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DOE OSTI2024

Inverse prediction of PuO2 processing conditions using Bayesian seemingly unrelated regression with functional data

Over the past decade, a variety of innovative methodologies have been developed to better characterize the relationships between processing conditions and the physical, morphological, and chemical features of special nuclear material (SNM). Different processing conditions generate SNM products with different features, which are known as “signatures” because they are indicative of the processing conditions used to produce the material. These signatures can potentially allow a forensic analyst to determine which processes were used to produce the SNM and make inferences about where the material originated. This article investigates a statistical technique for relating processing conditions to the morphological features of PuO 2 particles. We develop a Bayesian implementation of seemingly unrelated regression (SUR) to inverse-predict unknown PuO 2 processing conditions from known PuO 2 features. Model results from simulated data demonstrate the usefulness of the technique. Applied to empirical data from a bench-scale experiment specifically designed with inverse prediction in mind, our model successfully predicts nitric acid concentration, while results for Pu concentration and precipitation temperature were equivalent to a simple mean model. Our technique compliments other recent methodologies developed for forensic analysis of nuclear material and can be generalized across the field of chemometrics for application to other materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

An integral condition for core-collapse supernova explosions

Here, we derive an integral condition for core-collapse supernova (CCSN) explosions and use it to construct a new diagnostic of explodability. The fundamental challenge in CCSN theory is to explain how a stalled accretion shock revives to explode a star. In this manuscript, we assume that the shock revival is initiated by the delayed-neutrino mechanism and derive an integral condition for spherically symmetric shock expansion, v s > 0. One of the most useful one-dimensional explosion conditions is the neutrino luminosity and mass-accretion rate (${L}_{\nu }\mbox{--}\dot{{ \mathcal M }}$) critical curve. Below this curve, steady-state stalled solutions exist, but above this curve, there are no stalled solutions. Burrows & Goshy suggested that the solutions above this curve are dynamic and explosive. In this manuscript, we take one step closer to proving this supposition; we show that all steady solutions above this curve have v s > 0. Assuming that these steady v s > 0 solutions correspond to explosion, we present a new dimensionless integral condition for explosion, Ψ > 0. Ψ roughly describes the balance between pressure and gravity, and we show that this parameter is equivalent to the τ condition used to infer the ${L}_{\nu }\mbox{--}\dot{{ \mathcal M }}$ critical curve. The illuminating difference is that there is a direct relationship between Ψ and v s . Below the critical curve, Ψ may be negative, positive, and zero, which corresponds to receding, expanding, and stalled-shock solutions. At the critical curve, the minimum Ψ solution is zero; above the critical curve, Ψ min > 0, and all steady solutions have v s > 0. Using one-dimensional simulations, we confirm our primary assumptions and verify that Ψ min > 0 is a reliable and accurate explosion diagnostic.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Vertical profiles of trace gas and aerosol properties over the eastern North Atlantic: variations with season and synoptic condition

