On-line Fission Products measurements during a PWR severe accident the French DECA-PF project

International audienceFollowing the Fukushima accident, a lot of recommendations was drawn by international organizations (IAEA, OECD, NUGENIA network ) in order to improve the safety in such accidental conditions and mitigate their consequences. One of these recommendations was to improve the robustness of the instrumentation, which was dramatically lacking at Fukushima, as well as to better determine the Source Term involved in nuclear accident.The DECA-PF project (Diagnosis of a degraded reactor core through Fission Product measurements) was elaborated in this context and selected as one of 21 collaborative RandD projects in the field of nuclear safety and radioprotection, funded in May 2013 by the French National Research Agency.Over the months following the Fukushima accident, a CEA crisis team was held in order to analyze on-line the situation taking into account the data delivered by TEPCO and other organizations. Despite the difficulties encountered concerning the reliability of these data, the work performed showed the high capacity of Fission Products (FP) measurements to get a diagnosis relative to the status of the reactors and the spent fuel pools (SFP). Based on these FP measurements, it was possible to conclude that the main origin of the releases was coming from the cores and not from the SFP, in particular for SFP-4 which was of high concern, and that the degradation level of the reactors was very large, including probably an extensive core melting. To improve the reliability of this kind of diagnosis, the necessity to get such measurements as soon as possible after the accident and as near as possible from the reactor was stressed.In this way the present DECA-PF project intends to develop a new and innovative instrumentation taking into account the design of the French nuclear power plants on which sand bed filters have been implemented for severe accident management. Three complementary techniques, devoted to measure the FP release on-line, are being studied Gamma spectrometry, with an industrial objective to build a prototype aimed at improving the capacity of the present radiation monitoring system,Gas chromatography, for the quantification of the fission gases (Xe, Kr) as well as potential carbon oxides produced in case of Molten Corium Concrete Interaction,Optical absorption spectroscopy, the objective of this most innovative technique being to quantify the tetra-oxide of ruthenium, which could be produced in case of lower head failure, and the gaseous forms of iodine (molecular and organic) released in the environment.A global description and the present status of this project is presented, focusing on the Source Term establishment at the outlet stack of the sand bed filters and on the perspectives of implementation of the on-line gamma spectrometry equipment

DISCOMS : Capteurs Répartis pour le surveillance du corium et la sûreté

International audienceThe Fukushima-Daiichi nuclear disaster showed that the need for safety must always prevail. This paper discusses the development of remote monitoring technologies to improve Nuclear Power Plants (NPPs) safety, in operation (Pressurized Water Reactors), under construction (the EPR reactors, i.e. the GEN 3 PWR), or for any other next generations of reactors. At Fukushima, the total loss of electrical power supplies has quickly led most of the instrumentation inoperative and the operator (TEPCO) with no way to monitor the status and the evolution of the accident. To overcome these important drawbacks, advantage can be taken from the considerable potential of distributed sensing technologies based on both "Optical Fiber Sensors" (Raman, Brillouin, and Rayleigh Reflectometries) and long-length "Self Powered Neutron Detectors" (SPNDs). The goal consists in inquiring about the status of the third barrier of confinement and to define possible mitigation strategies in case of severe accident, namely: i) reactor pressure vessel breakthrough and corium relocation outside the vessel, ii) concrete basemat erosion and iii) corium cooling. Such monitoring should consist in "sensing cables" embedded in concrete basemat below the reactor vessel and interrogated from a rear base where operators can work safely. In this context, DISCOMS, which stands for "DIstributed Sensing for COrium Monitoring and Safety", is a five-year project, managed by the French National Research Agency (ANR), dealing with the NPP safety improvement, from normal situation to severe accidents. Monitoring phases include reactor vessel breaching, corium flow, along with post-accidental period (corium cooling ex-vessel). Thus, optical fibers selected for their resistance to ionizing radiations and long length SPNDs, both judiciously deployed within the reactor concrete basemat, and the structures around it, will provide a useful real-time or on-demand monitoring, in normal operation, and more important in accidental and post-accidental situations

Capteurs à fibres optiques répartis pour la surveillance du corium en cas d'accident grave de réacteur nucléaire avec percement de la cuve : le projet ANR RSNR DISCOMS

International audienceUne technique de surveillance fondée sur les Capteurs à Fibres Optiques (CFO) répartis (réflectomètres optiques associés à des câbles munis de fibres monomodes rad-hard gainées carbone) est proposée pour la surveillance à distance du corium en cas d’Accident Grave de réacteur nucléaire, avec fusion du coeur et percement de la cuve du réacteur

Capteurs à fibres optiques répartis pour la surveillance du corium en cas d'accident grave de réacteur nucléaire avec percement de la cuve : le projet ANR RSNR DISCOMS

International audienceUne technique de surveillance fondée sur les Capteurs à Fibres Optiques (CFO) répartis (réflectomètres optiques associés à des câbles munis de fibres monomodes rad-hard gainées carbone) est proposée pour la surveillance à distance du corium en cas d’Accident Grave de réacteur nucléaire, avec fusion du coeur et percement de la cuve du réacteur

Capteurs à fibres optiques répartis pour la surveillance du corium en cas d'accident grave de réacteur nucléaire avec percement de la cuve : le projet ANR RSNR DISCOMS

International audienceUne technique de surveillance fondée sur les Capteurs à Fibres Optiques (CFO) répartis (réflectomètres optiques associés à des câbles munis de fibres monomodes rad-hard gainées carbone) est proposée pour la surveillance à distance du corium en cas d’Accident Grave de réacteur nucléaire, avec fusion du coeur et percement de la cuve du réacteur