Modelling the electron anti-neutrino flux from nuclear reactors

点击翻译按钮获取中文摘要

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 electronanti-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 majoractinides within the core. As a result, this electron anti-neutrino flux is inherently tied to the operation ofa 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 utilisingneutrinos to monitor reactors has existed for some time, but it is only recently that the understanding of thehas made such prospects feasible [3]. In contrast to current IAEA procedures, anti-neutrino based safeguardsallow for bulk accountancy of nuclear fuel, yielding an estimate of the masses of fissile material producedwithout necessitating assumptions regarding the mass of items. Additionally, anti-neutrino methods arenon-invasive, being carried out through use of a detector at a standoff distance from the reactor and allowfor real time measurement of the core.In the near future, the most reasonable expectation for the utilisation of this technology is through thedeployment 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 neutrinodisappearance on the flux compared to detectors operating at far greater standoff distances, such as in theKamland experiment [4] [5]. Whilst far field monitoring of nuclear reactors through neutrino detection is adesirable prospect, the contributions of neutrino mixing and the increased background of the spectra greatlyincrease the complexity of modelling required.Use of the electron anti-neutrino spectra for the purposes of reactor monitoring is reliant on deviationsfrom an expected flux and energy spectra. Thus, models of an expected flux and energy spectra are neededin comparison with the measured rate, where through statistical methods, a threshold for a significant deviationfrom 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 providedfrom nuclear reactors, such as Hartlepool, along with spent fuel inventories. These source terms will bequantified to include to provide an estimation of the flux incident to a detector at varying distances, consid-1ering phenomena such the neutrino mixing of this flux along with the expected evolution of a nuclear core ona real time basis, something that existing applications, such as geo-neutrinos [7], do not consider and mighttherefore be used to inform such software.Beyond this, several avenues exist for further pursuit. These include phenomena such as the unexpectedexcess of anti-neutrinos detected at around 5 MeV with an unknown cause, speculated by some to be due topossibilities 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 reactoranti-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. Reviewsof Modern Physics, 74(2), pp.297-328.[3] Bowden, N., 2008. Reactor monitori