Long Term out-of-pile Thermocouple Tests in Conditions Representative for Nuclear Gas-cooled High Temperature Reactors

During irradiation tests at high temperature, failure of commercial Inconel 600 sheathed thermocouples is commonly encountered. To understand and remediate this problem, out-of-pile tests were performed with thermocouples in carburizing atmospheres which can be assumed to be at least locally representative for High Temperature Reactors. The objective was to screen those thermocouples which would consecutively be used under irradiation. Two such screening tests have been performed with a set of thermocouples embedded in graphite (mainly conventional Type N thermocouples and thermocouples with innovative sheaths) in a dedicated furnace with helium flushing. Performance indicators such as thermal drift, insulation and loop resistance were monitored and compared to those from conventional Type N thermocouples. Several parameters were investigated: niobium sleeves, bending, thickness, sheath composition, temperature as well as the chemical environment. After the tests, Scanning Electron Microscopy (SEM) examinations were performed to analyze possible local damage in wires and in the sheath. The present paper describes the two experiments, summarizes results and outlines further work, in particular to further analyze the findings and to select suitable thermocouples for qualification under irradiation.JRC.F.5-Nuclear Reactor Safety Assessmen

The Self-Powered Detector Simulation ‘MATiSSe’ Toolbox applied to SPNDs for severe accident monitoring in PWRs

In the framework of the French National Research Agency program on nuclear safety and radioprotection, the ‘DIstributed Sensing for COrium Monitoring and Safety’ project aims at developing innovative instrumentation for corium monitoring in case of severe accident in a Pressurized Water nuclear Reactor. Among others, a new under-vessel instrumentation based on Self-Powered Neutron Detectors is developed using a numerical simulation toolbox, named ‘MATiSSe’. The CEA Instrumentation Sensors and Dosimetry Lab developed MATiSSe since 2010 for Self-Powered Neutron Detectors material selection and geometry design, as well as for their respective partial neutron and gamma sensitivity calculations. MATiSSe is based on a comprehensive model of neutron and gamma interactions which take place in Selfpowered neutron detector components using the MCNP6 Monte Carlo code. As member of the project consortium, the THERMOCOAX SAS Company is currently manufacturing some instrumented pole prototypes to be tested in 2017. The full severe accident monitoring equipment, including the standalone low current acquisition system, will be tested during a joined CEA-THERMOCOAX experimental campaign in some realistic irradiation conditions, in the Slovenian TRIGA Mark II research reactor

New Temperature Monitoring Devices for High-temperature Irradiation Experiments in the High Flux Reactor Petten

Within the European High Temperature Reactor Technology Network (HTR-TN) and related projects a number of HTR fuel irradiations are planned in the High Flux Reactor Petten (HFR), The Netherlands, with the objective to explore the potential of recently produced fuel for even higher temperature and burn-up. Irradiating fuel under defined conditions to extremely high burn-ups will provide a better understanding of fission product release and failure mechanisms if particle failure occurs. After an overview of the irradiation rigs used in the HFR, this paper sums up data collected from previous irradiation tests in terms of thermocouple data. Some R&D for further improvement of thermocouples and other on-line instrumentation will be outlined.JRC.F.4-Safety of future nuclear reactor

The Self-Powered Detector Simulation ‘MATiSSe’ Toolbox applied to SPNDs for severe accident monitoring in PWRs

International audienceIn the framework of the French National Research Agency program on nuclear safety and radioprotection, the ‘DIstributed Sensing for COrium Monitoring and Safety’ project aims at developing innovative instrumentation for corium monitoring in case of severe accident in a Pressurized Water nuclear Reactor. Among others, a new under-vessel instrumentation based on Self-Powered Neutron Detectors is developed using a numerical simulation toolbox, named ‘MATiSSe’. The CEA Instrumentation Sensors and Dosimetry Lab developed MATiSSe since 2010 for Self-Powered Neutron Detectors material selection and geometry design, as well as for their respective partial neutron and gamma sensitivity calculations. MATiSSe is based on a comprehensive model of neutron and gamma interactions which take place in Selfpowered neutron detector components using the MCNP6 Monte Carlo code. As member of the project consortium, the THERMOCOAX SAS Company is currently manufacturing some instrumented pole prototypes to be tested in 2017. The full severe accident monitoring equipment, including the standalone low current acquisition system, will be tested during a joined CEA-THERMOCOAX experimental campaign in some realistic irradiation conditions, in the Slovenian TRIGA Mark II research reacto

