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At least 307 records · Page 17

PORFLOW Implementation of Vadose Zone Conceptual Model for Naval Reactor Component Disposal Areas in the E-Area Low Level Waste Facility Performance Assessment

PORFLOW models have been developed to implement the proposed conceptual models for the two Naval Reactor Component Disposal Areas (NRCDAs), 643-7E and 643-26E, for the purpose of evaluating dose impacts and producing disposal limits for the E-Area Low-Level Facility (LLWF). New NRCDA conceptual models were proposed by Wohlwend and Butcher (2019) for two areas within/adjacent to the E-Area LLWF used as storage/disposal sites for reactor components from the U.S. Navy since 1987. Naval Reactor (NR) waste is comprised of highly radioactive components consisting of activated corrosion-resistant metal alloy contained within welded thick-walled steel casks, and auxiliary equipment primarily contaminated with lower levels of Activated Corrosion Products (ACPs) residing on the metal surfaces and contained within thinner-walled bolted containers.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

PORFLOW Implementation of Vadose Zone Conceptual Model for Naval Reactor Component Disposal Area in the E-Area Low Level Waste Facility Performance Assessment

PORFLOW models have been developed to implement the proposed conceptual models for the two Naval Reactor Component Disposal Areas (NRCDAs), 643-7E and 643-26E, for the purpose of evaluating dose impacts and producing disposal limits for the E-Area Low-Level Facility (LLWF). New NRCDA conceptual models were proposed by Wohlwend and Butcher (2019) for two areas within/adjacent to the E-Area LLWF used as storage/disposal sites for reactor components from the U.S. Navy since 1987. Naval Reactor (NR) waste is comprised of highly radioactive components consisting of activated corrosion-resistant metal alloy contained within welded thick-walled steel casks, and auxiliary equipment primarily contaminated with lower levels of Activated Corrosion Products (ACPs) residing on the metal surfaces and contained within thinner-walled bolted containers.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

A Mouse Model for Microbeam Radiation Therapy of the Lung

Radiation therapy is an important treatment component for patients with lung cancer. However, the survival time gained with clinical radiation therapy techniques is relatively short. Data from preclinical experiments suggest that synchrotron microbeam radiation therapy could be much better suited to control malignant brain tumors than current clinical concepts of radiation therapy. Even at peak doses of several hundred gray, the extent of functional deficits is low.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Reevaluation of Radiation-Protection Standards for Workers and the Public Based on Current Scientific Evidence

President Trump’s recent executive orders to “Usher in a Nuclear Renaissance,” coupled with the global pledge to triple nuclear energy capacity by 2050, underscore nuclear energy’s importance to national security and economic prosperity. This renewed interest has prompted efforts to spur nuclear-energy deployment, including assessing factors impeding it. One issue that has previously been identified as adding to the cost of nuclear energy is excessively conservative requirements, including those related to radiation protection. This technical review, therefore, examines current radiation-protection standards that were established decades ago when more limited data were available and nuclear-energy expansion was not a national priority. The review focuses on scientific evidence regarding the health effects of ionizing radiation at annual doses of 10,000 mrem or less. The review evaluates epidemiological studies, radiobiological research, and positions of relevant professional organizations to assess whether such doses result in discernable or observable increases in negative health outcomes. The review also surveys the literature related to economic and practical implications of current radiation-protection standards and practices. Based on this assessment, we propose maintaining an annual occupational whole-body dose limit of 5,000 mrem/yr and eliminating all “as low as reasonably achievable” requirements and limits below this threshold. This change could potentially reduce radiation-protection costs by millions of dollars annually for each reactor, as well as decrease the overall costs and correct misconceptions about the risks associated with all nuclear technologies. The evidence further supports future consideration of a 10,000 mrem/yr limit that would maintain appropriate safety margins while further reducing protection costs. Similarly, given the data and that the average annual radiation dose per person in the U.S. is 620 mrem, we believe the public dose limits of 100 mrem/yr are unnecessarily restrictive; increasing to 500 mrem/yr would maintain substantial safety margins—a factor of 10 below the occupational limit—while reducing regulatory burdens and associated bureaucracy. While we acknowledge ongoing scientific debate and encourage continued research on the health effects of ionizing radiation, our review indicates current frameworks are overly conservative. These overly stringent limits not only impose unnecessary economic burdens without corresponding health benefits but also divert safety focus and resources from more important considerations. Although this study was motivated by nuclear-power considerations, reforms to radiation-protection requirements have significant positive implications for other areas, such as nuclear medical applications, environmental remediation, nuclear-waste management and disposal, and industrial applications of nuclear technologies.

