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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Light Water Reactor Sustainability Program: Evaluation of Localized Cable Test Methods for Nuclear Power Plant Cable Aging Management Programs

This Pacific Northwest National Laboratory (PNNL) milestone report describes progress to date on the investigation of nondestructive test (NDE) methods focusing particularly on local measurements that provide key indicators of cable aging and damage. The work includes a review of relevant literature as well as hands-on experimental verification of inspection capabilities. As NPPs consider applying for second, or subsequent, license renewal (SLR) to extend their operating period from 60 years to 80 years, it important to understand how the materials installed in plant systems and components will age during that time and develop aging management programs (AMPs) to assure continued safe operation under normal and design basis events (DBE). Normal component and system tests typically confirm the cables can perform their normal operational function. The focus of the cable test program is directed toward the more demanding challenge of assuring the cable function under accident or DBE. Most utilities already have a program associated with their first life extension from 40 to 60 years. Regrettably, there is neither a clear guideline nor a single NDE that can assure cable function and integrity for all cables. Thankfully, however, practical implementation of a broad range of tests allows utilities to develop a practical program that assures cable function to a high degree. The industry has adopted 50% elongation at break (EAB) relative to the un-aged cable condition as the acceptability standard. All tests are benchmarked against the cable EAB test. EAB is a destructive test so the test programs must apply an array of other NDE tests to assure or infer the overall set of cable’s system integrity. These cable NDE programs vary in rigor and methodology. As the industry gains experience with the efficacy of these programs, it is expected that implementation practice will converge to a more common approach. This report addresses the range of local NDE cable tests that are or could be practically implemented in a field test situation. These tests include: visual, infrared thermography, interdigital capacitance, indenter, relaxation time indenter, dynamic mechanical analyzer, infrared/near-infrared spectrometry, ultrasound, and distributed fiber optic temperature measurement.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2016

Preparation of NO 2 -Aged Silver-Functionalized Silica-Aerogel and Silver Mordenite Samples

Reprocessing used nuclear fuel can result in the volatilization of radioactive gaseous species, including 129 I, into the various process off-gas streams. In order to comply with US regulatory requirements, plant off-gas streams must be treated to remove the iodine prior to discharging the off-gas into the environment. The performance of available gas removal methods depends not only on the concentration of the volatile radioisotope of interest, but also on other constituents that could be present in the reprocessing off-gas streams. Some of the constituents, such as NOx produced during fuel dissolution, are known to have deleterious effects on the capture performance of silver-based sorbents used for iodine removal. Commercially available reduced silver mordenite (AgZ) has an iodine saturation concentration of 7.0-9.0 wt%, and its iodine sorption capacity is reduced by 20-50% as a result of NO2 aging. Silverfunctionalized silica aerogel (AgAerogel), an alternative for iodine capture, has an initial iodine saturation of 29.0 wt% and its iodine capacity is only reduced by 15% from NO2 aging. Understanding the differences in aging behavior between AgZ and AgAerogel is critical to determining the behavior of these sorbents under realistic off-gas conditions. To assist in future technical studies on this topic, samples of both AgZ and AgAerogel were aged with NO2. In the experiment, 10.2190 g of AgZ and 10.1771 g of AgAerogel were exposed to a static 0.75% NO 2 /dry air blend for a period of 28 days. The samples were then removed and stored under argon until needed for future experiments.=

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Crosslinking of SAVY-4000 O-rings as a Function of Aging Conditions

SAVY-4000 containers were developed as a part of DOE M 441.1-1 to protect workers who handle stored nuclear material from exposure due to loss of containment.1 The SAVY-4000 is comprised of three parts: a lid, a container, and a cross-linked fluoropolymer O-ring. Degradation of the O-ring during use could limit the lifetime of the SAVY-4000. In order to quantify the chemical changes of the Oring over time, the molecular weight between crosslinks was determined as a function of aging conditions using a swelling technique. Because the O-ring is a cross-linked polymer, it will absorb solvent into its matrix without dissolving. The relative amount of solvent uptake can be related to the degree of crosslinking using an equation developed by Paul Flory and John Rehner Jr3. This method was used to analyze O-ring samples aged under thermal and ionizing-radiation conditions. It was found that at the harsher thermal gaining conditions in absence of ionizing-radiation the average molecular weight between crosslinks decreased, indicating a rise in crosslinks, which may be attributable to advanced aging with no ionizing radiation present. Inversely, in the presence of ionizing radiation it was found that material has a higher level of cross-linking with age. This information could be used to help predict the lifetime of the O-rings in SAVY-4000 containers under service conditions.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Oxide Morphology of a FeCrAl Alloy, Kanthal APMT, following Extended Aging at 300-600C