Long Term out-of-pile Thermocouple Tests in Conditions Representative for Nuclear Gas-cooled High Temperature Reactors

During irradiation tests at high temperature failure of commercial Inconel 600 sheathed thermocouples is commonly encountered. As instrumentation, in particular thermocouples are considered safety-relevant both for irradiation tests and for commercial reactors, JRC and THERMOCOAX joined forces to solve this issue by performing out-of-pile tests with thermocouples mimicking the environment encountered by the HTR in-core instrumentation. The objective was to screen innovative sheathed thermocouples which would consecutively be tested under irradiation. Two such screening tests have been performed in high temperature environment (i.e. temperature in the range 1100 - 11500C) with purposely contaminated helium atmosphere (mainly CH4, CO, CO2, O2 impurities) representative for High Temperature Reactor carburizing atmospheres. The first set of thermocouples embedded in graphite (mainly conventional N type thermocouples and thermocouples with innovative sheaths) was tested in a dedicated furnace at THERMOCOAX lab with helium flushing. The second out-of-pile test in Petten with a partly different set of thermocouples replicated the original test for comparison. Performance indicators such as thermocouples thermal drift, insulation resistance measurements and loop resistance measurements were monitored. Through these long-term screening tests several effects were investigated: niobium sleeves, bending, diameter, sheath composition as well as the chemical environment. SEM examinations were performed to analyze local damage (bending zone, sheath). The present paper describes the two experimentations, sums up data collected during these tests in terms of thermocouple behavior and describes further work, in particular to select suitable thermocouples equipped with fixed point mini cells for qualification under irradiation.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Long term out-of-pile thermocouple tests in conditions representative for nuclear gas-cooled high temperature reactors

During irradiation tests at high temperature failure of commercial Inconel 600 sheathed thermocouples is commonly encountered. As instrumentation, in particular thermocouples are considered safety-relevant both for irradiation tests and for commercial reactors, JRC and THERMOCOAX joined forces to solve this issue by performing out-of-pile tests with thermocouples mimicking the environment encountered by high temperature reactor (HTR) in-core instrumentation. The objective was to screen innovative sheathed thermocouples which would consecutively be tested under irradiation. Two such screening tests have been performed in high temperature environment (i.e. temperature in the range 1100–1150◦C) with purposely contaminated helium atmosphere (mainly CH4, CO, CO2, O2impurities) representative for high temperature reactor carburizing atmospheres. The first set of thermocouples embedded in graphite (mainly conventional N type thermocouples and thermocouples with innovative sheaths) was tested in a dedicated furnace at THERMOCOAX lab with helium flushing. The second out-of-pile test at JRC with a partly different set of thermocouples replicated the original test for comparison. Performance indicators such as thermal drift, insulation resistance and loop resistance were monitored. Through these long-term screening tests the effect of several parameters were investigated: niobium sleeves, bending, diameter, sheath composition as well as the chemical environment. SEM examinations were performed to analyze local damage (bending zone, sheath). The present paper describes the two tests, sums up data collected during these tests in terms of thermocouple behavior and describes further instrumentation testing work with fixed point mini cells for qualification under irradiation.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

High Temperature Fire & Overheat Sensor Elements (FOSE) for aircraft Fire & Overheat Detection System (FODS)

