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DOE OSTI2019

Multi-scale processes driving tropical convection and influence of the aerosol (Final Technical Report)

This DOE GoAmazon collaborative project between scientists in the US and Brazil addresses fundamental processes that drive tropical deep convection including aerosol effects. The results provide guidance for improving the parameterizations of cloud and aerosol effects by increasing the knowledge of processes at work in tropical convection, especially over tropical land. Highlights include: • GoAmazon2014/5 observations permitted, for the first time, a comprehensive evaluation of the strong relationship between lower free tropospheric moisture and deep convective onset over the Amazon (Schiro et al. 2016, JAS; Schiro et al. 2018b, PNAS; Chakraborty et al. 2018, ACP; Schiro and Neelin 2018c). A set of diagnostics for deep convective onset has been established using data from the GoAmazon2014/5 campaign (Schiro et al. 2016, JAS), highlighting similarities and differences between the convective transition statistics over tropical land versus corresponding statistics from ARM campaigns in the tropical Western Pacific. The initial set of diagnostics has been provided as a module to be incorporated into the ARM Diagnostics Package of Shaocheng Xie and coworkers, which is being integrated into the PCMDI and E3SM diagnostics packages. Additionally, a set of downdraft diagnostics to inform model parameterizations has been developed (Schiro and Neelin 2018a, ACP). • These diagnostics have been used in constraining the behavior of modeled convective parameterizations. This includes using them with parameter perturbation experiments in the Community Earth System Model to show which parameter ranges are consistent with observed onset statistics, and to show that the primary causal direction of the water vapor-precipitation relationship is via the impact of mixing processes and free tropospheric moisture on convection (Kuo et al. 2017, JAS). Lintner et al. (2017, GRL) used this impact of free tropospheric moisture to systematically analyze issues in the simulation of Amazon rainfall in the CMIP5 model ensemble. • Leveraging the multi-instrument GoAmazon observations, Schiro et al. (2018, PNAS) are able to provide for the first time an empirical mixing using radar wind profiler data that provides a good predictor of precipitation for both mesoscale convective systems and smaller-scale convection. In addition, buoyancy estimated from these results is a good predictor of precipitation across the seasonal and diurnal cycles (Schiro and Neelin 2018c, JAS) and permits the effects of aerosols to be distinguished from those of the thermodynamic environment in the transition to deep convection (Chakraborty et al. 2018, ACP). • Placing the GoAmazon campaign in a larger context, in collaboration with U. São Paulo investigators, Rehbein et al. (2018) analyzed the characteristics of the mesoscale convective systems (MCS) that affect Amazon rainfall, including origins, lifetimes, propagation speed and displacement. de Barros Soares et al. (2017) establish statistically significant observed warming trends over much of South America and are able to attribute the origin of this to anthropogenic forcing based on the agreement of climate model simulations with and without anthropogenic forcings. This analysis left open the attribution of precipitation trends due to large natural variability. Barkhardorian et al. (2018) provide evidence indicating that the observed regional precipitation decrease and drying during recent over northern South America during recent austral springs will continue and intensify in the course of unfolding anthropogenic climate change.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Spectrally-engineered solar thermal photovoltaic devices

A solar thermal photovoltaic device, and method of forming same, includes a solar absorber and a spectrally selective emitter formed on either side of a thermally conductive substrate. The solar absorber is configured to absorb incident solar radiation. The solar absorber and the spectrally selective emitter are configured with an optimized emitter-to-absorber area ratio. The solar thermal photovoltaic device also includes a photovoltaic cell in thermal communication with the spectrally selective emitter. The spectrally selective emitter is configured to permit high emittance for energies above a bandgap of the photovoltaic cell and configured to permit low emittance for energies below the bandgap.

