Alarm systems at a nuclear weapons site were down for ten days after heavy flooding, leaving residents vulnerable to a potential accident.
A report said electricity to "virtually the whole of" the Atomic Weapons Establishment (AWE) site at Burghfield, Berkshire, was switched off when it was flooded during torrential rain on July 20 last year.
Campaign group Nuclear Information Service (NIS) said it was fortunate that staff had gone home for the weekend by the time the water peaked so no radioactive material was in use in the assembly area
It revealed that 84 buildings on the site were affected and "one key facility came close to being overwhelmed by the flood waters".
Campaign group Nuclear Information Service (NIS) said it was fortunate that staff had gone home for the weekend by the time the water peaked so no radioactive material was in use in the assembly area.
No site emergency was declared and the Environment Agency's Nuclear Regulation Group was not made aware of the flood damage for another two days although live nuclear work was suspended for several months, the NIS said.
It was alleged that information about the flooding was deliberately not made public by AWE.
A second AWE site at Aldermaston, also in Berkshire, "came very close to being overwhelmed" and was less than two hours away from failure despite a new water management system, the NIS report said.
The system was installed after AWE was prosecuted over the escape of contaminated flood water in 1989.
But a MoD spokeswoman said: "Like much of the UK, AWE's sites at Aldermaston and Burghfield were both affected by the extremely heavy rainfall on July 20, 2007, which led to flash flooding and water damage to some buildings.
"At no time during, or as a consequence of, the extreme weather conditions experienced on this date was there any threat to the operational safety of either AWE site; and no threat to the public or the environment was posed."