DOSE IMPLICATIONS OF VERY LOW-LEVEL RADIOACTIVE WASTE DISPOSAL
UKRSR09
November 2007

EXECUTIVE SUMMARY

The Scottish Environment Protection Agency (SEPA), the Environment and Heritage Service of Northern Ireland (EHS), and the Environment Agency for England and Wales (EA) are responsible for the regulation of radioactive waste disposal in the UK.  

In conjunction with the Environment Agencies, and with the support of the Scottish Government and the Department for Environment Food and Rural Affairs (Defra), the Scotland and Northern Ireland Forum for Environmental Research (SNIFFER) commissioned this research project to review the practice of disposing small amounts of very low-level radioactive waste (VLLW) with other wastes.  

The objective of the project was to establish whether current practices of VLLW management and disposal remain acceptable, and to provide guidance on any necessary revisions to the conditions of authorisations governing VLLW disposal.  

The project has identified the types and amounts of VLLW being produced, examined trends in waste management, and has assessed the potential impacts of exposure to VLLW during waste management and disposal.

A survey has been made focusing on non-nuclear industry organisations in the UK that hold VLLW disposal authorisations.  This survey found that in 2006, ~680 organisations, including hospitals, universities and pharmaceutical and biotechnology companies, were authorised to dispose of VLLW in the UK.  Of these, 562 were located in England and Wales, 100 in Scotland, and 24 in Northern-Ireland.

The project identified two main types of VLLW: primary VLLW, which is produced directly by, for example, universities and hospitals, and secondary VLLW, which is produced as a result of incinerating radioactive wastes.

The survey identified that approximately 3,600 tonnes of primary VLLW was produced by non nuclear industry organisations in 2005.  To put this into context, the mass of primary VLLW from non nuclear organisations was ~0.01% of the total annual mass of municipal waste produced in 2005.  The total activity of the primary VLLW produced by the non-nuclear industry in 2005 is estimated to have been <17.5 GBq.  The vast majority (~15 GBq) of this activity was short lived.  14C was by far the most abundant long-lived radionuclide and accounted for ~98% of the ~2.5 GBq of radionuclides with half-lives greater than 30 years.
  
Information from the primary VLLW producers suggests that in 2005, ~52% (by mass) was incinerated and ~48% sent for disposal in landfill.  In reality, these percentages will have been lower than this because an uncertain proportion of the wastes will have been recycled or composted.  Even so, the relative amount of primary VLLW incinerated is likely to have been greater than for municipal waste because much of the primary VLLW was treated as clinical waste.
 
The actual percentage of primary VLLW recycled or composted has not been quantified, but is thought to be significantly less than the percentage of municipal waste that is currently recycled or composted (i.e., <24%).
 
Secondary VLLW arises in residues of waste incineration arising from air pollution controls (lime, bicarbonate and sludge) and ash.  The radionuclide content arises from small amounts of LLW and VLLW in the general wastes incinerated.  Approximately 20,000 tonnes of secondary VLLW was produced in 2005.  Relatively little detailed information is available on the radionuclide content of secondary VLLW.  Secondary VLLW contains radionuclides that are not volatile and therefore has low levels of volatile radionuclides such as 14C, tritium, 35S and iodine, because these radionuclides are mainly discharged to the atmosphere in the incinerator flue gases despite lime scrubbers.  The radionuclide content of secondary VLLW also differs from that of primary VLLW because secondary VLLW inherits radionuclides from solid radioactive wastes with activities initially above the upper limit for VLLW.  For example, some secondary VLLW contains a relatively higher proportion of 90Sr than primary VLLW of average composition.

The sludge and the majority of the ash from the incineration process are sent to landfill.  Ash wastes may be considered to be hazardous.  A proportion of the ash from municipal waste incinerators may be used in road and building construction.  Some of the lime and bicarbonate may be used in the chemicals industry, and some sent to landfill.

Since the last review of VLLW disposal was conducted about 10 years ago, there have been several main changes in conventional waste management practice, including:
  1. The introduction of source segregation of waste streams.
  2. An increase in the proportion of waste being recycled.  
  3. Development of new waste recovery technologies.
  4. An increase in the proportion of waste composted.
  5. A decrease in the proportion of waste landfilled.
Over the next 10 years, these changes and trends are expected to continue and intensify, and the amounts of controlled waste and VLLW from non-nuclear industries following the various disposal/recovery routes may change quite significantly.  In addition, there is expected to be a shift away from conventional incinerators, in favour of incineration at energy-from-waste facilities, including those that use refuse-derived fuel pellets.  Results from the survey of non-nuclear industry VLLW production suggest that there may be a slight net increase in the quantities of primary VLLW over the coming years.  Increased waste incineration would lead to increased production of secondary VLLW.  It is expected that there will be fewer landfills that can take hazardous wastes.  Secondary VLLW in the form of ash may therefore be disposed of to relatively few landfills.