Lenert, Andrej↗

DOE OSTI2018

Capillary absorption spectrometer and process for isotopic analysis of small samples

A capillary absorption spectrometer and process are described that provide highly sensitive and accurate stable absorption measurements of analytes in a sample gas that may include isotopologues of carbon and oxygen obtained from gas and biological samples. It further provides isotopic images of microbial communities that allow tracking of nutrients at the single cell level. It further targets naturally occurring variations in carbon and oxygen isotopes that avoids need for expensive isotopically labeled mixtures which allows study of samples taken from the field without modification. The process also permits sampling in vivo permitting real-time ambient studies of microbial communities.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Distributed Fiber Optic Arrays: Integrated Temperature and Seismic Sensing for Detection of CO 2 Flow, Leakage and Subsurface Distribution (Final Report)

This report describes the seismic and heat-pulse monitoring equipment, surveys, results and accomplishments of the fiber optic (FO) project funded by the U.S. Department of Energy (DOE) under Agreement Number DE-FE0012700. The formal title of the project is “Distributed Fiber Optic Arrays: Integrated Temperature and Seismic Sensing for Detection of CO 2 Flow, Leakage and Subsurface Distribution.” The project focuses on the field acquisition of FO data using Distributed Acoustic Sensing (DAS) arrays for subsurface imaging of geologic structure and to track the CO 2 migration in the injection interval using time-lapse techniques. A second component of the project uses a novel heat-pulse monitoring method that relies on Distributed Temperature Sensing (DTS) to evaluate near-field leakage of CO 2 or brine in and around the wellbore. The Southeast Regional Carbon Sequestration (SECARB) partnership hosted the project at the Anthropogenic Test site near Citronelle, Alabama after the original site host, the Kansas Geological Survey (KGS), experienced significant delays in permitting its CO 2 injection well at the Wellington Oil Field site in Kansas. The KGS project was later terminated in 2017 before an injection permit issued. A second field trial was planned for the Livingston Oil Field, located in Louisiana, but the site host ran into financial troubles and the project was terminated in 2015. A replacement field-site host was not found for the Livingston field trial. Both the Wellington, Kansas and Livingston, Louisiana projects were funded by DOE. A novel sensor platform referred to as the Modular Borehole Monitoring (MBM) system deployed at the Citronelle field site was utilized by the FO project. Two different seismic sensor technologies were incorporated in the Citronelle MBM system design including: (1) a semi-permanent, tubing-deployed, 18-level geophone array with custom hydraulic clamps; and (2) two, single mode optical fibers for Distributed Acoustic Sensing (DAS). Incorporation of the 18-level geophone array in the MBM system provided an ideal opportunity to compare the DAS response to conventional geophones. A heat-pulse monitoring system consisting of two, multi-mode optical fibers for Distributed Temperature Sensing (DTS) and copper heater element were also incorporated into the MBM package. This report provides an overview of the design of the MBM, DAS, and DTS equipment and the surveys performed during the study. The heat-pulse monitoring technique was used to diagnose a completion problem with observation well D-9-8 #2 where the MBM system was installed in 2012, thus successfully demonstrating its application for leak detection. In 2015, CO 2 unexpectedly arrived at the observation well approximately one year after CO 2 injection and heat-pulse monitoring ended. It was determined at this time that saltwater intrusion had likely penetrated the stainless-steel capillary tube containing the fibers and copper heater elements, thus preventing the heater from being used. DTS measurements indicated that the fiber had also degraded probably due to hydrogen darkening. It is recommended that the capillary tube be constructed of a more corrosive resistant material (e.g., Inconel) in the future should it be deployed in similar harsh downhole environments. Geophysical imaging of the subsurface and monitoring of the CO 2 were successful using DAS in the vertical seismic profile (VSP) survey configuration. A high resolution VSP image of the subsurface was obtained in 2014 using DAS, which exceeded our expectations in comparison to a lower resolution image obtained by SECARB in 2012 using an 80-level geophone array. A time-lapse image of the redistribution of CO 2 after injection ended in September 2014 was obtained using two DAS VSP surveys from June 2014 and December 2015, thus successfully demonstrating its application. DAS data were also acquired during a crosswell seismic survey conducted in 2014. Unfortunately, the DAS technique was not success in the crosswell survey configuration because the noise level was too high, increasing by a factor of ten, over the high frequency output (100-1,200) of the piezoelectric source.

