1997 TMS Annual Meeting: Monday Abstracts

MATERIALS FOR SPALLATION NEUTRON SOURCES: Session I: Radiation Effects, A

Session Chairperson: M.S. Wechsler, North Carolina State University, 106 Hunter Hill Place, Chapel Hill, NC 27514-9128

CALCULATIONS OF RADIATION EFFECTS ON 316 STAINLESS STEEL CONTAINER MATERIALS FOR THE NSNS: M.S. Wechsler1, M.H. Barnett1, L.K. Mansur2, J.M. Barnes2, L.A. Charlton2, J.O. Johnson2; 1North Carolina State University, Dept. of Nuclear Engineering, Raleigh, NC 27695-7909; 2Oak Ridge National Laboratory, Computational Physics and Engineering Division Oak Ridge, TN 37831-6376

A current pre-conceptual design for the National Spallation Neutron Source (NSNS) considers the target to be flowing liquid mercury contained within a double-walled 316 stainless steel vessel. Calculations are underway to determine the neutron flux and to estimate the rates at which displacements, helium, and hydrogen are produced. The primary computational tools are MCNP, SPECTER, HETC, and LAHET. The displacement and helium production rates range up to about 10-7 DPA/s and 10-6 appm He/s due to the spectrum of neutrons produced by a 1700 MeV proton beam. The variation of calculated damage rates throughout the target region of NSNS is described and discussed.

2:30 pm

HELIUM PRODUCTION RATES ARISING FROM SPALLATION NEUTRONS IN THE LANSCE RADIATION EFFECTS FACILITY: F.A. Garner1, W. F. Sommer2, P. D. Ferguson2, M. S. Wechsler3, M.H. Barnett3, B.M. Oliver4; 1Pacific Northwest Laboratory, Richland, WA 99352; 2Los Alamos National Laboratory, MS H805, Los Alamos, NM 87545; 3North Carolina State University, Raleigh, NC 27695-7909; 4Rockwell International Corporation, Canoga Park, CA 91303-2790

Foils of pure Cu, Co, Fe and Ni were irradiated in the second inboard tube of the rabbit system adjacent to the beam stop of the LANSCE facility. After irradiation, the foils were cut in half to determine neutron fluence and spectra via measurement of gamma activation, and to measure helium generation via isotopic dilution mass spectroscopy. The measured helium concentrations were 0.110, 0.152, 0.122 and 0.097 appm for Fe, Ni, Cu, and Co, respectively. The dpa level calculated for copper was 0.011 dpa, yielding a value of 11.1 appm/dpa. Comparisons with improved calculations of neutron flux/spectra and helium and displacement production rates are in progress to characterize the neutron environment of the rabbit system and to assess its radiation damage effects.

3:00 pm

THE EFFECT OF THE NEW NUCLEON-NUCLEUS ELASTIC SCATTERING MODEL IN LAHET VERSION 2.8 ON DAMAGE CROSS SECTION CALCULATIONS: E.J. Pitcher1, P.D. Ferguson1, G.J. Russell1, J.D. Court1, L.L. Daemen1, M.S. Wechsler2, R.E. Prael1, D.G. Madland1; 1Los Alamos National Laboratory, Los Alamos, NM 87545; 2North Carolina State University, Raleigh, NC 27695-7909

The latest release of the medium-energy Monte Carlo transport code LAHET includes a new nucleon-nucleus elastic scattering treatment based on an interim global medium-energy phenomenological optical-model potential. Implementation of the model in LAHET allows nuclear elastic scattering for neutrons with energies greater than 15 MeV and for protons with energies greater than 50 MeV. Previous investigations on the impact of the new elastic scattering model revealed that the addition of the proton elastic scattering channel can lead to a significant increase in the calculated damage energy. We report here results of further investigations on the impact of the new elastic scattering model on calculated damage cross sections and recoil spectra for materials and particle energies prototypic of spallation target environments. With the new elastic scattering treatment, the damage cross section for 20-MeV neutrons on light nuclei (A < 30) as calculated by LAHET is in much better agreement with SPECTER calculations, where significant discrepancies have previously been observed.

3:30 pm BREAK

3:50 pm

THE INFLUENCE OF SUBCASCADE FORMATION ON DISPLACEMENT DAMAGE AT HIGH PKA ENERGIES: R.E. Stoller, Oak Ridge National Laboratory, Metals and Ceramics Division, Oak Ridge, TN 37831-6376

Molecular dynamics (MD) simulations of displacement cascades have been extended to energies as high as 40 keV. These simulations are the highest energy cascades completed to date and they provide valuable insight on the formation of primary damage in irradiated materials. An MD simulation at 40 keV is equivalent to a PKA energy of 61 keV, which is the average PKA energy from a neutron with an energy of 1.8 MeV. Although peak neutron energies in a spallation neutron source will be much higher than 1.8 MeV, the degree of subcascade formation observed at MD energies above 20 keV suggests that little change in the primary damage state will be observed for higher energies. This implies that fission reactor data should provide a good simulation of the displacement damage observed in a spallation neutron source. Thus, the effect of transmutation products is likely to be the most important difference between the two irradiation environments.

4:20 pm

INVESTIGATION OF HIGH-ENERGY-PROTON EFFECTS IN ALUMINUM: C.J. Czajkowski, C.L. Snead, M. Todosow, Brookhaven National Laboratory, Upton, NY 11973-5000

Specimens of 1100 aluminum were exposed to several fluences of 23.5-GeV protons at the Brookhaven Alternating Gradient Synchrotron. Although this energy is above those currently being proposed for spallation neutron applications, the results can be viewed as indicative of trends and other microstructural evolution with fluence that take place with high-energy proton exposures such as those associated with an increasing ratio of gas generation to dpa. TEM investigation showed significantly larger bubble size and lower density of bubbles compared with lower-energy proton results. Estimates of H and He gas generation made using Monte Carlo are also used in this comparison. Additional testing showed that the tensile strength increased with fluence as expected, but the microhardness decreased, a result for which an interpretation is still under investigation.

4:50 pm

RESPONSE OF STRUCTURAL MATERIALS TO RADIATION ENVIRONMENTS: C.J. Czajkowski, Brookhaven National Laboratory, Upton, NY 11973-5000

An evaluation of proton and neutron damage to various materials has been performed. The proton studies were conducted at energies of 0.2, 0.8, and 23.5 GeV and consisted of evaluation of proton-irradiated window/target materials from accelerators. The materials evaluated for the proton irradiations included high-purity (6 9's), 1100, and 5052 aluminum, 304 stainless steel, and inconel 718. The neutron damage research centered on 6061 T-6 aluminum from a control rod follower from the BNL HFBR, which received thermal fluence up to ~4 x 1023 n/cm2. The effects of thermal-to-fast neutron flux ratios are discussed. The increases in tensile strength in the proton-irradiated materials are shown to be due to atomic displacements, resulting in radiation hardening. Production of helium in the grain boundaries of proton-irradiated 6 9's aluminum is also discussed. The major factor contributing to the mechanical-property changes in the neutron-irradiated 6061 aluminum is transmutation products formed by interactions with thermal neutrons.