The organisation's experts have conceded that plutonium discharges up until 1984 had been significantly greater than previously thought. BNFL also underestimated the extent of uranium oxide discharges from its plant, Ben Hytner QC said.
His comments came at the start of a landmark case in which two families are claiming that childhood blood cancers were caused by contamination from Sellafield.
The families say that children have been genetically damaged as a result of the high levels of exposure suffered by their fathers.
Elizabeth Reay, whose husband George was a fitter at the plant, is claiming pounds 150,000 damages for the death from leukaemia of her 10-month-old daughter Dorothy in 1962. (Mr Reay also died of cancer). The second plaintiff, Vivien Hope, is claiming pounds 125,000 damages after developing leukaemia in 1988. She had worked at Sellafield, as had her father.
Opening the families' case yesterday, Mr Hytner told Mr Justice French he would show that BNFL could not be relied upon to provide correct information. 'When this body, which is discharging radioactivity into the environment, gives figures to either the public, or public bodies, or its own workforce, they really do not seem to appreciate the need for accuracy,' he said. Not only had BNFL supplied false information, he said, but it was impossible to ascertain the exact radiation levels. They might be higher than anyone suspected, even now.
Plutonium discharges were a case in point. In 1984, BNFL said total releases amounted to 67 giga Becquerels, the court was told. Two years later, this was revised upwards to 174 GBq. This year a report by Professor Steve Jones, an employee of BNFL, 'puts the total releases of plutonium prior to 1984 at the staggering figure of 3,400 GBq', Mr Hytner said.
He said that as Professor Jones produced his report, BNFL applied in April for a licence to discharge radioactive waste from its new Thorp reprocessing plant at Sellafield. It was 'bewildering' that officials referred in that application to the 'old figures', which were a massive underestimate of true pollution levels.
Asked by the Government to correct the application, BNFL supplied figures which were still 20-25 per cent lower than the information on plutonium discharges which they would provide to the High Court, Mr Hytner said. Afterwards, Alvin Shuttleworth, BNFL's legal director, said the figures 'would be shown to be consistent'.
Yesterday, Mr Hytner said that estimates of the discharges of uranium oxide from Sellafield had risen from 100g (3.5oz) to between 12kg (24lb) and 20 kilograms (40lb). He would demonstrate that the true figure was 40kg (80lb), he said.
The hearing, which is expected to last several months and cost pounds 10m, continues today.