58 GEOSCIENCES↗

DOE OSTI2018

Integrated membrane-pyrolysis systems and methods

A method of processing a mixture of heated vapors, at least two of which substantially differ in polarity from each other, the method comprising directing said mixture of heated vapors at a temperature of at least 150.degree. C. through a hydrophobic or hydrophilic mesoporous membrane comprising a mesoporous coating of hydrophobized or hydrophilized metal oxide nanoparticles, respectively, wherein the hydrophobic mesoporous membrane permits passage of one or more hydrophobic heated vapors and blocks passage of one or more hydrophilic heated vapors, and wherein the hydrophilic mesoporous membrane permits passage of one or more hydrophilic heated vapors and blocks passage of one or more hydrophobic heated vapors. The method is particularly directed to embodiments where the heated vapors emanate from a pyrolysis process. An apparatus for achieving the above-described method is also described.

42 ENGINEERING↗

DOE OSTI2018

Technical Requirements for Geothermal Resource Confirmation

In 2017-2018, the Bureau of Land Management's Renewable Energy Coordination Office, through its Geothermal Program, funded the National Renewable Energy Laboratory (NREL) to analyze technical and environmental considerations related to geothermal resource confirmation drilling. NREL solicited input from a group of technical and environmental experts in the geothermal industry, along with analyzing National Environmental Policy Act of 1969 (NEPA) documentation for previously approved projects. The collected data and analysis will be used by the Bureau of Land Management to examine the possibility of developing a new classification of wells and/or expediting the NEPA compliance process, which could potentially reduce permitting and regulatory compliance timelines when compared to the current process for obtaining a geothermal drilling permit for resource confirmation drilling activities. This paper provides a summary of the technical requirements for confirming a geothermal resource. The analysis showed that confirming a geothermal resource requires confirming reservoir temperature, chemistry, permeability, and flow rate. Obtaining these data requires drilling at least two-preferably three-successful wells into the resource to conduct the necessary tests, including an interference test. Bottom-hole well diameters of at least 6'' to 8'' (0.15 to 0.2 m) are needed to limit the wellbore frictional pressure drop to effectively perform well flow and interference tests. Drilling these wells requires a drill rig with a mud pump and derrick capable of holding three drill pipes. This type of rig requires a minimum well-pad size of 2.5 acres (104 m2) including surface area for a 1 million-gallon (3.8 million-liter) pit. Up to 15 acres (5x104 m2) of total surface disturbance are needed for developing access roads and well pads to drill a total of three to five wells.

15 GEOTHERMAL ENERGY↗

DOE OSTI2018

Handling and Treatment of Sodium-Potassium Alloy (NaK) after the Loss of Key Personnel – 19002

