1997 TMS Annual Meeting: Tuesday Abstracts

MATERIALS FOR SPALLATION NEUTRON SOURCES: Session II: Radiation Effects, B

Session Chairperson: W.F. Sommer, Los Alamos National Laboratory, Los Alamos, NM 87545

8:30 am

RESISTIVITY CHANGES IN SUPERCONDUCTING-CAVITY-GRADE Nb FOLLOWING HIGH-ENERGY PROTON IRRADIATION: C.L. Snead, A. Hanson, G.A. Greene, C.J. Czajkowski, Brookhaven National Laboratory, Upton, NY 11973-5000; K.C. Chan, Los Alamos National Laboratory, Los Alamos, NM 87545; H. Safa, DSM/DAPNIA/SEA--C.E. SACLAY, 91191 Gif sur Yvette, France

Niobium superconducting rf cavities are proposed for use in the proton LINAC for spallation neutron applications. Because of accidental beam loss and continual halo losses along the acceleration path, the concern of the degradation of the superconducting properties with accumulated irradiation arises. Residual-resistivity-ratio (RRR) specimens of Nb, with a range of initial RRR's, were irradiated at room temperature at energies from 200 MeV to 2000 MeV. Four-probe resistance measurements were made at room temperature and at 4.2 K both prior and after irradiations. Proton fluences ranged from 5 x 1014 to about 5 x 1016 p/cm2. These room-temperature results simulate the resistance changes to be expected in LINAC operation for the cavities having been exposed to the radiation and then cycled through an anneal to room temperature. The defect structures produced have been characterized using both scanning and transmission microscopy. Implications of the results to proposed cavity operation and recent results on cavity irradiations will be presented.

9:00 am

POST-IRRADIATION TESTING OF TARGET COMPONENTS AFTER SERVICE IN LAMPF: F. Carsughi, H. Derz, G. Pott, W.F. Sommer, H. Ullmaier, M. Zaslawsky; Institut für Festkörperforschung, D-52425 Jülich, Germany; Heissen Zellen des Forschungszentrum Jülich, D-52425 Jülich, Germany; Los Alamos National Laboratory, Los Alamos, NM 87545

Radiation damage is considered to be the most critical load for the lifetime of components in or close to the proton beam penetrating the target of high power spallation sources. Specimens irradiated in operating medium-power spallation devices are at present the only source of direct information on the behavior of materials in a spallation environment. Within an international cooperation, the following specimens will be investigated in the hot cells at KFA Jülich: (1) A hemispherical LAMPF window made of INCONEL 718, (2) A spherical LAMPF water degrader made of INCONEL 718 and 316 SS, (3) Two curved PSI windows made of DIN 1.4926 SS and irradiated in LAMPF, and (4) A complete target from ISIS consisting of Ta plates in a 304 SS housing. After cutting and preparation of different types of miniaturized specimens the following tests will be performed: 3 point bending tests, ball punch tests, microhardness measurements, scanning (and possibly transmission) electron microscopy, and tensile tests (only for ISIS specimens where ample material is available). First results for specimens obtained from (1) and (2) will be reported.

9:30 am

SIMULATION IRRADIATIONS OF TARGET AND STRUCTURE COMPONENTS FOR SPALLATION NEUTRON SOURCES: E. Camus, N. Wanderka, H. Wollenberger, Hahn-Meitner-Institut, D-14109 Berlin, Germany

Beside damage levels up to 10 dpa per month, the spallation reaction induces high levels of transmutation products, mainly hydrogen (up to 0.5 at.% per month) and helium (up to 0.1 at.% per month). Dual-beam irradiations with heavy ions, protons, and/or helium ions with energies up to 300 keV make it possible to introduce such damage levels and high hydrogen or helium contents within hours. We present experimental results on the microstructure evolution and on mechanical properties of simulation irradiated steels and tantalum. The cavity microstructure is investigated by means of transmission electron microscopy (TEM). Field-ion microscopy with atom probe (FIM-AP) shows fine scale radiation-induced segregation. Hardness measurements on specimens implanted at low temperature with heavy ions, protons, and/or helium have been performed and reveal a drastic increase of hardness. Both the displacement rate and the hydrogen or helium implantation rate used in simulation irradiations are orders of magnitude higher than those produced in spallation environments. Data correlation, with special emphasis on the influence of the hydrogen or helium implantation rate, is discussed.

