The state-owned rail company, SNCF, has made a legal complaint and police have opened an inquiry into the incident, which took place on 12 July, the same day as the crash that cost six lives at Brétigny-sur-Orge.
A previously unknown anti-nuclear group claimed responsibility for it in a statement sent to the regional newspaper, the Populaire du Centre.
The crash took place in the morning on a stretch of track used exclusively by nuclear giant Areva to transport nuclear waste near Bessines-sur-Gartempe, in central France.
An Areva convoy came of the rails and carried on for 100 metres, reportedly because a fishplate joining two rails had been removed and a rail disconnected.
Two railworkers aboard were not hurt but have filed a complaint for endangering their safety and wilful damage.
A fishplate also came loose at Brétigny-sur-Orge, causing a train to career off the track in the evening of the same day.
Although investigators are unclear how all the bolts holding it in place came loose at the same moment, they have found no evidence of sabotage and the site is clearly visible from a signal box opposite.