Abstract. Because of their extensive coverage, marine low clouds greatly impact the global climate. Presently, the response of marine low clouds to the changes in atmospheric aerosols remains a major source of uncertainty in climate simulations. One key contribution to this large uncertainty derives from the poor understanding of the properties and processes of marine aerosols under natural conditions and the perturbation by anthropogenic emissions. The eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary layer (MBL) clouds, where cloud albedo and precipitation are highly susceptible to perturbations in aerosol properties. Here we examine the key processes that drive the cloud condensation nuclei (CCN) population in the MBL using comprehensive characterizations of aerosol and trace gas vertical profiles during the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign. During ACE-ENA, a total of 39 research flights were conducted in the Azores: 20 during summer 2017 and 19 during winter 2018. During summer, long-range-transported aerosol layers were periodically observed in the lower free troposphere (FT), leading to elevated FT CCN concentrations (NCCN). Both biomass burning and pollution from North America contribute to submicron aerosol mass in these layers, with pollution likely the dominant contributor. In contrast, long-range transported continental emissions have a much weaker influence on the aerosol properties in the ENA during the winter season. While the entrainment of FT air is a major source of particle number in the MBL for both seasons, on average it does not serve as a direct source of CCN in the MBL because the average FT NCCN is the same or even lower than that in the MBL. The particle number flux due to FT entrainment is dominated by pre-CCN (particles that are too small to form cloud droplets under typical conditions, i.e., particles with sizes below the Hoppel minimum) due to the elevated Npre-CCN in the lower FT. Once these pre-CCN are entrained into the MBL, they can grow and reach CCN size range through condensational growth, representing an indirect and major source of MBL CCN in the ENA. The impact of synoptic conditions on the aerosol properties is examined. Under pre-front and post-front conditions, shallow convective activity often leads to a deep and decoupled boundary layer. Coalescence scavenging and evaporation of drizzle below clouds lead to reduced NCCN and larger accumulation-mode particle sizes in the upper cloud-containing decoupled layer, indicating that surface measurements overestimate the NCCN relevant to the formation of MBL clouds under decoupled conditions.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2013

Fatigue and Creep Crack Propagation behaviour of Alloy 617 in the Annealed and Aged Conditions

The crack propagation behaviour of Alloy 617 was studied under various conditions. Elevated temperature fatigue and creep-fatigue crack growth experiments were conducted at 650 and 800 degrees C under constant stress intensity (triangle K) conditions and triangular or trapezoidal waveforms at various frequencies on as-received, aged, and carburized material. Environmental conditions included both laboratory air and characteristic VHTR impure helium. As-received Alloy 617 displayed an increase in the crack growth rate (da/dN) as the frequency was decreased in air which indicated a time-dependent contribution component in fatigue crack propagation. Material aged at 650°C did not display any influence on the fatigue crack growth rates nor the increasing trend of crack growth rate with decreasing frequency even though significant microstructural evolution, including y’ (Ni3Al) after short times, occurred during aging. In contrast, carburized Alloy 617 showed an increase in crack growth rates at all frequencies tested compared to the material in the standard annealed condition. Crack growth studies under quasi-constant K (i.e. creep) conditions were also completed at 650 degrees C and a stress intensity of K = 40 MPa9 (square root)m. The results indicate that crack growth is primarily intergranular and increased creep crack growth rates exist in the impure helium environment when compared to the results in laboratory air. Furthermore, the propagation rates (da/dt) continually increased for the duration of the creep crack growth either due to material aging or evolution of a crack tip creep zone. Finally, fatigue crack propagation tests at 800 degrees C on annealed Alloy 617 indicated that crack propagation rates were higher in air than impure helium at the largest frequencies and lowest stress intensities. The rates in helium, however, eventually surpass the rates in air as the frequency is reduced and the stress intensity is decreased which was not observed at 650 degrees C.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Energy Extraction from a Slider-Crank Wave Energy under Irregular Wave Conditions: Preprint

A slider-crank wave energy converter (WEC) is a novel energy conversion device. It converts wave energy into electricity at a relatively high efficiency, and it features a simple structure. Past analysis on this particular WEC has been done under regular sinusoidal wave conditions, and suboptimal energy could be achieved. This paper presents the analysis of the system under irregular wave conditions; a time-domain hydrodynamics model is adopted and a rule-based control methodology is introduced to better serve the irregular wave conditions. Results from the simulations show that the performance of the system under irregular wave conditions is different from that under regular sinusoidal wave conditions, but a reasonable amount of energy can still be extracted.

