ABSTRACT

In situ gamma spectroscopy has been successfully used for decommissioning surveys and environmental remediation surveys for many years. With the recent advancements in technology of very portable and reliable Ge detectors, high quality digital MCAs, and mathematical efficiency calibration algorithms that are fast and accurate, this technology is now available to operating nuclear facilities.

In situ gamma spectroscopy offers advantages over the traditional method of extracting a representative sample, transporting it to a laboratory, and then preparing the sample for counting.

Getting the sample is the major problem. Some samples are physically difficult to obtain (subsurface soil, concrete, activated materials, material inside pipes or tanks, etc.). Some samples are physically dangerous to take (very radioactive items like resin beads, concrete cores or steel coupons, pressurized gases, hot water, corrosive or toxic items). Since In situ spectroscopy is a non-contact process, and since the sample doesn’t need to be physically extracted, these problems are greatly minimized. And, for high activity samples, the measurement time will be very short, much less than the sample extraction time, therefore the dose should be lower.

Some contamination situations are difficult because it is hard to find a truly representative sample for lab analysis. Because In situ spectroscopy measures the entire item, or a large portion of it, small local non-homogeneities are less of a problem. Since transporting the sample is not needed, and since preparing the sample in the lab is not needed, the costs, doses, risks of injury, and time associated with these tasks are eliminated.

In situ spectroscopy can give near-instantaneous results, and therefore allow prompt decisions to be made while the equipment is in the field. Frequently, new or unusual tasks have too much personnel protection required based upon a lack of knowledge of what might be encountered. This may cause the work to take longer, and increase the dose, rather than reduce it. The availability of nuclide-specific quantitative activity, rather than just gross count or dose-rate information can allow better decisions to be made by the plant HP to define the optimum amount of personnel protection for the job.