ABSTRACT In September 2010, during cleanup and removal efforts associated with a glovebox containing a sodium-potassium alloy (NaK) cooling system, a NaK reaction event occurred. Near the end of the evolution, which was at a Materials and Fuels Complex (MFC) research facility at the Idaho National Laboratory, a 2 to 3-ounce sample of NaK was being transferred from a metal can to a polyethylene bottle so it could be sent to the disposal outlet for verification analysis. During the transfer, a reaction of the NaK with ambient air was observed in both the metal can and sample container. The potential for a reaction was identified during the planning of this activity and mitigating steps were included in the procedures. In response, the two containers were flooded with argon, closed, and observed overnight. No additional reaction was noted. The sample container and metal can were packaged into a 10-gallon drum and transferred to a permitted storage location pending disposal. While the other containers generated from the deactivation and decommissioning activity were sent off-site for disposal, the 10-gal drum remained due to concerns by a staff specialist that the material could contain potassium superoxide (KO2) as a result of the reaction event. The intent at that time was to treat the NaK in a Resource Conservation and Recovery Act (RCRA)-permitted treatment facility at MFC, instead of sending it off-site for disposal. The container was labeled, inspected, and managed as a hazardous waste. Due to the complexities associated with safely handling and treating NaK and KO2, the container remained in storage. Treatment and disposal of the NaK and KO2 container was revisited in 2016, when researchers and chemists were consulted regarding the potential for superoxide formation and the best means to safely store and treat the container. The facility came to realize that due to the retirements of key personnel, it needed to provide current employees operational experience with the handling and treatment of NaK. An outside company was identified and contracted to provide training and consulting services. Several Battelle Energy Alliance, Inc. (BEA) personnel then attended an alkali metals safety training class. The training course provided participants with classroom and hands–on instruction associated with: • Hazards associated with handling and using sodium and NaK • Proper personal protection equipment, spill control techniques, and first aid • Common design approaches for buildings, systems, and equipment used to contain sodium and NaK • What to expect in the event of a water reaction and how to respond • How to properly prepare for a fire and contain/extinguish small metal fires • A hands-on demonstration of NaK reaction and controls. Following the training, a procedure was developed to open the container, and inspect and treat the NaK. In June 2017, facility operations personnel successfully completed the inspection and treatment of the NaK drum, eliminating the legacy liability.

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2015

Confirming the Strength of Residential Roof Structures for Solar Installations

The rooftop solar PV permitting process involves a number of steps and varies greatly, even between neighboring cities. Jurisdictions follow state or national codes, but each may interpret the codes in their own way and insert additional requirements. In some locations, a rooftop structural analysis conducted by a professional engineer is required before a rooftop solar permit is issued. The extra step is not universally applied across states or municipalities, and can alter scheduling logistics and add hundreds of dollars to the cost of the system.

14 SOLAR ENERGY↗

DOE OSTI2020

Turbine component and methods of making and cooling a turbine component

A turbine component includes a root and an airfoil extending from the root to a tip opposite the root. The airfoil forms a leading edge and a trailing edge portion extending to a trailing edge. A plurality of axial cooling channels in the trailing edge portion of the airfoil are arranged to permit axial flow of a cooling fluid from an interior of the turbine component at the trailing edge portion to an exterior of the turbine component at the trailing edge portion. A method of making a turbine component includes forming an airfoil having a trailing edge portion with axial cooling channels. The axial cooling channels are arranged to permit axial flow of a cooling fluid from an interior to an exterior of the turbine component at the trailing edge portion. A method of cooling a turbine component is also disclosed.

33 ADVANCED PROPULSION SYSTEMS↗

DOE OSTI2022

Monitor for measuring mercury emissions

A mercury emissions monitor includes a mercury sensor tape configured to be fed in a reel-to-reel manner between first and second tape reels, wherein the mercury sensor tape includes a thin metallic film configured to form an amalgam with detected mercury. A mercury collection unit is configured to receive into a chamber a sample of a gas containing mercury, wherein the mercury collection unit is further configured to permit passage of portions of the mercury sensor tape through the chamber containing the gas sample so that the amalgam is formed with the thin metallic film. A mercury analysis unit includes a total reflection x-ray fluorescence (“TXRF”) system configured to perform a TXRF analysis of the amalgam, wherein the mercury analysis unit is configured to permit passage of the mercury sensor tape within a proximity of an XRF detector of the TXRF system. The mercury collection unit and the mercury analysis unit are positioned between the first and second tape reels so that the mercury sensor tape can move in a continuous manner from the first tape reel through the chamber of the mercury collection unit, then within sufficient proximity to the XRF detector, to be then taken up onto the second tape reel.

