Guidance

Geological disposal of radioactive wastes: the inventory for disposal

Published 25 October 2021

Introduction

The purpose of the Committee on Radioactive Waste Management (CoRWM) is to provide independent advice on matters of radioactive waste management and disposal. Through its work associated with the siting process for a Geological Disposal Facility, CoRWM has recognised the need for a clear statement of the radioactive waste inventory for disposal, to enable informed engagement by host communities and other stakeholders. The purpose of this briefing note is to summarise the inventory of radioactive waste that could be emplaced within a Geological Disposal Facility, with due regard to developments in nuclear decommissioning strategy.

Background

The radioactive wastes to be managed for and consigned to a Geological Disposal Facility (GDF) are referred to as the inventory for disposal in the UK government’s Implementing Geological Disposal – Working With Communities policy of 2018 ^{[footnote 1]}, and as the Inventory for Geological Disposal in the most recent iteration of the Disposal System Safety Case (DSSC) developed by Radioactive Waste Management (RWM) ^{[footnote 2]}, ^{[footnote 3]}. A clear understanding of the inventory intended for disposal is essential both for the GDF design and safety case, and to inform potential host communities in their consideration of siting a GDF.

A GDF will be located at 200-1000 m depth below the surface in a suitable rock formation.

This note will use the following terms:

• Radioactive Waste Inventory, meaning: current (already produced) and future radioactive waste arising from existing facilities; summarised in the UK Radioactive Waste Inventory (UK RWI), last updated in 2019 ^{[footnote 4]}. The UK RWI does not include future radioactive waste arisings from the new build programme
• Radioactive Materials Inventory, meaning: civil nuclear materials not currently designated as waste (uranium, thorium, plutonium, spent nuclear fuel, unirradiated nuclear fuel) and land potentially contaminated with radioactivity; summarised in the UK Radioactive Materials Inventory (UK RMI), last updated in 2019 ^{[footnote 5]}. The UK RMI does not include civil nuclear materials from the new build programme
• Inventory for Geological Disposal, meaning: the radioactive waste intended for disposal in a GDF; this terminology is the same as that used by RWM and is synonymous with the term inventory for disposal, used in the UK Government’s Implementing Geological Disposal – Working With Communities policy of 2018. However, we use the term Inventory for Geological Disposal for explicit clarity on the waste intended to be disposed in a GDF

It should be noted that Scottish Government policy is that higher activity radioactive wastes within the defined scope of the policy should be managed in near surface facilities, located as near to the site where they are produced as possible ^{[footnote 6]}. Radioactive wastes managed in this way will therefore not form part of the Inventory for Geological Disposal. In Scotland, no radioactive waste will be classified as High Level Waste (HLW).

The Inventory for Geological Disposal

As noted above, the basis of the Inventory for Geological Disposal is set out in the UK government’s Implementing Geological Disposal – Working With Communities policy of 2018 (and previously in the Implementing Geological Disposal White Paper of 2014). This inventory is used as the baseline for the generic DSSC. The most recent Inventory for Geological Disposal was published in July 2021 ^{[footnote 3]}; the most recent version of the DSSC was published in 2016 ^{[footnote 2]}.

The Inventory for Geological Disposal represents the most complete picture of the radioactive wastes that could be disposed in a GDF. UK government policy leaves open the possibility that more than one GDF may be required to accommodate the Inventory for Disposal.

The Inventory for Geological Disposal includes components of both the Radioactive Waste Inventory and Radioactive Materials Inventory, but, crucially, not their entirety, this relationship is shown diagrammatically in Figure 1.

Figure 1: Showing definition of the Inventory for Geological Disposal and relationship with UK Radioactive Waste Inventory, UK Radioactive Material Inventory, and possible wastes from New Build Programme, established Low Level Waste Repository, potential future Near Surface Disposal Facility.

Note: SNF – Spent Nuclear Fuel (including unirradiated fuel), Pu – separated plutonium, U – uranium, MOX – mixed oxide fuel from plutonium reuse; from defence programmes, INF – irradiated nuclear fuel and NM – nuclear materials. It is recognised that some wastes in Scotland may not be suitable for near surface disposal. Such wastes will be stored until alternative waste management solutions are developed.

