Third quarter of 2001

COGEMA - La Hague : two simultaneous breakdowns behind significant gaseous releases

WISE-Paris, 7 August 2001

[Posted 21/08/2001]

On 18 May 2001, a breakdown of a ventilation system in the R7 vitrification plant, coinciding with a stuck valve, ended up in the release of radioactive materials into the environment. According to the independent laboratory ACRO, specializing in radioactivity measurements, within one hour, COGEMA released nearly 100 times as much gaseous effluents as it did in total in 1999, when it reached its record level (153 MegaBecquerel (MBq)), and approximately 10 times as much as the annual limit it committed itself to comply with last year (1850 MBq).

The R7 plant is an inaccessible building, designed with three containment barriers, meant to prevent radioactive leaks into the atmosphere. COGEMA operates the plant for vitrification operations aiming at solidifying concentrated solutions of radioactive products, mainly fission products, resulting from the reprocessing of spent nuclear fuel. Roughly, there are three ventilation systems, one for each of the containment barriers. The ventilation systems collect and filter radioactive gases before they are controlled and finally released into the atmosphere. Each system has a certain number of filters. The ventilation system within the first containment barrier is the most performing one. Given the fact that it collects highly volatile radioactive gases, notably ruthenium, it is designed with washing columns that turn them into liquid form, before they are vitrified in their turn as waste. (1)

On that day, while the R7 plant was operating, the first ventilation system broke down (2), which caused the emergency ventilation system to start. Attempts to restart the main system were unsuccessful. Furthermore, a valve of the emergency ventilation system remained stuck in open position, which led consequently to the reversing of the gas flow outside the containment barrier.

For nearly one hour, radioactive gases, instead of going through the first system, went through the second one, which has the same number of filters but is not designed with washing columns (3). Lower purification efficiency resulted in the release of more radioactive gases. The incident was classified at level 1 of the INES scale (International Nuclear Event Scale, graduated from 0 to 7).

On 22 May, ACRO (4) decided to undertake a first campaign of measures around the La Hague site. According to ACRO's calculating results , the gases released into the atmosphere reached 14 GigaBequerels (GBq), 1,000 times more than announced by COGEMA. "As far as the South-East-oriented trail is concerned, over a distance of less than 2.5 km and by assuming minimalist hypotheses, the activity on the grass is of the order of 40 MBq, which makes the source term (11 MBq) announced by the exploiting company hardly plausible". (5)

According to the Safety authority, "the measures undertaken by COGEMA, ACRO, IPSN (6) and OPRI (7), confirm that the 18 May incident had no significant consequences neither on the populations' health nor on the environment" (8). A dose received by an observer at one kilometer from the site would have been of the order of a few microsieverts, "compared to the regulatory 1,000 microsievert/year limit". (9)

DSIN has not communicated so far the underlying figures and details of the model used to calculate the potential health impact. Also, the obvious incoherence between the figures of the releases communicated by COGEMA and the results of the measures in the environment remains to be elucidated before classifying the accident as “insignificant”.


  1. Control authority: Directions régionales de l'industrie de la recherche et de l'environnement (DRIRE), telephone conversation, 07 August 2001
  2. Safety authority: Direction de sûreté des installations nucléaires (DSIN) :
  3. DRIRE, telephone conversation, 07 August 2001
  5. Report : Evaluation du terme source de l'incident du 18 mai 2001 survenu à l'établissement COGEMA-La Hague, ACRO, 26 July 2001. Excerpt translated by WISE-Paris
  6. Institute for nuclear protection and safety: Institut de protection et de sûreté nucléaire
  7. Office for the protection against ionizing radiation: Office de protection contre les rayonnements ionisants
  8. Letter dated 30 July 2001, from the Assistant director of DSIN, Jérôme GOELLNER, to Pierre BARBEY, Scientific advisor to ACRO : Excerpt translated by WISE-Paris

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