EDF Energy has rejected claims that a process called “steam venting” at the Sizewell B nuclear power station may expose local residents to a health risk.

Steam containing elements of radioactivity – well within emission limits imposed by regulators – is occasionally and with considerable noise vented to the environment because of conditions inside the reactor.

However, John Busby, a consultant to the coalition of groups fighting plans for a £14billion Sizewell C plant, believes that the process could expose residents to health risk – particularly if there is an unexpected loss of connection to the national grid and standby generators fail to operate.

In extreme conditions, he claims, this could lead to a catastrophic meltdown of the reactor core – as happened at Three Mile Island in the United States and at Fukushima in Japan.

Mr Busby, a former engineer who has spent many years studying the corrosion and heat transfer problems of the nuclear industry, has called on EDF to keep more detailed records of steam venting and provide local residents with reassurance over the impact of the process.

“Records should be kept of steam venting duration and the wind directions so that monitoring of the areas under the plumes of steam can be performed,” he said.

An EDF spokesman claimed there were a number of inaccuracies in Mr Busby’s analysis.

He said: “The state of the art design of Sizewell B incorporates features to ensure that the plant would always be safely shutdown and cooled, even in the very unlikely instance of a loss of connection to the electricity grid together with failure of the many back-up forms of generation at the site.

“Steam venting from Sizewell B, which is occasional but sometimes necessary for the operation of the station, does not present a radiological hazard to the public or to the workers at the station.

“Environmental monitoring is carried out at the station by our independent regulator the Environment Agency which publishes the findings. Sizewell B operates within an environmental permit and also carries out its own monitoring.”