In this chapter, the scientific and technical basis of nuclear fuel recycling and reprocessing is considered. A perspective is adopted with the aim to provide the reader, studying this from an engineering perspective, with an understanding of the salient concepts and chemical principles by which uranium and plutonium are separated from spent fuel, separated from each other and purified. An introduction to both hydrometallurgical and pyroprocessing is given.

In this chapter we explore this range of isotopes of relevance to nuclear power in order to establish a foundation on which to base the subsequent chapters. A relatively small number of radioactive species (approximately 20) arise routinely in nuclear engineering and nuclear power applications that can require management and attention in order to avoid inadvertent pollution of the natural environment. The central family of elements that concern us first in this chapter are the actinides and to a lesser extent the associated isotopes that follow in their decay chains. Derived from these there is also a selection of very light isotopes (arising either as a result of ternary fission or via neutron capture) and a mid-range group that arise as fission products (formerly referred to as secondary fission products as we are usually interested in them following primary beta decays) from the nuclear chain reaction. The fission products subdivide further between a light and a heavy fraction directly as a result of the asymmetry in yield with mass.

In this chapter the concept of nuclear fission is introduced with a particular focus on fission induced with thermal neutrons. The concepts of microscopic neutron cross section, macroscopic neutron cross section and neutron mean free path are introduced. The variety of potential interaction types is considered and the dependence of cross section with neutron energy is discussed. Nuclear binding energy is described and the dependence of binding energy per nucleon is explored in terms of the advantage gained by isotopes that fission in terms of stability. The energetics of fission, fission neutron spectra, the most probable and average neutron energies and the concept of neutron multiplicity are introduced.

Ground-level neutron monitors (NMs) are essential tools for monitoring space weather events, including the detection and alerting of ground-level enhancement (GLE) events. This study presents findings from a neutron monitoring survey using two compact N50L neutron slab-based subsystems deployed across various field sites in the United Kingdom (UK) with different geomagnetic cutoff rigidities. Data from these N50L subsystems were compared to data from established NM-64 monitors (Dourbes and Oulu) with similar geomagnetic cutoff rigidities and accessed via the Neutron Monitor Database (NMDB). The cosmic ray (CR) count rates measured by the N50L subsystems closely follow NMDB network trends, while absolute count rates differ due to site altitude, geomagnetic latitude, and local environmental conditions in the immediate vicinity of each detector. Key events observed during the campaign include two Forbush decreases and GLE-74. The data collected supported the development and deployment of the NM-2023 design initiative, specifically targeting the site of the first operational 4-NM-2023 in the UK. Additionally, data from the N50L subsystems were compared with the University of Surrey's Compact NM setup and the Lancaster University and Mirion Technologies developed NM-2023, enhancing GLE monitoring capabilities across UK geomagnetic cutoff rigidities. The preliminary measurements from the NM-2023 prototype conducted at the Warrington site suggest it can achieve performance comparable to the 6-NM-64 monitor but with a reduced footprint, volume, mass, and cost, utilizing environmentally friendly, non-toxic gas-filled counters. A full 4-NM-2023 system has been deployed at Met Office Camborne Observatory near Cornwall, with a 1-NM-2023 unit installed at Lancaster University.

A mobile robot platform was developed with on-board, stand-off LIBS and Raman probes as part of a broader system for in situ 'total characterisation' in nuclear environments. This includes gamma spectrometry and 3D imaging via LIDAR and photogrammetry. All characterisation techniques were guided by a 3D point-cloud model generated from the robot's imaging systems, enabling precise positioning near target zones. The LIBS probe operated at a stand-off distance of 10 cm and successfully detected lead in a single shot, with signal quality comparable to benchtop instruments. It also distinguished metals such as stainless steels, nickel, and Incoloy using principal component analysis. The Raman probe used a collimated laser beam and acquired spectra from several metres away. It identified organic materials common in decommissioning environments, including plastics and EDTA, and differentiated concentrations of dibutyl and tributyl phosphate in low-odour kerosene, organophosphates relevant to uranium and plutonium removal. Both probes were tested in a simulated hot cell environment, operating entirely on battery power. Contamination detection of non-radioactive analogues of radioactive decay products like strontium and caesium on stainless steel and cement was demonstrated, supporting clean-up and disposal operations and decision making. Spectral, spatial, and radiological data are integrated into a database that updates a digital twin, enabling layered visualisation in a virtual environment. The robot can be deployed for periodic surveys, such as annual inspections of disused hot cells, to monitor environmental degradation. This data-driven approach supports auditable decision-making for waste disposal and remediation priorities.

