Windscale cleared by UCD study

 

A new study by researchers at UCD seems to prove that no radiation from the fire at Windscale nuclear plant in 1957 reached Ireland, writes Cormac Sheridan.

A team of physicists at University College Dublin has obtained what appears to be definitive evidence that a fire at the Windscale nuclear reactor in 1957 did not leave any significant deposits of radioactive material on the east coast of Ireland.

The team used a highly sensitive new analytical method, Accelerator Mass Spectrometry (AMS), to show that no detectable amounts of Iodine-131 (I-131), the most important radioactive isotope that was released during the incident, could have reached Ireland.

The group, including laboratory head Prof Peter Mitchell, Dr Eddie McGee and PhD student Donal Gallagher, also quantified levels of other radioisotopes released during the fire, including Caesium-137 (Cs-137), Plutonium-239 (Pu-239), Pu-240, and Americium-241 (Am-241).

They employed coring techniques, routinely used by climate change researchers in the study of ice cores, to build up a picture of the deposition of each of these isotopes over a 70 year period. The samples were taken from the sediments of Ballywillan Lake, near Crossgar, Co Down, almost due west of the Windscale site in Cumbria, renamed Sellafield in 1981. They published their data this month in the journal Environmental Science & Technology.

"Our study is the first study to look at lake sediment profiles. There's nothing else comparable in the literature," McGee says.

The fire ranked as the world's biggest nuclear accident until the Chernobyl disaster in 1986. The resulting radioactive plume spread predominantly in a south-easterly direction, and is estimated to have been the cause of up to 100 fatal cancers in the UK.

A 1980s study linked the event to an apparent cluster of Down's syndrome births in Co Louth. Although subsequent epidemiological analysis has ruled out any connection, direct evidence of the possible involvement of I-131 was not available.

"In the past, it simply wasn't possible to measure it, along with awhole suite of other rare isotopes," McGee says. The AMS technology, which separates particles on the basis of their mass and electrical charge, has a sensitivity of 1 in 1016 atoms, several orders of magnitude greater than earlier techniques such as alpha and gamma spectrometry.

The UCD group conducted its analysis with the help of collaborators at Uppsala University in Sweden, one of a small number of AMS facilities in Europe. I-131, which can cause thyroid cancer, has a half-life of just eight days, so whatever amounts of the isotope were released during the 1957 fire have long since decayed. However, the UCD group was able to use a related isotope, I-129 as a tracer to build up a picture of what did - or did not - happen in Ireland in the period immediately after the fire on October 10th.

I-129, a harmless isotope, is much more persistent, having a half-life of 15.7 million years. It was released at extremely low concentrations but in a known ratio to the levels of I-131 that were released.

The team also measured the amount of radioactive lead (Pb-210) in order to establish a "chronology" or timeline, based on the concentration gradient of that isotope along the depth of the sediment cores.

Pb-210 is deposited in rainfall and has a half-life of 22 years. At some point down the sediment core the Pb-210 level will be half of the level at the core surface. This point corresponds to a point in time 22 years before the present.

A core depth with a Pb-210 concentration half that again represents a 44 year interval, and so on. The profiles established by the UCD group on all of the isotopes studied correlate well with international data. They show a steady increase from very low levels during the 1950s and early 1960s, which the team attributes to atmospheric weapons testing.

From the 1980s onwards, a more dramatic increase in fallout is detected, coinciding with greater discharges from nuclear reprocessing activities at Sellafield and at the French facility at Cap La Hague in Normandy. The signature of the 1986 Chernobyl fire is also evident, but there is no trace of the Windscale event.

This study is not a standalone analysis but is part of an ongoing, 25-year effort by Mitchell's lab to build up a comprehensive picture of fallout patterns across Ireland.

Recently, the group has also analysed radioisotope accumulation in peat bogs near Louisburgh, Co Mayo, and on the Carlingford Peninsula in Co Louth. It has also studied the buildup of Carbon-14 in tree rings on the east and the west coasts.

Although Sellafield continues to provoke controversy on both sides of the Irish Sea, this study appears to lay to rest whatever fears had persisted that the 1957 fire had any significant impact on Ireland's east coast.