17 WIND ENERGY↗

DOE OSTI2015

Energy Extraction from a Slider-Crank Wave Energy Converter under Irregular Wave Conditions

17 WIND ENERGY↗

DOE OSTI2016

Performance of R-410A Alternative Refrigerants in a Reciprocating Compressor Designed for Air Conditioning Applications

In response to environmental concerns raised by the use of refrigerants with high Global Warming Potential (GWP), the Air-Conditioning, Heating, and Refrigeration Institute (AHRI) has launched an industry-wide cooperative research program, referred to as the Low-GWP Alternative Refrigerants Evaluation Program (AREP), to identify and evaluate promising alternative refrigerants for major product categories. After successfully completing the first phase of the program in December 2013, AHRI launched a second phase of the Low-GWP AREP in 2014 to continue research in areas that were not previously addressed, including refrigerants in high ambient conditions, refrigerants in applications not tested in the first phase, and new refrigerants identified since testing for the program began. Although the Ozone Depletion Potential of R-410A is zero, this refrigerant is under scrutiny due to its high GWP. Several candidate alternative refrigerants have already demonstrated low global warming potential. Performance of these low-GWP alternative refrigerants is being evaluated for Air conditioning and heat pump applications to ensure acceptable system capacity and efficiency. This paper reports the results of a series of compressor calorimeter tests conducted for the second phase of the AREP to evaluate the performance of R-410A alternative refrigerants in a reciprocating compressor designed for air conditioning systems. It compares performance of alternative refrigerants ARM-71A, L41-1, DR-5A, D2Y-60, and R-32 to that of R-410A over a wide range of operating conditions. The tests showed that, in general, cooling capacities were slightly lower (except for the R-32), but energy efficiency ratios (EER) of the alternative refrigerants were comparable to that of R-410A.

Alternative Refrigerants↗

DOE OSTI2017

Method, system, and computer-readable medium for determining performance characteristics of an object undergoing one or more arbitrary aging conditions

A method, system, and computer-readable medium are described for characterizing performance loss of an object undergoing an arbitrary aging condition. Baseline aging data may be collected from the object for at least one known baseline aging condition over time, determining baseline multiple sigmoid model parameters from the baseline data, and performance loss of the object may be determined over time through multiple sigmoid model parameters associated with the object undergoing the arbitrary aging condition using a differential deviation-from-baseline approach from the baseline multiple sigmoid model parameters. The system may include an object, monitoring hardware configured to sample performance characteristics of the object, and a processor coupled to the monitoring hardware. The processor is configured to determine performance loss for the arbitrary aging condition from a comparison of the performance characteristics of the object deviating from baseline performance characteristics associated with a baseline aging condition.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2014

Modifications of impurity transport and divertor sources by lithium wall conditioning in the National Spherical Torus Experiment

In the National Spherical Torus Experiment (NSTX), lithium coatings are evaporated on graphite plasma facing components (PFCs) for wall conditioning. In lithium-conditioned H-mode discharges, carbon accumulation is observed with core concentrations <10%, leading to a lack of density control, while lithium ions have concentrations <0.1%. In this thesis, modifications of carbon and lithium divertor sources as well as scrape-off layer (SOL) and core transport due to lithium conditioning are studied. Spectroscopic impurity influxes (measured by filtered cameras) and 2D multi-fluid edge transport simulations via the UEDGE code are employed to study divertor impurity sources and SOL transport, respectively. Core transport of carbon and lithium is analyzed using the impurity transport code MIST and the neoclassical transport codes NEO and NCLASS. A reduction of the carbon sputtering yield in the lower divertor is observed with lithium evaporation. However, weaker divertor impurity retention resulting from reduced recycling (inferred from UEDGE simulations) and the possible importance of wall sources can counteract this reduction in divertor carbon influxes. The suppression of edge-localized-modes (ELMs) is the primary cause of the increased carbon inventories in lithium-conditioned discharges, leading to lack of density control. Deviations from neoclassical predictions for carbon transport are observed at the pedestal top in lithium-conditioned discharges, indicating the presence of anomalous outward convection. While the lithium sputtering yield from lithium-coated graphite in the divertor is consistent with physical and temperature-enhanced sputtering, a strong reduction in ionized lithium influxes is observed, possibly due to prompt re-deposition. The different poloidal source distribution and the stronger divertor retention for lithium (inferred from UEDGE simulations) contribute to a lower edge lithium source with respect to carbon. The latter is due to the shorter lithium ionization mean-free-path and weaker classical parallel forces. The high neoclassical lithium diffusivity, due to collisions with carbon ions, is partially responsible for the low lithium core densities. Furthermore, the higher neoclassical levels make lithium transport closer to neoclassical expectations. The NSTX-Upgrade baseline scenario includes lithium coatings on graphite PFCs for deuterium particle control. While the remarkably good lithium divertor retention makes it an attractive choice, the suppression of ELMs leads to carbon accumulation and therefore to the need to develop impurity mitigation techniques.