Kumar, Nalin↗

DOE OSTI2022

Turbine component and methods of making and cooling a turbine component

Dutta, Sandip↗

DOE OSTI2023

The Classical Equations of Motion of Quantized Gauge Theories, Part I: General Relativity

In this and a companion paper, we show that quantum field theories with gauge symmetries permit a broader class of classical dynamics than typically assumed. In this article, we show that the dynamics extracted from the path integral or Hamiltonian formulation of general relativity allows for classical states that do not satisfy the full set of Einstein's equations. This amounts to loosening the Hamiltonian and momentum constraints that are imposed on the initial state. Nevertheless, the quantum theory permits gauge invariant time evolution of these states. The time evolution of these states is such that at the classical level the full set of Einstein's equations would appear to hold, with the physical effects of these states being attributable to an auxiliary, covariantly conserved energy-momentum tensor with no internal degrees of freedom. We derive the generalized Einstein equations for these states and show that a homogeneous and isotropic initial background state contributes to expansion identical to cold dark matter. The inhomogeneous components of this state could source curvature perturbations that grow linearly at linear order. This auxiliary contribution to Einstein's equations could have either sign and thus provide a trivial way to violate the null energy condition, enabling novel gravitational dynamics such as cosmic bounces and wormholes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2023

Mooring latch for marine structures

A mooring latch includes a passive foundation portion and a latching portion. The latching portion includes a mechanism, a conical surface shaped to mate with a conical surface of the passive portion, a connector for connection to a mooring structure and permitting rotation about a horizontal axis. The mechanism has a latched configuration that mates the conical surfaces and permits rotations about a shared vertical axis of the conical surfaces. A mooring line threaded through the passive and latching portions and equipped with one or more stops may be used to guide the latching portion to or from the passive portion and to actuate latching or unlatching or the mooring latch.

Siegel, Stefan G.↗

DOE OSTI2023

Results of FY 2023 Alloy 617 and Alloy 709 High-Temperature Crack-Growth Testing

This report summarizes the work performed at Idaho National Laboratory under the “Creep, fatigue and creep-fatigue crack growth tests” task of the “Long-Term VHTR Material Qualification – INL” work package. Work was performed this year to validate the crack growth monitoring setup used with the test frames against both continuous crack length monitoring using an optical camera, as well as post-mortem analysis of marker bands on the fracture surface. Delays prevented the use of a gauge to measure load-line displacement for early tests, and so the creep-fatigue crack growth setup was evaluated using the actuator displacement for a load-line displacement setup. While not ideal, this allowed examination of the shortcomings with the current software setup that was originally designed for performing stress corrosion crack growth rate studies. The method for data collection was modified to link the crack growth monitoring software with Instron’s Wave Matrix software. Once the load-line displacement gauge arrived, the crack growth equipment was successfully modified to permit continuous monitoring of both load-line displacement and crack length. This is critical for creep-fatigue and creep crack growth rate studies for ductile material, as it permits the C* and Ct analyses. Test results are shown for Alloy 617 fatigue and creep-fatigue (without the gauge for load-line displacement measurements), as well as creep-fatigue of Alloy 709, which was performed with the completed test setup, allowing for crack length and load-line displacement monitoring.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2013

Performance Assessment Program for the Savannah River Site Liquid Waste Facilities - 13610

