Classification of radioactive waste involves placing the material within a category depending on its radioactive and, in some case, thermal properties. The two broad waste categories are higher activity waste (HAW) and low activity waste (LAW).
HAW includes High Level Waste (HLW) and Intermediate Level Waste (ILW). HAW is classified by having above 4 gigabecquerel (GBq) per tonne of alpha activity, or 12 GBq per tonne of beta/gamma activity. HLW differs from ILW by producing large amounts of heat due to its activity.
LAW includes Low Level Waste (LLW) and Very Low Level Waste (VLLW). LLW would be categorised as such if it is below the activity boundaries stated above, and VLLW is a subcategory of this which has a low enough activity to be disposed of within landfill.
There are some instances of waste that falls within boundaries between waste categories, and these should be assessed on a case by case basis in line with the waste management hierarchy and principles.
The key activities that take place within this stage include waste characterisation, defining and managing the inventory, developing appropriate safety cases and waste management planning.
Case study
Waste Characterisation – plutonium contaminated materials (PCM) and multi-element bottles (MEBs)
Successful application of the waste hierarchy – reassigning ILW correctly as LLW
PCM drums
Previously, all waste from plutonium contaminated materials (PCM)-contaminated areas in Sellafield had been classified as PCM. However, the introduction of the engineered drum store (EDS) assaying facility (known as the Waste Treatment Complex – WTC) has allowed items such as gloves and other PPE to be correctly classified as Low-Level Waste. This means that these drums containing LLW can be appropriately transferred to the LLW Repository site via the waste monitoring and compaction plant (WAMAC). This frees up space for PCM in stores and ensures those facilities are used for the most appropriate waste types. So far, more than 800 200 litre drums have been assayed as LLW, with more than 600 sent to WAMAC. It is estimated that a total of 4,800 drums (based on 800 drums per year for six years from 2020) will be assayed as LLW and processed via this route instead of being destined for a Geological Disposal Facility (GDF).
Multi-element bottles
Multi-Element Bottles (MEBs) originating as Higher Activity Waste (HAW) at Sellafield have been decay-stored in the Oxide Fuel Storage Pond before transfer to the MEB Intermediate Store (MEBIS) at Sellafield. Future opportunities being explored for MEBIS use centre around metal being extracted and recycled from LLW where previously this was not possible, with the waste materials being consigned to the LLW Repository site (rather than taking up ILW space in the GDF). A similar, decay-storage approach is being considered for use with Advanced Gas-cooled Reactor graphite containers, pond furniture from first generation Magnox storage pond (FGMSP) and pile fuel storage pond (PFSP) and other borderline ILW from legacy ponds.