French Nuclear Power Plants Research Articles

Environment: The Lifetime Extension of French Nuclear Power Plants

Environment: The Lifetime Extension of French Nuclear Power Plants

Inspection of Concrete/Steel/Concrete pipes by ultrasonic methods affected by corrosion

Concrete/Steel/concrete pipes are present in French nuclear powerplants. These pipelines are composed of three layers: an internal layer of centimeter concrete, a millimeter layer of steel and a layer of centimeter reinforced concrete. The pipelines located by the sea undergo corrosion of the steel part caused by the chlorides present in the seawater they transport. Nowadays, the diagnosis of corrosion is made with electrochemical measurements. But they provide a qualitative indicator about corrosion. In fact, the goal is to dispose of a Non-Destructive Technique capable of evaluating the extension of holes in the steel part with a minimum diameter of 1 cm and the steel thickness elsewhere with a 100 µm uncertainty. The inspection must be conducted from the outside of the pipe still working. Ultrasonic bulk waves, ultrasonic guided waves and vibration techniques are investigated. All of them are studied with a methodology from the lab to the field. In lab, specimens are manufactured and tested. The experimental results are compared to numerical results obtained with simulation tools like CIVA or Specfem2D. Then, the promising techniques are tested on a real concrete/steel/concrete pipe. For the bulk wave techniques, the major issue is to increase the frequency signal over 1 MHz to get a better resolution of the steel investigation. But at this frequency range, the multi-scattering phenomenon on concrete aggregates is prominent. First experimental results using pulse compression on lab samples are promising: holes in steel give a specific signature and compression techniques are used to get a better resolution in steel thickness after signal autocorrelation. For both guided wave and vibration techniques, simulations are used to determine modes sensitive to the steel thickness and Zero Group Velocity modes which will induce a strong characteristic frequency response. Experimental study is going on to reveal these modes on lab specimen.

In Situ Gas Monitoring by Fiber-Coupled Raman Spectrometry for H₂-Risk Management in Nuclear Containment During a Severe Nuclear Accident

During a severe nuclear accident leading up to core melting, molten corium–concrete interaction (MCCI) and core-coolant water reaction both release large amounts of hydrogen (H2) gas in the containment atmosphere. According to the Shapiro–Moffette ternary diagram and depending on local partial pressures of H2, air, and water vapor, deflagration/detonation may occur with potential deleterious impact over equipment and structures. CO and CO2 are also of interest, as revealing gases for MCCI. Pressurized Water Reactors (PWRs) of French Nuclear Power Plants (NPPs) are equipped with passive autocatalytic recombiners (PARs), partly mitigating the H2 risk. However, the H2-risk management strategy may be significantly improved by performing in situ monitoring of H2, O2, N2, H2O, CO, and CO2 partial pressures at several locations inside the containment, to account for potential local combustion risk. Raman spectrometry (RS) involves only one laser and spectrometer equipped with a 2-D charge-coupled device (CDD). Raman probes are chemically selective and may be radiation-hardened. Custom-made fiber-coupled Raman probes, linked with a readout unit, were qualified in a climatic chamber, a flame-propagation tube, a 60Co irradiation cell, a 3-D shaking table, a steam jet and the MISTRA facility (1/10 reduced-scale containment mock-up dedicated to thermo-hydraulic tests).

A long-term prediction approach based on long short-term memory neural networks with automatic parameter optimization by Tree-structured Parzen Estimator and applied to time-series data of NPP steam generators

Developing an accurate and reliable multi-step ahead prediction model is a key problem in many Prognostics and Health Management (PHM) applications. Inevitably, the further one attempts to predict into the future, the harder it is to achieve an accurate and stable prediction due to increasing uncertainty and error accumulation. In this paper, we address this problem by proposing a prediction model based on Long Short-Term Memory (LSTM), a deep neural network developed for dealing with the long-term dependencies in time-series data. Our proposed prediction model also tackles two additional issues. Firstly, the hyperparameters of the proposed model are automatically tuned by a Bayesian optimization algorithm, called Tree-structured Parzen Estimator (TPE). Secondly, the proposed model allows assessing the uncertainty on the prediction. To validate the performance of the proposed model, a case study considering steam generator data acquired from different French nuclear power plants (NPPs) is carried out. Alternative prediction models are also considered for comparison purposes.