In this chapter, the way in which reactors respond to external influences and changes in their state and composition are discussed. These behaviours constitute the framework within which nuclear reactor systems have to be controlled to ensure safe operation and optimum performance. This chapter is not exhaustive in that it does not explore the detailed response characteristics of each particular reactor variant but the salient response characteristics of a thermalised fission power environment using low-enriched uranium-based fuel are summarised. We introduce: the fundamental concepts of time and space in the context of nuclear reactor control, discuss population dynamics as applied to neutron economy in a fission environment, the significance of delayed neutrons, short-term effects associated with inherent feedback mechanisms and long-term effects associated with reactor poisoning.

In this chapter the fundamentals of radioactivity are introduced as a basis for the subsequent, more specialised nuclear engineering chapters that follow. Radioactivity is the salient feature that separates nuclear engineering from most other strands of the engineering discipline. Its discovery a little more than 100 years ago was the trigger for all of the beneficial applications of nuclear technology that have arisen since but it is also the important distinction why nuclear systems need to be managed carefully with the utmost respect for safety, health and the environment. In this chapter the radioactive decay law and its relationship with the decay constant is introduced; the various modes of radioactive decay are considered with particular reference to those of interest to nuclear power; the characteristic radiations from these decays are considered along with their interaction properties; secondary radiations and the relevance of the various radiation types is highlighted in terms of their implications for shielding and stopping power.

Results obtained from characterizing the capabilities of a collimated cerium bromide (CeBr3) detector developed for use on robotic platforms are reported. The detector's field-of-view is collimated by a lead slit, and experiments have been performed with point radiation sources configured in a-priori known geometric scenarios. The collimated detector is scanned over radiation sources using gimbal control, acquiring a spectrum at each angle to obtain energy-resolved angular responses. These responses are then approximated by mathematical transforms to enhance localization accuracy. Various combinations of radionuclides have been used to demonstrate the effectiveness of this approach. The results reveal that expressing X-ray and gamma-ray angular responses with an appropriate transform improves the resolving power of the slit collimator. This technique offers distinct advantages in robot deployments by enabling additional in-situ characterization capabilities without imposing additional limitations or requirements.

A modification of the integrated dry route (IDR) process for uranium conversion in nuclear fuel fabrication to render it responsive to react and adapt to changes in measured variables is described. Data conditioning techniques and feature extraction methodologies have been developed using real-world industrial datasets comprising 1685 valid IDR process batches. Bidirectional Long Short-Term Memory (Bi-LSTM) sequence classification networks were designed, trained, and tested by framing the IDR process and its assessed fluorine content results as a classification problem. Five comprehensive experiments were conducted using features extracted from both raw process data and domain knowledge provided by experienced process operators. The results of the five training scenarios are presented using confusion matrices, which report the mean Specificity for predicting defective batches and the mean Sensitivity for predicting satisfactory batches. Additionally, a Receiver Operating Characteristic (ROC) curve is included, showing the Area Under the Curve (AUC) values for the classification outcomes in each of the four training tasks. Both the confusion matrices and the ROC curve indicate that the best-performing model is trained with a combination of raw data features and post-processed features derived from prior experimental and technical knowledge. This model achieved classification accuracies of 97% or higher, confirming that a purely data-driven approach is insufficient. The primary objective is to predict the quality of the uranium dioxide (UO2) output, specifically its fluorine content, more quickly than is currently achieved in the factory. Test case results demonstrate the effectiveness of the trained Bi-LSTM network, suggesting its potential utility in developing a digital twin for the IDR system. With further development, such models could enable on-line feedback to kiln conditions, allowing for real-time responsiveness during IDR operations.

