Low dose radiation and its regulation30 October 2001
The annual Tucson meeting on radioactive waste management was held in early March 2001. To judge from its attendance – about 2500 from 40 countries – its popularity among scientists and engineers is as high as ever.
During recent years, the Tucson meetings on radwaste management have become the rallying point for discussions on low dose radiation, both its regulations and the Linear No Threshold (LNT) hypothesis on which the regulation is based.
The LNT hypothesis grew out of the study on the atomic bomb survivors of Hiroshima and Nagasaki. These were exposed to instantaneous and large doses of 6000mSv/sec. Extrapolation of the effects of these doses to occupational and public doses, that are orders of magnitude lower and taken over long periods of time (typically up to 50mSv/year), is being questioned seriously by increasingly large numbers of interested and qualified parties. Their arguments are basically that:
• There is no epidemiological evidence of increased risks of cancer at the occupational and public dose levels being considered today.
• It is even possible that, at these low dose levels, ionising radiation may stimulate the natural DNA repair mechanisms and thus be beneficial to human health. Some evidence of this has been presented at earlier WM conferences.
The International Commission on Radiological Protection (ICRP), on whose recommendations the regulations for radiation protection in most countries are based, considers that current evidence cannot prove or disprove the existence of a low dose threshold. Using a precautionary safety approach, the ICRP will continue to base its recommendations on the LNT hypothesis that ionising radiation carries finite risks of cancer down to zero exposure.
However, the radiation protection establishment has at long last admitted the existence of the controversy within the scientific community and that it has led to some loss of confidence in radiation protection on the part of decision makers and the public.
The obverse side of the precautionary approach
The precuationary approach is basically “better safe than sorry”. Dr Theodore Rockwell of Radiation, Science and Health, pointed out that this could be (and is being) taken too far, with deplorable consequences.
Alternative energy sources are being proposed and introduced to replace nuclear power without any deeper analysis of the consequences, especially to the environment. As Dr Rockwell said, these may result in: “Dams endanger salmon and the decaying vegetation they flood produces more CO2 than an equivalent coal plant. Windmills kill eagles and other rare birds. Solar panels produce more toxic waste than nuclear, but with infinite half-life. Making ethanol to replace gasoline burns up more fuel than it produces. A clean-air gasoline additive pollutes the ground water.
“When we solve an immediate problem without thinking of what migh follow,” Dr Rockwell said, “we might do more harm than good.”
Ramsar is a city on the Caspian Sea in northern Iran. The 2000 inhabitants of this city receive an annual absorbed dose from external beta-gamma radiation alone of up to 260mSv/year, which is many times higher than the 20mSv/year, that is the permitted dose for workers at many nuclear power stations. The high radiation levels are due to the presence of Ra-226 in the local rocks, which are used in the building of most of the houses in the city.
A presentation was made at the recent VALDOR (Values in Decisions on Risks) international conference on the results of some preliminary biological studies on the citizens of Ramsar.
In addition to the external beta-gamma radiation, the inhabitants are exposed to ground water radium concentrations of several hundred Bq/l plus radium in the food, and indoor radon concentrations of up to several thousand Bq/m3. The inhabitants of Ramsar have thus been subjected to a wide range of exposure levels and types of exposure (external beta-gamma, inhaled radon, ingested radium) over several generations. They constitute an appropriate group for being the basis for the formulation of radiation protection measures for the public.
The results of the preliminary biological studies show that:
• Cancer mortality and life expectancy do not appear to be different in the High Background Radiation Areas (HBRA) and in near-by Normal Background Radiation Areas (NBRA). These results are at present based on anecdotal information and an epidemiological study has been started to confirm them.
• Citogenic tests have shown that there are no statistically significant differences between HBRA and NBRA residents. Other testing has shown that there is no reduction in immune system functions or adverse hematological effects among Ramsar citizens compared with NBRA residents.
