The Nuclear Decommissioning Authority

Last Updated: 11 December 2011

Higher Activity Waste (HAW) includes High Level Waste (HLW), Intermediate Level Waste (ILW) and some Low Level Waste (LLW) that is not suitable for disposal in the Low Level Waste Repository (LLWR).  HAW arises from a number of activities such as

• reactor operation
• reprocessing of spent nuclear fuel and
• decommissioning.    

 Higher Activity Waste Credible Options February 2011 (200Kb)

Objective

To treat and package retrieved HAW and place it in safe, secure and suitable storage facilities until it can be disposed of, or be held in long-term storage in the case of a proportion of HAW in Scotland.

Scope and Boundaries

In the UK HLW is defined as heat-generating and is generally produced as a result of reprocessing spent nuclear fuel. Initially HLW is stored as a liquid in high integrity tanks prior to being converted to a vitrified glass product for longer term storage and disposal.

ILW is radioactive waste with radioactivity levels exceeding the upper boundaries for LLW and is generated from a number of activities as follows:

• decommissioning
• spent fuel reprocessing
• research facilities
• reactor operation
• historical waste storage practices

The major components of ILW are

• metals and Magnox sludges
• organic materials
• ion-exchange resins
• concrete and graphite.

Its chemical and physical form ranges from large solid waste items that are chemically inert, to wet sludges which could be chemically reactive and heavily contaminated.

A small quantity of LLW containing relatively high concentrations of long-lived radioisotopes will need to be treated as ILW because it is unsuitable for disposal in the LLW Repository near Drigg.

This topic strategy specifically excludes spent fuel, which is covered by the following strategies:

• Spent Magnox fuel strategy
• Spent Exotic fuel strategy
• Spent Oxide fuel strategy

Interfaces

The HAW strategy interfaces with a number of other topics including:

• Lower Activity Waste strategy is related because there are opportunities to explore waste re‑categorisation by decontamination, decay storage and waste segregation that could lead to an overall increase in LLW volumes
• Spent fuels and nuclear materials because of the potential for disposal in a Geological Disposal Facility (GDF)
• Decommissioning strategy is related because it could affect the rate at which HAW arises over time
• Transport and logistics strategy is related because of the potential need to move waste between sites and overseas

Credible Options

The Committee on Radioactive Waste Management (CoRWM) considered a broad range of alternative options for managing HAW and recommended geological disposal as the preferred solution.  Following Government acceptance of CoRWM's recommendation, the NDA has adopted the same approach and is developing options for managing HAW in the interim. More recently the Scottish Government have published their Policy on the long-term management of Higher Activity Waste.

Between now and availability of disposal routes, the NDA's approach is to:

• Prioritise retrieval, conditioning and passive storage of historical HAW
• Apply the waste management hierarchy
• Minimise the storage of HAW in raw form
• Minimise the volume of ILW produced from decommissioning
• Package HAW into a form that is compliant with disposal or long-term storage
• Ensure safe and secure interim storage pending availability of the GDF

As for developing credible alternative strategic options, HAW is split into two distinct categories:

• Alternative options that provide risk mitigation against the current baseline in certain areas of HAW management
• Alternative options that provide a step change in benefits against the current baseline position.

Current Position

The current strategy for HAW is to achieve passive safety as soon as reasonably practicable for interim storage and eventual disposal in a Geological Disposal Facility (* or long-term management in near-surface facilities for wastes in Scotland).

The different classes of HAW for which sub options exist or are being developed are:

• UK owned HLW – interim storage followed by disposal in a GDF*
• Overseas owned HLW – returned to country of origin
• Overseas owned ILW – substitution of additional HLW returned to country of origin
• Wet ILW – retrieval and waste conditioning followed by longer-term interim storage and disposal in a GDF*
• Solid ILW – retrieval, conditioning and interim storage followed by conditioning and disposal in a GDF*
  – facility decommissioning followed by disposal in a GDF*
• Graphite – retrieval, conditioning and interim storage followed by conditioning and disposal in a GDF*
  – facility decommissioning followed by disposal in a GDF*

* or long-term management in near-surface facilities for wastes in Scotland

The aim of the reference strategy, which will be actively pursued for the majority of the HAW inventory, is to achieve passive safety as soon as reasonably practicable, for longer-term storage and eventual disposal, or management in near-surface facilities for HAW in Scotland. Depending on the timing of waste arisings, a period of some decades of interim storage may be required. To this end the NDA is working to optimise the programme for retrieval, treatment and storage by considering:

• Strategic opportunities - e.g. alternative disposal scenarios and decay storage
• Strategic risks - a flexible approach to waste management that recognises the need for progressive risk and hazard reduction
• Baseline improvement initiatives - securing an NDA-wide approach to waste processing and storage and, where appropriate, co-ordinating with other waste producers