Iron-chromium-aluminum (FeCrAl) alloys are of interest to the nuclear materials community due to their resistance to high temperature steam oxidation under accident conditions. The present work investigates oxide formation at temperatures relevant to light water reactor cladding operation following extended aging to assess growth kinetics, chemical composition, and microstructure of oxide formation on a commercial FeCrAl alloy, Fe-21wt.%Cr-5wt.%Al-3wt.%Mo (Kanthal APMT). Aging treatments were performed for 100-1000 hours in stagnant air at 300, 400, 500, and 600 °C, respectively. Oxide growth behavior under the investigated conditions follows a logarithmic time dependence. When the oxidization temperature is 400 °C or below, the oxide is amorphous. At 500 °C, isolated crystalline regions start to appear during short period aging time and expand with extended exposures. Crystalline α-Al2O3 oxide film develops at 600 °C and the correlated logarithmic rate constant decreases significantly, indicating enhanced oxidation resistance of the formed oxide film. In addition, Mo segregation at grain boundaries has been observed when the aging temperature exceeds 500 °C. The results of this study can be viewed as an upper bounding result for potential oxide coarsening during reactor operation.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Low Temperature Age Hardening in Cast Uranium-6 wt. pct. Niobium

An investigation to determine whether cast U-6Nb would exhibit low temperature (<250°C) age hardening behavior, which has been well-documented in wrought U-6Nb, was performed using a 6 year old near-cylindrical U-6Nb casting, courtesy of AWE, UK. The casting was sectioned, and metallographic cubes and tensile bars were machined and subjected to a variety of heat treatments. Our results indicate that the cast U-6Nb has a larger grain size than wrought U-6Nb, ranging from ~200-500 μm, and that these grains are equiaxed. A significant quantity of inclusions are present at the <10 μm size range and appear to be carbides, based on their morphology (faceted) and color (dark gray). There does not appear to be significant porosity present and the few pores observed were <40 μm in size and spherical. Tensile bars (TBs) were lathe machined, solutionized, then water quenched prior to testing. A group of TBs were subjected to low temperature artificial aging heat treatments consisting of a hold at 200°C for 1 or 2h, followed by furnace cooling, all under a helium backfill. Mechanical testing confirms that cast U-6Nb TBs exhibit low temperature age hardening, with an increase in initial yield stress (Y1) of >425 MPa—a significant increase over wrought U-6Nb yield stress of 100-200 MPa for the same heat treatment. This increase is accompanied by a reduction in failure strain, which is indicative of a reduction in ductility. Modifying the heat treatment temperature and/or time may allow the properties to be tailored to the requirements. This study is intended as a preliminary investigation. Overall, this high impurity content casting exhibits a reasonable mechanical response which can be tailored in a consistent manner through low temperature heat treatment. As the result, a more comprehensive investigation of low temperature aging in cleaner cast U-6Nb, better representative of the state-of-the-art, shall be performed in FY19.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Developing a radiation-aging model for polymeric foam cushions

Motivation: A major component of the A&L constitutive modeling effort over the last couple of years has involved developing a thermal aging model for foam cushions. Through extensive studies of uniaxial compression data, we have established that the Ogden N = 2 Hyperfoam in conjunction with the Tobolsky two-network model [Ref. 4] provides an accurate theoretical framework to describe the results, both for the traditional (stochastic) as well as the AM (3D-printed) foam pads. The results display numerical accuracy over a wide range of compression levels, from low to moderate up to slightly over 90% of lock-up. Over the last few weeks we have been exploring radiation aging data on a specific 3D printed foam, i.e., SE1700 AM FCT foam, to see if the Ogden + Tobolsky model can explain such data as well, and if so, how the various model parameters change as a function of dosage. As this report shows, the answer is indeed yes. We find that the modulus of the second (i.e., induced network) increases nearly proportionally with the radiation dosage, with a smaller sub-linear decrease in the primary shear modulus of the original network. This is consistent with the interpretation that exposure to energetic gamma-radiation is dominated by the formation of new cross-links. Significance: An important goal of A&L modeling efforts is to develop a fully age-aware materials model that can describe the joint effects of commonly present aging drivers like temperature, radiation, humidity, etc. Such a model is necessary to assess the lifetime of essential components like polymeric foams and rubber pads.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Mechanistic Understanding of Silver Sorbent Aging Processes in Off-Gas Treatment

