French regulator Autorité de Sûreté Nucléaire (ASN) has called into question the medium-term safety of the evaporators at Areva's La Hague nuclear fuel processing facility. Measurements of the thickness of evaporators have shown greater levels of corrosion than expected and ASN has instructed Areva to increase its supervision of the units and install isolation facilities and advanced detection systems to limit the consequences of a leak or rupture. The evaporators, commissioned between 1989 and 1994, were designed in the 1980s using a steel selected by Areva for its corrosion resistance and were intended for an operating lifetime of 30 years.
At that time of their construction, Areva said it had ensured the thickness of their steel walls would provide good resistance to earthquakes and the pressure of the heating coils, even after corrosion. However, ASN noted: "In fact, the resistance of such equipment to the pressure of their heating circuits or earthquakes could be challenged in the coming years and potentially from 2018 for the most degraded evaporator."
In La Hague's R2/T2 workshops of the UP3-A and UP2-800 facilities, fission product solutions are concentrated using evaporators (three per plant) that heat the solution to evaporate the acid, which is then recycled. The concentrated solutions are then vitrified to form glass packages that are then stored at the La Hague site awaiting final disposal in a deep geological repository. The UP3-A and UP2-800 facilities at La Hague each contain 15 workshops dedicated to one particular phase of reprocessing operations. The evaporators causing concern are in the UP3-A plant, which has an annual processing capacity of around 800t of used nuclear fuel.
French nuclear operators are required to carry out comprehensive safety reviews of their installations every 10 years. As part of a review of the UP3-A facility, which began in 2010, ASN requested thickness measurements of the evaporators to monitor ageing. The initial measurements took place in 2012, followed by others in 2014 and 2015. The latest results - submitted in December 2015 - indicated a faster rate of corrosion than expected when the evaporators were designed.
ASN said it has decided to monitor the development of corrosion at the evaporators and will check that Areva complies with the conditions set for their continued operation. It noted, "ASN could enforce the shutdown of the plant in case of excessive deterioration."
According to Areva, La Hague has an overall capacity for the annual processing of used fuel from 80 to 100 nuclear reactors, amounting to 1,700t . This makes Areva world's biggest processing of used nuclear fuel.