61 RADIATION PROTECTION AND DOSIMETRY↗

Sensitivity and Detection Limit of Spectroscopic-Grade Perovskite CsPbBr 3 Crystal for Hard X-Ray Detection

We report spectroscopic-grade single crystal detectors can register the energies of individual X-ray interactions enabling photon-counting systems with superior resolution over traditional photoconductive X-ray detection systems. Current technical challenges have limited the preparation of perovskite semiconductors for energy-discrimination X-ray photon-counting detection. Here, this work reports the deployment of a spectroscopic-grade CsPbBr 3 Schottky detector under reverse bias for continuum hard X-ray detection in both the photocurrent and spectroscopic schemes. High surface barriers of approximate to ≈ 1 eV are formed by depositing solid bismuth and gold contacts. The spectroscopic response under a hard X-ray source is assessed in resolving the characteristic X-ray peak. The methodology in enhancing X-ray sensitivity by controlling the X-ray energies and flux, and voltage, is described. The X-ray sensitivity varies between a few tens to over 8000 μC Gy air -1 cm -2 . The detectable dose rate of the CsPbBr 3 detectors is as low as 0.02 nGy air s -1 in the energy discrimination configuration. Finally, the unbiased CsPbBr 3 device forms a spontaneous contact potential difference of about 0.7 V enabling high quality of the CsPbBr 3 single crystals to operate in "passive" self-powered X-ray detection mode and the X-ray sensitivity is estimated as 14 μC Gy air -1 cm -2 . The great potential of spectroscopic-grade CsPbBr 3 devices for X-ray photon-counting systems is anticipated in this work.

36 MATERIALS SCIENCE↗

Ultra-Fast High-Precision Metallic Nanoparticle Synthesis using Laser-Accelerated Protons

Laser-driven proton acceleration, as produced during the interaction of a high-intensity (I > 1 × 10 18 W/cm 2 ), short pulse (<1 ps) laser with a solid target, is a prosperous field of endeavor for manifold applications in different domains, including astrophysics, biomedicine and materials science. These emerging applications benefit from the unique features of the laser-accelerated particles such as short duration, intense flux and energy versatility, which allow obtaining unprecedented temperature and pressure conditions. In this paper, we show that laser-driven protons are perfectly suited for producing, in a single sub-ns laser pulse, metallic nanocrystals with tunable diameter ranging from tens to hundreds of nm and very high precision. Our method relies on the intense and very quick proton energy deposition, which induces in a bulk material an explosive boiling and produces nanocrystals that aggregate in a plasma plume composed by atoms detached from the proton-irradiated surface. The properties of the obtained particles depend on the deposited proton energy and on the duration of the thermodynamical process. Suitably controlling the irradiated dose allows fabricating nanocrystals of a specific size with low polydispersity that can easily be isolated in order to obtain a monodisperse nanocrystal solution. Molecular Dynamics simulations confirm our experimental results.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

Front shielding of the 25-kW beam absorber in Linac-to-Booster transfer line

The 25-kW beam absorber in the Linac-to-Booster transfer line is supposed to take in the beam from PIP-II 800-MeV Linac occasionally, on the average for one hour once a week. Such an operational scenario suggests that residual dose of the absorber front part can be relatively low. In order to simplify access to the front part of the absorber and beam window in case of repair or maintenance, using a slide-in shielding plug is considered as a preferred option.

