Classification of anomalies and incidents

The International Nuclear Event Scale is used to class nuclear events according to their level of gravity. There are eight different levels, ranging from a simple 'deviation' at level 0 to a 'major accident' at level 7.

NB : The French nuclear safety authority's website provides information on significant events at the ILL, as at all the other French nuclear installations.


The ILL (Institut Laue Langevin) is an international research institute which houses a 57-MW high neutron flux reactor (HFR) – known as the Installation Nucléaire de Base n° 67 – designed to produce extremely intense beams of neutrons for use in a broad spectrum of fundamental research fields, including solid-state physics, neutron physics and molecular biology. 

On 28 February 2019, during a routine operation to empty the reactor pool and the adjoining storage canal, the removable gate which separates the pool and the storage canal was raised by thirty centimetres, although it did not come out of the groove which guides its movement. The operation to lift the gate, which weighs 4 tonnes, was begun using the 6-tonne hook of the overhead crane. As this manoeuvre was unsuccessful, the crane’s 20-tonne hook was then used instead, despite the fact that the pool gate’s lifting cable is not designed to be subjected to such a potential force: its WLL (Working Load Limit) is 4 tonnes [1]. Exceeding the admissible load in this way created a risk of the pool gate falling 30 centimetres and damaging its guide groove. In view of the potential consequences had the pool gate fallen, the event was initially classified as a significant event at Level 0 on the INES scale.    

Following an in-depth examination, it was concluded that the crane operators had not adopted the appropriate questioning attitude before going on with their handling operation and switching to the 20-tonne hook. Moreover, at the start of the operation it had not been planned to raise the gate between the reactor pool and the storage canal. Procedures had therefore not been properly applied.  

Consequently, the incident was reclassified to Level 1 on the INES nuclear event scale, a scale which comprises 8 levels, from deviation (Level 0) to major accident (Level 7). 

It had no consequences for the crane operators, the public or the environment.

[1] with a factor-5 margin of safety

The ILL is an international research institute operating a nuclear reactor classified as a Basic Nuclear Installation.

On 17 May 2017 a spent fuel element became lodged in its handling cask, during a transfer operation inside the cooling pool.

The aim of this operation is to deposit the spent element on the floor of the cooling pool; it is performed entirely under water. On this occasion it could not be performed correctly. At the date of publication the element is still blocked in an intermediary position. The residual power of the element is low, at about 20 kW.
As the element has never left the water of the pool, there is no radiological hazard and no risk of any rise in temperature. Once it has been extracted from the cask it will be positioned on the bottom of the pool, as is usual practice.

The fuel element transfer operation is a common practice at the ILL and has already been performed nearly 200 times without incident.

As is standard practice for this type of anomaly, the incident has been classed at level 1 on the INES scale for nuclear incidents, out of 8 (from a simple deviation, level 0, to a major accident at level 7).
There was never at any point any risk for the facility, its personnel or the environment. 

The ILL is an international research institute operating high-flux reactor INB no. 67, classified as a Basic Nuclear Installation.

The facility's operating parameters are regularly controlled every twelve hours. At 9 a.m. on 9 July the reactor shift leader observed that some of the zones inside the internal containment of the reactor building were under a slight overpressure (0.5 to 1 mbar). At the previous control the pressure readings had been compliant with requirements. The anomaly had not been detected immediately because the alarm on the internal reactor containment pressure levels was disabled. It should be noted that the reactor operates within a double containment; the pressure in the external containment had remained at its nominal level of 135 mbar.

This event was of no consequence for either people or the environment. As the alarm had been disabled without formal analysis this event is classed as a level 1 event ('anomaly') on the International Nuclear Event Scale. Information on the event is therefore published for the general public. 

The Institut Laue-Langevin (ILL), which operates a high-flux neutron reactor on its site in Grenoble, declared a significant radiological event to the ASN on 26 June 2015, concerning the exposure of the hand of an operator beyond the annual limit for body extremities of 500 mSv.

The exposure took place on 24 June 2014 when the operator was checking a health physics instrument. The check requires the use of a radioactive calibration source, which is fixed to the end of a rod in order to approach the source as close as possible to the measuring devices positioned high above.

In the course of the operation the operator grasped the rod by the wrong end, thus coming into direct contact with the source for several minutes. The operator only realised the error when putting the rod down. ILL considers that the operator had held the source for 3 to 4 minutes.

The dose received by the palm of the hand is estimated at about 250 mSv, which is half of the regulatory annual limit. The operator's passive dosimeter measured no efficient dose, given the distance from the source.

As the level of one quarter of the annual regulatory radiological limit had clearly been exceeded, the ASN has classified this significant event at level 1 on the INES scale, which is graduated from 0 to 7 in increasing order of severity.

L'Institut Laue-Langevin (ILL), exploitant le réacteur à haut-flux de neutrons sur son site de Grenoble, a déclaré le 15 juillet 2013 un événement significatif pour la radioprotection relatif à la présence d’un faisceau de rayonnements ionisants issu d’un dispositif expérimental, en dehors du bâtiment réacteur, dans une zone non prévue à cet effet.

Samedi 13 juillet 2013 vers 23h15, deux expérimentateurs qui stationnaient à proximité du bâtiment réacteur ont été alertés par leur dosimètre opérationnel de la présence d’un débit de dose significatif. Les investigations du service de radioprotection ont permis de déterminer l’origine de cette anomalie et d’y mettre un terme. Cette anomalie était présente depuis le vendredi 12 juillet en fin de journée. Elle était occasionnée par la mise en service d’un instrument expérimental dont la protection radiologique n’était pas complètement en place et qui a été arrêté dès la découverte de l’anomalie.

Le relevé des dosimètres opérationnels des deux expérimentateurs montre qu’ils auraient reçu une dose efficace maximale de 15µSv pour l’expérimentateur le plus exposé, pour une limite autorisée de 20mSv ou 20 000µSv par an. Des investigations complémentaires ont été engagées pour les seize personnes ayant potentiellement circulé dans la zone pendant la période concernée. Ces investigations n’ont pas mis en évidence d’exposition radiologique supérieure aux seuils d’enregistrement.

L'ASN a procédé à une inspection réactive à l’ILL le 17 juillet 2013. Cette inspection a mis en évidence que l’événement résultait notamment d’un mauvais positionnement du dispositif d’arrêt du faisceau de rayonnements ionisants. Les inspecteurs ont également vérifié les actions immédiatement engagées par l’exploitant.

A la lumière des résultats des investigations conduites sur les personnes ayant circulé dans la zone considérée, l'incident n'a pas eu d'impact sur le personnel, le public ou l’environnement.

Toutefois, en raison de la dégradation de la défense en profondeur mise en évidence par cette anomalie et de l’impact potentiel sur la radioprotection des travailleurs, cet incident a été classé au niveau 1 de l'échelle internationale des événements nucléaires (INES) qui en compte 8.