An analysis of sintered uranium dioxide has been conducted using a hyperspectral camera sensitive to short-wave infrared wavelengths in the range 949–2472 nm. Three groups of sintered UO2 nuclear fuel pellets were prepared and analysed, with stable sub-group surrogates introduced at the preparation stage to emulate the presence of fission product elements. Results show a clear, consistent, and reproducible spectral response across the pellet groups for pure UO2. Furthermore, the addition of fission product elements is observed to affect the shortwave infrared response, causing an overall flattening of the spectra. We have shown that this spectral change is correlated significantly with the presence of lanthanides in the fuel matrix. This result could have important potential in post-irradiation examination for quantifying nuclear fuel burn-up and radiotoxicity at discharge, as the hyperspectral imaging setup allows multiple (> 20) samples to be analysed in a single image, captured in under 30 s.

Small and advanced nuclear technologies are viewed as key to meeting future low-carbon dioxide energy demands. Big Tech companies are even planning to build their own nuclear reactors to power the digital revolution, including those that are yet to leave the drawing board. Building disposal solutions for the radioactive waste that these mainly novel reactors, which come with novel fuel, is essential too. Experience from 70 years of nuclear energy generation tells us that focusing on the cradle, and not adequately considering the grave of nuclear reactors, leads to significant and unconstrained costs that investors and governments might prefer to avoid.

Space weather events impose a threat on critical infrastructures such as electrical power grids, global navigation satellite systems, satellite operations, aviation technology and radio communication channels at various frequencies. We present an update on a new ground-level neutron monitor (NM-2023) which will be used to monitor space weather events, namely the detection and alert of ground-level enhancement (GLE) events. The NM-2023 will provide data to entities such as the United Kingdom Meteorological Office, the Neutron Monitor Database (NMDB), and the University of Surrey. We also report on a neutron monitoring survey conducted using a pair of subsystems deployed at several UK field sites. The data collected by these subsystems will be compared across the various sites, to data collected using a partial NM-2023 instrument and with data from established NMDB instruments with similar geomagnetic cutoff rigidities.

Accelerator mass spectrometry measurements of trace plutonium were conducted on soil samples from a relatively undisturbed site in the United Kingdom. Average isotopic ratios were measured across 15 samples for 240Pu/239Pu and across 13 samples for 244Pu/239Pu, yielding values of 0.181 +/- 0.003 and (11.1 +/- 1.1)x10-5, respectively. The latter is noted to be lower than the global background. A balance equation was employed to determine the local 239Pu contribution at (23 +/- 13)%. Revisiting this in terms of 240Pu suggests a 240Pu/239Pu ratio of 0.20 +/- 0.06 for the local contribution. Whilst inconsistent with materials associated with the Windscale and Chernobyl accidents, this ratio aligns with prior 240Pu/239Pu measurements of spent Magnox fuel.

This paper benchmarks two Proportional Technologies, Inc. (PTI) boron-coated straw (BCS) detector offerings against commercial helium-3 (3He) detectors for ground-level neutron monitoring. This study aims to assess if BCS-based detectors are a viable detector choice for the construction of a cosmic ray neutron monitor (NM) that is less expensive, smaller and produces comparable results to the 6-tube NM-64, typically used in the existing global NM network. The experimental methodology, data and analysis for the observed detection efficiency of the PTI-110 BCS module as a function of distance are presented. The PTI-204 BCS detector tube is benchmarked against a 7.5atm 3He-filled cylindrical proportional counter using a high-density polyethylene (HDPE) moderating test rig. Monte Carlo N-Particle (MCNP) models are validated against the experimental data. The experimental and simulation data for PTI-110 BCS unit detection efficiency agreement is within 4.5%. This confirms that the response of charged particles from the B4C layer is accounted for. The measured 3He tube detection efficiency was nearly three times greater than the PTI-204 detector. A trade-off analysis of 3He (at various fill pressures) versus BCS-based detector options, with supporting experimentally validated MCNP calculations, is used to provide confidence in the calculation of the 4 atm 3He tube-based ground-level NM design.

