Probabilistic seismic hazard assessment for a new-build nuclear power plant site in the UK

A probabilistic seismic hazard analysis (PSHA) has been conducted as part of the Safety Case justification for a new-build nuclear power plant in the UK. The study followed a cost-efficient methodology developed by CH2M and associates for safety-significant infrastructure where high-level regulatory assurance is required. Historical seismicity was re-evaluated from original sources. The seismicity model considered fourteen seismic sources which, when combined, formed six alternative seismic source models. Separate models for the median ground-motion and aleatory variability were considered. The median ground-motion model comprised a suite of ground-motion equations adjusted to the site-specific conditions using VS-kappa factors. A partially non-ergodic sigma model was adopted with separate components for the inter-event variability, and single-station intra-event variability, adjusted by a partially ergodic site-to-site variability term. Site response analysis was performed using equivalent-linear random vibration theory with explicit incorporation of the variability in the ground properties using Monte Carlo simulations. The final PSHA results were obtained by convolution of the hazard at the reference rock horizon with the site amplification factors. The overall epistemic uncertainty captured by the logic tree was assessed and compared against results from earlier PSHA studies for the same site

Pathogen-Induced Proapoptotic Phenotype and High CD95 (Fas) Expression Accompany a Suboptimal CD8+ T-Cell Response: Reversal by Adenoviral Vaccine

MHC class Ia-restricted CD8+ T cells are important mediators of the adaptive immune response against infections caused by intracellular microorganisms. Whereas antigen-specific effector CD8+ T cells can clear infection caused by intracellular pathogens, in some circumstances, the immune response is suboptimal and the microorganisms survive, causing host death or chronic infection. Here, we explored the cellular and molecular mechanisms that could explain why CD8+ T cell-mediated immunity during infection with the human protozoan parasite Trypanosoma cruzi is not optimal. For that purpose, we compared the CD8+ T-cell mediated immune responses in mice infected with T. cruzi or vaccinated with a recombinant adenovirus expressing an immunodominant parasite antigen. Several functional and phenotypic characteristics of specific CD8+ T cells overlapped. Among few exceptions was an accelerated expansion of the immune response in adenoviral vaccinated mice when compared to infected ones. Also, there was an upregulated expression of the apoptotic-signaling receptor CD95 on the surface of specific T cells from infected mice, which was not observed in the case of adenoviral-vaccinated mice. Most importantly, adenoviral vaccine provided at the time of infection significantly reduced the upregulation of CD95 expression and the proapoptotic phenotype of pathogen-specific CD8+ cells expanded during infection. In parallel, infected adenovirus-vaccinated mice had a stronger CD8 T-cell mediated immune response and survived an otherwise lethal infection. We concluded that a suboptimal CD8+ T-cell response is associated with an upregulation of CD95 expression and a proapoptotic phenotype. Both can be blocked by adenoviral vaccination

Style-of-faulting in ground-motion prediction equations

Equations for the prediction of response spectral ordinates invariably include magnitude, distance and site classification as independent variables. A few equations also include style-offaulting as a fourth variable, although this has an almost negligible effect on the standard deviation of the equation. Nonetheless, style-of-faulting is a useful parameter to include in ground-motion prediction equations since the rupture mechanism of future earthquakes in a particular seismic source zone can usually be defined with some confidence. Current equations including style-of-faulting use different schemes to classify fault ruptures into various categories, which leads to uncertainty and ambiguity regarding the nature and extent of the effect of focal mechanism on ground motions. European equations for spectral ordinates do not currently include style-of-faulting factors, and seismic hazard assessments in Europe often combine, in logic-tree formulations, these equations with those from western North America that do include style-of-faulting coefficients. In this article, a simple scheme is provided to allow style-of-faulting adjustments to be made for those equations that do not include coefficients for rupture mechanism, so that style-of-faulting can be fully incorporated into the hazard calculations. This also considers the case of normal fault ruptures, not modelled in any of the current Californian equations, but which are the dominant mechanism in many parts of Europe. The scheme is validated by performing new regressions on a widely used European attenuation relationship with additional terms for style-of-faulting

Development of a suite of stochastic ground-motion models for the United Kingdom

Since 1995, various estimates of stochastic ground-motion parameters have been computed for UK earthquakes and a few UK stochastic models proposed. These models have been developed by inverting the available weak-motion data to estimate ranges for the key parameters and using expert judgement and evidence from other regions when data are insufficient. The resulting ground-motion models have been used within site-specific seismic hazard assessments for critical infrastructure and for the 2020 UK National Seismic Hazard Model developed by the British Geological Survey. Often stochastic models have been given a lower weight within these assessments than empirical models from other regions, particularly due to doubts over how the stochastic models scale to larger magnitudes. As part of a broader project to develop a backbone ground-motion model using a hybrid stochastic-empirical method, here we present a summary of analysis conducted using an expanded ground-motion database from the UK and surrounding region to determine stochastic parameters. The ground-motion data have been adjusted to a single rock condition using an approximate technique. We used an approach to determine the stochastic models that is appropriate for their final use, namely within a scaled backbone approach that provides a suite of consistent models with appropriate weights. Due to the trade-off amongst the key parameters (e.g., stress (drop) parameter, geometrical spreading and site attenuation), constraints from the literature and expert judgement are applied. The resulting suite of models captures the uncertainties inherent in the inversion owing to the limited magnitude, distance and structural period range of the ground-motion data. These models will be the basis of a UK ground-motion model due for completion in 2023