Integrated Radiation Transport and Nuclear Fuel Performance for Assembly-Level Simulations

The Advanced Multi-Physics (AMP) Nuclear Fuel Performance code (AMPFuel) is focused on predicting the temperature and strain within a nuclear fuel assembly to evaluate the performance and safety of existing and advanced nuclear fuel bundles within existing and advanced nuclear reactors. AMPFuel was extended to include an integrated nuclear fuel assembly capability for (one-way) coupled radiation transport and nuclear fuel assembly thermo-mechanics. This capability is the initial step toward incorporating an improved predictive nuclear fuel assembly modeling capability to accurately account for source-terms and boundary conditions of traditional (single-pin) nuclear fuel performance simulation, such as the neutron flux distribution, coolant conditions, and assembly mechanical stresses. A novel scheme is introduced for transferring the power distribution from the Scale/Denovo (Denovo) radiation transport code (structured, Cartesian mesh with smeared materials within each cell) to AMPFuel (unstructured, hexagonal mesh with a single material within each cell), allowing the use of a relatively coarse spatial mesh (10 million elements) for the radiation transport and a fine spatial mesh (3.3 billion elements) for thermo-mechanics with very little loss of accuracy. In addition, a new nuclear fuel-specific preconditioner was developed to account for the high aspect ratio of each fuel pin (12 feet axially, but 1 4 inches in diameter) with many individual fuel regions (pellets). With this novel capability, AMPFuel was used to model an entire 17 17 pressurized water reactor fuel assembly with many of the features resolved in three dimensions (for thermo-mechanics and/or neutronics), including the fuel, gap, and cladding of each of the 264 fuel pins; the 25 guide tubes; the top and bottom structural regions; and the upper and lower (neutron) reflector regions. The final, full assembly calculation was executed on Jaguar using 40,000 cores in under 10 hours to model over 162 billion degrees of freedom for 10 loading steps. The single radiation transport calculation required about 50% of the time required to solve the thermo-mechanics with a single loading step, which demonstrates that it is feasible to incorporate, in a single code, a high-fidelity radiation transport capability with a high-fidelity nuclear fuel thermo-mechanics capability and anticipate acceptable computational requirements. The results of the full assembly simulation clearly show the axial, radial, and azimuthal variation of the neutron flux, power, temperature, and deformation of the assembly, highlighting behavior that is neglected in traditional axisymmetric fuel performance codes that do not account for assembly features, such as guide tubes and control rods

Highly ionized Ar plasma waveguides generated by a fast capillary discharge

Includes bibliographical references.Highly ionized Ar plasma channels were created by a fast capillary discharge and used to guide laser pulses with peak intensities up to 2.2 × 1017 W/cm2 over a 5.5-cm distance. These plasmas are of interest for the generation of efficient soft X-ray lasers by longitudinal laser excitation. The guides were characterized using plasma interferometry, modeling, and near field imaging.This work was supported in part by the National Science Foundation under Grant ECS-9977677, in part by the National Science Foundation Engineering Research Center for Extreme Ultraviolet Science and Technology, in part by the W. M. Keck Foundation, and in part by the U.S. Department of Energy, Chemical Sciences, Geosciences and Biosciences Division of the Office of Basic Energy Science

High repetition rate tabletop soft x-ray lasers with saturated output at wavelengths down to 13.2 nm

Includes bibliographical references (page 26).Compact, soft x-ray laser sources capable of producing high average powers could make possible a variety of new studies in science and enable development of unique metrology and processing tools for industry

High repetition rate collisional soft X-ray lasers based on grazing incidence pumping

Includes bibliographical references (pages 11-12).We discuss the demonstration of gain-saturated high repetition rate table-top soft X-ray lasers producing microwatt average powers at wavelengths ranging from 13.9 to 33 nm. The results were obtained heating a precreated plasma with a picosecond optical laser pulse impinging at grazing incidence onto a precreated plasma. This pumping geometry increases the energy deposition efficiency of the pump beam into the gain region, making it possible to saturate soft X-ray lasers in this wavelength range with a short pulse pump energy of only 1 J at 800-nm wavelength. Results corresponding to 5-Hz repetition rate operation of gain-saturated 14.7-nm Ni-like Pd and 32.6-nm line Ne-like Ti lasers pumped by a table-top Ti:sapphire laser are reported. We also discuss results obtained using a 1 ⍵1054-nm prepulse and 2 ⍵527-nm short pulse from a Nd:glass pump laser. This work demonstrates the feasibility of producing compact high average power soft X-ray lasers for applications