10:00 am BREAK

10:20 am

TRIPLE ION-BEAM STUDIES OF RADIATION DAMAGE EFFECTS IN A HIGH POWER SPALLATION NEUTRON SOURCE ENVIRONMENT: L.K. Mansur, K. Farrell, E.H. Lee, G.R. Rao, J.D. Hunn, P.M. Rice, M.B. Lewis, S.W. Cook, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6376

The unique Triple Ion-Beam Facility (TIF) at ORNL allows researchers to mimic significant features of the NSNS irradiation environment by producing displacement damage and injecting He and H simultaneously. In this work, therefore, austenitic EC316LN and ferritic 9Cr2WVTa alloys were irradiated using the TIF to investigate radiation damage effects. Irradiations were carried out using 4 MeV Fe++, 400 keV He+, and 200 keV H+ simultaneously to accumulate 50 dpa, 10,000 appm He, and 50,000 appm H, respectively. Irradiations were carried out at temperatures from 50 to 200°C. The specific ion energies were chosen to maximize the damage and the gas accumulation at the same depth of ~1 µm. Microstructure and surface hardness of irradiated specimens were evaluated by TEM and the Nanoindenter, respectively. This report summarizes damage microstructure as a function of irradiation depth from cross-sectioned TEM specimens and hardness variation of the bombarded surfaces.

10:50 am

IRRADIATION DAMAGE OF FERRITIC/MARTENSITIC STEELS: FUSION PROGRAM DATA APPLIED TO THE SPALLATION NEUTRON SOURCE APPLICATION: R.L. Klueh, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6376

Ferritic/martensitic steels in the target structure of a spallation neutron source will experience many of the extreme conditions expected in a fusion power plant (i.e., high-energy neutrons that produce large amounts of displacement damage and transmutation helium). Thus, studies of the steels for fusion are relevant for the spallation neutron source application. The ferritic/martensitic steels are candidates for fusion because of superior swelling resistance, better liquid-metal compatibility, higher thermal conductivity, and lower thermal expansion than austenitic steels. The major problem with ferritic/martensitic steels involves the effect of irradiation on fracture, as determined by a Charpy impact test. Fast reactor irradiation produces an increase in the ductile-brittle transition temperature and decrease in the upper-shelf energy. The effect saturates with fluence for fast-reactor irradiation, but the saturation values observed for irradiation in a fast reactor do not apply for irradiation in a mixed-spectrum reactor under conditions where transmutation helium is generated simultaneously with displacement damage. This helium effect is one of the critical issues that needs to be understood, since high helium concentrations will be generated in conjunction with the displacement damage in a fusion reactorand in the target of a spallation neutron source, should a ferritic/martensitic steel be chosen for that application.

11:20 am

ACTIVATION OF MATERIALS PROPOSED FOR USE IN SUPERCONDUCTING LINAC APPLICATIONS: A. Hanson, C.L. Snead, G.A. Greene, C.J. Czajkowski, K.C. Chan, H. Safa; Brookhaven National Laboratory, Upton, NY 11973-5000; Los Alamos National Laboratory, Los Alamos, NM 87545; DSM/DAPNIA/SEA, C.E. SACLAY, 91191 Gif sur Yvette, France

Linacs are proposed for spallation neutron sources which are capable of relatively high beam currents. Associated with the transport of these high currents will be relatively high beam losses to the linac structures from the beam halo and occasional mis-steering. A series of irradiations have been conducted at the Saturne, France, accelerator in which specimens of steel, copper, NbTi, aluminum, and niobium were exposed to protons with energies from 400 to 2000 MeV. Gamma activation measurements were made for various times subsequent to the end of the beam. Absolute and relative activity levels have been achieved on which estimates of the exposure levels to maintenance personnel can be made. Particular attention was given to Nb because of its prominence in scenarios that call for superconducting rf-cavity linacs. For Nb the activation products for the various irradiations were determined and compared with code predictions.