Evaporator corrosion at La Hague threatens future reprocessing - Time for a strategy rethink?

Yves Marignac and Mycle Schneider

On 24 February 2016, operator Areva and the French Nuclear Safety Authority (ASN) released information about serious corrosion problems challenging the safety of high-level liquid waste evaporators at the French spent fuel reprocessing plants at La Hague. Impact on the operational performance will also increase pressure on spent fuel storage capacities and exacerbate the financial situation of the virtually bankrupt operator.

The corrosion problems at La Hague were identified through conformity checks requested as part of an in-depth decennial safety review of the UP3 plant. Such a procedure, which has been applied to French reactors since startup, was only introduced for fuel-chain facilities by the 2006 nuclear security and transparency law. The first application to UP3 started in 2010. This plant and its sister plant UP2-800 respectively started operation in 1989 and 1994 with a 30-year design lifetime.

The evaporator corrosion is the first of a number of ageing problems expected to develop over the coming years. The six evaporators (three on each reprocessing line) are large stainless steel boilers heated by pressurized half-tubular welded circuits circulating on their outer surface, which concentrate liquid waste arising for the chemical separation of plutonium and uranium in spent fuel, prior to the vitrification and conditioning of this waste. While their safety requires a designated minimal thickness of steel to be maintained in the circuits, they are subject to corrosion mostly due to the acid nature of the solution they are exposed to.

A projected rate of the corrosion mechanism was accounted for in the initial design. However, it was not planned to closely monitor the evolution of the corrosion, as the lack of access within the reinforced concrete structures surrounding the evaporators and the level of radioactivity in the rooms make direct measurement difficult. Under request of ASN, measurements were performed for the first time in 2011 on two evaporators (one for each plant). These tests, confirmed in 2012, showed a corrosion rate higher than projected.

The ASN therefore requested Areva to conduct more extensive measurements on all evaporators. The latest results of the tests conducted in 2014-2015, obtained in December 2015, confirm the initial findings. Although Areva claims to modify operation to reduce the ongoing corrosion, at the observed rate, the wall thickness could still rapidly drop below the required minimum, which ASN said could trigger the decision "to enforce the shutdown of the plant" as early as 2018 for the most corroded evaporator, and gradually until 2021 for the others . The Institute for Radiation Protection and Nuclear Safety (IRSN) issued a number of recommendations including upgrading of inspections, monitoring and more frequent rinsing of the piping system. All of the recommendations will likely affect the performance of the facilities.

The operator hardly anticipated this situation. In a meeting of the Local Information Commission (CLI), on 25 February 2016 in Cherbourg, Areva said it plans for the replacement of all evaporators by 2021 (the presentation is not yet available online). This would be faster than ASN's own estimate, as Chairman Chevet said during a Parliamentary hearing four days later that it would require at least six years to manufacture a new evaporator . The replacement of evaporators is also likely to require the building of new workshops and the subsequent relocation of the piping system, which could prove technically challenging. Areva's trade union representatives stated at the CLI meeting it could require to stop reprocessing for up to three years to carry on replacement work.

The experience of the THORP plant at Sellafield in the UK, where the addition of a fourth evaporator to the reprocessing plant started in 2006, illustrates the kind of delays and cost escalations at stake. The startup of the evaporator is six years beyond schedule and still delayed, while its projected cost skyrocketed from an initial £90 million to a current £670 million estimate. In 2015, Areva's own projected cost was said to be €350 million for the change of three evaporators.

A more or less lengthy interruption of reprocessing could have more dramatic impacts, in a context where spent fuel storage capacity is already feared to fall short in the coming decade.

The cumulative nominal capacity of the four spent fuel pools operating at La Hague is 17,600 tHM, but their actual capacity, taking into account operational conditions, is rated at 12,352 tHM (or 2,796 storage positions). According to Areva's CLI presentation, a total of 9,935 tHM of spent fuel was stored in the pools as of 31 December 2015 . With at least 175 storage positions (equivalent to 780 tHM) occupied by diverse materials and possibly around 110 storage positions (equivalent to 490 tHM) occupied by unirradiated scrap MOX fuel (Areva's estimate does not account for the specific presence of this material in the La Hague pools), the available capacity could be as low as 1,150 tHM. This roughly corresponds to the amount of spent fuel unloaded annually from EDF's 58 reactors.

With EDF's own spent fuel pools at reactors sites close to saturation and ASN vetoing plans to densify storage, it is projected that additional spent fuel storage capacities could be needed by 2025. EDF is therefore planning to introduce later in 2016 a project for a new centralized interim spent fuel storage pool, which it would use in priority for spent MOX and reprocessed uranium fuel that is currently not reprocessed. Under current planning, design, siting, licensing and construction might take at least ten years.

The corrosion of La Hague evaporators might long before lead to the occlusion of the French spent fuel management scheme. With Areva's and EDF's finances stretched to the limits, and the industrial infrastructure reaching the end of the lifetime or simply inexistent--no reprocessed uranium is currently reused--this would be the appropriate time to reassess the entire strategy.

Areva lost €10 billion ($11.3 bn)--six times its stock market value--over the past five years and the French government has promised to save it by injecting €5 billion in capital. However, it is uncertain whether the European Commission will accept the measure under EU competition rules. EDF has rapidly increasing production costs, a shrinking client base that uses decreasing amounts of power and faces ferocious competitors. It is hard to see how EDF will pay back its €37.4 billion ($42.2 bn) debt under these conditions. Both companies have pledged to massively cut jobs. At La Hague alone, Areva plans to cut about 500 jobs of a total workforce of 3,000. Safety and security are at risk.

While the move to dry-storage would also take some initial investment, abandoning the plutonium economy would save huge amounts of money overall. Areva is already a leader in dry-cask fabrication in the U.S. It could add plutonium conditioning, and extend its decommissioning and waste management portfolio. Business guaranteed.