impurity trasport↗

DOE OSTI2019

Conditions Databases at FNAL

Conditions databases is an important class of database applications where the database is used to record the state of a set of quantities as a function of observation time. Conditions databases are used in Hight Energy Physics to record the state of the detector apparatus during data taking, and then to use the data during the event reconstruction and analysis phases. At FNAL, we have a set of 3 different conditions database products, Minerva Conditions DB, ConDB and UConDB, which cover the whole range of the use cases presented by the FNAL experiments. These products have common features such as conditions data representation model, data version control, ability to restore the database to a previous state, scalable web service data access interface. In the paper, we will present the common features of the products, common solutions used to build them and also the differences between the products and their target use cases.

Mandrichenko, Igor V.↗

DOE OSTI2022

Effect of Initial Water Saturation on The Performance of Fracturing Fluids With and Without Polyallylamine under Simulated EGS Conditions

Objectives/Scope: StimuFrac (US Patents 9,873,828 B2 and 9,447,315 B2), a CO2-reactive polymer aqueous solution [polyallylamine (PAA) 1wt% in water] combined with CO2, can be used as a less water-intensive fracturing fluid for enhanced geothermal systems (EGS). Our previous results show that in hot dry rock (HDR), PAA/CO2 fracturing fluids outperformed other fluids such as water, CO2, and CO2/water in generating large fractures with less fluid consumed. The objective of this work is to study the effect of initial water saturation of rock on the performance of StimuFrac fluid in ½ foot cubic rock samples and under representative EGS pressure/temperature conditions using cyclic and constant flow rate injection strategies. The fracturing results are compared with results using different fracturing fluids in terms of controlling fracture propagation rates, fracture hydraulic conductivity, breakdown pressures and volumes of fluids required. Methods/Procedures/Process: In all tests, water was initially injected into the rock to increase the water saturation before the fracturing processes to simulate actual geothermal reservoir conditions. For the cyclic injection, one complete cycle consisted of (1) a PAA slug (or water slug) injection followed by (2) CO2 injection to initiate the fracture. In the second step of the first cycle, the pressure of CO2 is increased until a maximum pressure is reached (fracture is initiated at this moment), and then the injection of CO2 is allowed for another 30 seconds to propagate the fracture. Then, the two-step cycle of PAA followed by CO2 injection (up to 2-4 mL/min) was continued. For the constant flow rate injection strategies, the initial water saturation was increased by injecting water at 1000 psi and 200°C for three days. After that, an initial slug of water, CO2, or PAA was injected and then fracturing was initiated and propagated by injecting CO2 at a constant flow rate. Applications/Significance/Novelty: The results of this study suggest that water saturation, especially near the wellbore region, will significantly affect the fracturing fluid transmission into the rock porous media by changing the relative permeability of CO2 or water, thus affecting the fracture initiation and propagation. In this study, fracturing with cyclic injection or constant flow rate injection methods were performed using three different kinds of fluids systems. These fluids are water, CO2, or CO2 with PAA. Splitting the rock samples in half after fracturing reveals that the fracture propagation is significantly limited under these high water saturated conditions compared to dry initial conditions: The fractures propagate less than 1/3 length of the distance from the wellbore to rock surface, and in some cases no fracture is generated. This may be caused by the fact that leak-off is dominating the fracturing process and the injected fluid flow rate is not high enough to overcome the leak-off even under high flow rate injection conditions. Additionally, CO2 could be leaking off into the wellbore annulus and this may be making it more difficult to generate pressure gradients away from the near-wellbore region.