Radioinactive: Do nuclear power plant outages in France affect the German electricity prices?

Do nuclear power plant outages in France affect the German electricity prices? In the case of the extensive inspections from October 2016 to February 2017 in 12 French nuclear power plants: Yes. This capacity shock increased the French electricity spot market price on average by 27.1%. The German-Austrian electricity spot market price was affected through cross-border trade. Due to increased electricity exports from Germany to France, the German-Austrian electricity spot market price increased on average by 3.2%. Moreover, due to decreased electricity imports from France to Germany, the German-Austrian electricity spot price increased on average by 7.6%. These results derive from a quasi-experimental approach based on coarsened exact matching, where the exogenous nature of the capacity shock is exploited as a random treatment in order to identify causal effects.

Trapping measurements of volatile iodine by sand bed and metallic filters

A series of experimental tests were performed to measure the efficiency of volatile iodine trapping on sand bed filters and metallic filters. These filtering media are used in French nuclear power plants to mitigate releases in case of severe accident. The results show that molecular iodine is more easily trapped than methyl iodide due to its high chemical affinity with stainless steel or with silver and cesium cations included in the filter medium. For methyl iodide, the trapping efficiency is low.

Limestone-siliceous and siliceous concretes thermal damaging at high temperature

Limestone-siliceous and siliceous concretes are used in reactor pits of French nuclear power plants. In case of severe nuclear reactor accident, failure of the reactor vessel would lead to interaction between molten corium (hot melt of nuclear fuel) and concrete. This paper focuses on the thermal degradation of both limestone-siliceous and siliceous concretes till 1000 °C. Thermo-Gravimetric Analysis (TGA) and Mercury Intrusion Porosimetry (MIP) are used to measure mass loss and porosity modification. As concretes are heterogeneous materials, sampling and representativeness have been addressed. TGA experiments show larger mass loss for limestone-siliceous concretes due to the decarbonation of calcium carbonate gravels when T > 800 °C. MIP experiments demonstrate a 100% increase of porosity for limestone-siliceous (resp. siliceous) concretes when T > 500 °C (resp. T > 800 °C). The consequences of these results are discussed in the frame of experimental tests on prototypical corium systems aimed at describing the key-phenomena involved in molten corium concrete interaction.

Африканский капкан для Эммануэля Макрона

Статья посвящена выяснению причин наращивания Францией военного присутствия в странах Тропической Африки. История африканской политики Пятой республики рассматривается в контексте энергетического кризиса, порожденного истощением запасов урановых руд на территории Франции. Специфика энергосистемы Французской республики состоит в несоразмерно высокой доле (около 75%) электроэнергии, вырабатываемой на АЭС. Это обстоятельство обусловливает зависимость бывшей метрополии от закупок урановой руды в странах субсахарской Африки, бывших в прошлом колониями Французской империи. По мнению автора, в условиях обострения конкурентной борьбы за африканские минеральные ресурсы Франция может сохранить свои эксклюзивные права на закупку сахельского урана по демпинговым ценам, только наращивая свое военное присутствие в зоне Сахеля и Центральной Африке. Автор обосновывает вывод о том, что президент Э. Макрон столкнулся с почти неразрешимой проблемой: чем выше затраты на военные операции, тем дороже африканский уран для французских АЭС, тем меньше смысла в проведении дорогостоящей военной кампании на Черном континенте.

Initiation and propagation of fatigue cracks from surface imperfections on 304L austenitic stainless steel

Given the stringent requirements of high levels of safety in nuclear components, stakeholders of French nuclear industry must anticipate the presence of residual surface imperfections in these components. Such imperfections could be introduced during manufacturing or maintenance operations. The incidence of surface irregularities on the fatigue strength of metallic components must be considered. Meanwhile, nuclear components are generally loaded under low-cycle fatigue and large-scale plasticity conditions. The present work aims at assessing the impact of a controlled surface irregularity on the fatigue life of typical nuclear materials. The influence of characteristic parameters under low-cycle fatigue conditions is also investigated. A 304L austenitic stainless steel used in components of French nuclear power plants was studied. Fatigue tests were conducted under fully-reversed total axial strain control in air at ambient temperature with total strain amplitudes ranging from Δεt/2=0.2% to Δεt/2=0.6%. Surface irregularities, whose depth varies between 100 and 350 micrometers, have been introduced on polished cylindrical samples. The direct current potential drop method has been used to monitor the crack propagation, and thereafter, to derive crack growth rate data. Experimental markings of the crack front for different cycle numbers have been carried out to calibrate the variation of the potential as a function of crack depth. It appears that the fatigue life is strongly reduced in presence of a surface irregularity.

