BNFL Instruments, British Nuclear Fuels plc. Gamma Imaging as a Complementary Technique to Health Physics Monitoring Karl Hughes BNFL Instruments, British Nuclear Fuels plc.

The Sellafield Site, UK

The Sellafield Site, UK Located in North West England. Home to most aspects of the nuclear fuel cycle :- Nuclear Reactors (Calder Hall, now shut-down) Fuel Storage Ponds Reprocessing Facilities Fuel Manufacture (MOX) Waste Processing and Waste Storage Facilities Decommissioning of Redundant Facilities

Health Physics Surveys Area gamma dose rate surveys carried out for two main reasons :- To map dose rates to calculate the dose uptake associated with a task for ALARA planning To help develop strategy for reducing dose rates find ‘hot spots’ plan removal, decontamination or shielding May be carried out remotely Speeds up overall task if good information is produced

Gamma Ray Imaging 10 years of use at Sellafield mainly in decommissioning projects : shielded cells, gloveboxes, crated wastes also in operational plants : blockages, spillages Originally designed as a ‘hot spot’ detector Developments have looked at producing dose maps from imaging devices

Gamma Ray Imager : RadScan®: 800

Dose Mapping Using Gamma Imaging For “simple” geometries gamma imaging has been used to produce accurate dose maps Showed the technique works. Benchmarked. The maps have been of use in job planning Generally not used for job dose planning if the dose rates require gamma imaging, manual work is not likely The main benefit has been from the directional nature of the technology identify extent of contamination used to plan strategy

Dose Mapping Using Gamma Imaging In complex geometries the production of dose maps is difficult can’t always see into shine paths can’t always measure all sources; they may already be partially shielded need to combine data from more than one scan need to accurately align measured data with a model Most real-life geometries are complex Dose mapping from gamma imaging is not likely to replace the conventional ‘dose rate survey’

Dose Mapping Using Gamma Imaging

Dose Mapping Using Gamma Imaging

Dose Mapping Using Gamma Imaging

Dose Mapping Using Gamma Imaging

Dose Mapping Using Gamma Imaging Care is needed when producing dose maps from gamma imaging : there are many pitfalls ! Gamma imaging is very useful for identifying the origins of dose Spectroscopy can help interpret the scene scatter is present in the vicinity of shine paths can indicate whether looking at a scatter body or unshielded contamination

Lessons Learned Use gamma imaging early when dose rates are high and shielding is needed helps get shielding right first time Use gamma imaging with HP data directional nature of gamma imaging says where the dose is coming from helps develop the strategy for reduction of dose rates Better, earlier characterisation helps ALARA – reduced time, reduced dose (and reduced cost)

Lessons Learned EDUCATION and UNDERSTANDING There is frequent misunderstanding between “dose”, “count” and “activity”. Confusion between “overlays” and “dose maps” In particular there is a belief that gamma imaging can measure directly the dose “over there” from the point of deployment

Lessons Learned Gamma imaging helps implement ALARA identifying origins of dose rates mapping the extent of contamination remote deployment; little operator dose uptake monitors large areas automatically and systematically Provides good quality data for determining strategy man access, shielding, decontamination, clean-up often reduces the time taken to accomplish a task where dose rates are high permanent, reproducible, visual record

Conclusions Gamma ray imaging is a complementary technique to health physics gamma dose rate monitoring surveys The two in combination are a powerful means of characterising a radioactive environment