Radiation is both a cause of and a possible cure for cancer. Marie Curie, the scientist who carried out original work on its therapeutic benefits, paid a price for repeated exposure when she developed bone marrow failure.
Thyroid cancers and leukaemia, a cancer of the blood, are known to occur in individuals exposed to nuclear explosions. The children of Chernobyl are still paying a price for the nuclear disaster which befell their city.
Sellafield has been a suspect in clusters of cancers and Down's Syndrome cases which have been noted at various times over the last 25 years. Despite thorough scientific research, an association with Sellafield's radioactivity has never been proven.
The concept of a "cluster" is central to an understanding of the health concerns associated with Sellafield. Basically, a random distribution of naturally- occurring disease can occur in clusters, which, although suspicious, can be explained by a routine statistical test used to determine cause and effect.
This has been the fate of many health concerns related to Sellafield - they have not stood up to rigorous scientific analysis. The major concern, a possible link between Sellafield and childhood leukaemia, is still being studied.
The worries about childhood leukaemia and the activities of the nuclear plant were first raised in 1983 when a cluster of childhood leukaemias was identified in the village of Seascale, West Cumbria.
Prof Martin Gardner studied a group of children attending schools in the village. His work led to what is now known as Gardner's Hypothesis: could the father's occupational exposure to radiation (before conception) lead to his child having an increased risk of leukaemia?
Prof Gardner published his results in 1990 suggesting a definite link. The study caused considerable concern and follow-up research was quickly commissioned, which reached a different conclusion.
In 1997, a large-scale study by Draper et al reported findings which rejected a link between paternal irradiation and the development of childhood leukaemia.
Draper and his colleagues looked at 36,000 children diagnosed with cancer and found that fathers of children with leukaemia were significantly more likely to have been radiation workers. However, there was no dose response relationship - the amount of the father's exposure did not tie in with the development of the blood cancer.
The Nuclear Industry Family Study (NIFS) was set up to investigate the health of children of workers at three separate British organisations - the Atomic Weapons Establishment, British Nuclear Fuels (the operators of Sellafield) and the UK Atomic Energy Authority.
The study found the incidence of cancer and leukaemia at the nuclear installations to be similar to that in the general population. With a total of 49,000 children studied, no significant trends were found between increasing radiation dose and leukaemia in children.
Most commentators accept that the NIFS and Draper studies point to a lack of evidence that parental irradiation is a cause of leukaemia in the offspring of radiation workers.
Many people will react to these studies by quoting that old, but wise, scientific adage: "Absence of evidence does not mean evidence of absence."
So what is the correct conclusion as far as leukaemias and Sellafield are concerned?
Certainly, an examination of the evidence for a cause and effect between radiation and leukaemias suggests that the case is not proven. There is no dose response relationship between the two factors - something we know there should be from the cancer cases associated with the Chernobyl fallout, for example. Nor has the Sellafield cluster been reproduced at other reprocessing facilities such as Dounray in Scotland or La Hague in France. Scientists are now examining a possible viral cause.
None of this absolves Sellafield from the damning revelations of the last few weeks. If safety data have been falsified, could there have been even larger releases of radioactive material into the Irish Sea? Nearly 20 years after Gardner first picked up the cluster of childhood leukaemias in West Cumbria, the jury is still out as far as an adequate explanation is concerned.