The effect of aging in various off-gas streams including dry air, humid air, 1% NO/N 2 , 2% NO 2 /air, and a gas mixture consisting of 99.25% humid air (dew point: -15 °C), 0.25% NO/N 2 , and 0.5% NO 2 /air in terms of concentration on reduced silver exchanged mordenite (Ag 0 Z) and silver functionalized silica aerogel (Ag 0 -aerogel) were studied in this project. Utilizing simple and sophisticated experimental information combined with molecular and macroscopic mechanistic modeling, this project has significantly advanced the current understanding of aging for silver bearing adsorbents in nuclear-fuel-reprocessing off-gas streams. In addition, this project has produced models that can be utilized to predict the influence of adsorbent aging on the uptake kinetics and capacity of aged adsorbents for iodine and iodine-containing organic compounds. The results of the study have been published in the open literature, and can be used to help DOE better predict the removal of radioactive gases from nuclear-fuel-reprocessing off-gas streams.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2016

A Compilation of Tensile Data for Quenched and Aged Uranium-Niobium Alloys

A compilation of tensile test data in uranium-niobium (U-Nb)binary alloys containing up to 10wt.% Nb is presented, capturing over900heat-treat conditions. It is based on a comprehensive survey of the literature and includes recent Los Alamos data, especially from long-term aging. The data are restricted to ambient-temperature, quasi-static strain-rate measurements. The emphasis is on controlled gamma-solutionize+quench and isothermal aging data from temperatures as high as 625oC and times as long as 10 years. Elastic, plastic (strength), and ductility properties reported include first-yield modulus, first-yield strength, second-yield strength, ultimate tensile strength,uniform elongation, total elongation, and reduction in area. Total elongation data were also converted to a common standard for ease in comparing data from different tensile specimen geometries. Material pedigree and machining damage condition are included among the metadata recorded here. With a view towards modeling these properties as a function of age(to be reported in future publications), the data were categorized according to the microstructure present (i.e., before or after the appearance of lamellar decomposition products) and the phenomenological time-trend of aging (initial softening, classic hardening, classic overaging-softening).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Ageing Management for Extended Long-Term Dry Storage of Spent Nuclear Fuel and Transportation

The principal objectives of the Coordinated Research Project (CRP) and CRADA were to (1) investigate how ageing effects leading to degradation of materials used in the spent fuel dry storage systems could be managed by ageing management programs (AMPs) and (2) using existing AMPs as a basis, establish guidance on how to develop, generate, and maintain AMPs for dry storage systems of spent nuclear fuel (SNF) that can be accomplished in various ways. The PI (Dr. Liu) is an internationally recognized expert on ageing management for license renewal of nuclear power plants and independent spent fuel dry storage installations. Dr. Liu was invited by IAEA to participate in this CRP and served as Chair of the Working Group, supporting the IAEA CRP Lead, with other members from Argentina, the Czech Republic, France, Germany, Hungary, Japan, Pakistan, Spain, Switzerland, United Kingdom, and the United States of America. Argonne’s scope of work in the CRADA for the CRP included (1) ageing management guidance documents developed by Argonne for DOE and used by the Nuclear Regulatory Commission (NRC) and industry and (2) research leveraged from the DOE Office of Nuclear Energy on the mechanical properties of high-burnup fuel cladding and the ARG-US remote monitoring systems technology developed for the DOE Packaging Certification Program, Office of Packaging and Transportation, Office of Environmental Management.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Role of n-phenyl-β-naphthylamine in the Acid-Nitroplasticizer Thermal Aging (ANTA) Experiment