Risk due to creep of prestressed concrete at moderate temperature

This study is a part of a French national project dealing with the mechanical behaviour of the containment vessel of French Nuclear Power Plants in case of a severe accident. The accident conditions are characterized by the increases of internal pressure, +0.5 MPa, and of temperature, up to 180°C, during two weeks. Heating can induce a strong increase of creep deformations kinetics leading to prestressing losses of concrete. Associated to internal pressure, tensile stress could occur in some areas of the structure and the potential cracking could affect the containment capacity of the vessel. One of the objectives of the project was thus to provide original creep data to develop accurate models, taking into account the coupled effects of temperature, desiccation and damage, and able to predict the behaviour of prestressed concrete structures in such insitu conditions. A wide experimental program consisted of numerous creep tests under various thermo-hydro-mechanical conditions in the values range of the accident. The presented results concern uniaxial compressive and flexural creep tests respectively performed on concrete cylinders and prestressed concrete beams, at 20°C and 40°C without desiccation.

Evaluation of internal exposure in French nuclear power plants based on whole body counting

Evaluation of internal exposure in French nuclear power plants based on whole body counting

Analysis of the risk associated with coastal flooding hazards: a new historical extreme storm surges dataset for Dunkirk, France

Abstract. This paper aims to demonstrate the technical feasibility of a historical study devoted to French nuclear power plants (NPPs) which can be prone to extreme coastal flooding events. It has been shown in the literature that the use of historical information (HI) can significantly improve the probabilistic and statistical modeling of extreme events. There is a significant lack of historical data on coastal flooding (storms and storm surges) compared to river flooding events. To address this data scarcity and to improve the estimation of the risk associated with coastal flooding hazards, a dataset of historical storms and storm surges that hit the Nord-Pas-de-Calais region during the past five centuries was created from archival sources, examined and used in a frequency analysis (FA) in order to assess its impact on frequency estimations. This work on the Dunkirk site (representative of the Gravelines NPP) is a continuation of previous work performed on the La Rochelle site in France. Indeed, the frequency model (FM) used in the present paper had some success in the field of coastal hazards and it has been applied in previous studies to surge datasets to prevent coastal flooding in the La Rochelle region in France. In a first step, only information collected from the literature (published reports, journal papers and PhD theses) is considered. Although this first historical dataset has extended the gauged record back in time to 1897, serious questions related to the exhaustiveness of the information and about the validity of the developed FM have remained unanswered. Additional qualitative and quantitative HI was extracted in a second step from many older archival sources. This work has led to the construction of storm and coastal flooding sheets summarizing key data on each identified event. The quality control and the cross-validation of the collected information, which have been carried out systematically, indicate that it is valid and complete in regard to extreme storms and storm surges. Most of the HI collected is in good agreement with other archival sources and documentary climate reconstructions. The probabilistic and statistical analysis of a dataset containing an exceptional observation considered as an outlier (i.e., the 1953 storm surge) is significantly improved when the additional HI collected in both literature and archives is used. As the historical data tend to be extreme, the right tail of the distribution has been reinforced and the 1953 “exceptional” event does not appear as an outlier any more. This new dataset provides a valuable source of information on storm surges for future characterization of coastal hazards.

Impact of the phase out of French nuclear reactors on the Italian power sector

The present paper proposes an analysis concerning the impact of the reduction of the net electricity flow between France and Italy due to the phase out of French nuclear power plants. The analysis is performed by using a bid stack model which offers an approximate, but reliable representation of the Italian power system, as shown by extensive validation on historical data.The study takes into account sixteen scenarios given by the combination of different assumptions on the operating life of French nuclear reactors, fuel price, renewables development and demand level. Furthermore, a Business As Usual scenario is implemented as reference case.The results have shown that some scenarios determine tight conditions for the Italian power market and provoke an increase of the clean spark of 13 €/MWh with respect to the Business As Usual scenario. At the same time, an increase of the load factor of gas turbines from 0.5% to 4% is also detected. This situation requires substantial interventions in order to re-balance the system.On the contrary, scenarios which imply a more aggressive development of renewables and low increase of the demand, even in the case of a relevant phase out of nuclear capacity in France, do not determine tight conditions on the Italian power market, therefore it is not necessary to adopt particular measures.