43 PARTICLE ACCELERATORS↗

Quantitative Risk Assessment for Hydrogen-Powered Locomotive Refueling

Hydrogen powered locomotives are being explored to reduce emissions in rail applications. The risks of operations like refueling should be understood to ensure safe environments for workers and members of the public. Sensitivity analyses were conducted using HyRAM+ to identify major drivers of risk and compare effects of system parameters on individual risk. The consequences of jet fires from full-bore leaks dominated the risk, compared to explosions or smaller leaks. Pipe size, leak detection capability, and leak frequencies of system components greatly affected risk while overpressure modeling parameters and ambient conditions had little effect. The effects of personal protective equipment (PPE) materials on individual risk were quantified by reducing the individual’s exposure time or absorbed thermal dose. PPE only showed a risk reduction in low-risk cases. This study highlighted target areas for risk mitigation, including leak detection equipment and component maintenance, and indicated that the minimal effects of other parameters on risk may not justify prescriptive requirements for refueling operators.

08 HYDROGEN↗

SAXS studies of X-ray induced disulfide bond damage: Engineering high-resolution insight from a low-resolution technique

A significant problem in biological X-ray crystallography is the radiation chemistry caused by the incident X-ray beam. This produces both global and site-specific damage. Site specific damage can misdirect the biological interpretation of the structural models produced. Cryo-cooling crystals has been successful in mitigating damage but not eliminating it altogether; however, cryo-cooling can be difficult in some cases and has also been shown to limit functionally relevant protein conformations. The doses used for X-ray crystallography are typically in the kilo-gray to mega-gray range. While disulfide bonds are among the most significantly affected species in proteins in the crystalline state at both cryogenic and higher temperatures, there is limited information on their response to low X-ray doses in solution, the details of which might inform biomedical applications of X-rays. In this work we engineered a protein that dimerizes through a susceptible disulfide bond to relate the radiation damage processes seen in cryo-cooled crystals to those closer to physiologic conditions. This approach enables a low-resolution technique, small angle X-ray scattering (SAXS), to detect and monitor a residue specific process. A dose dependent fragmentation of the engineered protein was seen that can be explained by a dimer to monomer transition through disulfide bond cleavage. This supports the crystallographically derived mechanism and demonstrates that results obtained crystallographically can be usefully extrapolated to physiologic conditions. Fragmentation was influenced by pH and the conformation of the dimer, providing information on mechanism and pointing to future routes for investigation and potential mitigation. The novel engineered protein approach to generate a large-scale change through a site-specific interaction represents a promising tool for advancing radiation damage studies under solution conditions.

59 BASIC BIOLOGICAL SCIENCES↗

The Study of TRR Radial Thermal Shielding Dismantling Process - 20063

The decommissioning of nuclear facilities has become an important worldwide topic because many nuclear power facilities will permanently cease operation in the foreseeable future. Taiwan Research Reactor (TRR) has stepped into the decommissioning phase in 2004, and the dismantling processes will start in 2022. TRR is a heavy water reactor designed by Canatom Company with output thermal power 40 MW. On January 3, 1973, it reaches criticality. TRR had been operated for 15 years and was permanently shut down in early 1988. The decommissioning plan of TRR was approved in 2004. According to the Nuclear Reactor Facilities Regulation Act in Taiwan, a nuclear facility must be dismantled in 25 years after stepping into the decommissioning phase. Therefore, TRR decommissioning must be completed before 2029. One of the most important tasks of TRR decommissioning is to dismantle reactor body. In the task of TRR decommissioning, mechanical cutting with remote handling is used to dismantle radial thermal shielding, which are the internal components of the TRR. This study outlines the internal components of the TRR and explains the difficulties encountered during the dismantling processes. Considering the structure and radiation dose rate of TRR and its internal components, the dismantling method and packaging method are properly arranged to complete the TRR dismantling task. This study describes the process of dismantling the radial thermal shielding during the dismantling processes and considers the impact of the radiation dose on the staff during the operation. The calculation of the radiation dose rate for the personnel during the segmentation process is based on the evaluation result by using VRdose. If the calculation of personnel working dose rate is too high, we will increase the shielding or use remote handling to reduce the operator's exposure dose in the dismantling processes to comply with the As Low As Reasonably Achievable (ALARA) principle. In this study, the latest developments in the TRR decommissioning program are described. It also provides usable experience and information regarding the future decommissioning of other nuclear facilities or nuclear power plants in Taiwan. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

