Assessment of safety margins of exposure to non-genotoxic chemical substances in food

[EN] The concept of Food Safety Margin (FSM) was introduced in microbiological risk analysis as an alternative approach to risk characterization within the informed-risk decision-making process. Its aim was to verify compliance with food safety objectives by assessing the effects of uncertainties. This paper describes the fundamentals and develop a new formulation of safety margins to verify compliance with food safety goals in relation to exposure to non-genotoxic chemical hazards. Both classical and probabilistic metrics were used to compare a given exposure to an estimated daily intake (EDI) with a given safety goal, the acceptable daily intake (ADI). The safety margins of these metrics were assessed in the exposure of peaches to organophosphorus pesticides. The pesticides considered were Azinphos-methyl, Chlorpyrifos, Diazinon, Dimethoate, Methamidophos, Parathion-methyl and Phosmet. The concentrations were obtained from the USDA pesticide database. The study period included the 11 years in which peaches were analysed from 1994 to 2014. The results show the importance of using the effect of uncertainty instead of mean values for risk characterization and that not only safety margins increased during this period but also that uncertainty was reduced. In general, large safety margins were observed in the period studied and few situations were found in which exposure was outside the safety limits. (C) 2017 Elsevier Ltd. All rights reserved.Doménech Antich, EM.; Martorell Alsina, SS. (2017). Assessment of safety margins of exposure to non-genotoxic chemical substances in food. Food Control. 79:1-9. doi:10.1016/j.foodcont.2017.03.018S197

Definition and usage of food safety margins for verifying compliance of food safety objectives

[EN] Over the last decade, risk analysis has gradually been introduced as a tool to make decisions about food safety policies. In this framework, the ALOP (Appropriate Level of Protection) concept, which can be seen as a statement of the degree of public protection that should be attained in a country, was introduced. In addition, FSO (Food Safety Objectives) was introduced to provide a link between the ALOP and target points/goals in the supply chain. Historically, ALOP and FSO decisions have been based on the ALARA (As Low As reasonably Achievable) approach. Since an ALARA approach is based on the status of current technology, it is likely that the ALOP is attainable, provided a substantial portion of the industry complies with technological requirements or adopt “best practices” that will achieve the FSO. Food managers must control and government agencies must enforce and monitor the fulfilment of FSO. Once FSO has been established and adopted by the food industry, a major concern is to evaluate the results of the implementation of FSO in order to verify compliance. This paper introduces the concept of food safety margin (FSM) and its formulation based on classical and probabilistic approaches, which are intended to be used as a tool to measure the degree of compliance with FSO. For a better understanding of how food safety margins perform, FSM are estimated for Listeria monocytogenes in three different products, (semi-soft cheese, heat treated meat and cold smoked salmon). The results obtained, adopting both classical and probabilistic approaches, are discussed.Doménech Antich, EM.; Martorell Alsina, SS. (2016). Definition and usage of food safety margins for verifying compliance of food safety objectives. Food Control. 59:669-674. doi:10.1016/j.foodcont.2015.05.042S6696745

Formulation and application of the probability of exceedance metric for risk characterization of non-threshold chemical hazards in food

[EN] The aim of this work is to present the rationale, formulation, and application of the probability of exceedance (POE) as a metric capable of characterizing public health risks due to exposure to non-threshold chemical hazards in food. One of the main advantages of this metric is that it complements the information provided by the MOE and supports risk managers in decision-making, especially when the distribution of the estimated intake is positively biased. For a better understanding of its benefits, MOE and POE values were calculated in relation to the exposure to inorganic arsenic (iAs) and lead (Pb) in the diet of the Australian, Chinese, European, Japanese and American adult populations. The findings showed that similar MOE values, and therefore similar levels of concern, can have differences in POE results of up to several orders of magnitude, suggesting that more effective risk management measures should be prioritised.Doménech Antich, EM.; Martorell Alsina, SS. (2021). Formulation and application of the probability of exceedance metric for risk characterization of non-threshold chemical hazards in food. Food Control. 124:1-8. https://doi.org/10.1016/j.foodcont.2021.107910S1812

