French National Electricity Company Research Articles

Tall tales from the hydrological crypt: are models monsters?

“Bizarre,” “monstrous”: in society as well as in science, this is the way we are used to describing objects that deviate from an expected standard. Hydrology is no exception. The bizarre or the monstrous describes every object that has a low probability of occurring, or that our models fail to represent. Actually, the bizarre or the monstrous is often a demonstration of the limits of our models rather than an intrinsic characteristic of the objects we study. This article provides a reflection on the definition of bizarre and monstrous in the context of hydrology. We base our reflection on 60 years of experience in hydrometeorological operational management and applied research at the French national electricity company (EDF-DTG). First, we describe several classical a priori models or conceptions trusted by hydrologists, sometimes erroneously. These include classical rainfall or streamflow measurement issues, certain limits of the watershed concept or problems in the spatialization of local measurements. Then we attempt to show how the misuse of statistical models can generate bizarre or monstrous results. We give examples related to outliers and to the homogeneity and stationarity hypotheses. We show how difficult it may be for operational forecasters to anticipate and believe that extreme (monstrous) events will occur in the near future. Finally, we wish to show that the bizarre or the monstrous should not be rejected in hydrology, but instead is something to study in greater depth. We believe that this type of analysis offers new opportunities to improve the explanatory and predictive capacity of our models. Citation Mathevet, T. & Garçon, R. (2010) Tall tales from the hydrological crypt: are models monsters? Hydrol. Sci. J. 55(6), 857–871.

Mortality of workers exposed to ionizing radiation at the French National Electricity Company

Exposure to ionizing radiation increases the risk of cancer in humans. Nuclear workers receive low doses over a relatively long period of time. A mortality study of a cohort of workers exposed to ionizing radiation at Electricité de France (EDF) was conducted. The cohort consisted of 22,395 individuals monitored for radiation exposure between 1961 and 1994, and followed-up for an average of 11.7 years. Our study demonstrates a clear healthy worker effect (HWE) since mortality is less than half what is expected from National mortality statistics. The HWE is greater among workers who have spent most of their career in the nuclear sector. The analysis by cancer site shows no excess compared with the general population. No significant trend was observed according to level of exposure to ionizing radiation. The mortality of workers exposed to ionizing radiation at the French National Electricity company is very low compared to the French national mortality.

Intelligent system for transient data collection and fatigue monitoring of pressurised water reactors nuclear steam supply system

Electricité de France (EDF), the French national electricity company, is operating 54 standardised pressurised water reactors. This about 500 reactor-years experience in nuclear stations operation and maintenance area has allowed EDF to develop its own strategy for monitoring of age-related degradations of NPP systems and components relevant for plant safety and reliability. After more than fifteen years of experience in regulatory transient data collection and seven years of successful fatigue monitoring prototypes experimentation, EDF decided to design a new system called SYSFAC (acronym for SYstème de Surveillance en FAtigue de la Chaudière) devoted to transient logging and thermal fatigue monitoring of the reactor coolant pressure boundary. The system is fully automatic and directly connected to the on-site data acquisition network without any complementary instrumentation. A functional transient detection module and a mechanical transient detection module are in charge of the general transient data collection. A fatigue monitoring module is aimed towards a precise surveillance of five specific zones particularly sensible to thermal fatigue. After a first step of preliminary studies, the industrial phase of the SYSFAC project is currently going on, with hardware and software tests and implementation. The first SYSFAC system will be delivered to the pilot power plant by the beginning of 1996. The extension to all EDF’s nuclear 900 MW is planned after one more year of feedback experience.