Retrospective search for evidence of the 1957 windscale fire in NE Ireland using 129I and other long-lived nuclides

The accident at Windscale in October 1957 resulted in the release to the atmosphere of a large quantity of radioactivity. The presented work is a retrospective search for evidence of contamination from the accident in the northeastern region of Ireland. A lake yielding a high-resolution sedimentary record was identified near the northeast coast of Ireland. This site was used to reconstruct the history of radionuclide input to the region, based on the analysis of a set of cores extracted from the lake. A chronology for sediment accumulation within the lake was established using radioisotopic dating techniques (including 21%). High-resolution gamma and alpha spectrometry techniques were used to quantify concentrations of Cs-137, Pu-239,Pu-240 and (241)- Am, all of which were released during the accident. The primary radioactive component of the release was I-131 (T-1/2 = 8 days), but this short-lived isotope has long since decayed. However, I-129 (T-1/2 = 1.57 x 10(7) years) was also released during the accident, and in a known ratio to I'll. Recent advances in accelerator mass spectrometry now make it feasible to measure I-129 at ultra-trace level and thereby retrospectively reconstruct I'll deposition. Clearly resolved concentration profiles for Cs-137, Pu-239,Pu-240 and (241)- Am in the lake cores reflect known historical fallout trends. The data suggest that any contamination from the Windscale fire that might have reached this catchment has been overwritten by input from the testing of nuclear weapons in the atmosphere. A time-series for I-129 in lake sediment shows that concentrations in recent sediments are approximately 10 times greater than concentrations recorded in strata corresponding to the period of maximum fallout of other radionuclides from atmospheric testing of nuclear weapons (1964). These recent increases in I-129 are attributed to increased emissions from the nuclear industry. The study yields no evidence of any enhancement in radioisotope concentrations, over and above global contamination from the Windscale fire had negligible impact on the northeastern region of Ireland.