The Inventory for Geological Disposal is defined as comprising:

1. From the UK Radioactive Waste Inventory:

• High Level Waste (HLW) arising from reprocessing of nuclear fuel at Sellafield, in the form of vitrified glass product
• Intermediate Level Waste (ILW) arising from nuclear licenced sites, and medical, industrial, research, education and defence activities
• a small fraction of Low Level Waste (LLW) that is not suitable for consignment to the Low Level Waste Repository

2. From the UK Radioactive Materials Inventory, nuclear material not currently declared as waste:

• spent nuclear fuel from current reactors not destined for reprocessing
• all UK plutonium either reused in spent nuclear fuel,a or as immobilised product if not reused
• uranium from enrichment and fuel fabrication, not reused as nuclear fuel

3. Other nuclear fuels and material not within the UK Radioactive Waste Inventory or Materials Inventory:

• spent nuclear fuel and ILW from new build up to a defined amount, currently being that arising from a programme with a generating capacity of 16 GWe
• irradiated fuel and nuclear materials from the UK defence program

The above summary is identical to that of the inventory for disposal set out in the UK government policy of 2018 and the Inventory for Geological Disposal in the generic DSSC of 2016.

Changes to the Inventory for Geological Disposal

The UK government policy of 2018, states:

As component parts of the inventory for disposal in a GDF it is not expected that the categories of waste and material listed… will change significantly. For the purposes of discussions with communities that are considering hosting a GDF, this description provides the most complete picture of the possible inventory for disposal at this point in time.

Since the publication of this policy, the Nuclear Decommissioning Authority (NDA), has stated its intention to consider the possibility of Near Surface Disposal of some radioactive wastes that do not necessarily require the isolation and containment afforded by a Geological Disposal Facility ^{[footnote 7]}. This consideration is included in the most recent NDA Strategy, adopted in March 2021, which provides a summary of the disposal capability needed to complete the UK nuclear decommissioning mission, and a summary diagram representing the relative depth, isolation, and containment offered by Near Surface and other disposal facilities ^{[footnote 8]}.

A Near Surface Disposal facility could be located either at the surface or several tens of metres below the surface and constructed as an arrangement of vaults or silos. However, it should be noted that no decision has yet been made to dispose of radioactive wastes in this way. The radioactive wastes that could be consigned to Near Surface Disposal are not yet decided, but could include some of the LLW currently not suitable for disposal in the existing Low Level Waste Repository and suitable ILW.

Therefore, if Near Surface Disposal facilities are created, it is now conceivable that the Inventory for Geological Disposal could be reduced in comparison to that set out in the UK government’s Implementing Geological Disposal – Working With Communities policy of 2018, and DSSC of 2016. Furthermore, the volume of the inventory for disposal could be reduced against the current baseline by application of the waste hierarchy (decontamination, reuse and recycle of waste) and advanced waste treatment technology (for example thermal treatment), which are within NDA Strategy ^{[footnote 8]}.

At the current time, the assumption is that the Inventory for Geological Disposal will be that defined in the UK government policy of 2018 and DSSC of 2016, as summarised above and in Figure 1. However, it should be noted that the volume of the Inventory for Geological Disposal is a best estimate and will be subject to change as the UK decommissioning and waste management programme progresses.

1. HM Government, Department for Business, Energy & Industrial Strategy, Implementing Geological Disposal – Working With Communities, December 2018. ↩

2. Radioactive Waste Management, Geological Disposal, Overview of the generic Disposal System Safety Case, December 2016. ↩ ↩²

3. Radioactive Waste Management, Inventory for geological disposal, Main Report, July 2021. ↩ ↩²

4. Nuclear Decommissioning Authority, Radioactive Waste Inventory, 2019. ↩

5. Nuclear Decommissioning Authority, Radioactive Material Inventory, 2019. ↩

6. The Scottish Government, Scotland’s higher-activity radioactive waste policy, January 2011. ↩

7. Nuclear Decommissioning Authority, Near-Surface Disposal Strategic Position Paper, August 2020. ↩

8. Nuclear Decommissioning Authority, Strategy Effective from March 2021, March 2021. ↩ ↩²