Liquid waste discharged from the plant owned by British Nuclear Fuels (BNFL) ends up in the Irish Sea and nuclear waste is transported across the sea. A serious accident at Sellafield could shower Ireland with radioactive fallout.

In 1997, the Radiological Protection Institute of Ireland announced that reports monitoring fallout over Ireland from a 1957 accident at Sellafield were never included in the final data recording the fallout pattern from a nuclear fire. According to Eddie McGrady, SDLP MP for South Down, a full fallout survey was never completed.

An investigation the following year by the Green Audit Irish Sea Research Group focused on coastal areas in Wales believed to be affected in ways similar to the Irish coast. The Welsh survey revealed between 1974 and 1989, children living close to the Irish Sea were on average 4.6 times more likely to contract leukaemia. The statistics also showed a reduction in risk as the distance from the seashore increased and appeared to give credence to the belief that seashore spray could carry radioactive particles several kilometres inland. Dundalk, just 60 miles from Sellafield, has a cancer rate 12% higher than the Irish average. Out of a population of only 3,000, 76 died of cancer over a three year period.

In 1997, an investigation by Britain's own Department of Health found plutonium in the teeth of some 3,000 teenagers in the UK and Ireland, but declined to speculate on its source. Anti-nuclear campaigners believe it could only have come from Sellafield, either by airborne particles or spray. Sellafield emissions fell somewhat in the 1970s-80s. But the advent of reprocessing at the THORP plant in Sellafield has led to a dramatic increase in levels of technetium 99 another toxic radionuclide in the Irish Sea. Levels of krypton 85, a radioactive gas monitored since 1993, are also up.

Some Dundalk residents initiated court action against BNFL and the Irish Government, the latter on grounds they were not bringing enough pressure on the British to close Sellafield nor to prevent the THORP plant from opening.

Since 1979 the State has backed opposition to Sellafield which has intensified within Ireland following ongoing disclosures of BNFL's systematic falsification of MOX fuel records and the exposure of its indequate 'safety culture'.

By the spring of 2000, the Irish Government lost patience with Britain's prevarication on the issue. Exasperated by Tony Blair's reluctance to adequately address Ireland's concerns, in March the Taoiseach announced: "British Nuclear Fuel's facilities at Sellafield represent a clear and totally unacceptable danger to the Irish people. This Government's objective is to bring about the closure of the Sellafield operations as soon as possible. I believe enough is enough."