Doses from the disposal of primary and secondary VLLW were estimated.  Doses from the disposal of primary VLLW from the non-nuclear industry are low and fall below 20 μSv/yr.  The annual arisings of primary VLLW (~3,600 tonnes, with an overall specific activity of 400 kBq per 0.1 m3) could be consigned to a single landfill site for 15 - 20 years without exceeding the 20 μSv/yr radiological dose criterion.  

The estimated annual arisings of primary VLLW could be incinerated at one incinerator and give annual doses of less than 20 ÁSv.  The most significant radionuclide in terms of radiological impact and quantity is 14C because of its long half-life.

Doses to waste workers from sorting of primary wastes that may contain VLLW are also low and below 20 ÁSv/yr.

A single landfill could take ~3,000 tonnes of secondary VLLW at the 400 kBq per 0.1m3 level without calculated doses exceeding 20 ÁSv/yr.

On a case by case basis, some VLLW authorisations in England and Wales allow disposal of alpha emitting radionuclides - at lower levels than the standard conditions.  The study identified that more than 1 MBq of 241Am, 226Ra, and 228Ra were disposed of in primary VLLW in 2005.  Doses from the alpha emitters were generally low; however, doses from items containing 226Ra handled by waste sorters were close to 20 ÁSv/yr.

A dose of 20 μSv/yr can be broadly equated to an annual risk of death of about one in a million.  Government Policy is that where exposures are calculated to be less that 20 μSv/yr, the Environment Agencies should not seek to secure further reductions in the exposure of members of the public, provided they are satisfied that the operator is using the Best Practicable Means to limit discharges.

We conclude that current practices of management and disposal for VLLW from the non nuclear industry remain acceptable, and that the increasing occurrence of waste segregation and recycling does not appear to be significant in terms of radiological safety, taking into account current waste disposal practises including waste segregation and sorting.  However doses from some alpha emitters in individual waste items handled during sorting come close to 20 μSv/yr.

The study however recommends as follows:  
  1. The Environment Agencies use clearer, simpler language in Certificates of Authorisation, and give clear guidance on how authorisations allowing VLLW disposal should be interpreted (e.g., in relation to current waste management practices).  
  2. Because of the low radiological impact, the current arrangements allow VLLW to be disposed of with a minimum of regulatory and administration burden.  There is currently no requirement to report to the Environment Agencies the quantities disposed of or to track the fate of the wastes.  This study confirms that the radiological impact of the disposal of VLLW remains low and that, therefore, there is no need on radiological protection grounds to significantly alter these low burden arrangements.
  3. 14C is the most significant radionuclide in primary VLLW in terms of dose.  However, the low overall doses from VLLW means that there are no radiological protection grounds to require a change to the current relaxation in the limit for 14C adopted by the Environment Agency and now in Government Policy for LLW.
  4. Doses are low from incineration of primary VLLW.  Therefore, there are no radiological protection grounds for suggesting incineration is not appropriate for wastes containing VLLW.
  5. There are large quantities of secondary VLLW, in particular ash, that may have to be consigned to a limited number of hazardous landfill sites.  These volumes may increase in future whilst the number of hazardous landfill sites that can accept ash wastes may not increase.  It may therefore be appropriate to keep generation and disposal of secondary VLLW under review.
  6. In ten years time a review similar to this current review would be advisable to check the validity of the current findings in the light of the expected changes in waste management practices that will have occurred.
The study also notes that the Environment Agencies substitute fuel protocol currently precludes the inclusion of radioactive waste.  The low administration burden associated with VLLW disposal does not require the tracking of VLLW.  Therefore, it will not be possible to be confident that VLLW is not being inadvertently included in wastes used as substitute fuel.  However, the radiological consequences of VLLW being combusted in substitute fuels will be very small.

There may be advantages in requiring the returning of records of VLLW disposal to the Environment Agencies in future, in particular to prevent inclusion in substitute fuel and to allow future radiological assessments.  However, these benefits would have to be weighed against the costs of increasing the administration burden associated with a low impact disposal route.

Limitations to the study

The study focused on the production of primary VLLW from the non-nuclear industry.  Cognisance was given to the production of VLLW by the nuclear industry, both operational and decommissioning.  However, it was identified at an early stage that the volumes and fingerprints of these wastes were significantly different and could not be covered by this project.  Likewise, VLLW production by the oil and gas industry was not considered by the project.

The disposal of VLLW from the non-nuclear industry has low regulatory and administration burdens for users.  This impacted on the information that could be obtained from users who have not been required to keep records on their disposal of VLLW.  Additionally, the response rate to the questionnaires was such that only limited interpretation of the waste produced in terms of activity and mass by sector and geographic region was possible.

Key words: Dose, Exposure, Incineration, Landfill, Very Low-Level Radioactive Waste (VLLW), Controlled Waste, Waste Management, Waste Disposal

Copies of this report are available from the Foundation, in electronic format on CDRom at ú20.00 + VAT or hard copy at ú35.00, less 20% to FWR members.

N.B. The report is available for download from the SNIFFER Website