The Liquid Waste facilities at the U.S. Department of Energy's (DOE) Savannah River Site (SRS) are operated by Liquid Waste Operations contractor Savannah River Remediation LLC (SRR). A separate Performance Assessment (PA) is prepared to support disposal operations at the Saltstone Disposal Facility and closure evaluations for the two liquid waste tank farm facilities at SRS, F-Tank Farm and H-Tank Farm. A PA provides the technical basis and results to be used in subsequent documents to demonstrate compliance with the pertinent requirements identified in operations and closure regulatory guidance. The Saltstone Disposal Facility is subject to a State of South Carolina industrial solid waste landfill permit and the tank farms are subject to a state industrial waste water permit. The three Liquid Waste facilities are also subject to a Federal Facility Agreement approved by the State, DOE and the Environmental Protection Agency (EPA). Due to the regulatory structure, a PA is a key technical document reviewed by the DOE, the State of South Carolina and the EPA. As the waste material disposed of in the Saltstone Disposal Facility and the residual material in the closed tank farms is also subject to reclassification prior to closure via a waste determination pursuant to Section 3116 of the Ronald W. Reagan National Defense Authorization Act of Fiscal Year 2005, the U.S. Nuclear Regulatory Commission (NRC) is also a reviewing agency for the PAs. Pursuant to the Act, the NRC also has a continuing role to monitor disposal actions to assess compliance with stated performance objectives. The Liquid Waste PA program at SRS represents a continual process over the life of the disposal and closure operations. When the need for a PA or PA revision is identified, the first step is to develop a conceptual model to best represent the facility conditions. The conceptual model will include physical dimensions of the closed system, both the engineered and natural system, and modeling input parameters associated with the modeled features, both initial values (at the time of facility closure) and degradation rates/values. During the development of the PA, evaluations are conducted to reflect not only the results associated with the best available information at the time but also to evaluate potential uncertainties and sensitivities associated with the modeled system. While the PA will reflect the modeled system results from the best available information, it will also identify areas for future work to reduce overall PA uncertainties moving forward. DOE requires a PA Maintenance Program such that work continues to reduce model uncertainties, thus bolstering confidence in PA results that support regulatory decisions. This maintenance work may include new Research and Development activities or modeling as informed by previous PA results and other new information that becomes available. As new information becomes available, it is evaluated against previous PAs and appropriate actions are taken to ensure continued confidence in the regulatory decisions. Therefore, the PA program is a continual process that is not just the development of a PA but seeks to incorporate new information to reduce overall model uncertainty and provide continuing confidence in regulatory decisions. (author)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2023

Sodium Components Maintenance Shop (SCMS) Carbonation Vessel – Partial HWMA/RCRA Closure Certification Report

This report documents the Hazardous Waste Management Act (HWMA)/ Resource Conservation and Recovery Act (RCRA) Partial Closure Certification of the Sodium Components Maintenance Shop (SCMS) Carbonation Vessel. The HWMA/RCRA Closure followed the multi step review and evaluation closure process identified in the Idaho National Laboratory (INL) Materials and Fuels Complex (MFC) HWMA/RCRA Partial Permit Closure Plan, October 1, 2015. This closure certification report documents that the SCMS Carbonation Vessel was removed from the SCMS, packaged as hazardous waste and stored for future treatment and disposal, and therefore has met the closure performance standards in accordance with the Department of Energy Idaho National Laboratory Materials and Fuels Complex HWMA/RCRA Partial Permit Closure Plan (EPA No. ID4890008952, October 1, 2015).

99 GENERAL AND MISCELLANEOUS↗

DOE OSTI2013

Demonstration Testing of a Thermal Desorption Unit to Receive and Treat Waste with Unlimited Concentration of PCBs - 13437

For the last nine years, EnergySolutions and TD*X Associates LP have teamed up to provide the most comprehensive organic removal treatment process in the radioactive waste industry. The high performance thermal desorption unit (HP-TDU) located at the EnergySolutions Clive facility in Utah has successfully processed over 1,850 tons of organically contaminated radioactive mixed waste. Products from the HP-TDU system include a radioactively contaminated dry solid material that can be disposed in the on-site landfill and an organic condensate with high thermal energy content that is generally below background radiation and capable of free-release to a non-radioactive incinerator. Over the years, Permits and approvals have been obtained through the state of Utah, United States Environmental Protection Agency (USEPA) Region 8, and USEPA headquarters that enable the treatment of several waste categories including volatile and semi-volatile organic compounds, combustion-coded (CMBST) compounds, volatile metals, and polychlorinated biphenyls (PCBs). The unit has recently successfully completed Demonstration Testing for PCB concentrations up to 660,000 ppm (parts per million). Solid processed material from this Demonstration Testing was less than two ppm PCBs in three separate treatment runs; reprocessing or additional treatment was not needed to meet this limit. Through post-demonstration permitting, the system is unlimited in scope as approval has been given to receive and solidify up to pure PCBs down to this processing limit concentration to complete treatment of mixed waste. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2015

