'Family members screaming for help makes it very difficult to don PPE'. A qualitative study on UK ambulance staff experiences of infection prevention and control practices during the COVID-19 pandemic

© 2024 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), https://creativecommons.org/licenses/by/4.0/BACKGROUND: During the first wave of the COVID-19 pandemic in the UK, ambulance staff continued to deliver direct patient care whilst simultaneously adapting to a considerable escalation in evolving infection prevention and control (IPC) practices. AIM: To enable learning to benefit future planning, this qualitative article aims to describe ambulance staff's experiences of this rapid escalation of IPC practices. METHOD: Three online surveys were presented during the acceleration, peak, and deceleration phases of the pandemic's first wave in the UK (2020). Overall, 18 questions contributed 14,237 free text responses that were examined using inductive thematic analysis at both descriptive and interpretive levels. FINDINGS: Many participants lacked confidence in policies related to the use of personal protective equipment (PPE) because of perceived inadequate supporting evidence, confusing communication, and low familiarity with items. Compliance with policy and confidence in PPE use were further influenced by discomfort, urgency, and perceptions of risk. Various suggestions were made to improve IPC practices within the work environment, including reducing unnecessary exposure through public education and remote triage improvements. DISCUSSION: Some participants' poor experiences of escalating IPC practices were shared with health care workers studied in other environments and in previous epidemics, emphasising the need for lessons to be learnt. PPE should be developed with consideration of ambulance staff's unique working environment and regular familiarisation training could be beneficial. Pragmatic, evidence-based, clearly communicated policies implemented with sufficient resources may protect staff and facilitate them to maintain standards of care delivery during a pandemic.Peer reviewe

Spatial Effects in Low Neutron Source Start-up and Associated Stochastic Phenomena

This work concerns the calculation of the neutron source strength necessary to start up a nuclear reactor such that the likelihood of an undesirable stochastic transient is reduced to a specified value (e.g. 10−8). We extend our earlier point model work on low source calculations to include the spatial variation of the neutron source. Results for the source multiplier for a given safety factor are obtained for slab, cylindrical and spherical systems. The spatial term in the Pál-Bell equation is dealt with by Chebyshev-Gauss-Lobatto collocation methods and this enables an extrapolation distance to be included, thereby simulating a reflector. Results are given for a range of system sizes, and corresponding source multipliers for safe source determination are obtained. The saddlepoint method is used to invert the generating function. In addition to the low source calculations, we have also tested the collocation method on the survival probability in a sphere which demonstrates excellent convergence. We also comment on the usefulness of the Gamma pdf for spatially dependent problems. For clarity of presentation, some of the detailed mathematical work is relegated to Appendices

The energy dependent Pál–Bell equation and the influence of the neutron energy on the survival probability in a supercritical medium

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Coupled probabilistic and point kinetics modelling of fast pulses in nuclear systems

AbstractThis paper describes a probabilistic method of modelling point nuclear systems with low numbers of neutrons including the effects of delayed neutron precursors and its coupling with standard point kinetics equations. This coupling allows the simulation of the non-deterministic progression of a system transitioning from subcritical to supercritical and the resulting power peak. Through analysis of large numbers of realisations various statistical parameters of such transients can be obtained. The method of simulation presented here successfully replicates the survival and extinction probabilities predicted by the Backwards Master Equation and experimental and analytic results from the literature regarding the Godiva reactor and extends the examination of that reactor. In particular the effect of delayed neutrons on the simulated response of Godiva is highlighted. With its implementation in a parallel computer code, the model is able to simulate at a reasonable speed a range of systems where low neutron populations are important

CALLISTO-SPK: A Stochastic Point Kinetics Code for Performing Low Source Nuclear Power Plant Start-up and Power Ascension Calculations

This paper presents the theory and application of a code called CALLISTO which is used for performing NPP start-up and power ascension calculations. The CALLISTO code is designed to calculate various values relating to the neutron population of a nuclear system which contains a low number of neutrons. These variables include the moments of the PDF of the neutron population, the maturity time and the source multiplier. The code itself is based upon the mathematics presented in another paper and utilises representations of the neutron population which are independent of both space and angle but allows for the specification of an arbitrary number of energy groups. Five examples of the use of the code are presented. Comparison is performed against results found in the literature and the degree of agreement is discussed. In general the agreement is found to be good and, where it is not, plausible explanations for discrepancies are presented. The final two cases presented examine the effect of the number of neutron groups included and finds that, for the systems simulated, there is no significant difference in the key results of the code

Importance of parametric uncertainty in predicting probability distributions for burst wait-times in fissile systems

