Irradiated Graphite Activity Measurement for Reactor Waste Sentencing

Can we recycle the UK's nuclear reactors? Possibly, but first we need to make measurements!

Would you be interested in allowing the UK to deal with its radioactive material in an environmentally sustainable way through the measurement of radioactive graphite?

Graphite is a major component of the UK’s nuclear reactor fleet, which is being decommissioned. The current strategy plans for interim storage to dispose graphite, then perhaps a geological facility, which will cost the taxpayer many £billions due to the large volume taken up.

The NDA needs measurements to underpin safety justifications in dismantling, handling, storing and disposing of graphite. We do not have enough measurements of its radioactive constituents to safely dispose of graphite yet, these are predicted to be carbon-14 and chlorine-36, both beta emitting isotopes with long half-lives. To complicate matters, the location of carbon-14 inventory throughout the bulk structure of the graphite core is unknown, this restricts the decommissioning strategy.

There is therefore an opportunity to make these measurements whilst developing new expertise in this important field. This will include gamma spectroscopy and beta measurements using liquid scintillation counting.

This builds on

previous work on characterisation of graphite, described in this video: https://www.youtube.com/watch?v=fc4DNo4zlaU

Details:

The UK faces the challenge of disposing 95,000 tonnes of graphite waste from research piles, Magnox reactors, and AGRs. NDA is formulating its disposal strategy through the UK Irradiated Graphite Management Programme (IGraMP), led by Nuclear Restoration Services (NRS). A graphite disposal strategy is required that is justified based on data, but at present this strategy would be based merely on modelling: insufficient information about the graphite waste inventory, with a potentially over-conservative disposal strategy the result.

This project addresses the knowledge gap by measuring the beta and gamma activity of a wide selection of samples from the NDA’s graphite reactor cores, providing crucial data on irradiated graphite activity to enable strategic disposal decisions.

Samples are ready: trepanned samples from NDA’s graphite-moderated reactors are distributed across NNL's Central Labs, Berkeley and other sites, and the Universities of Plymouth, Manchester and Bristol, so there is an opportunity for collaboration to bring samples to Bristol for detailed measurement and analysis.

The PhD's objectives include:

• Developing a database and virtual archive of known trepanned samples across the UK.

• Measuring beta and gamma activity in sub-samples using a liquid scintillation counter (LSC) and high resolution gamma spectrometer.

• Analysing activity distribution through each sample as a function of depth, to understand where radioisotopes are located.

• Analysing activity distribution across reactor cores for each reactor in the NDA estate.

Supervisors will be Dr Chris Hutson and Professor Tom Scott.

For informal enquiries, please contact chris.hutson@bristol.ac.uk.

The deadline for applications is 11:59pm on Wednesday 30^th April.

Please apply online at https://www.bristol.ac.uk/study/postgraduate/apply/ Once you have applied please notify chris.hutson@bristol.ac.uk.

University of Bristol

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Irradiated Graphite Activity Measurement for Reactor Waste Sentencing