Introduction to High Heat Generating Waste
This page provides introductory information on High Heat Generating Waste (HHGW).
HHGW is one of three major categories of radioactive waste for which Nuclear Waste Services defines waste package specifications (WPS). The current HHGW specification covers two main subcategories of radioactive material that may require geological disposal.
These are:
- spent fuel (SF)
- vitrified High Level Waste (HLW)
Nuclear fuel is the material (usually particular species of uranium, but sometimes plutonium or other elements) that is used in a nuclear reactor to sustain a nuclear chain reaction. SF is the nuclear fuel that is removed from the reactor after it is no longer useful in sustaining a chain reaction in an ordinary reactor. Different types of nuclear reactor have operated in the UK for energy generation, research or military purposes, and each reactor type results in different forms of SF. HLW is produced as a liquid by-product from reprocessing SF. A process called ‘vitrification’ converts the liquid HLW into a (solid) glass form.
High fissile activity wastes, that is, plutonium (Pu) and highly enriched uranium (HEU), are also included as HHGW. This is because they have similar disposal requirements, even though they don’t generate significant amounts of heat.
For more information on waste classification of HHGW, see the 2022 Inventory for Geological Disposal.
Most or all HHGW in the UK will be disposed of in a Geological Disposal Facility (GDF) - options to recycle some of the plutonium stockpile are being considered. There are currently three illustrative disposal system concepts, each defined by the generic nature of the host rock. Information on these concepts can be found in the Generic Disposal System Specification Part B. For HHGW, a high integrity container is required to ensure the waste package maintains its condition for a sufficient period of time. The management of many different properties will need to be accounted for by the disposal system for HHGW, including (but not limited to):
- durability of the waste container
- heat output
- gas generation
- fissile material concentrations
This will be achieved by a combination of the GDF and disposal container design, and also the interactions between the waste, disposal container and host rock.
See next: Preparation of High Heat Generating Waste for Disposal