Material recycling – what’s the NORM to be?30 June 1998
The recycling and reuse of material arising from the decommissioning of nuclear facilities can significantly reduce the volumes to be disposed of as radioactive waste. Internationally accepted release levels for such material are necessary to be able to do this. This issue dovetails with the NORM question – what to do about “naturally occurring radioactive material” (NORM) which becomes concentrated in various non-nuclear industrial processes and which can have the same activity levels as the potentially reusable material from decommissioning, but occurs in much larger quantities.
The decommissioning of nuclear facilities will give rise to large amounts of redundant material over a relatively short period. One characteristic of this material is that much of it is metal, most of which is surface contaminated. The conditioning and disposal of these large volumes of materials represent one of the most substantial cost fractions of decommissioning projects. Consequently, the minimisation of the volumes that have to be disposed of is a high priority goal. The recycling of such material (or its reuse or disposal) without radiological restrictions has been identified, by a task group of the OECD Nuclear Energy Agency’s Co-operative Programme on Decommissioning, as a significant means of achieving this aim. Moreover, recycling has its beneficial aspects, such as conservation of natural resources and protecting the environment. However, the absence of consistent, internationally accepted criteria to regulate the release of recyclable material significantly restricts recycling and reuse as material management practices.
CONCEPTS AND DISCUSSIONS
The international discussions on release of materials for reuse or recycling are taking place mainly through:
• The International Commission on Radiological Protection (ICRP), which has supplied the basic recommendations regarding principles for protection from ionising radiation.
• The International Atomic Energy Agency (IAEA), which has translated these general principles into recommendations on nuclide specific release levels.
• The European Commission (EC), which is preparing its own recommendations for countries within the European Union.
• The OECD/NEA’s Task Group on Recycling and Reuse which has analysed the international proposals from the point of view of the potential implementers of the recommendations and criteria that are being drawn up by the IAEA and the EC.
In 1988, the IAEA and the Nuclear Energy Agency (NEA), in co-operation, issued Safety Series No 89 recommending a policy for exemptions from the basic safety system of notification, registration and licensing that form the basis of regulatory control. Safety Series No 89 suggests:
• A maximum individual dose/practice of about 10 µSv/year and
• A maximum collective dose/practice of 1 man-Sievert/year to determine whether the material can be cleared from regulatory control or other options should be examined.
A revised International basic safety standards for protection against ionising radiation and the safety of radiation sources (BSS) was published in 1994. It was based on the recommendations of the ICRP and jointly sponsored by the Food and Agricultural Organisation (FAO), the IAEA, the International Labour Organisation (ILO), the OECD/NEA, the World Health Organisation (WHO) and the Pan American Health Organisation (PAHO). The International BSS gives a list of nuclide specific exemption values (both quantities and concentrations).
In May 1996 the EC issued a Council Directive laying down its BSS for radiation protection, with nuclide specific exemption values very similar to those in the International BSS. However, the EC BSS makes a difference between “practices” covering processes utilising the radioactive, fissile or fertile properties of natural or artificial radionuclides (ie the nuclear industry) and “work activities” where radioactivity is incidental, but can lead to significant exposure of workers or the public. The EC BSS list of exemption values covers only practices.
In January 1996, the IAEA published recommended nuclide specific clearance levels, for solid materials in TECDOC 855, which was issued on an interim basis and will be revised after about three years to react to comments received and to experience gained in its implementation.
The EC has also published, very recently, recommended clearance levels for steel, aluminium, copper and alloys of these metals. While the IAEA TECDOC 855 treated only unconditional clearance, the EC approach provides two options for releasing material:
• Direct release based only on surface contamination.
• Melting at a commercial foundry followed by recycle and reuse. Mass specific and surface specific levels are provided.
In its analysis of the international recommendations published by the IAEA and the EC, the NEA Task Group has noted that both organisations consider only the radiological risks associated with the release of material. The exclusion of other considerations means, for instance, that valuable recyclable materials like stainless steel and inconel (75% nickel) and non-recyclable burnable trash are treated in the same manner. The NEA Task Group, studying the recycling of scrap metals, viewed recycling in a broader context, evaluating both the radiological risks with recycling as well as the non-radiological risks associated with the replacement of the disposed material.