A short-term aging study, which was named as Acid-Nitroplasticizer Thermal Aging (ANTA), was conducted to explore the complex chemistry between n-phenyl-β-naphthylamine (PBNA), HNO x , and nitroplasticizer (NP). Aging of NP with PBNA and acid treatments have demonstrated that PBNA is an effective antioxidant and an anti-hydrolytic agent (e.g., inhibits HNO 3 ) and have allowed the identification of nitroso-PBNA (PBNA-NO). The direct conversion of PBNA to PBNA-NO via scavenging of HONO, known as nitrosation, is a preceding event of PBNA nitration, which provides evidence to the HONO elimination as the key mechanism in the early stage of NP aging. Through the kinetics of both nitrosation and nitration, the accuracy of a prediction on PBNA consumption in NP degradation is further improved.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Race/Ethnicity Disparities in Dysglycemia Among U.S. Women of Childbearing Age Found Mainly in the Nonoverweight/Nonobese

To describe the burden of dysglycemia—abnormal glucose metabolism indicative of diabetes or high risk for diabetes—among U.S. women of childbearing age, focusing on differences by race/ethnicity. Using U.S. National Health and Nutrition Examination Survey data (1999–2008), we calculated the burden of dysglycemia (i.e., prediabetes or diabetes from measures of fasting glucose, A1C, and self-report) in nonpregnant women of childbearing age (15–49 years) by race/ethnicity status. We estimated prevalence risk ratios (PRRs) for dysglycemia in subpopulations stratified by BMI (measured as kilograms divided by the square of height in meters), using predicted marginal estimates and adjusting for age, waist circumference, C-reactive protein, and socioeconomic factors. Based on data from 7,162 nonpregnant women, representing >59,000,000 women nationwide, 19% (95% CI 17.2–20.9) had some level of dysglycemia, with higher crude prevalence among non-Hispanic blacks and Mexican Americans vs. non-Hispanic whites (26.3% [95% CI 22.3–30.8] and 23.8% [19.5–28.7] vs. 16.8% [14.4–19.6], respectively). In women with BMI <25 kg/m 2 , dysglycemia prevalence was roughly twice as high in both non-Hispanic blacks and Mexican Americans vs. non-Hispanic whites. This relative increase persisted in adjusted models (PRR adj 1.86 [1.16–2.98] and 2.23 [1.38–3.60] for non-Hispanic blacks and Mexican Americans, respectively). For women with BMI 25–29.99 kg/m 2 , only non-Hispanic blacks showed increased prevalence vs. non-Hispanic whites (PRR adj 1.55 [1.03–2.34] and 1.28 [0.73–2.26] for non-Hispanic blacks and Mexican Americans, respectively). In women with BMI >30 kg/m 2 , there was no significant increase in prevalence of dysglycemia by race/ethnicity category. Our findings show that dysglycemia affects a significant portion of U.S. women of childbearing age and that disparities by race/ethnicity are most prominent in the nonoverweight/nonobese.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

A mathematical approach to survey electrochemical impedance spectroscopy for aging in lithium-ion batteries

Electrochemical impedance spectroscopy (EIS) is a valuable technique to detect the health status and aging phenomena in lithium-ion batteries (LiB). Equivalent circuit modeling (ECM) is conventionally used when interpreting EIS data and gaining physical insights into the aging mechanisms. However, performing ECM is resource intensive and expert-level of knowledge is usually required to select suitable models and fitting parameters. This article presents a quick and user-friendly data analysis algorithm as an alternative to ECM by mathematically fitting geometric features in Nyquist plots and obtaining the growth trends of the features. The evolving trends in the Nyquist plots, such as chord lengths of the arcs and interception points, are consistent with the growth of resistance components obtained using ECM with R 2 values from 0.67 to 0.99, and therefore can be used as indicators of battery aging. Our results show that the quick-fitting approach is suitable for analyzing a series of EIS data acquired during battery cycling and identifying the underlying aging mechanisms.

