE 10th April) some seven weeks after the incident – an extended closure that may well reflect a significantly greater problem than currently acknowledged.
Whilst full details of the incident and knock-on effects to the magnox reprocessing schedule are unlikely to be publicly available until Sellafield’s in-house investigation and ONR’s assessment are completed, it is already clear that the annual reprocessing target for the plant will have been missed by a considerable margin. Set a target of 664 tonnes for financial year 2013/14, B205 had reprocessed just 352 tonnes by late January 2014, just weeks before the enforced shut-down which then extended beyond the financial year end.
The annual reprocessing targets are documented in the Sellafield Plan, published in 2011. This shows that whilst 2159 tonnes of magnox fuel were scheduled to be reprocessed by B205 during the three-year period 2011/12 to 2013/14, only 1338 tonnes were actually completed. With this average annual rate of some 440 tonnes (which hardly differs from the past 9-year average), the outstanding stock of 3125 tonnes magnox fuel still to be reprocessed will take 8 years to complete – taking the closure of B205 to 2022.
Given that B205’s reprocessing operations are acknowledged as being the largest source of radioactive discharge to the marine environment from Sellafield, the plants closure in 2022 (or beyond) inevitably presents yet a further significant threat to the Oslo-Paris Convention (OSPAR) requirement – signed up to in 1998 by the UK Government – that ‘by the year 2020, the OSPAR Commission will ensure that discharges, emissions and losses of radioactive substances are reduced to levels where the additional concentrations in the marine environment above historic levels, resulting from such discharges, emissions and losses, are close to zero’ (emphasis added).
With the radioactive discharges from magnox reprocessing set to continue two years or more beyond OSPAR’s 2020 target – and with several more years of discharges to come during the plant’s post-closure clean out, the prospect of concentrations of radioactivity in the marine environment (above historic levels) being close to zero must now itself be close to zero.
Whilst Government and Sellafield are likely to make full use of an existing loophole – that no-one has yet defined in exact terms what ‘close to zero’ means – the Nuclear Decommissioning Authority (NDA) is likely to take a different approach. In March 2010, the Authority told a National Stakeholder meeting that if the 2020 target could not be met then ‘we need to move to a contingency plan – i.e. agree not to meet OSPAR deadline (emphasis added) or put in place a different strategy’.
With Government support, the industry maintains that because of the well documented corrosion problems suffered by magnox spent fuel if pond-stored for too long, reprocessing the fuel remains the preferred option. In January this year however the NDA published its ‘Plan B’ (Magnox Fuel Strategy Contingency Options) in the event that B205 was to suffer an irretrievable breakdown. The options include the development of fuel drying and dry storage technology, the case for extended interim wet storage and the case for extended in-reactor storage of the fuel.
Though claiming that significant progress has been made with these ‘fallback technologies’, the NDA’s colours appear to remain firmly nailed to the reprocessing mast because the relevant additional cost of employing the options is considerably more than reprocessing – ‘a factor informing the NDA’s preference to see magnox reprocessing operations complete as soon as reasonably practicable’.