Zero power reactors in support of current and future nuclear power systems

Zero-power reactors stand as indispensable tools for shaping the future of the nuclear industry. Addressing safety concerns, advancing reactor technology, mitigating proliferation risks, fostering education, and promoting economic viability, these reactors hold the key to unlocking the full potential of nuclear energy in a sustainable and responsible manner. As the world seeks cleaner and more efficient energy solutions, the importance of zero-power reactors cannot be overstated in charting the course for the nuclear industry’s future. The paper presents a short history of the various zero-power/zero-energy experimental facilities constructed and used worldwide. Many of the names seemed to be lost to history and archives, which means that all the experimental data carried in the those facilities is lost as well. However, re-introducing the various names can spark an interest in ”digging up” and revisit experiments of the past, which can help in the design of experiments and new systems in the future. It is clear that a new experimental facility should be built. The next frontier in zero-power reactor design envisions a design for versatility, this future concept addresses diverse energy needs while contributing to a sustainable and responsible nuclear energy landscape. This was demonstrated in the framework of the Zero-power Experimental PHYsics Reactor design proposed by French Atomic Energy Commission

A topological realization of the congruence subgroup Kernel A

A number of years ago, Kumar Murty pointed out to me that the computation of the fundamental group of a Hilbert modular surface ([7],IV,${\S}$6), and the computation of the congruence subgroup kernel of SL(2) ([6]) were surprisingly similar. We puzzled over this, in particular over the role of elementary matrices in both computations. We formulated a very general result on the fundamental group of a Satake compactification of a locally symmetric space. This lead to our joint paper [1] with Lizhen Ji and Les Saper on these fundamental groups. Although the results in it were intriguingly similar to the corresponding calculations of the congruence subgroup kernel of the underlying algebraic group in [5], we were not able to demonstrate a direct connection (cf. [1], ${\S}$7). The purpose of this note is to explain such a connection. A covering space is constructed from inverse limits of reductive Borel-Serre compactifications. The congruence subgroup kernel then appears as the group of deck transformations of this covering. The key to this is the computation of the fundamental group in [1]

Utilising 241Am as burnable poison in proliferation resistant PWR

The increased need for energy, as well as the necessity for energy-intensive solutions to tackle climate change, has increased interest in nuclear power generating as a low-carbon energy source. While nuclear energy offers substantial benefits in reducing greenhouse gas emissions, it also raises concerns regarding nuclear proliferation. In this study, the viability of utilising nuclear proliferation-resistant fuel in a PWRs without the need for an additional burnable absorber was assessed by integrating 241Am into the fuel composition. When 241Am was used as a burnable absorber instead of IFBAs, the potential changes in reactivity feedback parameters, peaking factors, and power profiles were investigated. The influence of 241Am-doped fuel on the cycle's duration and the shutdown margin was also explored. It is shown that using 241Am-doped fuel can enable a PWR to operate safely and reliably within its design boundaries. Moreover, it offers a proliferation-resistant fuel cycle without requiring any additional burnable absorbers

Burnup-Dependent Neutron Spectrum Behaviour of a Pressurised Water Reactor Fuel Assembly

Understanding the behaviour of a neutron spectrum with burnup is important for describing various phenomena associated with reactor operation. The quest to understand the neutron spectrum comes with a lot of questions. One question that is usually asked by students is: Does the neutron spectrum harden or soften with burnup? Most textbooks used by students do not provide a definite answer to this question. This paper seeks to answer this question using a 3D model of a standard 17 × 17 pressurised water reactor fuel assembly. Two cases were studied using the Serpent Monte Carlo code: the first considered the fuel assembly with constant boron concentration (traditionally found in many published papers), and the second considered boron iteration (where the boron concentration was reduced with burnup). Neutron spectra for the two cases at beginning of life and end of life were compared for spectral shifts. In addition, thermal spectral indices were used to assess spectrum hardening or softening with burnup. Spectral shifts to lower energies were observed in the thermal region of the neutron spectrum, whereas the fast region experienced no spectral shift. There was an increase in thermal spectral indices indicating that the spectrum became soft with burnup

Flow characterisation using fibre Bragg gratings and their potential use in nuclear thermal hydraulics experiments

With the ever-increasing role that nuclear power is playing to meet the aim of net zero carbon emissions, there is an intensified demand for understanding the thermal hydraulic phenomena at the heart of current and future reactor concepts. In response to this demand, the development of high-resolution flow analysis instrumentation is of increased importance. One such under-utilised and under-researched instrumentation technology, in the context of fluid flow analysis, is fibre Bragg grating (FBG)-based sensors. This technology allows for the construction of simple, minimally invasive instruments that are resistant to high temperatures, high pressures and corrosion, while being adaptable to measure a wide range of fluid properties, including temperature, pressure, refractive index, chemical concentration, flow rate and void fraction—even in opaque media. Furthermore, concertinaing FBG arrays have been developed capable of reconstructing 3D images of large phase structures, such as bubbles in slug flow, that interact with the array. Currently a significantly under-explored application, FBG-based instrumentation thus shows great potential for utilisation in experimental thermal hydraulics; expanding the available flow characterisation and imaging technologies. Therefore, this paper will present an overview of current FBG-based flow characterisation technologies, alongside a systematic review of how these techniques have been utilised in nuclear thermal hydraulics experiments. Finally, a discussion will be presented regarding how these techniques can be further developed and used in nuclear research

Spin-orbit interaction and spin relaxation in a two-dimensional electron gas

Using time-resolved Faraday rotation, the drift-induced spin-orbit Field of a two-dimensional electron gas in an InGaAs quantum well is measured. Including measurements of the electron mobility, the Dresselhaus and Rashba coefficients are determined as a function of temperature between 10 and 80 K. By comparing the relative size of these terms with a measured in-plane anisotropy of the spin dephasing rate, the D'yakonv-Perel' contribution to spin dephasing is estimated. The measured dephasing rate is significantly larger than this, which can only partially be explained by an inhomogeneous g-factor.Comment: 6 pages, 5 figure