Jian, Guoqing↗

DOE OSTI2022

Integrated Risk-Informed Condition Based Maintenance Capability and Automated Platform: Technical Report 3

This project is a collaborative research effort between PKMJ Technical Services LLC, Idaho National Laboratory, and Public Service Enterprise Group (PSEG) Nuclear, LLC. The collaboration, led by PKMJ Technical Services LLC, is part of the industry Funding Opportunity Announcement (FOA) award under Advanced Nuclear Technology Development FOA #DE-FOA-0001817. The pilot demonstration focuses on the Circulating Water System (CWS), an important non-safety-related system that impacts the power generation capability of the plant site. Achieving riskinformed condition-based Predictive Maintenance (PdM) on the CWS will result in significant economic benefits, and the developed methodologies can also be applied to other plant systems. This approach supports an industry goal of ensuring that nuclear power generation remains a viable, economically competitive option in the energy market. Operation and Maintenance (O&M) costs include labor-intensive Preventive Maintenance (PM) programs that involve manually performed inspection, calibration, testing, and maintenance of plant assets at periodic frequencies as well as time-based replacement of assets, irrespective of condition. This project offers an alternative by focusing on riskinformed condition-based maintenance to reduce O&M costs while still maintaining plant health and safety. This report summarizes the progress made toward achieving a risk-informed condition-based maintenance approach. The research and development (R&D) activities presented in this report are associated with development of a nuclear digital platform application, integration of fault signature models, and automated work management processes. The fault signatures and Machine Learning (ML) models are key components in predictive analytics and are heavily leveraged to improve the insights received by existing plant process data sources. Availability of the analysis results within a centralized digital platform enhances efficiency by enabling automation of activities otherwise performed manually. Personnel are presented with enhanced information that can be used to evaluate plant status and risks. Utilizing the enhancements to data analytics supports automated responses, (i.e. issuance of work orders) to address developing equipment faults and thus preventing forced, unplanned shutdowns of components or systems. The R&D activities described within this report lay the foundation for developing and demonstrating a digital automated platform to centralize the implementation of condition monitoring and response to equipment faults. The digital automated platform is cloud-based and designed to enable improved efficiency of plant processes. The digital platform includes content related to maintenance optimization, fault signature analysis, and plant records, which can all be used to support efficiencies when located within a centralized digital platform. These efficiencies could be further enhanced when deployed through industry-wide deployment of the technology to improve insights and processes based upon economies of scale.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2013

Conditioning and Repackaging of Spent Radioactive Cs-137 and Co-60 Sealed Sources in Egypt - 13490

Radioactive Sealed sources (RSSs) are widely use all over the world in medicine, agriculture, industry, research, etc. The accidental misuse and exposure to RSSs has caused significant environmental contamination, serious injuries and many deaths. The high specific activity of the materials in many RSSs means that the spread of as little as microgram quantities can generate significant risk to human health and inhibit the use of buildings and land. Conditioning of such sources is a must to protect humans and environment from the hazard of ionizing radiation and contamination. Conditioning is also increase the security of these sources by decreasing the probability of stolen and/or use in terrorist attacks. According to the law No.7/2010, Egyptian atomic energy authority represented in the hot laboratories and waste management center (centralized waste facility, HLWMC) has the responsibility of collecting, conditioning, storing and management of all types of radioactive waste from all Egyptian territory including spent radioactive sealed sources (SRSSs). This paper explains the conditioning procedures for two of the most common SRSSs, Cs{sup 137} and Co{sup 60} sources which make up more than 90% of the total spent radioactive sealed sources stored in our centralized waste facility as one of the major activities of hot laboratories and waste management center. Conditioning has to meet three main objectives, be acceptable for storage, enable their safe transport, and comply with disposal requirements. (authors)

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2012

Carbonation Behavior of Pure Cement Hydrates under Supercritical Carbon Dioxide Conditions - 12199