• The most interesting results were those of an in vitro exposure of blood samples from people from both HBRA and NBRA to a ‘challenge’ does of 1.5Gy of gamma radiation. Here, the HBRA residents showed only 56% of the average number of induced chromosomal abnormalities of NBRA inhabitants, indicating the development of certain adaptive response to radiation dose in the HBRA residents. Adaptive response means that cells exposed to low doses often become less sensitive to the harmful effects of subsequent higher doses. Some researchers say that adaptive response also produces ‘hormesis’, which is the induction of beneficial effects (such as reduction of cancer frequency, longer life span) resulting from exposure to low doses.
It was also noted that similar studies at other HBRAs such as Yangjiang, China and Kerala, India had also given similar results regarding cancer mortality, life expectancy, chromosone aberrations and immune function.
Based on the preliminary biological studies at Ramsar, it has been suggested that the current regulatory dose-response paradigm (the LNT model) is scientifically questionable and results in exaggerated fears of radiation. The 2000 Ramsar residents can be the basis of a long-term study at the same level of scientific scrutiny as that conducted by the Radiation Effects Research Foundation, Hiroshima, Japan.
The regulatory front
Currently, the regulatory structure for exempting or releasing material from radiological regulation is based on the principle of triviality of individual doses to members of the public. The ICRP criterion of “some tens of microsieverts” (per year) became “ten microsieverts or less” in the IAEA Safety Series 89, which was created at a time when naturally occurring radioactive material (NORM) was unknown. The same criterion was later used for two regulatory concepts, exemption (from entering regulation), and clearance (for release from regulation), with generally a factor ten higher activity concentration values for exemption as for clearance. The difference in activity levels was explained by ‘quantities’, exemption being applied to small quantities and clearance to large quantities.
In the USA, the NRC rules for the release of nuclear sites are based on a 250mSv/year individual dose criterion, while the draft regulation for the release of the material from sites (eg decommissioning) has a 10mSv/year criterion. The American National Standards Institute’s (ANSI) Surface and Volume Radioactivity Standards for Unconditional Releases from 1997 was endorsed by the US Health Physics Society. It is interesting to note that the 1997 draft was based on a 100mSv/year criterion, with corresponding derived nuclide specific clearance levels. In the final version, the dose criterion was changed to 10mSv/year, but the volumetric specific activities remained unchanged.
During the mid 1990s, the issue of technologically enhanced naturally occurring radioactive material (TENORM) emerged. TENORM arisings occur in huge quantities: two to three orders of magnitude larger than those used in European studies on recycling in the nuclear industry. The activity levels in such arisings are generally the same as in very low level nuclear waste. Their occurrence in a large number of industries, as well as their activity levels and quantities, have not been generally known, even to regulatory authorities, until fairly recently. It has become obvious that the triviality approach can no longer be used.
Some organisations, regulators and institutes, such as the European
Commission in its directive of May 1996 laying down basic safety standards (BSS) against ionising radiation, propose to solve this problem by dividing occurrences of radioactivity into:
• Practices, which utilise the radioactive properties of materials.
• Work activities, where radioactivity is incidental, ie TENORM industries.
The EC BSS prescribes an individual dose constraint of 10mSv/year/practice. For work activities, a 300mSv/year is being proposed. The IAEA approach had earlier been optimisation in each individual case of TENORM regulation. Lately, it seems to be swinging towards the 300mSv criterion. In effect, this will mean the release to the public domain of huge quantities of material from the non-nuclear TENORM industries at much higher levels of individual dose as release criterion than from the nuclear industry. It is difficult to reconcile the EC and IAEA approaches to the views of the US National Academies of Sciences which, in its evaluation of the EPA Guidelines for Exposure to TENORM, states that there is no plausible difference in the judgement of risks due to exposure to natural or artificial radioactivity.
