Modelling the electron anti-neutrino flux from nuclear reactors

Since the first experimental detection of the neutrino, with the Cowan-Reines experiment in the 1950s,
nuclear test reactors have played a central role within the field of neutrino physics as a source of electron
anti-neutrinos. These electron anti-neutrinos can be detected through an inverse beta decay reaction:
[1] and arise from the beta decay of neutron rich nuclei formed by the fission of major
actinides within the core. As a result, this electron anti-neutrino flux is inherently tied to the operation of
a reactor, and related to the power of the reactor and the fissile inventory of its core [2].
Given the dependence on the operational parameters and fissile inventory of a reactor, the concept of utilising
neutrinos to monitor reactors has existed for some time, but it is only recently that the understanding of the
has made such prospects feasible [3]. In contrast to current IAEA procedures, anti-neutrino based safeguards
allow for bulk accountancy of nuclear fuel, yielding an estimate of the masses of fissile material produced
without necessitating assumptions regarding the mass of items. Additionally, anti-neutrino methods are
non-invasive, being carried out through use of a detector at a standoff distance from the reactor and allow
for real time measurement of the core.
In the near future, the most reasonable expectation for the utilisation of this technology is through the
deployment of tonne-scale portable anti-neutrino detectors at a standoff distance of the order of 10 metres.
At these distances, neutrino oscillation experiments have demonstrated the vastly reduced effects of neutrino
disappearance on the flux compared to detectors operating at far greater standoff distances, such as in the
Kamland experiment [4] [5]. Whilst far field monitoring of nuclear reactors through neutrino detection is a
desirable prospect, the contributions of neutrino mixing and the increased background of the spectra greatly
increase the complexity of modelling required.
Use of the electron anti-neutrino spectra for the purposes of reactor monitoring is reliant on deviations
from an expected flux and energy spectra. Thus, models of an expected flux and energy spectra are needed
in comparison with the measured rate, where through statistical methods, a threshold for a significant deviation
from the model, and the time frame needed to detect this deviation, can be established [6].
This anti-neutrino modelling is likely to form the main underpinning of a thesis in anti-neutrino physics.
This will include generation of anti-neutrino source terms for reactors based on operational data provided
from nuclear reactors, such as Hartlepool, along with spent fuel inventories. These source terms will be
quantified to include to provide an estimation of the flux incident to a detector at varying distances, consid-
1
ering phenomena such the neutrino mixing of this flux along with the expected evolution of a nuclear core on
a real time basis, something that existing applications, such as geo-neutrinos [7], do not consider and might
therefore be used to inform such software.
Beyond this, several avenues exist for further pursuit. These include phenomena such as the unexpected
excess of anti-neutrinos detected at around 5 MeV with an unknown cause, speculated by some to be due to
possibilities such as neutrino induced deuteron disintegration or coherent elastic neutrino-nucleus scattering
[8]. Another, further, anomaly that may lend itself to investigation is that of the drop in expected reactor
anti-neutrino events in short baseline experiments [9].
2 References
[1] Cowan, C., Reines, F., Harrison, F., Kruse, H. and McGuire, A., 1956. Detection of the Free Neutrino:
a Confirmation. Science, 124(3212), pp.103- 104.
[2]Bemporad, C., Gratta, G. and Vogel, P., 2002. Reactor-based neutrino oscillation experiments. Reviews
of Modern Physics, 74(2), pp.297-328.
[3] Bowden, N., 2008. Reactor monitori

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.