Review of risk assessments associated with the proposal to establish a national radioactive waste repository
Supervising Scientist Report 174
A Johnston & A Zapantis
Department of the Environment and Heritage, 2003
ISBN 0 642 24381 6
- SSR174 - Review of risk assessments associated with the proposal to establish a national radioactive waste repository (PDF - 770 KB)
On 12 February 2003, the Minister for the Environment and Heritage requested that the Supervising Scientist provide scientific and technical advice on certain aspects of a proposal to construct a National Radioactive Waste Repository (NRWR). The specific issue on which advice has been sought is the risk to the proposed repository associated with activities of the Department of Defence in the Woomera Instrumented Range. This report has been prepared in response to the Minister's request.
A complete review of all aspects of the risks assessed in the Environmental Impact Statement has not been attempted. Rather, consistent with the Minister's request, we have focused on the primary area where significant disagreement remains between the assessments by the proponent, the Department of Education, Science and Training (DEST), and by the Department of Defence, namely the risk assessment associated with Defence operations in the Woomera Instrumented Range. Our report includes the derivation of estimates of the probability that Defence operations could lead to a breach of the NRWR and a review of the radiological dose calculations relevant to such a breach. Our review of these issues identified a need for a full review of all radiological dose calculations in the EIS (Environmental Impact Statement). This review has been conducted and the results are included in this report.
We have concluded that, in the absence of any more detailed information from Defence, the probability of breaching the NRWR as a result of Defence activities is likely to be in the range 0.1% to 2% per annum. These values are higher than the probability values adopted by DEST in the EIS by factors of 25 and 500 respectively.
Our estimate of the radiation dose to members of any recovery crew following a missile strike or aircraft strike on the repository is lower than that provided in the EIS by a factor of almost ten. The consultants who derived the estimates contained in the EIS have now acknowledged this error. Our radiological risk assessment has concluded that the risk of a fatal cancer subsequently arising from recovery operations following a missile impact on the repository is probably less than 1x10-6 per annum (one chance in a million). Hence, location of the repository at Site 52a would probably satisfy requirements of the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA).
However, our assessment of non-radiological risks reaches a different conclusion. We found that the general risk assessment in the EIS was in error because it used the annual probability of breaching the repository rather than the probability of breaching the NRWR over its lifetime. If the probability estimates contained in the EIS had been used correctly, the conclusion should have been that the suitability of Site 52a is questionable.
Further, using the probability estimates derived in this review, the probability of a breach of the NRWR occurring as a result of a missile strike during the operational stage of the repository lies between 5% and 100%. We conclude that Site 52a is an unsuitable location for the NRWR. This conclusion becomes even more firm if the life of the repository is considered to include the Institutional as well as the Operational period.
The scenarios considered in the EIS for accidental human intrusion of the repository after the institutional control period have been assessed as constituting a very comprehensive range of possible or plausible scenarios. Our review has found that the radiation dose values listed in the various appendices of the EIS could not be reproduced precisely. With the exception of the dose associated with a missile strike or aircraft crash, which has already been considered above, all discrepancies are relatively small and have probably arisen from unspecified assumptions made in the EIS. The residual differences in dose estimates do not affect any conclusions on the acceptability of the repository. We have concluded that the establishment of the repository at a site other than Site 52a should not be precluded on radiological safety grounds.
However, we make the following two recommendations on radiation safety issues that should be addressed when a licence is being considered:
- If the establishment of the NRWR is approved, ARPANSA should determine appropriate waste acceptance criteria and waste conditioning requirements for high intensity gamma sources.
- If the establishment of the NRWR is approved, ARPANSA should consider requiring the integration of barriers within the waste to impede radon emanation.
The overall conclusions of this review are:
- Site 52a in the Woomera Intrumented Range is not a suitable location for establishment of the National Radioactive Waste Repository because the probability of breaching the repository by Defence Force activities is considered to be unacceptably high.
- Estimates of both short-term and very long-term radiation exposure to members of the public arising from accidental intrusion into the National Radioactive Waste Repository have demonstrated that establishment of the repository at another site would be acceptable on radiological safety grounds.