Carbonation of cement-based waste forms using a supercritical carbon dioxide (SCCO{sub 2}) is a developing technology for the waste immobilization of radioactive and non-radioactive wastes. However, the detail carbonation behaviors of cement matrices under the SCCO{sub 2} condition are unknown, since cement matrices forms very complex phases. In this study, in order to clarify the crystal phases, we synthesized pure cement hydrate phases as each single phases; portlandite (Ca(OH){sub 2}), ettringite (Ca{sub 6}Al{sub 2}(SO{sub 4}){sub 3}(OH){sub 12}.26H{sub 2}O), and calcium silicate hydrate (n CaO---m SiO{sub 2} ---x H{sub 2}O), using suspensions containing a stoichiometric mixture of chemical regents, and performed carbonation experiments using an autoclave under supercritical condition for carbon dioxide. The XRD results revealed both the carbonate phases and co-product phases depending on the initial hydrate phases; gypsum for Ettringite, amorphous or crystalline silica for calcium silicate hydroxide. Thermogravimetric analysis was also performed to understand carbonation behaviors quantitatively. According to the experimental results, it was found that the major reaction was formation of calcium carbonate (CaCO{sub 3}) in all cases. However, the behaviors of H{sub 2}O and CO{sub 2} content were quietly different: Portlandite was most reactive for carbonation under SCCO{sub 2} conditions, and the CO{sub 2} content per one molar CaO was ranged from 0.96 ∼ 0.98. In the case of Ettringite, the experiment indicates partial decomposition of ettringite phase during carbonation. Ettringite was comparatively stable even under the SCCO{sub 2} conditions. Therefore, a part of ettringite remained and formed similar phases after the ettringite carbonation. The CO{sub 2} content for ettringite showed almost constant values around 0.86 ∼ 0.87. In the case of calcium silicate hydrate, the carbonation behavior was significantly influenced by the condition of SCCO{sub 2}. The CO{sub 2} content for the calcium silicate hydrate had values that ranged from 0.51 ∼ 1.01. The co-products of the carbonation were gypsum (CaSO{sub 4}) for ettringite, silica gel (SiO{sub x}) and silica (SiO{sub 2}) for calcium silicate hydrate, which also contributed to the densification of the particles. The production of co-products enhanced the change to their morphology after the carbonation. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2016

Modeling used fuel response to normal conditions of transportation package drops to access geometric sensitivities

The US Department of Energy Used Fuel Disposition program is performing research to determine the loading conditions that used nuclear fuel (UNF) experiences during normal conditions of transportation (NCT). This loading environment includes mechanical shock and vibration as the UNF is transported by rail or truck, and it also includes potential package free drop conditions, which are the topic of this study. NCT drop test requirements for UNF package designs are defined in 10 CFR 71.71. The free drop test height is 30 cm for the UNF packages considered in this study. Explicit dynamic finite element models of generic rail and truck UNF packages containing a highly resolved 17x17 PWR fuel assembly are used to estimate the potential range of loading experienced by UNF during NCT horizontal package drops onto an unyielding surface. There are many variables and uncertainties that can affect the loading of UNF during this type of free drop scenario. This study focuses on geometric variables, such as gap conditions and small adjustments to the angle of impact, in a number of analysis cases. The LS-DYNA finite element analyses calculate detailed results for all the components of the fuel assembly. The results show that the peak localized axial strain in the fuel cladding is estimated to be 0.006421 (nominal) with an upper bound of 0.014511, based on the peak instantaneous bending moment of 63.65 N-m and other uncertainty factors. For the assumed low burnup condition of the UNF, the cladding yield strain is 0.011027 and the failure strain is 0.015574, which means that the calculated upper bound strain approaches the cladding failure limit without exceeding it. The peak shear force on the cladding was calculated to be 7879 N. This could be significant to cladding integrity if applied to the UNF in a situation where the fuel pellets do not support the shear transfer. Further evaluation is needed to determine if this is a credible threat to cladding integrity for these 30 cm free drop scenarios.