The NEA total health risk approach has later received support at a number of international meetings:
• One of the observations and recommendations of the First European ALARA Network Workshop was “the need to take into account a total risk approach with various trade-offs such as radiological and conventional risks ...”
• The Belgian waste management agency – ONDRAF/NIRAS – in a presentation at the SFEN Conference on Decommissioning (Avignon, March 1998), interprets one of the IAEA Safety Principles for Radioactive Waste Management as follows:
“... the ethical principle is the conservation of raw materials for future generations ... the analysis on the risks and the inconvenience of a practice needs to take the whole chain of the practice into account. That means, for example, that the risk attached to recycled materials needs to be compared to the risk of the extraction and the transformation of new materials.”
Specifically, the Task Group compared the recycling of 50 000 t of scrap metal, utilised so that the individual radiological exposure was limited to 10 µSv/y, to the disposal and replacement of the same amount of material in the USA. The results of this comparison are given in the table on previous page, and show that:
• The radiological risks associated with both alternatives are very small in comparison with the non-radiological industrial safety risks.
• These non-radiological risks are much lower for recycling because product manufacture starts from scrap metal. The risks associated with mining and refining of metal are avoided.
EMERGENCE OF THE NORM ISSUE
Radiation protection and the management of radioactive material have hitherto been concerned mainly with artificial nuclides arising within the nuclear fuel cycle. In the last few years there has been an increasing awareness of naturally occurring radioactive material and the enhancement of its concentration in various non-nuclear industrial (NNI) processes. This technologically enhanced NORM can be of the same activity levels as low level waste and is very similar to the candidate material for exemption and clearance in the nuclear industry (NI), but occurs in quantities that are huge in comparison, as is illustrated in the table above, which shows the volumes and the radioactivity in some of the technologically enhanced NORM arising in the United States.
The current management of NORM materials is very inconsistent with that of similar materials arising in the nuclear industry. Some examples are discussed below:
• The currently operative EC Directive 84/467/Euratom of 1984 exempts (from reporting and prior authorisation) activity concentrations lower than 100 Bq/g or, for “solid natural material,” 500 Bq/g. This rule is interpreted differently in different countries:
• In the Netherlands, NORM wastes from the oil and gas industry are exempted on the 100 Bq/g basis, including the short-lived decay products assumed to be in equilibrium with the long-lived parent nuclides. Scales from the decontamination of “tubulars,” under this activity level, are considered to be not radioactive, but chemical waste, and is returned to the customer for disposal under his responsibility.
• In Germany, the same type of material is exempted at the 500 Bq/g level, without taking into account the short-lived decay nuclides.
• At off-shore installations in several countries, the scales from tubulars (with activity concentrations of up to several hundreds of Bq/g) are ground into a powder (“macerated”), mixed with seawater and discharged into the sea.
• Concrete from the demolition of certain buildings at the MZFR Reactor Decomm-issioning Project, Karlsruhe, Germany, was released at the level of 0.5 Bq/g (b/g nuclides) and 0.05 Bq/g (a nuclides). Some of this concrete was used for road surfacing in the neighbourhood of the Forschung-szentrum, Karlsruhe.
Recently a German company was authorised to use 100 t/y of the slag, arising from the melting of scrap from the oil and gas industry, also as road building material, provided that the Ra-226 activity concentration in the slag was below 65 Bq/g and the slag was diluted by a factor of at least four with other material. This means effectively a release level of 16 Bq/g.
The table of exemption values in the recently issued EC BSS covers only practices. The exemption values for work activities are not explicitly given. However, in various reports published by the EC, there are statements that seem to imply an inconsistent double standard and that other criteria could be considered for the exemption/clearance of material from NNI. Some examples:
• “The same radiological criteria as for exemption (in NI) cannot be applied.”
