Waste Characterization During Decommissioning in a Swedish Uranium Facility - 'Good Enough is Great' - 23317

This paper describes the lessons learned from setting up a characterization procedure for loose items, equipment and waste during decommissioning of a shutdown uranium facility. Effective routines and a 'good enough' approach were needed to deal with the radiometric challenges that arose from clearing out the buildings. The Ranstad site in Sweden was used for uranium extraction from ore and recycling of uranium from filters used in the nuclear fuel industry. The composition of the radioactive contamination in the waste, i.e., the fingerprint, was a mixture of unbroken and broken decay chains of uranium nuclides and a varying grade of U-235 enrichment up to 3.5 %. This, in combination with the lack of historic background information for individual items, made the waste characterization challenging. To meet the conditional clearance for landfill deposition of the waste, a measurement procedure was created to get an effective routine for the characterization. Heterogeneity in both material composition and radioactivity contamination were quantified to be the largest sources of uncertainties in the determination of the radioactivity content. Sorting and packaging instructions were then implemented not only due to logistic reasons but also to reduce the measurement uncertainties. To optimize the procedure, it's important to define what is needed to be achieved in the characterization, 'What is good enough to fulfill the purpose?'. For quick and easy emptying of loose items from the buildings during decommissioning, the containers are preferably big, but to have good precision in the measurements for radiological characterization, the measured volume is preferable small. This requires an optimization of the characterization that is acceptable to fulfill the requirements for the conditional clearance. Gamma spectrometry and specific nuclide relationships based on gamma measurement results, gave the basis for the characterization of enrichment, amount of uranium and the calculation of the sum for the individual nuclides contribution to the free release level. The measurement time was optimized to give a high throughput of objects, but long enough to give a reliable result from a counting statistics perspective. Many of the nuclides in the decay chains from uranium are difficult to measure due to poor gamma yield and low gamma energies. Nonetheless, information can be obtained from studying the decay chains and by using a conservative approach in the characterization the conditional free release limits can be met. The reported activity must not be true but conservative. The paper will discuss lessons learned from solving a radiometric and logistic problem in a decommissioning project. Even though the special nuclide fingerprint for this project required special solutions for determination of uranium contents, the general ideas can be adopted to other projects. (authors)