Brittle fracture analysis of Dissimilar Metal Welds between low-alloy steel and stainless steel at low temperatures

Dissimilar Metal Welds (DMW) between low-alloy steel (A533 steel) and austenitic 316L stainless steel are widely used within the French nuclear power plants where they connect the main components to the primary circuit pipes. In these DMW, the welding process and the post-weld heat-treatment generate a hard thin layer of carburized martensite and austenite in the vicinity of the fusion line (FL), resulting in a heterogeneous microstructure with high mechanical properties gradient, hence potentially, a higher sensitivity to brittle fracture in the hard layer. The present study aims to evaluate the brittle behavior of the DMW at low temperatures and more particularly of the interface between the carburized martensite and austenite (MA interface). Fracture toughness tests were carried out at temperatures between - 120°C and -50°C, with a precrack tip located on the ferritic side near the FL (i.e., between the ferritic steel and the stainless steel buttering). The analysis of the fracture behavior of the DMW was based on a SEM examination of CT (Compact Tension) specimens fracture surfaces. Coupled with a 2D plane strain numerical simulation of the tests, the results show that the presence of austenite in the fatigue precrack front and subsequent ductile tearing towards FL produced higher solicitations on the hard layer and caused intergranular fracture on the MA interface, resulting in lower toughness values for the specimen. To model the brittle behavior of the MA interface, a stress based criterion was used. Tensile tests on axisymmetric specimen, which were machined to initiate intergranular fracture in the MA interface and tested at -170°C, were used to define a threshold stress (σth), below which brittle fracture cannot occur. Then, a criterion to evaluate the brittle fracture risk of the DMW was proposed and applied to the CT specimen.

Cancer incidence in adults living in the vicinity of nuclear power plants in France, based on data from the French Network of Cancer Registries.

Nuclear power plants (NPPs) release toxic emissions into the environment that may affect neighboring populations. This ecologic study was designed to investigate the possibility of an excess incidence of cancer in the vicinity of French NPPs by examining the incidence by municipality of 12 types of cancer in the population aged 15 years and older during the 1995-2011 period. Population exposure to pollution was estimated on the basis of distance from towns of residence to the NPP. Using regression models, we assessed the risk of cancer in a 20-km zone around NPPs and observed an excess incidence of bladder cancer (Relative Risk (RR), 95% Credibility Interval (95% CI)) in men and women (RRmen = 1.08; 95% CI: 1.00, 1.17 and RRwomen = 1.19; 95% CI: 1.02, 1.39). Women living within the 20-km proximity areas had a significantly reduced risk of thyroid cancer (RRwomen = 0.86; 95% CI: 0.77, 0.96). No excess risk of hematologic malignancies in either sex was seen. The higher than expected incidence of bladder cancer may be due to an excess incidence localized around the Flamanville NPP and the nearby La Hague nuclear waste treatment center, which is a source of chemical contaminants, many (including arsenic) of them known risk factors for bladder cancer. Differences in medical practices could explain the reduced risk of thyroid cancer. In this first study of adults living near NPPs in France, cancer incidence is significantly higher than in the references populations for one of the cancer types studied: bladder cancer.

The Square of PErceived ACtion Model (SPEAC Model) Applied in Digital Ethnography for Work Activity Analysis: Performance and Workers’ Perception

The SPEAC protocol using first-person perspective ethnography and subsequent replay interviews was applied to analyze work activities at a French nuclear power plant during real operating situations of Operations shift teams (15 situations and 30 participants, about 1950 min. video recordings and 2400 min. audio recordings). Results were compared with those obtained with the standard method applied in the French nuclear fleet (Systemic Approach to Training: SAT). Both SPEAC and SAT methods provided knowledge and know-how necessary to perform work activities. Following each analysis, participants were presented with a questionnaire for assessment of the method. Items addressed efficiency, constraints, extended application to colleagues or other activities. SPEAC method showed a significantly higher level of identification of knowledge and know-how per activity (from 1.9 to 9 times more) than SAT and at a lower cost. The SPEAC method evaluation by participants was positive, with a good consistency of answers. Trainees considered that i) analyzing the subjective film was perceived as a real added value compared to a classic method (without subjective film, ii) the new method induced faster progress iii) the overall perception was positive) iv) the method was worth being deployed to other activities. Bias, limits and perspectives are discussed.

