The first vital step in combating and reducing the highest hazard area at Sellafield – the High Level Waste (HLW) storage tanks – has been put out to tender by Sellafield Ltd. Invitations to tender for the work contract, which appeared recently in the Official Journal of the European Journal (OJEU), relates to ‘the design and build of a highly active liquid effluent plant’. In a number of phases stretching over the next 8 or 9 years, the contract is believed to be worth up to £1.5Bn.
Sellafield Ltd has confirmed that the contract relates to the provision of a number of new HLW storage tanks as well as additional ‘evaporative capacity’ – a reference to downstream plant that condense the liquid HLW prior to its conversion to solid glass form. The deal is further described in construction and contract journals as including the construction of a new building to hold the new storage tanks, associated process plant and a proposed replacement facility for one of the site’s older storage assets.
Sellafield has 21 HLW storage tanks. Whilst the older tanks, numbered 1-8 and commissioned between 1955 and 1968, are no longer in service, the condition of some of the newer tanks 9-21 (1970-1990) has been the subject of significant concern by the Health & Safety Executive’s Nuclear Installations Inspectorate (NII) in recent years. In its 2008 Biennial Review on HLW, the NII warned that ‘recent cooling coil failure rates and specifically the location of recent failed coils has led to uncertainties over the ability of the newer storage tanks to continue to service the needs of the Highly Active Liquor (HAL) stocks strategy’.
The potential hazards (and off-site consequences) posed by the tank storage of liquid HLW is reflected in the potential loss of cooling to the tanks being designated as the ‘worst credible accident’ (the Reference Accident) under Sellafield’s Emergency Plans. Just such a loss of coolant occurred on 1st April this year and, whilst fortunately of relatively short duration, the event remains under formal NII investigation. In the week prior to the accident, Norway’s Ministry of the Environment published a critical report on a hypothetical Sellafield accident involving the HLW tanks. It calculated that if just 1% of the stored HLW was released to the air, the radioactive fallout in Western Norway could be 5 times higher than the areas of Norway worst affected by the Chernobyl accident.
The £1.5Bn contract for the new HLW tanks and associated facilities has drawn interest from a number of consortia which include international players such as Robert McAlpine, Costain, Balfour Beatty and Amec, as well as Singapore-based Simon Carves and Australian Worley Parsons and DZ Constructions. Expected to be awarded in early 2010, the contract will be conducted in three phases, the first being an initial mobilisation and familiarisation stage for contractors. This will be followed by the design phase, estimated to commence around mid-2012, which includes design of the new HLW storage tanks, ventilation and abatement systems and access and connection to existing plant. The final phase, subject to approval by the Nuclear Decommissioning Authority (NDA) and Government, will see the construction of the facilities. The work estimated to be completed in 2018.
The reference by Sellafield to ‘additional evaporative capacity’ as forming part of the overall contract is likely to refer to a new Evaporator E that is known to be required if existing and future arisings of HLW from the site’s reprocessing operations and from decommissioning programmes are to be dealt with. Work on new Evaporator D is already underway and is expected to be in operation in 2014. D will relieve the pressure on the site’s existing Evaporators A,B & C which have all been prone to failure in recent years. Evaporator C, which serves the THORP reprocessing plant, is currently out of service for a 7-month engineering investigation. THORP will remain closed until the Evaporator is reinstated next Spring.
Sellafield’s existing HLW storage tanks (9-21) are each designed to hold up to 150 cubic metres of liquid HLW. Each is fitted with 7 internal cooling coils as well as external cooling jackets. Whilst the jackets on tanks 9-11 cover the tank base and extend 1 metre up the side, the jackets on tanks 12-21 cover not only the tank base but also extend the full height of the tanks to a point above the maximum liquor level.
Whilst the failure of some of the cooling coils, which cannot be replaced, has led to repeated concerns in recent years, new warnings have been issued by the NII on other high risk facilities at Sellafield. Included in the high risk category is an old fuel storage pond B30 known to the workforce as ‘Dirty Thirty’. Built in 1959 to prepare and store Magnox reactor fuel prior to reprocessing, B30 was closed in the early 1970’s. Now under decommissioning, its inventory includes large quantities of sludge from corroded fuel and a variety of old operational equipment. At a local liaison meeting on the 1st October, NII warned that the risks of something serious happening in Sellafield’s old plants are far too high. “We are concerned that the risk of a major event caused by the further degradation of legacy plants, or increased time at risk due to deferrals is far too high”. The Environment Agency reinforced the serious nature of the hazards and insisted that clean-up and risk reduction remain absolute priorities.