42 ENGINEERING↗

DOE OSTI2016

Secondary creep behavior of Zr-4 claddings under LOCA conditions

The thermo-mechanical behavior of Zircaloy-4 fuel rods under Loss-Of-Coolant Accident (LOCA) conditions in water cooled reactors is investigated. A custom experimental setup is dedicated to the high-temperature creep ballooning study of 90 mm long cladding samples. Creep tests were performed under an inert environment (argon), for temperatures from 750 to 850 C. degrees and internal pressures ranging from 1 to 5 MPa. During its operating life, Zr-4 cladding is submitted to oxidation and hydriding. These parameters strongly influence the creep behavior of Zirconium alloys at high temperatures. A first campaign on as-received Zr-4 was performed. Creep-rates are computed using 2-Dimensional Digital Image Correlation (2D-DIC) and are correlated to local temperatures measured using Near Infra-Red thermography. As-received Zr-4 behavior laws are determined using Finite Element Model Updating (FEMU). Norton exponents and activation energies are determined for thermal-mechanical conditions of the performed tests. The results show that the effect of applied stress on the Norton exponent is evidenced in the study for both α-phase and (α + β)-phase domains. The determined stress exponent magnitudes are very consistent with literature data depending on the thermomechanical test conditions. The activation energy parameter is very sensitive to the thermo-mechanical conditions and remains valid within a limited temperature and stress ranges to the authors' knowledge. The beginning of the (α + β)-phase domain is clearly identified with the activation energy increase. Finally, steady-state creep is accurately modeled depending on ballooning thermo-mechanical conditions.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2016

Clad to coolant heat transfer during RIA in PWR conditions

The power pulse during an insertion of reactivity accident (RIA) leads to a transient heating of the fuel. Heat transfer toward the coolant through the clad and associated temperature transient of the clad is of safety significance since it may largely impact the risk of clad failure. For sufficiently large enthalpy deposited within the fuel, clad temperature increases rapidly and this can lead to coolant boiling. This paper concerns the critical review of the present understanding and of the models for the clad to coolant heat transfer in RIA for PWR conditions. The results of past experiments are reviewed and the reliability of current models dedicated to these conditions is analyzed. It appears that the use of classical models for wall to fluid heat transfer does not allow predicting the clad temperature transient as measured in RIA-related experiments. The deviation is all the more large when film boiling conditions are reached. To reproduce the experimental data, some correlations of heat transfer can be fitted but the reliability of such model out of the range of conditions of the experimental data is low. It is mainly due to a rather low level of understanding of the heat transfer in very transient conditions (i.e. when the time scale of variation of the main heat transfer parameters, like a wall temperature, is less than the typical internal time scale of the heat transfer process itself). It results in a very large scattering in the numerical simulation of clad temperature when several fuel codes are considered. To improve the reliability of these calculations, it is believed that the study of transient boiling heat transfer thanks to devoted experimental facilities is required.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2017

Flow Rate Dependency of Permeability Changes with the Deposition of CSH under the Highly Alkaline Ca-rich Condition - 17175

The formation of calcium silicate hydrate (CSH) around the geological repository is one of the notable factors for the assessment of the radionuclide migration. This study discussed the clogging effect of CSH in flow path with the change in the flow rate based on the flow experiments using micro flow cell. In the experiment, the change of the permeability with the alteration of granite under the highly alkaline and Ca-rich condition was examined. As a result, the permeability in flow path gradually decreased with the periodical increase and decrease of the permeability. In addition, under the condition of the lower flow rate (0.06 ml/h), the permeability became much smaller than those for other conditions of the higher flow rates. These suggest that the clogging of flow path will progress with the local deposition/moving of CSH, in particular, under the condition of the lower flow rate. Retardation effect of radionuclide migration will be expected because it is prospected that flow rate of groundwater is lower than that of this study in the actual condition of repository. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