WASTE TYPES: SNF and HLW
The current waste classification describes the most important classes as follows:
- Spent nuclear fuel (SNF): those are fuel elements irradiated in a nuclear reactor, which have not been further processed.
- High-level waste (HLW) is the high activity waste that results from reprocessing of SNF.
Following an international practice, for both classes the generic terms heat-generating or high-level waste are used.
Over the years a particular fuel element design evolved for each power rector, which can be considered today as standard fuel design for the given reactor type.
- The fuel elements for pressurized water reactors PWR and boiling water reactors BWR are heavy metallic constructions.
- Fuel elements of commercial heavy water reactors like CANDU or gas-cooled reactors like AGR have a similar, but much shorter design.
- High-temperature reactors use cylindrical or spherical fuel elements with graphite cladding.
Vitrified waste from reprocessing is enclosed in steel casks (0.5 m diameter, 1.2 m height)
The waste matrix together with its primary fuel cladding or primary packing from reprocessing forms the initial barrier in the disposal system.
Spent fuel elements and vitrified waste are generally assumed to be destined for disposal in a deep geological repository. And, what is important for the disposal package design:
For safety reasons nobody is planning to damage the initial barrier: no re-melting, no cutting of rods!
This means: the waste has to be taken as it is for final packaging!