Unavailability model for demand-caused failures of safety components addressing degradation by demand-induced stress, maintenance effectiveness and test efficiency

[EN] The reliability, availability and maintainability (RAM) modelling of safety equipment has long been a topic of major concern. Some RAM models have focused on explicitly addressing the effect of component degradation and surveillance and maintenance policies, searching for an optimum level of the safety component RAM by adjusting surveillance and maintenance related parameters. As regards the reliability contribution, these components normally have two main types of failure mode that contribute to the probability of failure on demand (PFD): (1) by demand-caused and (2) standby-related failures. The former is normally associated with a demand failure probability, which is affected by the degradation caused by demand-related stress. Surveillance testing therefore not only introduces a positive effect, but also an adverse one, which it compensates by performing maintenance activities to eliminate or reduce the accumulated degradation. This paper proposes a new model for the demand failure probability that explicitly addresses all aspects of the effect of demand-induced stress (mostly test-induced stress), maintenance effectiveness (PAS or PAR model) and test efficiency. A case study is included on an application to a typical motor-operated valve in a nuclear power plant.The authors are grateful to the Spanish Ministry of Science and Innovation for the financial support received (Research Projects ENE2013-45540-R and ENE2016-80401-R) and the doctoral scholarship awarded (BES-2014-067602). The study also received financial support from the Spanish Research Agency and the European Regional Development Fund.Martorell-Aygues, P.; Martón Lluch, I.; Sánchez Galdón, AI.; Martorell Alsina, SS. (2017). Unavailability model for demand-caused failures of safety components addressing degradation by demand-induced stress, maintenance effectiveness and test efficiency. Reliability Engineering & System Safety. 168:18-27. https://doi.org/10.1016/j.ress.2017.05.044S182716

Análisis de transitorios base de diseño de un reactor avanzado refrigerado por sodio utilizando modelos tridimensionales con acoplamiento neutrónico-termohidráulico

Entre los objetivos marcados por el Generation IV International Forum (GIF) se encuentra el dotar a la nueva generación de reactores nucleares de un nivel de seguridad igual o superior a la generación actual. Diferentes iniciativas europeas (SNTP, ESNII) han establecido en su agenda los esfuerzos en I+D necesarios para alcanzar esos ambiciosos objetivos. Entre ellos se encuentra el desarrollo de herramientas para simular el comportamiento de estos diseños en condiciones de accidente de forma precisa y detallada. El artículo describe las diferentes etapas seguidas para desarrollar un modelo del diseño preliminar del European Sodium Fast Reactor (ESFR). Partiendo del desarrollo con el código TRACE de un modelo unidimensional con realimentación neutrónica de cinética puntal contrastado con los resultados obtenidos con modelos equivalentes que se tomó como referencia, se extendió a un modelo tridimensional termohidráulico para posteriormente ser acoplado con un código neutrónico de cinética espacial (PARCS). La conclusión del trabajo es la demostración de que las herramientas de cálculo convencionales pueden ser adaptadas y utilizadas en el análisis de seguridad de reactores avanzados. Se identifican también las aplicaciones y desarrollos posibles del modelo acoplado y sus implicaciones en el estudio de seguridad del reactor.Lázaro Chueca, A.; Ammirabile, L.; Martorell Alsina, SS. (2014). Análisis de transitorios base de diseño de un reactor avanzado refrigerado por sodio utilizando modelos tridimensionales con acoplamiento neutrónico-termohidráulico. Sociedad Nuclear Española. http://hdl.handle.net/10251/71946

Optimization of test and maintenance of ageing components consisting of multiple items and addressing effectiveness

