Corrosion of fission products evaporator-concentrators at La Hague: ASN regulates continued operation by means of prescriptions

The evaporators concentrating fission products on the La Hague site, designed for an operating life of thirty years, were commissioned in 1989 and 1994.

The first thickness measurements were taken on these devices by Areva in 2012 at the request of ASN, as part of the first ten-yearly periodic safety review of the UP3‑A plant. Areva conducted further measurements in 2014 and 2015. The latest results reveal faster corrosion of the evaporators than originally anticipated in their design.

In the light of these data, ASN decided to regulate the continued operation of this equipment in its resolution of 23^rd June 2016. ASN thus issues prescriptions applicable to the licensee on the following topics, which represent the main safety issues for these evaporators:

• definition of final shutdown criteria for this equipment,
• reinforced thickness checks on the evaporators: extension of the inspection zones, annual inspections of sensitive areas, annual pressurized hydrotesting of the heating circuits,
• implementation of measures to limit the corrosion phenomenon: limitation of temperature and pressure,  steps to make the solutions less corrosive, regular rinsing,
• reinforced monitoring of scheduled evaporator maintenance outages,
• preparedness for emergency management in the event of evaporator perforation,
• six-monthly transmission to ASN of a report giving the results of all these measures.

This resolution and all the prescriptions it contains were the subject of a public consultation from 4^th to 19^th May 2016.

ASN will be particularly attentive to the development of corrosion in these evaporators and may demand shutdown of the facility in the event of excessive deterioration.