1997 TMS Annual Meeting: Tuesday Abstracts

MATERIALS FOR SPALLATION NEUTRON SOURCES: Session III: Corrosion

Session Chairperson: L.K. Mansur, Oak Ridge National Laboratory

2:00 pm

LIQUID METAL COMPATIBILITY OF STRUCTURAL MATERIALS WITH LIQUID LEAD-BISMUTH AND MERCURY: J.R. Weeks, Brookhaven National Laboratory, Upton, NY 11973-5000

Both liquid mercury and liquid lead-bismuth eutectic have been proposed as possible target materials for spallation neutron sources. During the 1950's and 1960's a substantial program existed at Brookhaven National Laboratory as part of the Liquid Metal Fuel Reactor program on the compatibility of bismuth, lead, and their alloys with structural materials. Subsequently, compatibility investigations of mercury with structural materials were performed in support of the development of Rankine-cycle mercury turbines for nuclear applications. The present talk will review our understanding of the corrosion/mass-transfer reactions of structural materials with these liquid-metal coolants. Topics to be discussed include the basic solubility relationships of iron, chromium, nickel, and refractory metals in these liquid metals, the results of inhibition studies, the role of oxygen on the corrosion processes, and specialized topics such as cavitation corrosion and liquid-metal embrittlement. Emphasis will be placed on utilizing the understanding gained in this earlier work in the development of heavy-liquid-metal targets for spallation neutron sources.

2:30 pm

MODELING AND OPTICAL STUDIES OF THE WATER-METAL INTERFACE IN SPALLATION NEUTRON SOURCE TARGETS: L.L. Daemen, G.J. Kanner, R.S. Lillard, D.P. Butt, T.O. Brun, W.F. Sommer, Los Alamos National Laboratory, Los Alamos, NM 87545

In spallation neutron sources neutrons are produced when a beam of high-energy particles (e.g., 1 GeV protons) collides with a (water-cooled) heavy metal target such as tungsten. The resulting spallation reactions produce a complex radiation environment (which differs from typical conditions at fission and fusion reactors) leading to the radiolysis of water molecules. Most water radiolysis products are short-lived but extremely reactive. When formed in the vicinity of the target surface they can react with metal atoms, thereby contributing to target corrosion. We will describe the results of calculations and experiments performed at Los Alamos to determine the impact on target corrosion of water radiolysis in the spallation radiation environment. Our computational methodology relies on the use of the Los Alamos radiation transport code, LAHET, to determine the radiation environment, and the AEA code, FACSIMILE, to model reaction-diffusion processes. The experiments make use of ultra-fast Raman spectroscopic techniques. Laser Raman spectroscopy enables us to identify the chemical species formed in water and at a metal surface during irradiation, as well as to observe the growth of corrosion products at the water-metal interface.

3:00 pm

IN SITU STUDIES OF AQUEOUS CORROSION OF TARGET AND STRUCTURAL MATERIALS IN WATER IRRADIATED BY AN 800 MEV PROTON BEAM: D.P. Butt, G.S. Kanner, L.L. Daemen, R.S. Lillard, Los Alamos National Laboratory, Los Alamos, NM 87545

Radiation enhanced, aqueous corrosion of solid spallation-neutron-source targets, such as tungsten, or target cladding or structural materials, such as superalloys and stainless steels, is a significant concern in accelerator-driven transmutation technologies. In this paper we describe methods for control and in situ monitoring of corrosion in accelerator cooling water loops. Using electrochemical impedance spectroscopy, we have measured the corrosion rates of aluminum 6061, copper, Inconel 718, and 304L stainless steel in the flow loop of a water target irradiated by a milliamp, 800 MeV proton beam. We also briefly describe our second generation experiments, scheduled to begin in early 1997. In these experiments we will measure the corrosion rates of tungsten, tantalum, Inconel 718, aluminum 5053, and 316L, 304L, and HT-9 stainless steel. We also discuss our laser diagnostic techniques for directly observing the production of corrosive radiolysis products as well as corrosion products near the surface of target materials.

3:30 pm BREAK

3:50 pm

STATIC CORROSION OF MARTENSITE/FERRITE AND AUSTENITIC STEELS IN MERCURY AT 300°C: Y. Dai, Paul Scherrer Institute, CH-5232 Villigen PSI, Switzerland

Mercury corrosion will be one of the critical problems for a spallation neutron source using Hg as target material. Preliminary results of static corrosion tests on 316L austenitic steel and on MANET and F82H martensitic/ferritic steels will be presented. Smooth and notched C-ring-shaped specimens were prestressed before putting them into Hg. The tests were performed at 300C and interrupted after different durations. After cooling down to room temperature, the change of morphology of specimen surfaces was examined. For 316L specimens after 160 hrs of corrosion, Hg covered all surfaces. However, for F82H and MANET, there was almost no Hg on surfaces after 500 hrs, but surfaces were covered with Hg after an additional 500 hrs. F82H had the thickest oxide layer (about 0.5 µm thick after 1000 hours), MANET was next, and 316L had the thinnest oxide layer. The mechanisms for wetting and oxidation will be discussed.

4:20 pm

SURFACE OXIDES AND THE BEHAVIOR OF ALUMINUM COMPONENTS IN THE APT TARGET/BLANKET SYSTEM: M.R. Louthan, Jr., Savannah River Technology Center, Aiken, SC 29808

The mechanical properties of the aluminum alloys in the accelerator production of tritium (APT) target/blanket system are sensitive to exposure and processing history. Several of the APT applications require exposure to flowing, hot water under heat transfer conditions. The thermal conductivity of the protective film is low and limits the temperature drop across the aluminum. This reduction in heat transfer will raise metal-oxide interface temperature and play a major role in the corrosion processes. Under heat transfer conditions, the oxide-metal interface temperature will increase both oxide thicknesses and service temperatures for aluminum. Interrelationships among service, oxide development and water chemistry are similar to those for reactor service and this paper relates anticipated performance in the APT system to reactor experience.