When assaying special nuclear materials using the passive neutron multiplicity counting method, due account must be taken of prompt neutron leakage self-multiplication in interpreting the various counting rates observed. Most often, in practical work, it is treated as an unknown model parameter to be determined from the experimental data. However, in a learning environment and when planning experiments, it is useful to have a straightforward means to estimate the leakage self-multiplication of a measurement item. In the present work, we develop a simple, hybrid, one energy-group, point-like source model for leakage self-multiplication, implemented with interaction probabilities calculated based on spherical and cylindrical bodies. We use published criticality tables to demonstrate the procedure. We show how the prompt neutron leakage self-multiplication may be estimated rudimentarily, including the effects of neutron scattering within the item. This treatment has considerable pedagogic value because it completes, in a similar conceptual framework, the physical point-model picture commonly used to interpret such neutron correlation counting-based measurements. It provides a straightforward quantitative physics-informed structure for making a forward prediction of the leakage selfmultiplication factor of a compact non-reentrant measurement item, which otherwise is introduced as an unknown model parameter to be estimated only from experimental data with no guidance on how the value can be estimated a priori. The numerical scheme has been developed with weakly multiplying objects in mind because they are typical of the kind of items measured by thermal-neutron well-counters for nuclear safeguards accountancy and nonproliferation verification purposes. Another potential use is for the assay of measurement items of known geometry and composition where the prompt neutron self-leakage multiplication can be estimated using the simple model developed, thereby allowing the (alpha,n) production rate to be treated as the unknown in the practical solution (or inversion) of the usual point-model coincidence equations.

Advancements in radiation detection for robotic deployments are described concerning the use of low-density, multifunctional, metal-foam materials as collimators. The use of nichrome (NiCr) metal foam, poly(methyl methacrylate) (PMMA) foam with stainless steel powder, and 3D-printed tungsten foam experimentally to isolate radioactive isotopes in constrained environments has been explored. This research demonstrates that these materials used in this way might reduce the payload associated with heavy metal collimators significantly relative to conventional, homogeneous alternatives such as solid lead and tungsten, and hence that they might enable spatial characterisation tasks that would otherwise be infeasible due to payload constraints—particularly in robotic systems where the use of conventional high-Z, dense collimators can limit their flexibility. The results suggest that metal foams and related materials can make collimation-aided localisation viable in such constrained settings, offering advantages in mass and characterisation granularity.

In recent years, the impacts of solar activity on the earth’s surface, atmospheric and orbital environments have become increasingly important. Governments around the world have identified “space weather” as a potentially significant risk to critical infrastructure. However, the monitoring and forecasting capabilities for these events are currently rudimentary compared to terrestrial weather.A global network of galactic and solar cosmic ray ground level monitors produce data for academic study and Ground Level Enhancement (GLE) event alerting. A GLE is typically characterised by a sudden large increase flux of fast neutrons over a wide area of the Earth’s surface for a period of 15 minutes or longer followed by a relatively gradual drop to the quiescent level. The flux of energetic subatomic particles during these events can degrade solar arrays, damage electronic components or cause single event effects (malfunctions) in semiconductor devices, potentially leading to significant disruption.However, this network is built primarily using a neutron monitor (NM) design from 1964, named the NM-64. In the intervening years computer driven digital acquisition and processing have been added, but the monitor itself remains the same. Consequently, a new cosmic ray NM has been commissioned, the design for which has been optimised using Monte Carlo N-Particle simulations and experimentally validated. The counting performance of this design matches the NM-64 whilst using alternative non-toxic detectors, and being significantly smaller and lighter.The new NM-2023, soon to be installed at a UK Meteorological Office site, will send its data to the Met Office Space Weather Operations Centre (MOSWOC) and the Neutron Monitor DataBase (NMDB) for global dissemination. Supporting real-time data processing and transmission to recipients facilitates their integration into operation forecast products, such as the nowcasting of atmospheric radiation exposure for end-users in the aviation sector.As the accuracy of NM-2023 data is vital, a series of algorithms are applied to perform error checking and correction, along with air pressure correction and data formatting, before the data is disseminated. Two anomaly detection methods are employed, one on the immediate data and the other on the long-term trends. Multiple approaches have been developed for the immediate analysis, one using Principal Component Analysis. Weekly averages of count rates and measurements of neutron multiplicity form some of the long-term analysis. Concurrently with code development, a prototype for the NM-2023 has been gathering cosmic ray data at multiple locations in the UK. The results track trends seen by nearby NM-64s. The presentation will cover a discussion of the anomaly correction algorithms, in combination with a comparison of some data from the current NM-64 network with both the prototype and early results from the NM-2023.

