The Safe Storage of Plutonium Oxide

The safe and secure storage of plutonium (Pu) materials is a matter of international concern with ~250 tonnes of separated Pu stockpiled worldwide. Over half of this, resulting from ~50 years civil nuclear fuel reprocessing, is in long term storage in the UK whilst the Government considers options for its final treatment and disposition. This Pu is stored as calcined PuO2 powder in nested, sealed steel storage cans. Under certain circumstances, gas generation may occur with consequent storage package pressurisation. In practice, this is rarely seen and empirically derived criteria are used to maintain safe storage conditions. Nonetheless, this is a potential scenario that must be avoided in practice - thus the fundamental mechanisms that could lead to pressurisation must be understood. 5 main routes have been suggested:
(i) Helium accumulation from alpha decay;
(ii) Decomposition of polymeric packing material;
(iii) Steam produced by H2O desorption from hygroscopic PuO2 due to self-heating;
(iv) Radiolysis of adsorbed water; and,
(v) Generation of H2 by chemical reaction of PuO2 with H2O.
The last 4 mechanisms are being studied as part of the work of the EPSRC TRANSCEND (TRANSformative SCience & Engineering for Nuclear Decommissiong) consortium (www.transcendconsortium.org). This project, a collaboration between the University of Lancaster, the National Nuclear Laboratory (NNL) and Sellafield Ltd, seeks to understand the role that the first of these mechanisms, helium from alpha decay, might play in pressurisation. Innovative sample preparation and thermal / gravimetric analysis methods for the study of this will first be developed at the university and then deployed on real samples at NNL. Data & knowledge generated will be transferred to Sellafield Ltd via the NNL and used in better underpinning of the Pu storage safety cases.
This studentship is offered as part of the "Growing skills for Reliable Economic Energy from Nuclear" (GREEN) Centre for Doctoral Training (https://www.nuclear-energy-cdt.manchester.ac.uk/), a collaboration between the Universities of Lancaster, Manchester, Liverpool, Leeds and Sheffield. GREEN aims to develop and deliver the research and skills required to address key challenges in the field of nuclear energy across the entire fuel cycle.

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.