Amentum’s radiation protection specialists supplied the crucial know-how for a clean-up operation on Scotland’s most radioactive beach.
Radioactive residues were first detected on the foreshore of Dalgety Bay, near Dunfermline, in 1990, not far from a former airfield where radium-coated ‘glow in the dark’ aircraft dials and instruments were incinerated and landfilled at the end of the second world war.
The beach was safe for walking and sailing but the residues presented a potential health hazard if material was disturbed or removed. The contaminated area was popular with the public and close to housing and a local sailing club, so the issue had received a high media profile and significant scrutiny from the Scottish Environmental Protection Agency.
The Amentum team developed instrumentation to detect and segregate radium sources of 10 kilobecquerels (kBq) with a 95% confidence interval, giving assurance to our clients and the regulator that our readings can be relied upon.
Our technology was based on the use of three-inch sodium iodide detectors placed over spoil — waste material brought up during an excavation or a dredging or mining operation — from the beach. The team modelled the detector response to sources buried in sand at a series of distances from the detector. They then developed an Excel/Visual Basic tool to control the detector system and interrogate gamma spectrometry data to establish whether material under the detector contained radium.
The system used four detectors, each covering a 1.7 ft² (1,600 cm²) area of spoil up to 5.9 ins (15 cm) deep. It was designed to examine up to 1765.7 ft³ (50 m³) of material within an eight-hour working day. Although the system was able to achieve this, the excavation process struggled to maintain a steady stream of material. This problem was compounded by that fact that more sources were found than early characterization of the site had suggested, slowing throughput.
To help our client meet its program targets, we doubled the capacity of the detector system, adding four additional sodium iodide probes. The eight-detector system successfully got the work back on track, with more than 100 m³ of material examined on some days.
Once a particle was detected, it was located and removed by hand using a two-inch sodium iodide probe. The system was designed to detect a 10 kBq particle about 30 cm away from the detector under 15 cm of spoil. At a more favorable position, particles of less than 0.1 kBq were detected. This has enabled Amentum to significantly reduce waste volumes – and also disposal costs – because the system enabled us to extract very small radium particles without having to remove clean spoil from the site.
Jen Barnes, Radiation Protection Advisor and radiometrics lead, said: “We were selected to carry out this work because we have a multidisciplinary team capable of handling all technical aspects of radiation protection and remediation.
“We were able to call on a very diverse mix of skills including radiometrics, radiation protection and also physics modelling capability, where we used Monte Carlo techniques to predict what a detector would see when it was looking at material in a certain geometry. We have operatives with years of site experience who know how to deal with problems safely and all the elements of this multi-disciplinary team are available to us in-house.”
“We were able to call on a very diverse mix of skills including radiometrics, radiation protection and also physics modeling capability, where we used Monte Carlo techniques to predict what a detector would see when it was looking at material in a certain geometry. We have operatives with years of site experience who know how to deal with problems safely and all the elements of this multi-disciplinary team are available to us in-house.”