The influence of nitrogen and nitrides on the structure and properties of proton irradiated ferritic/martensitic steel

The 12Cr1MoWV (wt%) ferritic/martensitic steel HT9 is a candidate material for fuel cladding in advanced nuclear reactors, such as the Versatile Test Reactor currently under development. As such, understanding the relationship between microstructure and mechanical properties in the context of irradiation environments for these steels is critical. N content, and more specifically interstitial N, has been hypothesized to be detrimental to irradiated properties at lower temperatures (less than 0.3T m ) to a total of 6 dpa; however, in this work at a dose of 1 dpa the irradiated microstructure was improved with added N, leading to less irradiation hardening. Three variants of HT9 were irradiated with 1.5 MeV protons to a dose of 1 dpa at 300°C. The HT9 variants included Low (10 ppm), Mid (190 ppm), and High (440 ppm) N alloys that were otherwise nearly identical. Changing the N content had a variety of effects on the irradiated defect structures. As N content increased, the average dislocation loop diameter decreased, while the number density of loops increased. Additionally, extensive Ni clustering was observed on dislocations and interfaces. The Mid and High N specimens exhibited significantly less hardening (ΔHV≃100) relative to the Low N specimen (ΔHV≃160). The decrease in hardening is attributed to vanadium carbonitride acting as a sink for Ni clusters that would otherwise form on dislocations. Under the irradiation conditions used, these results suggest increasing the N content in HT9 may have a desirable effect on the irradiated structure and properties at the dose studied, as well as the swelling resistance at higher doses. In other words, N content appears to be a powerful tool for tailoring the self-interstitial atom cluster mobility in F/M steels for different temperature and dose applications.

36 MATERIALS SCIENCE↗

Intermediate scattering potential strength in electron-irradiated YBa 2 Cu 3 O 7-δ from London penetration depth measurements

Temperature-dependent London penetration depth, λ(T), of a high quality optimally-doped YBa 2 Cu 3 O 7-δ single crystal was measured using tunnel-diode-resonator technique. Controlled artificial disorder was induced by low-temperature 20 K irradiation by 2.5 MeV electrons at two large doses of 3.8 x 10 19 and 5.3 x 10 19 electrons per cm 2 . The irradiation caused significant suppression of the superconductor's critical temperature, T c , from 94.6 K to 90.0 K, and to 78.7 K, respectively. The low-temperature behavior of λ(T) evolves from a T-linear in pristine state to a T 2 behavior after irradiation, expected for a line-nodal d-wave superconductor. However, the original theory that explained such behavior assumed a unitary limit of the scattering potential, whereas usually in normal metals and semiconductors, Born scattering is sufficient to describe the experiment. To estimate the scattering potential strength, we calculated the superfluid density, ρ s (t = T/T c ) = λ 2 (0)/λ 2 (T), varying the amount and strength of non-magnetic scattering using a self-consistent t-matrix theory. Fitting the obtained curves to a power law, ρ s = 1 - Rt n , and to a polynomial, ρ s = 1 - At - Bt 2 , and comparing the coefficients n in one set and A and B in another with the experimental values, we estimate the phase shift to be around 70 and 65°, respectively. We correlate this result with the evolution of the density of states with nonmagnetic disorder.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

All-MOCVD-grown gallium nitride diodes with ultra-low resistance tunnel junctions

In this work, we carefully investigate three important effects including postgrowth activation annealing, delta (δ) dose and magnesium (Mg) buildup delay as well as experimentally demonstrate their influence on the electrical properties of GaN homojunction p–n diodes with a tunnel junction (TJ). The diodes were monolithically grown by metalorganic chemical vapor deposition (MOCVD) in a single growth step. By optimizing the annealing parameters for Mg activation, δ-dose for both donors and acceptors at TJ interfaces, and p + -GaN layer thickness, a significant improvement in tunneling properties is achieved. For the TJs embedded within the continuously-grown, all-MOCVD GaN diode structures, ultra-low voltage penalties of 158 mV and 490 mV are obtained at current densities of 20 A cm –2 and 100 A cm –2 , respectively. The diodes with the engineered TJs show a record-low differential resistivity of 1.6 × 10 –4 Ω cm 2 at 5 kA cm –2 .

