The first time anyone knew something was wrong was when Lorraine Kelly felt a lump on her husband Paul's stomach. She persuaded him to see a doctor. The diagnosis was cancer.

 Three years later he died, aged 47, and now his brother, Peter Kelly, is going to the High Court for answers. He also wants to know why his daughter, Sarah, developed cancer when she was eight.

 He believes the cause of his family's tragedy lies just yards from his home where the nuclear submarines dock at Plymouth's Devonport naval base. Paul had worked for months as a roofer in the site, sometimes carrying out projects within the submarine compound. Sarah grew up in its shadow, in one of the tightly packed streets that nestle right up to the docks.

 'I don't want anything else to happen to my family,' Peter Kelly said. 'I want to know if we are safe or not.'

 Kelly has launched a legal fight to have a public hearing held into the environmental risks of the work that goes on at Devonport's nuclear dock and a plan to increase radioactive discharges. His case is expected to be heard within the next three months.

 DML, a company that is going to refit the Trident nuclear submarines, wants to boost the amount of tritium released into the River Tamar by 700 per cent and into the atmosphere as steam by 500 per cent.

 Tritium is radioactive water used as a coolant in submarines' reactors. DML has also applied for permission to emit radioactive carbon-14 and argon-41.

 Company officials insist their plans are safe and that levels of radiation would be indistinguishable from natural background radiation. 'We take our environmental and public health responsibilities very seriously indeed,' a DML spokesman said.

 But some scientists have concerns. Tritium's radiation passes easily into the human body because it is carried by water molecules. Also known as 'heavy water', it was used in the Seventies to make luminous exit signs and phone dials, but was banned because it was thought to be too dangerous. Tritium radiation fixes firmly to chemicals in human cells, including DNA, by a process called organic bonding. This can then disrupt a cell when it replicates, leading to mutations, which in turn can lead to cancer.

 With a half-life of 12 years, tritium could build up in the Tamar estuary and eventually enter the human food chain. Most of the tritium released at Devonport is piped directly into the river in an area rich in wrecks and sealife and popular with diving clubs.

 Another possible concern is tritium fog, condensing from effluent released by the docks into the air. Tritium has a higher freezing point than water and so could condense into a fine mist indistinguishable from normal fog.

 Concerns about the possible risks for pregnant women, whose foetuses may be vulnerable to tritium radiation, were raised by Dr Ian Fairlie, a radiation biologist who works as an independent consultant. 'I would advise all pregnant women not to be near the docks when the emissions are taking place. I don't think that is an unreasonable request at all.'

 DML, however, insists the risks are small. Tritium can be produced naturally from cosmic rays reacting with the atmosphere. DML also says its proposed emissions are within government safety guidelines. 'We are being as careful as we can,' a spokesman said.

 But critics point out it was only two years ago that DML discovered it had unknowingly been producing radioactive carbon-14 as a waste product. Carbon-14 can be dangerous if ingested.

 DML's parent company, Brown and Root, paid $750 million after being sued for mismanaging a nuclear construction project in Texas.

 Residents and environmentalists are concerned that Plymouth is becoming a nuclear dumping ground for the whole country. As well as becoming the sole British yard for refitting Trident submarines, Devonport is also to become a future site for storing up to 26 nuclear reactors from submarines going out of service.

 The council has put an emergency radiation leak plan on its website which reads like a throwback to the Cold War. It advises people to stay indoors and take iodine tablets to thwart the effects of radiation.

 A special plan, called DevPubSafe, has been developed for those living in and around the docks. The local primary school nearest the naval base, Barne Barton, has an annual nuclear emergency drill.

 Certainly Sarah Kelly, now aged 20, is afraid. After five years of chemotherapy her thyroid cancer went into remission, though she still has to have annual checks. She is concerned for her young son, Harry, born on the day Paul Kelly died.

 'You just worry about it all the time now. You can't go swimming in the river or walking down the streets without wondering what exactly you might be breathing in,' she said.

paul.harris@observer.co.uk