[EN] There are many models in the literature that have been proposed in the last decades aimed at assessing the reliability, availability and maintainability (RAM) of safety equipment, many of them with a focus on their use to assess the risk level of a technological system or to search for appropriate design and/or surveillance and maintenance policies in order to assure that an optimum level of RAM of safety systems is kept during all the plant operational life. This paper proposes a new approach for RAM modelling that accounts for equipment ageing and maintenance and testing effectiveness of equipment consisting of multiple items in an integrated manner. This model is then used to perform the simultaneous optimization of testing and maintenance for ageing equipment consisting of multiple items. An example of application is provided, which considers a simplified High Pressure Injection System (HPIS) of a typical Power Water Reactor (PWR). Basically, this system consists of motor driven pumps (MDP) and motor operated valves (MOV), where both types of components consists of two items each. These components present different failure and cause modes and behaviours, and they also undertake complex test and maintenance activities depending on the item involved. The results of the example of application demonstrate that the optimization algorithm provide the best solutions when the optimization problem is formulated and solved considering full flexibility in the implementation of testing and maintenance activities taking part of such an integrated RAM model.Authors are grateful to the Spanish Ministry of Science and Innovation for the financial support of this work (research project ENE2013-45540-R) and the Doctoral fellow (BES-2011-043906 and BES-2014-067602).Martón Lluch, I.; Martorell Aigües, P.; Mullor, R.; Sánchez Galdón, AI.; Martorell Alsina, SS. (2016). Optimization of test and maintenance of ageing components consisting of multiple items and addressing effectiveness. Reliability Engineering and System Safety. 153:151-158. https://doi.org/10.1016/j.ress.2016.04.015S15115815

Parameter Estimation of a Reliability Model of Demand-Caused and Standby-Related Failures of Safety Components Exposed to Degradation by Demand Stress and Ageing That Undergo Imperfect Maintenance

[EN] One can find many reliability, availability, and maintainability (RAM) models proposed in the literature. However, such models become more complex day after day, as there is an attempt to capture equipment performance in a more realistic way, such as, explicitly addressing the effect of component ageing and degradation, surveillance activities, and corrective and preventive maintenance policies. Then, there is a need to fit the best model to real data by estimating the model parameters using an appropriate tool. This problem is not easy to solve in some cases since the number of parameters is large and the available data is scarce. This paper considers two main failure models commonly adopted to represent the probability of failure on demand (PFD) of safety equipment: (1) by demand-caused and (2) standby-related failures. It proposes a maximum likelihood estimation (MLE) approach for parameter estimation of a reliability model of demand-caused and standby-related failures of safety components exposed to degradation by demand stress and ageing that undergo imperfect maintenance. The case study considers real failure, test, and maintenance data for a typical motor-operated valve in a nuclear power plant. The results of the parameters estimation and the adoption of the best model are discussed.The authors are grateful to the Spanish Ministry of Science and Innovation for the financial support received (Research Project ENE2016-80401-R) and the doctoral scholarship awarded (BES-2014-067602). The study also received financial support from the Spanish Research Agency and the European Regional Development Fund.Martorell Alsina, SS.; Martorell-Aygues, P.; Sánchez Galdón, AI.; Mullor, R.; Martón Lluch, I. (2017). Parameter Estimation of a Reliability Model of Demand-Caused and Standby-Related Failures of Safety Components Exposed to Degradation by Demand Stress and Ageing That Undergo Imperfect Maintenance. Mathematical Problems in Engineering. (7042453):1-11. https://doi.org/10.1155/2017/7042453S111704245

Influencia de la fiabilidad humana en la evaluación del impacto en el riesgo de cambios de CLO