42 ENGINEERING↗

Hanford Site Composite Analysis: Dose Sensitivity Analyses

This environmental calculation file (ECF) documents the methodologies, assumptions, and results of five analyses that evaluate parameter changes to the revised Hanford Site Composite Analysis (CA) (DOE-RL-2019-52, Composite Analysis for Low-Level Waste Disposal in the Hanford Site Central Plateau). Specifically, this ECF describes the impact on total dose and analyte-specific doses for five sensitivity cases where changes to the following exposure-related parameters were implemented – (1) inventory, (2) recharge rate, (3) external dose conversion factors (DCFs) based on Federal Guidance Report (FGR) No. 15 in (EPA-402-R-19-002, Federal Guidance Report No. 15, External Exposure to Radionuclides in Air, Water, and Soil) instead of FGR No. 12 (EPA 402-R-93-081, Federal Guidance Report No. 12, External Exposure to Radionuclides in Air, Water, and Soil) for groundwater pathway scenario; (4) use of mean instead of 95th percentile intake assumptions for groundwater pathway scenario; and (5) consideration of limited sources based on U.S. Department of Energy (DOE) owned waste sites regulated under DOE O 435.1, Radioactive Waste Management. It should be noted that dose assessments for both base and sensitivity cases are based on the all-pathways representative person groundwater exposure scenario presented in DOE/RL-2022-52, Composite Analysis for Low-Level Waste Disposal in the Hanford Site Central Plateau.

54 ENVIRONMENTAL SCIENCES↗

Additively manufactured refractory high-entropy alloys with superior radiation resistance

Refractory high-entropy alloys (RHEAs) are promising candidates for next-generation nuclear and high-temperature applications. Among many approaches to manufacture RHEAs, additive manufacturing (AM) represents the most recent and advanced metal manufacturing method which allows near-net-shape manufacturing to reduce material waste and post-processing time. However, performance of AM RHEAs under complex irradiation conditions remains largely unexplored. Here, in this study, we demonstrate for the first time the response of directed energy deposition (DED) AM quaternary RHEAs (HfTaVW, CrTaVW) subjected to sequential dual-beam ion irradiation, consisting of helium pre-implantation followed by high-dose heavy ion bombardment. Compositions of DED AM RHEAs were selected using Monte Carlo (MC) simulations based on a cluster expansion (CE) Hamiltonian parameterized by density functional theory (DFT). Post-irradiation microstructural characterization revealed that the AM RHEA maintained remarkable stability, with suppressed helium bubble growth and reduced defect accumulation compared to conventional alloys. Even at high doses (∼100 dpa), the alloy exhibited no void swelling, a low density of dislocation loops, and no evidence of severe degradation. These results highlight the intrinsic ability of AM-derived microstructures and multicomponent chemistry to synergistically mitigate irradiation effects. Our findings establish AM RHEAs as a class of materials with superior resistance to radiation damage under conditions relevant to advanced fusion and fission environments and demonstrate the importance of sequential ion beam studies in evaluating their long-term performance.

