The electrochemistry of Ag(II) and its application in spent fuel dissolution

To maximise the benefits of near-zero carbon nuclear energy, closed nuclear fuel cycles may need to be implemented in the UK or elsewhere later this century.Closed fuel cycles are those in which actinides are recovered from used nuclear fuel for recycling into new fuels for advanced reactors. In the UK, this recovery was effected by the PUREX (Plutonium-Urananium Redox EXtraction) process. This involves several stages:
(i) The headend stage, involving the dissolution of the spent fuel in nitric acid; and
(ii) The separations stage where the actinides are separated from the acid solution by solvent extraction.
(iii) The finishing stage where the separated actinides are converted to pure U and Pu products.
Closed cycles offer the potential advantages of minimising high level wastes and maximising use of natural uranium resources. The UK is seeking to develop advanced fuel cycles that offer further advantages in separation processes with enhanced standards in economics, safety, proliferation resistance, sustainability and flexibility. This has led to the concept of an "Advanced PUREX" process that can produce a mixed (U,Pu) and a pure U product by recycling either conventional uranium oxide-based fuels - albeit operated to higher uranium usage or "burnup" - and/or new uranium/plutonium mixed oxide (MOX) fuels to.
However, a key issue in the dissolution of used high plutonium content fuels - such as high burnup UO2 and MOX based fuels - is the presence of insoluble plutonium rich particles that require more aggressive dissolution methods at the headend stage than those offered by nitric acid alone. One such method involves the use of powerful oxidising agents such as silver(II) to oxidatively dissolve the Pu-rich regions of the fuel.
This project, a collaboration with the UK's National Nuclear Laboratory (NNL), will provide experimental evidence to support such a fuel dissolution process, with the main focii being on understanding how oxidising species such silver(II) or ozone dissolve fuel, and how this may be impacted upon by the presence of insoluble fission products (e.g. Ru, Pd, Pt, Rh, Mo) as potential interferrants in the oxidative dissolution process. Using new, advanced simulants for real fuels (so-called SIMFUELs), experimental work will be conducted primarily in Lancaster's UTGARD (Uranium-Thorium beta-Gamma Active R&D) Lab, with results informing and complementing studies on real spent fuel conducted at NNL's Central Laboratory.

In GREEN we envisage there are potentially Impacts in several domains: the nuclear Sector; the wider Clean Growth Agenda; Government Policy & Strategy; and the Wider Public.

The two major outputs from Green will be Human Capital and Knowledge:

Human Capital: The GREEN CDT will deliver a pipeline of approximately 90 highly skilled entrants to the nuclear sector, with a broad understanding of wider sector challenges (formed through the training element of the programme) and deep subject matter expertise (developed through their research project). As evidenced by our letters of support, our CDT graduates are in high demand by the sector. Indeed, our technical and skills development programme has been co-created with key sector employers, to ensure that it delivers graduates who will meet their future requirements, with the creativity, ambition, and relational skills to think critically & independently and grow as subject matter experts. Our graduates are therefore a primary conduit to delivering impact via outcomes of research projects (generally co-created and co-produced with end users); as intelligent and effective agents of change, through employment in the sector; and strong professional networks.

Knowledge: The research outcomes from GREEN will be disseminated by students as open access peer reviewed publications in appropriate quality titles (with a target of 2 per student, 180 in total) and at respected conferences. Data & codes will be managed & archived for open access in accordance with institutional policies, consistent with UKRI guidelines. We will collaborate with our counterpart CDTs in fission and fusion to deliver a national student conference as a focus for dissemination of research, professional networking, and development of wider peer networks.

There are three major areas where GREEN will provide impact: the nuclear sector; clean growth; Policy and Strategy and Outreach.

the nuclear sector: One of our most significant impacts will be to create the next generation of nuclear research leaders. We will achieve this by carefully matching student experience with user needs.

clean growth - The proposed GREEN CDT, as a provider of highly skilled entrants to the profession, is therefore a critical enabler in supporting delivery of both the Clean Growth agenda, Nuclear Industry Strategy, and Nuclear Sector Deal, as evidenced by the employment rate of our graduates (85% into the sector industry) and the attached letters of support.

Policy and Strategy: The GREEN leadership and supervisory team provide input and expert advice across all UK Governments, and also to the key actors in the nuclear industry (see Track Records, Sections 3.3 & 5.1, CfS). Thus, we are well positioned to inculcate an understanding of the rapidly changing nuclear strategy and policy landscape which will shape their future careers.

Outreach to the wider public: Building on our track record of high quality, and acclaimed activities, delivered in NGN, GREEN will deliver an active programme of public engagement which we will coordinate with activities of other nuclear CDTs. Our training programme provides skills based training in public and media communication, enabling our students to act as effective and authoritative communicators and ambassadors. Examples of such activities delivered during NGN include: The Big Bang Fair, Birmingham 2014 - 2017; British Science Week, 2013 - 2017; ScienceX, Manchester; 2016 - 2018; and The Infinity Festival, Cumbria, 2017.