Chen, Bor-Rong↗
DOE OSTI2016

THE SCHULHOF FAMILY: SOLVING THE AGE PUZZLE

The Schulhof family, a tight cluster of small asteroids around the central main belt body (2384) Schulhof, belongs to a so far rare class of very young families (estimated ages less than 1 Myr). Characterization of these asteroid clusters may provide important insights into the physics of the catastrophic disruption of their parent body. The case of the Schulhof family has been up to now complicated by the existence of two proposed epochs of its origin. In this paper, we first use our own photometric observations, as well as archival data, to determine the rotation rate and spin axis orientation of the largest fragment (2384) Schulhof. Our data also allow us to better constrain the absolute magnitude of this asteroid, and thus also improve the determination of its geometric albedo. Next, using the up-to-date catalog of asteroid orbits, we perform a new search of smaller members in the Schulhof family, increasing their number by 50%. Finally, the available data are used to access Schulhof's family age anew. We now find that the younger of the previously proposed two ages of this family is not correct, resulting from a large orbital uncertainty of single-opposition members. Our new runs reveal a single age solution of about 800 kyr with a realistic uncertainty of 200 kyr.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The age, mass, and size distributions of star clusters in M51

We present a new catalog of 3816 compact star clusters in the grand design spiral galaxy M51 based on observations taken with the Hubble Space Telescope. The age distribution of the clusters declines starting at very young ages, and can be represented by a power law, dN/dτ∝τ{sup γ}, with γ=−0.65±0.15. No significant changes in the shape of the age distribution at different masses is observed. The mass function of the clusters younger than τ ≈ 400 Myr can also be described by a power law, dN/dM∝M{sup β}, with β ≈ −2.1±0.2. We compare these distributions with the predictions from various cluster disruption models, and find that they are consistent with models where clusters disrupt approximately independent of their initial mass, but not with models where lower mass clusters are disrupted earlier than their higher mass counterparts. We find that the half-light radii of clusters more massive than M ≈ 3×10{sup 4} M{sub ⊙} and with ages between 100 and 400 Myr are larger by a factor of ≈3–4 than their counterparts that are younger than 10{sup 7} years old, suggesting that the clusters physically expand during their early life.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The age and distance of the Kepler open cluster NGC 6811 from an eclipsing binary, turnoff star pulsation, and giant asteroseismology

We present the analysis of an eccentric, partially eclipsing long-period (P = 19.23 days) binary system KIC 9777062 that contains main-sequence stars near the turnoff of the intermediate-age open cluster NGC 6811. The primary is a metal-lined Am star with a possible convective blueshift to its radial velocities, and one star (probably the secondary) is likely to be a γ Dor pulsator. The component masses are 1.603 ± 0.006(stat.) ± 0.016(sys.) and 1.419 ± 0.003 ± 0.008 M{sub ⊙}, and the radii are 1.744 ± 0.004 ± 0.002 and 1.544 ± 0.002 ± 0.002 R{sub ⊙}. The isochrone ages of the stars are mildly inconsistent: the age from the mass–radius combination for the primary (1.05 ± 0.05 ± 0.09 Gyr, where the last quote was systematic uncertainty from models and metallicity) is smaller than that from the secondary (1.21 ± 0.05 ± 0.15 Gyr) and is consistent with the inference from the color–magnitude diagram (1.00 ± 0.05 Gyr). We have improved the measurements of the asteroseismic parameters Δν and ν {sub max} for helium-burning stars in the cluster. The masses of the stars appear to be larger (or alternately, the radii appear to be smaller) than predicted from isochrones using the ages derived from the eclipsing stars. The majority of stars near the cluster turnoff are pulsating stars: we identify a sample of 28 δ Sct, 15 γ Dor, and 5 hybrid types. We used the period–luminosity relation for high-amplitude δ Sct stars to fit the ensemble of the strongest frequencies for the cluster members, finding (m−M){sub V}=10.37±0.03. This is larger than most previous determinations, but smaller than values derived from the eclipsing binary (10.47 ± 0.05).