It should be noted that the 300mSv/year criterion is currently used as the basis for the discharge of effluents from nuclear plants to the atmosphere and water. It is also the exemption level proposed by the EC for building materials in Radiation protection 112. This wide use of the 300mSv/year criterion in so many instances and affecting orders of magnitude larger numbers of people than the release/recycling of material from nuclear facilities makes it even more difficult to understand and explain the insistence of a 10mSv/year rule for the latter.
Indeed, against the background of the Ramsar data and of similar data from other high background radiation areas like Yangjiang and Kerala, this whole approach of regulating at dose levels well below the ambient seems to be questionable.
The US National Acadamies of Sciences was requested by the US Nuclear Regulatory Commission to undertake a study on “Alternatives for Controlling the Release of Solid Materials from Nuclear Regulatory Commission-Licensed Facilities”. A committee was set up under the National Research Council for the purpose. Among other activities, the Committee held an ‘open information gathering session’ with international presentations in June 2001, including reports from the IAEA and EC.
The IAEA presentation represented a remarkable change in IAEA’s previous position on clearance/exemption, exemplified by the following two quotes:
• It is sensible to use just one unique set of radionuclide specific levels for the purpose of indicating a boundary between radioactive material that may not warrant the imposition of the regulatory system and material that may warrant regulation.
• Preliminary proposals:
Single set of values for defining scope of BSS in terms of Bq/g would, in principle, replace previous generic exemption levels, clearance levels, and commodity levels.
Applies to all materials except food and water.
The BSS would be modified by introducing a definition of its scope and removing existing exemption levels and references to clearance.
These proposals are laid out in a report entitled: “The scope of radiation protection safety standards – strategy for rationalisation of policy”. It was underlined that the proposals are preliminary and may be modified down the line. A closer reading of the hitherto published material reveals the possibility of continued inconsistencies. For instance, ‘scope-defining levels’ are to be based on 10mSv/year for realistic assessment and 1mSv for pessimistic assessment. The difficulties will arise in the definition of realistic and pessimistic assessments and under which circumstances each type of assessment should be used. These will have to be based on subjective judgements that can lead to the same kind of inconsistencies that dog the current discussions on the clearance/exemptions of radioactive material from nuclear and non-nuclear industries. Examples of scope-defining levels were 0.1Bq/g for Co-60 and for Ra-226. If ‘scope defining’ is the boundary between regulation and non-regulation, most of the 280 million tons of coal ash arising annually will come under regulation. Is this practical?
In the EC presentation, it was noted that the word practices, which earlier had been reserved for material whose radioactive properties were used, now also covers ‘(processed) natural sources’. It was not made clear if this meant that the oil and gas, fertiliser and coal industries will now be treated as practices with a 10mSv/year individual dose criterion – as for the nuclear industry – for the release of material.
It was obvious from the presentations that a great deal seemed to be happening all of a sudden in this area of the release of slightly contaminated material.
Cost to society?
For the nuclear industry, the stringent dose criteria for release lead to extremely high disposal costs, especially for decommissioning redundant plants, as much of the material arising from such projects are radioactively contaminated to very low levels. These costs are passed on to the electricity consumer, and thus the cost for reducing the dose to the public is finally carried by society at large.
A study was carried out jointly by a number of institutions in the USA and Israel in the cost-effectiveness of life-saving interventions. It was probably the most comprehensive compilation ever made of such data and covered 587 interventions in the fatal accident reduction, toxin control, and medical areas. The data indicated that reducing radiation dose is a far more expensive way of saving lives than virtually all the other life saving measures studied.
Professor Zbigniew Jaworowski, ex-Chairman of UNSCEAR, stated that: “Each human life hypthetically saved in a Western industrial society by implementation of the present radiation protection regulations is estimated to cost about $2.5 billion.” He pointed to immunisation against measles, diphtheria and pertussis entail costs of $50-99 per human life saved. Jaworowski feels that spending such huge sums of money on protecting humans from the hypothetical dangers of radiation is ‘absurd and immoral’, especially when ‘much smaller resources for the real saving of lives in poor countries are scandalously lacking.’