Integrated Radiation Transport and Nuclear Fuel Performance for Assembly-Level Simulations

The Advanced Multi-Physics (AMP) Nuclear Fuel Performance code (AMPFuel) is focused on predicting the temperature and strain within a nuclear fuel assembly to evaluate the performance and safety of existing and advanced nuclear fuel bundles within existing and advanced nuclear reactors. AMPFuel was extended to include an integrated nuclear fuel assembly capability for (one-way) coupled radiation transport and nuclear fuel assembly thermo-mechanics. This capability is the initial step toward incorporating an improved predictive nuclear fuel assembly modeling capability to accurately account for source-terms and boundary conditions of traditional (single-pin) nuclear fuel performance simulation, such as the neutron flux distribution, coolant conditions, and assembly mechanical stresses. A novel scheme is introduced for transferring the power distribution from the Scale/Denovo (Denovo) radiation transport code (structured, Cartesian mesh with smeared materials within each cell) to AMPFuel (unstructured, hexagonal mesh with a single material within each cell), allowing the use of a relatively coarse spatial mesh (10 million elements) for the radiation transport and a fine spatial mesh (3.3 billion elements) for thermo-mechanics with very little loss of accuracy. In addition, a new nuclear fuel-specific preconditioner was developed to account for the high aspect ratio of each fuel pin (12 feet axially, but 1 4 inches in diameter) with many individual fuel regions (pellets). With this novel capability, AMPFuel was used to model an entire 17 17 pressurized water reactor fuel assembly with many of the features resolved in three dimensions (for thermo-mechanics and/or neutronics), including the fuel, gap, and cladding of each of the 264 fuel pins; the 25 guide tubes; the top and bottom structural regions; and the upper and lower (neutron) reflector regions. The final, full assembly calculation was executed on Jaguar using 40,000 cores in under 10 hours to model over 162 billion degrees of freedom for 10 loading steps. The single radiation transport calculation required about 50% of the time required to solve the thermo-mechanics with a single loading step, which demonstrates that it is feasible to incorporate, in a single code, a high-fidelity radiation transport capability with a high-fidelity nuclear fuel thermo-mechanics capability and anticipate acceptable computational requirements. The results of the full assembly simulation clearly show the axial, radial, and azimuthal variation of the neutron flux, power, temperature, and deformation of the assembly, highlighting behavior that is neglected in traditional axisymmetric fuel performance codes that do not account for assembly features, such as guide tubes and control rods

Dense capillary discharge plasma waveguide containing Ag ions

Includes bibliographical references.Interferometry of plasmas generated by fast discharge excitation of Ag2S microcapillary channels shows the formation of dense plasma waveguides capable of guiding intense laser beams. Discharge ablation of capillaries, 330 μm or 440 μm in diameter, with 3-5.5-kA current pulses formed concave plasma density profiles with axial electron density >1 × 1019 cm-3. These dense plasma waveguides containing highly ionized metal atoms are of interest to the development of a longitudinally pumped soft X-ray lasers.This work was supported in part by the U.S. Department of Energy Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, in part by the National Science Foundation under Grant ECS-9977677, in part by the National Science Foundation Engineering Research Center for Extreme Ultraviolet Science and Technology, and in part by the W. M. Keck Foundation

Characteristics of a saturated 18.9-nm tabletop laser operating at 5-Hz repetition rate

Includes bibliographical references.We report the characteristics of a saturated high-repetition rate Ni-like Mo laser at 18.9 nm. This table-top soft X-ray laser was pumped at a 5-Hz repetition rate by 8-ps 1-J optical laser pulses impinging at grazing incidence into a precreated Mo plasma. The variation of the laser output intensity as a function of the grazing incidence angle of the main pump beam is reported. The maximum laser output intensity was observed for an angle of 20°, at which we measured a small signal gain of 65 cm-1 and a gain-length product g × l > 15. Spatial coherence measurements resulting from a Young's double-slit interference experiment show the equivalent incoherent source diameter is about 11 μm. The peak spectral brightness is estimated to be of the order of 1 × 1024 photons s-1 mm-2 mrad-2 within 0.01% spectral bandwidth. This type of practical, small scale, high-repetition soft X-ray laser is of interest for many applications.This work was supported in part by the National Science Foundation Center for Extreme Ultraviolet Science and Technology under NSF Award EEC-0310717, with equipment developed under NSF Grant ECS-9977677, and by the W. M. Keck Foundation. Part of work was also performed under the auspices of the U.S. Dept. of Energy by the University of California Lawrence Livermore National Laboratory under Contract W-7405-Eng-48