National Physical Laboratory

Measuring radioactivity in waste

NPL has developed a mock radioactive waste drum traceable to national standards so nuclear decommissioning teams can test their procedures for characterising potentially radioactive waste, providing increased confidence in how this is measured.

Nuclear drum

This work was funded by the National Measurement System (NMS).

Background

Accurate measurement of radioactivity in waste materials is a major challenge in site decommissioning. Waste on a typical site ranges widely, both in activity level and physical form, and it is usually impractical to prepare a range of standard sources which match all the samples. To deal with this, nuclear sites oftenuse modelling software to predict detector responses, although some sites prepare their own 'in-house standards'.

The overestimation of uncertainties for measurements of this type can have major cost implications. For example, where the activity level is 'borderline'; between two radioactive waste categories, companies will always err on the side of caution and this may result in material being incorrectly assigned to the higher category. If measurements were more accurate, less waste would be incorrectly assigned, saving money for both the government and the companies involved.

NPL is helping nuclear companies to address this. It can provide the standards, reference materials and support needed to ensure that measurements of the radioactivity content of waste materials are accurate and can provide tests which are independent of the nuclear industry.

Results

As part of this, NPL developed a mock radioactive waste drum traceable to national standards so nuclear decommissioning teams can test their procedures for characterising potentially radioactive waste.

The drum was sent to 16 nuclear sites across the UK for 18 measurement teams to test their ability to measure gamma emitters in 'soft waste' (e.g. tissues and plastic) at the border between Low Level Waste (LLW) and 'Exempt' waste. The test was voluntary and the drum was sent out as a 'blind' sample. The results were discussed at a follow-up workshop where any problem results were discussed with the participants.

The exercise led to some of the companies concerned re-examining their results or procedures and there was great interest in a second exercise.

Impact

This work brings added confidence to companies measuring low and intermediate levels of nuclear waste. It can help to reduce disposal costs, for example, by helping companies to correctly identify Exempt waste that would otherwise have been sent to an LLW repository at a much greater cost (typically a factor of 50 higher). The NMS underpins existing efficiency models and reassures industry, regulators and the public that radioactive waste is dealt with safely and cost effectively.

"What the inter-comparison exercises enable me to do is to demonstrate the validity of our approach to regulators and the public as well as to some of our more discerning clients," says Ian Pearman, Senior Radiation Protection Adviser at Nuvia Ltd. "It has also enabled me to meet with other participants and develop good working relationships. All in all these inter-comparisons have enabled us to develop our 'Gamma Spectrometry Product' and has made winning new business easier."

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Last Updated: 17 Nov 2014
Created: 8 Dec 2010

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