Progress in the development of the neutron flux monitoring system of the French GEN-IV SFR: simulations and experimental validations [ANIMMA--2015-IO-392]

France has a long experience of about 50 years in designing, building and operating sodium-cooled fast reactors (SFR) such as RAPSODIE, PHENIX and SUPER PHENIX. Fast reactors feature the double capability of reducing nuclear waste and saving nuclear energy resources by burning actinides. Since this reactor type is one of those selected by the Generation IV International Forum, the French government asked, in the year 2006, CEA, namely the French Alternative Energies and Atomic Energy Commission, to lead the development of an innovative GEN-IV nuclear- fission power demonstrator. The major objective is to improve the safety and availability of an SFR. The neutron flux monitoring (NFM) system of any reactor must, in any situation, permit both reactivity control and power level monitoring from startup to full power. It also has to monitor possible changes in neutron flux distribution within the core region in order to prevent any local melting accident. The neutron detectors will have to be installed inside the reactor vessel because locations outside the vessel will suffer from severe disadvantages; radially the neutron shield that is also contained in the reactor vessel will cause unacceptable losses in neutron flux; below the core the presence of a core-catcher prevents from inserting neutron guides; and above the core the distance is too large to obtain decent neutron signals outside the vessel. Another important point is to limit the number of detectors placed in the vessel in order to alleviate their installation into the vessel. In this paper, we show that the architecture of the NFM system will rely on high-temperature fission chambers (HTFC) featuring wide-range flux monitoring capability. The definition of such a system is presented and the justifications of technological options are brought with the use of simulation and experimental results. Firstly, neutron-transport calculations allow us to propose two in-vessel regions, namely the above-core and under-core structures. We verify that they comply with the main objective, that is the neutron power and flux distribution monitoring. HTFC placed in these two regions can detect an inadvertent control rod withdrawal that is a postulated initiating event for safety demonstration. Secondly, we show that the HTFC reliability is enhanced thanks to a more robust physical design and the fact that it has been justified that the mineral insulation is insensitive to any increase in temperature. Indeed, the HTFC insulation is subject to partial discharges at high temperature when the electric field between their electrodes is greater than about 200 V/mm or so. These discharges give rise to signals similar to the neutron pulses generated by a fission chamber itself, which may bias the HTFC count rate at start-up only. However, as displayed in Figure 1, we have experimentally verified that one can discriminate neutron pulses from partial discharges using online estimation of pulse width. Thirdly, we propose to estimate the count rate of a HTFC using the third order cumulant of its signal that is described by a filtered Poisson process. For such a statistic process, it is known that any cumulant, also called cumulative moment, is proportional to the process intensity that is here the count rate of a fission chamber. One recalls that the so-called Campbelling mode of such a detector is actually based on the signal variance, which is the second-order cumulant as well. The use of this extended Campbelling mode based on the third-order cumulant will permit to ensure the HTFC response linearity over the entire neutron flux range using a signal processing technique that is simple enough to satisfy design constraints on electric devices important for nuclear safety. We also show that this technique, named high order Campbelling method (HOC), is significantly more robust than another technique based on the change in the HTFC filling gas, which consists in adding a few percent of nitrogen. Finally, we also present an experimental campaign devoted to the required calibration process of the so-called HOC method. The Campbelling results show a good agreement with the simple pulse counting estimation at low count rates. It is also shown that the HOC technique provides a linear estimation of the count rates at higher power levels as well.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