El tratamiento y estudio de las incertidumbres epistémicas resulta de especial importancia en la aplicación del análisis probabilista de seguridad a la toma de decisiones informadas en el riesgo, tal y como señala la guía reguladora 1.174[1] (Regulatory Guide 1.174, RG1.174). Concretamente, la RG 1.177 [2] particulariza la evaluación del impacto en el riesgo referida a cambios en las Especificaciones Técnicas de Funcionamiento (ETF). Partiendo del marco definido por dichas guías reguladoras, se evaluará el efecto de las incertidumbres epistémicas asociadas al análisis de fiabilidad humana en el contexto de las Condiciones Limites de operación. Como ejemplo de aplicación, se realizará un estudio de sensibilidad del tiempo de Inoperabilidad (Completion Time, CT) del Sistema de Extracción del Calor ResidualMartorell Aigües, P.; Martorell Alsina, SS.; Marton Lluch, I.; Saiz, M. (2014). Influencia de la fiabilidad humana en la evaluación del impacto en el riesgo de cambios de CLO. Sociedad Nuclear Española. http://hdl.handle.net/10251/71944

Adaptación y aplicación del código TRACE para el análisis de transitorios en diseños de reactores rápidos refrigerados por plomo

El Generation IV International Forum aglutina los diferentes esfuerzos internacionales en I+D para el desarrollo de una nueva generación de reactores nucleares. Entre las tecnologías identificadas destacan los reactores rápidos refrigerados por metales líquidos, tales como el sodio o el plomo, con gran potencial para cumplir con los ambiciosos objetivos marcados. La falta de experiencia operativa previa obliga al uso de herramientas capaces de simular el comportamiento de los sistemas basados en esta tecnología. El artículo expone las modificaciones implementadas en el código TRACE para incluir las tablas termodinámicas del plomo líquido extraídas de resultados experimentales. A continuación, explica el proceso seguido para el desarrollo de un modelo termohidráulico para el prototipo ALFRED y el análisis de una selección de transitorios representativos realizado en el marco de proyectos internacionales de investigación. El estudio demuestra la aplicabilidad del código TRACE para simular diseños de reactores rápidos refrigerados por plomo y expone los altos márgenes de seguridad con los que cuenta esta tecnología para acomodar los transitorios más severos identificados en su estudio de seguridad.Lázaro Chueca, A.; Ammirabile, L.; Martorell Alsina, SS. (2014). Adaptación y aplicación del código TRACE para el análisis de transitorios en diseños de reactores rápidos refrigerados por plomo. Sociedad Nuclear Española. http://hdl.handle.net/10251/71945

Coincidence summing correction factors for 238U and 232Th decay series using the Monte Carlo method

[EN] Environmental samples analyzed in gamma spectrometry laboratories usually contain natural radionuclides such as 238U and 232Th. Using gamma spectrometry techniques is possible to estimate the activity of these radionuclides by measuring the gamma emissions of radionuclides belonging to their decay chain. Nonetheless, some of these radionuclides emit photons in cascade presenting Coincidence Summing (CS), which if not corrected, may affect the final activity quantification. The aim of this work is to apply the Monte Carlo method to calculate the True Summing Correction Factors (TSCFs) for 238U and 232Th decay series for different sample configurations (geometry and matrix) using the GEANT4 toolkit. In order to validate the results provided by GEANT4 using the RDM, the software TRUECOINC has been applied to calculate also the TSCFs. In addition, the influence of the geometry/matrix on the TSCFs is analyzed.The authors gratefully acknowledge financial support from the Catedra CSN-UPV Vicente Serradell, Spain as well as the Laboratorio de Radiactividad Ambiental (Universitat Politecnica de Valencia), Spain for the dedicated funding and resources to this research work under Grant no. FPI-2015-S2-1576Ordóñez-Ródenas, J.; Gallardo Bermell, S.; Ortiz Moragón, J.; Martorell Alsina, SS. (2019). Coincidence summing correction factors for 238U and 232Th decay series using the Monte Carlo method. Radiation Physics and Chemistry. 155:244-247. https://doi.org/10.1016/j.radphyschem.2018.09.013S24424715