• “The concept of triviality of individual doses does not seem to be relevant.”
• “Table A of Annex 1 (EC BSS) ... is not meant to apply to natural radioactive substances arising in bulk from oil and gas production.”
The papers and discussions at an Amsterdam meeting in 1997 on radioactivity in the non-nuclear industries also reflected these views.
One major stumbling block for the rational and consistent radiological regulation of technologically enhanced NORM is represented by the current international recommendations for exemption and clearance for material in the nuclear industry.
Both exemption and clearance values are derived from the same SS 89 criteria for individual and collective doses. The higher levels for exemption are explained by the moderate quantities considered, while studies on clearance has involved much larger quantities of material (typically 10 000 t of scrap metal in Europe). The currently proposed clearance levels are already at (or below, according to some experts) the limit at which release measurements can be made on large quantities of candidate material at reasonable costs.
If radioactivity is to be regulated in a consistent manner, it will be practically impossible to relate release levels to quantities, when the much larger volumes of radioactive material arising in the non-nuclear industries will be brought under regulation in the near future. The problem can be illustrated in the table.
A possible way out of this dilemma could be a proposal made at an IAEA meeting in May 1997 on Exclusion, Exemption and Clearance. The proposal was to “collapse” the values for exemption and clearance into one set, based on the BSS exemption levels. It found a lot of support at the meeting. Some of the reasons are the following:
• The values for clearance and exemption for the various nuclides “are always within a factor of 100 of each other, usually much closer and sometimes the same.” For nuclides of most significance to the nuclear industry, such as Co-60, Cs-137 and Ra-226, the factor is 10.
• That, in any case, the IAEA TECDOC 855 groups the nuclides in decades because “uncertainties ... allow ... only categorisation by order of magnitude.”
• The BSS exemption levels are to be adopted for transport regulation.
• Legal aspects of trans-frontier movement: strictly speaking, the BSS requires reporting only if exemption levels are exceeded.
• The rapporteur on the session on “Implementer’s perspectives” states that “Few people, except experts, understand the difference between exemption and clearance. Having two sets of values would only confuse the public.” Even at this specialists’ meeting, the rapporteur pointed out that it was “apparent from the presentations and subsequent discussions that there remains confusion over the concepts exclusion, exemption and clearance.....”
• In the overall summary of the meeting, it is suggested that “another use of such a (single) set of values could be in the context of the Waste Safety Convention where, at some future time, an international definition of radioactive material is likely to be needed.”
• This “collapsed” list could also be used for exemption/clearance in the non-nuclear industries.
Before the recycling and reuse of material arising from the decommissioning of nuclear facilities can be in wide use, internationally accepted radioactivity release levels are necessary. In the meantime, various national and international bodies have issued interim or draft recommendations on exemption and clearance levels. These have been discussed at a number of fora during the last few years. Recent discussions have also covered the management of radioactivity in “non-nuclear” industries, where naturally occurring radioactivity is “technologically” enhanced to levels, at which aspects of radiological protection to workers and the public would have to be considered.
These discussions indicate that:
• There is a well-motivated case put forward by decommissioners for the adoption of a single set of values for both exemption and clearance, eg the exemption levels specified in the Basic Safety Standards.
• There should be a perceivable consistency in the regulatory treatment of radioactivity in the nuclear and non-nuclear industries. Any other approach would be difficult to explain and justify from the radiation protection point of view.
|There are a number of related terms regarding the release and recycling of low level contaminated material which are often confused. The following are the definitions: • Exclusion. Exclusion covers activity sources not amenable to control, such as K-40 in the human body, cosmic radiation, etc. • Exemption. The term exemption had earlier been used to denote all radioactive material placed outside regulatory control because of the low risk they give rise to and because control would be a waste of resources. Later this term has been restricted to cover radioactive sources which never enter the regulatory regime, typically small sources such as tracers used in research, calibration tracers and some consumer products containing small sources or low levels of activity per unit mass. • Clearance. Clearance is used to denote material that has been released from regulatory control. Clearance can either be unconditional or conditional.|