A method of uncertainty quantification in the calculation of wait-time probability distributions in delayed supercritical systems is presented. The method is based on Monte Carlo uncertainty quantification and makes use of the computationally efficient gamma distribution method for prediction of the wait-time probability distribution. The range of accuracy of the gamma distribution method is examined and parameterised based on the rate and magnitude of the reactivity insertion, the strength of the intrinsic neutron source and the prompt neutron lifetime. The saddlepoint method for inverting the generating function and a Monte Carlo simulation are used as benchmarks against which the accuracy of the gamma distribution method is determined. Finally, uncertainty quantification is applied to models of the Y-12 accident and experiments of Authier et al. (2014) on the Caliban reactor

Wetting-induced volumetric collapse of UO2 powder beds and the consequence on transient nuclear criticality excursions

Mathematical and computational models are proposed to simulate wetting-induced volumetric collapse of fissile powder beds. Slumping, nuclear thermal hydraulics, radiolytic gas, and steam production models are coupled with point neutron kinetics to investigate transient nuclear criticality excursions in two 5-wt% enriched UO2 fissile powder beds with varying levels of wetting-induced volumetric collapse. The two beds are distinguished by their mean powder particle size of 30 μm and 100 μm. For the UO2 powder beds modelled, the re-distribution of UO2 powder and moderator due to slumping introduced a negative reactivity into the system. This increased the amount of time taken for a delayed critical state to be reached once infiltration began, and also reduced the total fission energy generated over the course of the simulated transient. The total fission energy generated ranged from 42 MJ to 48 MJ 100 seconds after the initial nuclear criticality excursion was observed for the 30 μm sized UO2 powder bed. The fission energy of the larger sized powder bed (100 μm), varied from 42 MJ to 57 MJ. Larger discrepancies between the slumped and un-slumped initial peak power are predicted. Peak powers varied from 29.2 MW to 106 MW for the smaller-sized powder particles, whereas for larger particles, the peak powers varied from 255 MW to 501 MW

Transient nuclear criticality excursion analysis of highly dispersed particulate three-phase fluidised systems

The aim of this study was to perform sensitivity analysis, investigating how different fluidisation and sedimentation characteristics of three-phase wetted UO2 powder beds, may affect a transient nuclear criticality excursion initiated through the addition of water into a fissile powder bed. This type of postulated nuclear criticality accident scenario may occur in nuclear fuel fabrication facilities when a fire is fought through the use of water, supplied via an automatic or manual fire-suppression system. A similar scenario may also develop as a result of water leaks or flooding of the process area housing UO2 powder. The article introduces a model for gas-bubble induced fluidisation of a UO2 powder bed and examines how this phenomenon may affect the neutron kinetic response of a three-phase fluidised fissile powder system. Empirical analysis has shown that fissile suspensions form agglomerated structures when suspended in water, at agglomerate sizes that range from 18 to 40 . Simulation results indicate that both the critical gas velocity and rate of fluidisation may significantly affect transient nuclear criticality excursion dynamics. The re-distribution of fissile mass into a highly dispersed suspension generally reduces the reactivity of the system, however, depending on the H/U ratio, a positive reactivity may be added to the system. Low Péclet numbers in the suspension suggest that gas-bubble induced motion of the suspension causes a highly dispersive flow field. An oscillatory power response is predicted for low critical gas velocities where the reactivity of the system is predominantly governed by the re-distribution of fissile mass within the system. The frequency of these oscillations is greater for a higher hindered settling rate of powder particles. At a higher critical gas velocity, the transient nuclear criticality excursion is governed by the voidage reactivity feedback, making the response quite independent of fluidisation. In all cases, large volumes of UO2 powder may leave the domain due to overflowing of the suspension. Transient nuclear criticality excursions in UO2 powder beds with a low critical gas velocity are terminated once the bed becomes fully saturated

Numerical comparison of mathematical and computational models for the simulation of stochastic neutron kinetics problems

This paper concerns numerical comparisons between five mathematical models capable of modelling the stochastic behaviour of neutrons in low extraneous (extrinsic or fixed) neutron source applications. These models include analog Monte-Carlo (AMC), forward probability balance equations (FPB), generating function form of the forward probability balance equations (FGF), generating function form of the backward probability balance equations (P´al-Bell), and an Itˆo calculus model using both an explicit and implicit Euler-Maruyama discretization scheme. Results such as the survival probability, extinction probability, neutron population mean and standard deviation, and neutron population cumulative distribution function have all been compared. The least computationally demanding mathematical model has been found to be the use of the P´al-Bell equations which on average take four orders of magnitude less time to compute than the other methods in this study. The accuracy of the AMC and FPB models have been found to be strongly linked to the computational e ciency of the models. The computational e ciency of the models decrease significantly as the maximum allowable neutron population is approached. The Itˆo calculus methods, utilising explicit and implicit Euler-Maruyama discretization schemes, have been found to be unsuitable for modelling very low neutron populations. However, improved results, using the Itˆo calculus methods, have been achieved for systems containing a greater number of neutrons