Basic creep of concrete-coupling between high stresses and elevated temperatures

The prestressed concrete confinement vessel is the third and last barrier in French Nuclear Power Plants (NPP). In case of a severe accident (loss of cooling agent of the reactor for instance), pressure and temperature will increase in the nuclear vessel (+0,5 MPa and 180 °C during 2 weeks). Due to elevated temperatures, the evolution of basic creep will be accelerated. High compressive stresses would appear and induce higher delayed strains and damage. The modelling of basic creep and its couplings with temperature is then very important for the safety of the structure (tightness of the concrete vessel). Here, we present a model considering the following elements: a coupling between creep and damage is introduced, kinetics of basic creep is affected by temperature by the means of an Arrhenius thermo-activation, damage due to the increase in temperature (under stress or not) is taken into account. The model is compared with the available experimental results. This work is a part of the MACENA project.

The future of nuclear power in France: an analysis of the costs of phasing-out

Nuclear power is an important pillar in electricity generation in France. However, the French nuclear power plant fleet is ageing, and the possibility of reducing the technology's share in power generation or even a complete phase-out has been increasingly discussed. This paper focuses on three inter-related questions: First, what are the costs of phasing-out nuclear power in France? Second, who has to bear these costs, i.e., how much of the costs will be passed on to the rest of the European power system? And third, what effect does the uncertainty regarding future nuclear policy in France have on system costs? Applying a stochastic optimization model for the European electricity system, the analysis showed that additional system costs in France of a nuclear phase-out amount up to 76 billion €2010. Additional costs are mostly borne by the French power system. Surprisingly, the analysis found that the costs of uncertainty are rather limited. Based on the results, it can be concluded that a commitment regarding nuclear policy reform is only mildly beneficial in terms of system cost savings.

External heating of electrical cables and auto-ignition investigation

Electric cables are now extensively used for both residential and industrial applications. During more than twenty years, multi-scale approaches have been developed to study fire behavior of such cables that represents a serious challenge.Cables are rather complicated materials because they consist of an insulated part and jacket of polymeric materials. These polymeric materials can have various chemical structures, thicknesses and additives and generally have a char-forming tendency when exposed to heat source.In this work, two test methods are used for the characterization of cable pyrolysis and flammability. The first one permits the investigation of cable pyrolysis. A description of the cable mass loss is obtained, coupling an Arrhenius expression with a 1D thermal model of cables heating. Numerical results are successfully compared with experimental data obtained for two types of cable commonly used in French nuclear power plants. The second one is devoted to ignition investigations (spontaneous or piloted) of these cables.All these basic observations, measurements and modelling efforts are of major interest for a more comprehensive fire resistance evaluation of electric cables.

Structural Integrity for the RPV of French NPP during the LRA

Most of the French Nuclear Power Plants (NPPs) are currently embarking upon efforts to renew their operating license, while the pressurized thermal shock (PTS) events and environmentally assisted fatigue (EAF) pose potentially significant challenges to the structural integrity of the reactor pressure vessel (RPV) which has the potential to be NPP life-limiting conditions. In the assessment of the PTS events, the deterministic fracture mechanics (DFM) is still used as the basic mechanics in most countries except for the USA. While the maximum nil-ductility-transition temperature (RTNDT) is about 80°C for 54 French RPVs after 40 years operation, the maximum allowable RTNDT is only about 70 oC and 80 oC for the typical PTS events in the IAEA and NEA reports, respectively. On the other hand, the effects of light water reactor (LWR) environmental (other than moderate environment in the code) were not considered in the original design, while the effects of LWR environmental are needed to be considered in the LRA according to the USA regulations. In this paper, the challenges of the PTS and EAF are discussed, and some suggestions are also given for the LRA