The much delayed update from the Nuclear Decommissioning Authority (NDA) on its plans for dealing with Sellafield’s burgeoning plutonium stockpile was quietly published at the end March 2019 under the title ‘Progress on plutonium consolidation, storage and disposition’. The lack of fanfare for its publication may be attributable to the absence of any major breakthrough in progress since the NDA’s 2014 Position Paper and the subsequent warning given to a Sellafield Stakeholder Group in 2016.
It was in 2008 that the NDA launched its initial Comment Paper on the options for managing the plutonium stockpile accumulating from the reprocessing of UK and Overseas spent fuel at Sellafield – a stockpile estimated by NDA to reach 140+ tonnes (in the form of plutonium oxide powder) when all reprocessing operations at Sellafield have ceased (after 2020). In 2011 the Government launched a public consultation on the options and concluded in December of that year that the re-use of plutonium was its preferred option – a preference it retains today. The options subsequently assessed by the NDA include plutonium’s re-use as Mixed Oxide (MOX) fuel in reactors, its use as CANMOX fuel in Canada’s Candu reactors its use as feed stock for fast reactors, and its immobilisation as nuclear waste. In the latest update, the NDA’s ‘forward look’ of the options is summarised below:
Plutonium re-use in reactors as Mixed Oxide (MOX) fuel – requiring the construction of a new MOX production facility at Sellafield which would utilise as much as 95% of the stockpile. ‘However, this option carries significant risks and uncertainties since it is fundamentally dependent on the availability of suitable new reactors in the UK and their operators’ willingness to use MOX fuel.At this time, and given the current status of the UK’s nuclear new build programme, work is focused on generic LWR-type fuels rather than specific fuels from reactors in the UK’s new build programme. (The costly failure of the last production plant – the Sellafield MOX Plant SMP in 2011 together with the recent abandonment of construction of a similar plant on cost and other grounds at Savanah River in the US – will present further challenges to the option).
Re-use in Candu Reactors.This ‘CANMOX’ option was offered by a consortium led by SNC Lavalin and would require the building of a CANMOX fuel plant (at Sellafield) and at least two CANDU EC-6 reactors in the UK to irradiate the fuel. ‘Building on previous findings, this work is focused on applying and integrating the proven Orano (Areva) MOX fuel fabrication process to CANMOX fuel production. As there are some notable differences in the CANMOX fuel design, a programme of pellet production and testing is planned to demonstrate that the SNC Lavalin, BWXT and Orano technologies can be successfully integrated’.
Re-use in PRISM fast reactors – an option proposed by GE Hitachi Nuclear Energy (GEH) involving the construction at Sellafield of a fuel fabrication plant and two PRISM reactors (all ‘first of a kind’ facilities) to irradiate a plutonium alloy fuel. The option was put forward by GEH as ‘ready to deploy’ and therefore capable of quickly dispositioning the complete plutonium stockpile.‘However, the studies undertaken by NDA with GEH over the past few years have shown that a major research and development programme would be required, indicating a low level of technical maturity for the option with no guarantee of success. At this time, it is noted that the cost, scope and extent of work required to progress Fast Reactor options, such as the GEH PRISM, as well as the timeframe for these options to become available, means it is not credible for the NDA to develop these options, or have them available for implementation within the next 20 years. Therefore no further work with GEH has been funded by NDA’.
Options for immobilisation as nuclear waste. Regardless of the final solution for managing the stockpile, a proportion of the plutonium would be unsuitable for use as a fuel (historic scraps and other contaminated materials) and will have to be disposed of. The NDA is working to better understand the proportion that will need to be immobilised, and also continues to develop approaches that could immobilise and dispose of the entire inventory. The three main immobilisation options being examined are a) hot isostatic pressing (HIP) to produce a monolithic ceramic product, b) pressing and sintering process similar to MOX manufacturing to produce (‘off-spec’) MOX pellets and c) encapsulation in cement-based matrices as used in the UK for Intermediate Level Wastes. For options a) & b) ‘NDA has engaged National Nuclear Laboratory (NNL) to install a pilot test facility for the HIP process in its laboratories at Sellafield – with the intention of manufacturing small-scale plutonium-active products in the early 2020s as a demonstration of the technology using UK materials’. For option c) ‘This approach is already used at Sellafield for immobilising ‘plutonium contaminated materials’ arising from some processing operations – but is not considered suitable for bulk plutonium oxide powder because of the large volumes of waste requiring storage and eventual disposal underground ‘.
The NDA’s update concludes that a programme to implement a long-term solution for the disposition of separated plutonium will be complex, incorporating significant technical challenges and uncertainties, and will take many decades to complete. For these reasons, the UK government has been clear that a decision cannot be taken quickly and, when taken, must be underpinned by the right evidence. A ‘prudent estimate’ of £10Bn (discounted) has been identified by the NDA as the potential costs of either the reuse or the immobilisation options.
Irrespective of which option is eventually chosen by Government, the NDA must, in the interim, ensure that the Sellafield plutonium stockpile is stored safely and securely. The hazards of current storage systems were highlighted in a 2018 National Audit Office report (NAO) which described some storage facilities as being amongst the ‘highest hazard’ facilities at Sellafield and flagged up concerns about stored plutonium canisters decaying faster than anticipated – with a leak from any package leading to an ‘intolerable risk’ as defined by the Office for Nuclear Regulation (ONR). Such hazards were to be mitigated by the transfer of plutonium from old to new stores (principally the Sellafield Product & Residue Store SPRS which opened in 2010 and saw the first transfers in 2012) and the repackaging of plutonium in a new repackaging plant (SRP) to be built at Sellafield.
Whilst a number of references to the new SRP facility are made in the NDA’s latest update, little light is shed on the scale of the development, its cost and build-time or the opposition from neighbouring parish councils. The new facility, originally costed by the NDA at £470M is now put at up to £1.5Bn and its build-time (to operation readiness) extended from 5 to 12 years. Plans for SRP, approved by Copeland BC in December 2018, described the facility as consisting of the main process building, a change & welfare facility, a tank farm (4 x 13 m high metal tanks which will hold cryogenically stored gas and 2 high level enclosed link bridges connecting the process building to the new change & welfare facility and to the existing plutonium store SPRS respectively – the latter requiring modification to receive repackaged plutonium from SRP.
The plans show that the new plutonium repackaging complex will be located in the south-west corner of the Sellafield site adjacent to the perimeter fence where it immediately overlooks the public railway line and the Irish Sea coast. This siting has led to complaints from local parishes and communities that because of the size of the main process building which will measure 74m(w) x 48m (d) x 42m (h), the ‘eyesore will blight the local skyline and hit the beach tourist industry’(?) as well as impacting on local villages via the increase in traffic during construction which is expected to involve some 600 workers.