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THE ASSESSMENT PROCESS OF WASTE PACKAGES FOR DISPOSAL AT GDF

Author: Rita Vasconcelos, Lead Consultant

Since I started working for NSG, I have been involved in the development of a number of Letters of Compliance (LoC) submissions, and this quickly became one of my favourite subjects to work on.

You need to develop an LoC submission when you are considering disposing of nuclear waste into a future Geological Disposal Facility (GDF). Essentially, the LoC process is a way for Nuclear Waste Services (NWS)—the entity responsible for delivering the GDF—to ensure the waste packages will comply with the requirements for disposal in a GDF. One important point is that there isn’t yet a GDF, so defining the requirements for disposal at one can be challenging… but more on that later!

LoC Submission Process

An LoC submission is a collection of documents generated by, or on behalf of, a nuclear waste packager. The aim of an LoC is to detail all the information relevant to a waste packaging proposal—i.e., how a specific nuclear waste stream is going to be packaged for disposal at a future GDF. Some of the topics that an LoC submission needs to cover include:

• the nature and quantity of the waste (including radionuclide inventory),
• the proposed packaging process,
• waste container design,
• wasteform properties,
• waste package characteristics and evolution, and
• criticality safety.

There are different stages of an LoC submission process, based on the maturity of the packaging proposal:

Conceptual stage: focuses on the general feasibility of the packaging proposal and whether it could meet NWS requirements for GDF disposal. This stage should be completed before significant design or infrastructure development and helps inform any trials or development work needed to support the proposal.

Interim stage: provides evidence that the packaging proposal will be compliant with NWS requirements for GDF disposal. This is typically much more detailed than the conceptual stage and is supported by a robust body of evidence before formal engineering development of a new facility begins.

Final stage: focuses on the practical side of producing the waste packages in a facility ready to be commissioned. It confirms that the facility will achieve what was planned and that the waste packages produced will comply with NWS requirements.

In the early days of waste packaging, this process followed a clear step-through, as new waste streams and packaging facilities were being designed for the first time (e.g., the Magnox Encapsulation Plant at Sellafield). In recent years, however, the process has become more flexible, as waste producers seek to maximise the use of existing assets by processing previously unconsidered waste streams.

This means that a packaging proposal is no longer always “brand new.” Instead, it often involves using an existing process with a high degree of established acceptability, but with a new waste stream that it was not originally designed for. In such cases, the operation of the packaging plant may already be well established at a “final stage” level, requiring limited further assessment by NWS, while aspects of the new waste stream may only be understood at an “interim stage,” requiring more detailed assessment.

What an LoC submission looks like today depends on how similar the packaging proposal is to existing processes, whether a facility is already in operation, and how different the proposed new waste stream is.

Once LoC submission documentation has been provided to NWS, they will assess it through a process known as Disposability Assessment. The outcome of this assessment may include areas of concern, where more information or clarification is needed before NWS can endorse the packaging proposal.

Real-Life Impact

Although there isn’t a GDF yet, the LoC process provides a way to accelerate the retrieval and packaging of high-activity wastes currently in hazardous facilities.

NSG has supported several waste producers in developing LoC submissions. The submission of an LoC, followed by NWS endorsement, has led to the acceleration of retrieval and packaging of dangerous wastes in high-hazard nuclear facilities. Many of these facilities are quite old, and the wastes within them are in danger of not being kept in safe and appropriate conditions; therefore, they require urgent decommissioning.

By developing a packaging strategy for these wastes and securing acknowledgement from NWS that the packages will be suitable for disposal at a GDF, decommissioning work can begin. The packaged waste can then be stored under appropriate conditions until a GDF becomes available.

In addition, developing LoC submissions has led to innovative approaches to waste packaging that challenge conventional methods. These have provided benefits to waste producers, such as reducing overall waste volume, accelerating retrieval and packaging, and lowering costs. Successful NWS endorsement of such innovative approaches has opened opportunities for other wastes across the UK to be packaged and disposed of in similar ways.

Although a GDF is not yet available, completing the LoC process has already enabled the safe retrieval, packaging, and storage of dangerous wastes. This has accelerated decommissioning of several hazardous facilities in the UK and reduced the risks associated with leaving wastes in their original locations.

Navigating Uncertainties

As I mentioned earlier, there isn’t yet a GDF. NWS is still in the process of selecting a site, and the final design has not been fully defined. Setting specific requirements for something that doesn’t yet exist brings challenges, and some assumptions must be made. For example, requirements may vary depending on the geology of the chosen site.

Some requirements are well defined and will not change with location, but a small number will depend on the final GDF design. For those, assumptions must be made. This requires open discussions with NWS to ensure the right level of evidence is used during the LoC submission process—not overly conservative, but still robust. NSG supports waste producers in engaging early and continuously with NWS throughout the process.

The LoC submission is complex and carries uncertainties because a GDF is not yet available. However, it has proven to be an effective way of accelerating the decommissioning of some of the UK’s most hazardous facilities by ensuring dangerous wastes are safely packaged and stored until a GDF exists.

For me, that’s what makes working on LoC submissions so rewarding—it’s a process that not only plans for the future but also delivers tangible safety benefits today.

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