36 MATERIALS SCIENCE↗

First-Principles Dissociation Pathways of BCl 3 on the Si(100)-2 × 1 Surface

BCl 3 is a promising acceptor precursor for atomic-precision δ-doping of silicon, as it has been observed to rapidly dissociate into boron doped into the silicon surface and surface chlorine, which can be removed upon annealing. The chemical pathway and the resulting kinetics, through which BCl 3 adsorbs and dissociates on silicon, however, have only been partially explained. Here, in this work, we use density functional theory to expand the dissociation reactions of BCl 3 to include reactions that take place across multiple silicon dimer rows and reactions which end in a bare B atom either at the surface, substituted for a surface silicon, or in a subsurface position. We further simulate the resulting scanning tunneling microscopy images for each of these BCl x dissociation fragments, demonstrating that they often display distinct features that may allow for relatively confident experimental identification. Finally, we input the full dissociation pathway for BCl 3 into a kinetic Monte Carlo model, which simulates realistic reaction pathways as a function of environmental conditions, such as the pressure and temperature of dosing. We find that BCl 2 is broadly dominant at low temperatures, while high temperatures and ample space on the silicon surface for dissociation encourage the formation of bridging BCl fragments and B substitutions on the surface. This work provides the chemical mechanisms for understanding atomic-precision doping of Si with B, enabling a number of relevant quantum applications, such as bipolar nanoelectronics, acceptor-based qubits, and superconducting Si.

Campbell, Quinn T. [Sandia National Laboratories (↗

Hydroxyl radical mediated damage of proteins in low oxygen solution investigated using X-ray footprinting mass spectrometry

In the method of X-ray footprinting mass spectrometry (XFMS), proteins at micromolar concentration in solution are irradiated with a broadband X-ray source, and the resulting hydroxyl radical modifications are characterized using liquid chromatography mass spectrometry to determine sites of solvent accessibility. These data are used to infer structural changes in proteins upon interaction with other proteins, folding, or ligand binding. XFMS is typically performed under aerobic conditions; dissolved molecular oxygen in solution is necessary in many, if not all, the hydroxyl radical modifications that are generally reported. In this study we investigated the result of X-ray induced modifications to three different proteins under aerobic versus low oxygen conditions, and correlated the extent of damage with dose calculations. We observed a concentration-dependent protecting effect at higher protein concentration for a given X-ray dose. For the typical doses used in XFMS experiments there was minimal X-ray induced aggregation and fragmentation, but for higher doses we observed formation of covalent higher molecular weight oligomers, as well as fragmentation, which was affected by the amount of dissolved oxygen in solution. The higher molecular weight products in the form of dimers, trimers, and tetramers were present in all sample preparations, and, upon X-ray irradiation, these oligomers became non-reducible as seen in SDS-PAGE. The results provide an important contribution to the large body of X-ray radiation damage literature in structural biology research, and will specifically help inform the future planning of XFMS, and well as X-ray crystallography and small-angle X-ray scattering experiments.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Cavity Swelling in Irradiated Materials

Cavity swelling, due to three-dimensional clustering of vacancies, is an undesirable isotropic volume expansion of materials under irradiation. This phenomenon occurs above stage-III recovery temperature where vacancies are mobile, between ~0.3–0.6 Tm where Tm is the absolute melting temperature. The primary mechanism for cavity swelling is “dislocation bias”, i.e., preferential absorption of interstitials by network dislocations, causing a vacancy supersaturation. Cavity swelling is highly temperature dependent and typically follows a bell-shaped curve with peak swelling occurring at an intermediate temperature. With increasing temperature, cavity size increases, and number density decreases logarithmically. With increasing dose, cavity swelling increases, but follows a hockey-stick type pattern, characterized by a low-swelling transient incubation period and then a steady-state regime. The incubation period, dominant in cavity nucleation, is dependent upon material’s chemistry and irradiation conditions such as dose rate/temperature. Cavity swelling increases linearly with dose in the steady-state regime, that is independent of chemistry and dose rate. This regime is dominated by cavity growth. Transmutation gases like He enhance cavity nucleation such that an early onset of cavity formation occurs. However, swelling magnitudes can be either increased or suppressed when He is present. Results in austenitic steels and Cu indicate that cavity swelling peaks at intermediate He/dpa ratios of ~10 appm He/dpa. The most effective method to mitigate cavity swelling is by increasing the fixed point-defect sink density, by promoting precipitation or dispersion strengthening.

Bhattacharya, Arunodaya↗