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

The trends high-contrast imaging survey. VI. Discovery of a mass, age, and metallicity benchmark brown dwarf

The mass and age of substellar objects are degenerate parameters leaving the evolutionary state of brown dwarfs ambiguous without additional information. Theoretical models are normally used to help distinguish between old, massive brown dwarfs and young, low-mass brown dwarfs but these models have yet to be properly calibrated. We have carried out an infrared high-contrast imaging program with the goal of detecting substellar objects as companions to nearby stars to help break degeneracies in inferred physical properties such as mass, age, and composition. Rather than using imaging observations alone, our targets are pre-selected based on the existence of dynamical accelerations informed from years of stellar radial velocity (RV) measurements. In this paper, we present the discovery of a rare benchmark brown dwarf orbiting the nearby (d = 18.69 ± 0.19 pc), solar-type (G9V) star HD 4747 ([Fe/H] = −0.22 ± 0.04) with a projected separation of only ρ = 11.3 ± 0.2 au (θ = 0.″6). Precise Doppler measurements taken over 18 years reveal the companion’s orbit and allow us to place strong constraints on its mass using dynamics (msin i=55.3±1.9M{sub Jup}). Relative photometry (ΔK {sub s} = 9.05 ± 0.14, M{sub K{sub s}}=13.00±0.14, K{sub s}−L{sup ′}=1.34±0.46) indicates that HD 4747 B is most likely a late-type L-dwarf and, if near the L/T transition, an intriguing source for studying cloud physics, variability, and polarization. We estimate a model-dependent mass of m=72{sub −13}{sup +3} M{sub Jup} for an age of 3.3{sub −1.9}{sup +2.3} Gyr based on gyrochronology. Combining astrometric measurements with RV data, we calculate the companion dynamical mass (m=60.2±3.3M{sub Jup}) and orbit (e = 0.740 ± 0.002) directly. As a new mass, age, and metallicity benchmark, HD 4747 B will serve as a laboratory for precision astrophysics to test theoretical models that describe the emergent radiation of brown dwarfs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

NLTE Stellar Population Synthesis of Globular Clusters Using Synthetic Integrated Light Spectra. II. Expanded Photometry and Sensitivity of Near-IR Spectral Features to Cluster Age and Metallicity

We present an expanded investigation of the library of globular cluster (GC) synthetic integrated light (IL) spectra of Young and Short, focusing on the impact of non-local thermodynamic equilibrium (NLTE) modeling effects on cluster parameters derived from photometric colors and sensitivity of near-IR spectral features to cluster age and metallicity. Johnson–Cousins–Bessel UBVIJK photometric colors are produced for 910 synthetic IL spectra with two degrees of α enhancement, in both NLTE and local thermodynamic equilibrium (LTE). These color values are used to investigate the GC age–metallicity degeneracy and compare NLTE and LTE derived [M/H] values for NGC 104, NGC 5139, and NGC 6205. For a given age, derived [M/H] values are shown to increase by up to 0.05 dex when modeled in NLTE. A total of 86 spectral lines in the range λ = 12000–22000 Å, representing 14 different atomic species, were identified as sensitive to either cluster age or metallicity, 12 of which were identified as sensitive to both. Equivalent widths of the lines are measured in NLTE and LTE spectra, with NLTE effects changing the widths by up to {sub −0.15}{sup +0.25} Å depending on the atomic species.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Clarissa Family Age from the Yarkovsky Effect Chronology

The Clarissa family is a small collisional family composed of primitive C-type asteroids. It is located in a dynamically stable zone of the inner asteroid belt. In this work we determine the formation age of the Clarissa family by modeling planetary perturbations as well as thermal drift of family members due to the Yarkovsky effect. Simulations were carried out using the SWIFT-RMVS4 integrator modified to account for the Yarkovsky and Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effects. We ran multiple simulations starting with different ejection velocity fields of fragments, varying proportion of initially retrograde spins, and also tested different Yarkovsky/YORP models. Our goal was to match the observed orbital structure of the Clarissa family which is notably asymmetrical in the proper semimajor axis, a {sub p}. The best fits were obtained with the initial ejection velocities ≲20 m s{sup −1} of diameter D ≃ 2 km fragments, ∼4:1 preference for spin-up by YORP, and assuming that ≃80% of small family members initially had retrograde rotation. The age of the Clarissa family was found to be t {sub age} = 56 ± 6 Myr for the assumed asteroid density ρ = 1.5 g cm{sup −3}. Small variation of density to smaller or larger value would lead to slightly younger or older age estimates. This is the first case where the Yarkovsky effect chronology has been successfully applied to an asteroid family younger than 100 Myr.

79 ASTRONOMY AND ASTROPHYSICS↗