One of the 21st century major challenges is to answer the growing mobility by a carbon saver solution. For aeronautics, improvement of engine architecture (NIPSE European project) permits to reduce its volume and so to get more space for passengers & freight (15%), to save weight and fuel consumption (2-3% i.e. 1% CO2 emissions). This optimization hinges on integrating the engine and the nacelle into single assembly (Ultra High-Bypass Ratio turbofan engines or UHBR) that means equipment close to engine (calculator, valves, but also sensors and their extension cables…) have to resist higher temperatures. The Fire and Overheat Detection System (FODS) is a critical component for safe working of the aircraft as it controls and prevents from overheat and fire all those electrical equipment and the engine itself. THERMOCOAX, manufacturer of Mineral Insulated Cable (MIC) for over 60 years, is a privileged partner of the aeronautics industry (anti-icing for air inlet, pitot sensor, drain mast and thermal measurement from thermocouples to complete systems such as harnesses). For 25 years THERMOCOAX has manufactured Fire and Overheat Sensor Elements (FOSE) - the sensitive part of FODS - and as a specialist has taken part in this innovative project. The sensing principle of FOSE lies on electrical insulation resistance (IR) drop as the cable is exposed to heat. A wide range of research was made to find technical solutions for the new thermal specification. The difficulty comes from having IR with good sensitivity and linearity at temperature, covering a large temperature range: overheat threshold of either 473K ( 200°C) or 873K ( 600°C) depending on the location of the sensor. Also, the FOSE has to remain functional after 2 fires at 1453K ( 1180°C) during 5 min each, so the sensor sensitive insulant must not be deteriorated. Several solutions based either on thermistor powders or on percolation effect powders have been tested by miscellaneous trials: repeatability, thermal cycling, fire resistance test, local response at different room temperatures (from RT to 723K) and homogeneity along the cable. Finally, a new insulant solution has been selected to be integrated to the FOSE future generation. The other aspect of those new temperature rates is the electrical connectics that should not deteriorate the FOSE response, especially when the aircraft is in overheat or fire situation. So, a new design of 3 contacts ceramic-metal connector has been developed to resist more than 2 fires without generating parasite responses and to fit with aeronautics standards. Severe environment requested by NIPSE project forces THERMOCOAX to develop a new technology of FOSE based on insulant advanced studies and specific connectors to resist high temperature

Long length SPNDs and Distributed Optical Fiber Sensors for Severe Accident remote monitoring and their contribution to Nuclear Safety in the post-Fukushima context

International audienceThe Fukushima-Daiichi nuclear accident of March 2011, and the subsequent loss of internal power supplies after the NPP (Nuclear Power Plant) water flooding caused by the tsunami, leaving the operator TEPCO with almost no information from the reactor pits, demonstrates that safety must always prevail. Accordingly, the French public authorities initiated the RSNR research program, to stimulate and fund new R&D projects to improve the safety of nuclear reactors in service and those of future NPPs. The DISCOMS project (Distributed Sensing for Corium Monitoring and Safety) aimed at developing and testing innovative and passive sensors dedicated to Nuclear Safety, namely an instrumented pole equipped with long length SPNDs (Self-Powered Neutron Detectors)-Thermocouple poles, and Distributed Optical Fiber Sensors, to be installed ex-core in both the reactor pit and concrete floor. The sensors, remotely operated from a safe place, will not only provide additional information during the Severe Accident, but also in post-accidental situation, even in case of loss of all power supplies.The modelling of a 60 year normal operation followed by a Severe Accident for two generations of reactors (Gen II, Gen III) permitted to demonstrate that ex-core long length SPNDs can identify differentscenarios: reactor shut down, Normal Operation, Severe Accident without corium relocation, and Severe Accident with corium pouring on the concrete floor. Long length SPNDs were designed and manufactured, along with their electronics, to measure low currents ranging from 1 pA to 100 nA collected under radiations, and qualified in a research reactor with fluxes compliant with modelled scenarios. Optical Fibers Sensor cables are devoted to monitor the Molten Core – Concrete Interaction (MCCI): temperature and strain profiles can be provided in the concrete depth by embedded cables, as a result ofusing the Raman DTS, Brillouin and Rayleigh OFDR reflectometry techniques, based on the analysis of the backscattered light in single-mode optical fibers, for distributed measurements potentially up to1000°C with Brillouin instrumentations. Additionally, such sensor cables can be used as fuses with telecom or photon counting OTDRs to detect corium vicinity.Sensor cables and radiation resistant optical fibers have been selected and tested to comply with the radiation conditions in the reactor pits as depicted by the modelling.A final MCCI experiment with prototypical corium, performed at the VULCANO CEA facility, involving also two instrumented SPNDs-Thermocouple poles, has demonstrated the ability of both kinds of sensors and corresponding instrumentations to deliver useful information about the corium status and its progression through the concrete