The ILL's high-flux reactor first diverged in August 1971.

The operation of the reactor is the subject of two 'authorisation decrees':

that of 19 June 1969,
and that of 5 December 1994, authorising the reactor start-up after the replacement of the reactor vessel (whose lifetime is of 40 years). 
From the very beginning the possibilities of internal or external aggression were taken into account.

Changes in regulations prompted reviews of the reactor's safety by the authorities in 1986, 1994 and 2002.