Signs that the Nuclear Decommissioning Authority (NDA) has little confidence in predicting the closure of Sellafield’s B205 magnox reprocessing plant are evident in documents published by the Authority this week. The Magnox Operating Plan (MOP9) and accompanying Strategy Position Paper reveal how the NDA has been forced into a ‘pick and mix’ approach because of what it describes as the inconsistent and unpredictable performance of the plant and associated facilities. Many observers will rightly question why the NDA has only now woken up to the obvious fallibilities of an almost 50-year old plant it inherited over 7 years ago.
When the last operating plan MOP8, published in 2010, had projected a plant closure in 2016, the date was based on a ‘single assumed’ annual throughput being achieved. Continuing poor performance however resulted in an almost immediate extension of the closure date to 2017, and even this is now is deemed to be ‘increasingly unrealistic’. Published this week, MOP9 now tentatively suggests at least 2 closure dates (or something between the two) for B205 by assuming two different annual reprocessing rates – an upper bound of 740 tonnes per year and 450 tonnes per year lower bound. Put in context, the latter rate tallies almost exactly with the average throughput achieved annually by B205 over the last 5 years of operation, whilst the upper bound of 740 tonnes per year has not been achieved for 8 years.
As the NDA publications show, 3800 tonnes of magnox fuel remained due for reprocessing as at April this year – 3000 tonnes held in reactor/dry storage and 800 tonnes in pond storage at Sellafield or reactor sites. Reprocessing this fuel at 740 tonnes per year would see a 2017/18 closure of the reprocessing plant whereas, at 450 tonnes per year, reprocessing would continue to 2020 at least. Added to this workload is the 44 tonnes of metallic fuel from the Dounreay Fast Reactor (DFR), with transports to Sellafield expected to begin from Scotland this year. MOP9 recognises that the addition of this fuel could impact on the overall MOP progamme but confirms that, with priority given to magnox fuel, reprocessing the DFR fuel will not be allowed to significantly extend the programme without a strategy review.
Though a number of initiatives to improve reprocessing performance are incorporated in a Magnox Throughput Improvement Plan (MTIP) set up last year, the NDA acknowledges that if improvements do not materialise, the annual throughput rate of 450 tonnes for B205 would ‘seem a reasonable value to select’ and will result in a 2020 end to reprocessing. If implemented, it will result in further years’ of radioactive discharges to the environment from the reprocessing plant at levels that pose an added threat – denied by the NDA – to meeting the already jeopardised international treaty targets on marine pollution signed up to by the UK Government at the OSPAR convention in 1998. At greatest risk would be the target of concentrations of radioactivity in the marine environment being ‘close to zero’ by 2020.
In operational terms, this ‘reasonable value’ of 450 tonnes per year represents a significant downgrading of reprocessing targets made by the NDA just 5 months ago in a supplement to its much vaunted Sellafield Plan. Described as ’the first credible and underpinned lifetime plan for the Sellafield site’, it projected throughput rates for magnox reprocessing from 2012 to 2017 which ranged from 650-800 tonnes per year. Given the well documented frailties and problems of the ageing reprocessing plant and associated facilities – and its recent track record – these projections were patently incredible and appear to have been plucked from thin air rather than being based on a professional appraisal of the plant’s operational capabilities.
The possibility of an acute or chronic failure of the reprocessing plant is recognised by the NDA in MOP9. Contingency plans for an acute failure – described as a situation where reprocessing stops without prior warning and does not restart – include the removal of all pond-stored magnox fuel to Sellafield’s central Fuel Handling Plant (FHP) ponds for short/medium term management, drying the ‘wetted’ fuel and placing it in containers (an option considered technically feasible by the NDA despite it never having been employed in the UK) and retaining dry fuel ‘in reactor’ until other conditioning /disposal options are available. Whilst these plans may be considered to constitute a fall-back (Plan B) in the event of a catastrophic accident in B205, the reality is that they are insufficiently developed to be initiated immediately.
A chronic failure is described as a situation where reprocessing rates fall to such low levels that keeping facilities operational for extended timescales is impractical or uneconomic. Citing its assessment of what it describes as a pessimistic rate of just 250 tonnes per year (leading to plant closure around 2028) the NDA concludes that the outstanding inventory of magnox fuel at the time of chronic failure could still be dealt with by reprocessing which would remain as its preferred strategy. Contingency plans for a chronic failure include reducing the amount of magnox fuel held in wet storage, attempting to reduce the number of sire locations where the fuel is stored and employing ‘alternative management options’.
Alternative options for dealing with magnox fuel are detailed in the NDA’s Startegy Position Paper which describes two top-level strategic options – reprocessing or disposal. Sub-options for the reprocessing option include the use of new facilities, the use of the existing plant, the use of the Thermal Oxide Reprocessing Plant (THORP) or the use of non-NDA third-party facilities. Apart from the use of the existing plant, none are considered to be credible – on the grounds of either costs, timescales, technical or regulatory requirements. The sub-options for disposal are interim dry storage with conditioning and disposal, interim wet storage with conditioning and disposal or conditioning wetted fuel and disposal. Of these, only the first sub-option is deemed credible. The second sub-option, which is likely to require the construction of additional pond storage capacity remains however as a possibility with additional research and work by the NDA.
Designed to reprocess 1500 tonnes of magnox fuel annually, the B205 plant was opened in 1964 and routinely achieved 1000+ rates in the early years of operation. The current failure to accurately predict throughput rates and the closure of B205 is not however confined to the NDA, for the site’s previous owners British Nuclear Fuels Ltd (BNFL) showed a similar inability. In 2000, announcing revised closure dates for the UK’s magnox power stations, BNFL projected that B205 could close around 2012 with all fuel reprocessed. Though hotly disputed at the time by NGO’s and others, BNFL remained adamant that the plant was capable of achieving an annual rate of at least 1000 tonnes from 2000 to 2012. In the event, that level was achieved only twice (2003 & 2004) with subsequent rates plummeting to a low of 233 tonnes in 2010.