An evaluation of graded density, metal foam collimator plates for use with single-detector localization systems on robotic platforms is described. Linear attenuation measurements have been made of three foams of different bulk densities, and a combination of these has been used to manufacture a barrel-type collimator. The angular responses obtained with this device reveal the distinct shape consistent with the response of a conventional, higher-density, homogeneous alternative which enables localization of radioactivity at gamma-radiation energies up to and potentially exceeding 2.5 MeV. This suggests that the use of low-density metal foam collimators might reduce the payload demand in nuclear robotic applications to enable a range of new nuclear characterization tasks.

A qualitative approach to discern the relative contributions of 137Cs and 90Sr in-solution with a monitoring probe is described, based on a comparison of X- and gamma-ray photon spectra. The bremsstrahlung yield from 90Sr has been measured as a function of distance (x) from a cerium bromide scintillation detector relative to the 137Cs gamma-ray full-energy peak response. The utility of two, count-independent shape factor parameters has been compared: the ratio of the sum of the counts in the 60-800 keV region to the full-energy peak response associated with the 137Cs 662 keV gamma-ray line, termed for the benefit of this paper as SF1, and the ratio of counts in the 60-350 keV region to those in the 350-450 keV region, defined in this work as SF2. These parameters probe the presence of isotopes associated with clear full-energy spectral lines and bremsstrahlung, respectively. They have been calibrated as a function of x with sealed sources in the laboratory and both are observed to be asymptotic as x-*0. This approach has been tested with a variety of open, laboratory-based liquid samples comprising 90Sr and 137Cs, and in a waterbased, contaminated medium in the field associated with a sump at a low-level waste disposal facility on the former fast reactor site at Dounreay, UK. The highest response in both SF1 and SF2 measured in this work is observed in these on-site measurements, consistent with x-*0, implying both 90Sr and 137Cs presenting together in solution. This is consistent with prior, laboratory-based analysis of the sump media, and suggests that the 3- -emitter contribution (anticipated to comprise 90Sr and 90Y) is very near the probe, consistent with the solution being in contact with it. This is of relevance where the 3- /gamma composition of contaminated groundwater, in-situ, is not well understood or where migratory changes in activity are suspected.

The performance of a europium -doped strontium iodide scintillator for uranium enrichment measurement of a variety of sintered uranium dioxide fuel pellets is described and compared to that of caesium iodide and sodium iodide. Enrichment has been determined via passive gamma-ray spectrometry of the 186 keV line from uranium -235 using gross count, net count, and peak ratio analyses. The 38 mm & Oslash; x 38 mm strontium iodide crystal demonstrates superior energy resolution (3.43 +/- 0.03% at 662 keV) and competitive detection efficiency for its size in the energy range of interest for uranium enrichment analysis (<250 keV). It demonstrates better chi v2 and coefficient of determination values than caesium iodide and sodium iodide when measuring uranium enrichment using the gross- and net -count from the 186 keV emission. It is shown to have the least measurement variance of the three scintillators studied in determining the uranium enrichment of pellets in a blind test, with a relative error comparative to sodium iodide and smaller than caesium iodide. This research heralds the potential of strontium iodide in passive gamma-ray uranium enrichment applications.