The Prime Minister, Lionel Jospin, has demanded an urgent report on the affair, which has provoked a press outcry against the sloppiness and arrogance of the French nuclear industry.
According to internal studies leaked to the Liberation newspaper, wagons carrying nuclear waste to La Hague plant, on the Cotentin peninsula - opposite the Isle of Wight - are frequently contaminated.
The external casing of "secure" rail containers, and even the wagons, are often stained with traces of nuclear materials, at up to 50 times the official safety limit and on one occasion at 500 times the limit.
The three publicly owned companies which are responsible for generating electricity, transporting and processing waste were all aware of the problem but did not inform the government, or the French railway company, the SNCF.
As a result, a dozen railwaymen who have handled the shipments at a depot in Normandy in the past few years may have been exposed to dangerously high levels of radiation.
The Environment Minister, Dominique Voynet - who is also leader of the Green party and a campaigner against the French nuclear industry - described the revelations as "shocking" and "unacceptable".
She said the industry, which has long been a by-word for secrecy and political string-pulling, must now realise "openness is the price of its survival".
Greenpeace has revealed in recent months that the large waste-processing complex at La Hague has been breaching its own, and official, safety guidelines in its discharges into the Channel.
The former environment minister Corinne Lepage - a centre-right politician, not a Green - has just written a damning book, called We can do nothing, Madame le Ministre, detailing her failing struggles to bring the nuclear industry to account.
"It is difficult to imagine, until one has seen the system functioning from the inside, the extent to which the state has become the prisoner of the [nuclear] lobby," she said.
The plant at La Hague receives 1,200 tonnes of nuclear material a year from the 57 French nuclear power plants, plus waste materials from Germany and Switzerland.
All of this material crosses France by rail, in special sealed containers. There is no suggestion the containers are leaking.
They are "splashed" with nuclear materials, especially cobalt 60 and caesium 137, while they are being loaded. The suspicion is that the official cleansing procedures are inadequate or patchily applied.
The industry has played down the importance of the findings. There is no suggestion that anyone has been exposed to dangerous levels of radiation, says Jean-Louis Ricaud, the head of Transnucleaire, the company which is responsible for transporting the waste.
"Should we have to reveal to the public the slightest little problem, as soon as it is signalled to the authorities, even if it presents no public danger?"Reuse content