Natraj C. Iyer

Corrosion of Metals and Alloys in High Radiation Fields

Abstract Degradation in the properties of structural materials in high-energy proton accelerators will occur as a result of the radiation environment during routine accelerator operations. The potential for such degradation must be included in design and service life assessments of the materials and components. Structural materials in the window, target/blanket, and reflector regions of high-energy proton accelerators will be exposed to a mixed proton–neutron flux that will change the materials exposure environment and cause displacement damage and implant spallation products in the exposed metal. The effects of implantation and displacement damage on materials behavior have been studied on a more or less continuous basis for decades, while radiation effects on corrosion and corrosion related degradation processes has received relatively little attention. The high radiation fields will accelerate corrosion, enhance hydrogen uptake and permeation, and promote corrosion fatigue through environmental changes induced by radiolysis and the deposition of spallation products. Aluminum alloys are particularly susceptible to radiation-induced acceleration of corrosion, and may experience a decreased resistance to fatigue damage. The irradiation fields and the (n, p) reactions associated with tritium production will enhance the uptake and permeation of tritium through austenitic stainless. These radiation-induced effects must be considered in any realistic assessment of material performance in the APT target/blanket region. This paper rationalizes the impact of high radiation fields on corrosion, hydrogen embrittlement, and corrosion fatigue, and relates that impact to radiation-induced changes in chemical reactivity, hydrogen fugacity, and surface chemistry.

Application of smart materials/technology at the Savannah River site

Large scale implementation of smart materials and smart technology to engineered structures in any particular location requires the demonstration of cost effective applicability to the construction, repairs/upgrades and in- service inspections required by that site. The potential for using smart materials/technology at the Savannah River Site can be demonstrated through the repair, upgrade and construction of two bridges. The design and construction philosophy for one of the bridges will incorporate smart materials and technologies while the other parallel bridge has already been constructed using standard construction practices. This demonstration of smart materials/technology at the Savannah River Site is still in the planning stage and will advance quickly as funding is acquired.

Materials considerations in accelerator targets

Future nuclear materials production and/or the burn‐up of long lived radioisotopes may be accomplished through the capture of spallation produced neutrons in accelerators. Aluminum clad‐lead and/or lead alloys has been proposed as a spallation target. Aluminum was the cladding choice because of the low neutron absorption cross section, fast radioactivity decay, high thermal conductivity, and excellent fabricability. Metallic lead and lead oxide powders were considered for the target core with the fabrication options being casting or powder metallurgy (PM). Scoping tests to evaluate gravity casting, squeeze casting, and casting and swaging processes showed that, based on fabricability and heat transfer considerations, squeeze casting was the preferred option for manufacture of targets with initial core cladding contact. Thousands of aluminum clad aluminum‐lithium alloy core targets and control rods for tritium production have been fabricated by coextrusion processes and successfully irradiated in the SRS r...

Water Chemistry Control for the Target/Blanket Region of the Accelerator Production of Tritium

High-energy particle interactions in the various components of the target/blanket region of the Accelerator Production of Tritium lead to heat generation and deposition. Heavy-water and light-water systems are used to cool the target/blanket system and associated equipment. Structural materials include Inconel alloy 718, aluminum-clad lead rods, aluminum tubes containing helium-3 and tritium gas, and stainless steel components. Proper coolant chemistry is required to maximize neutron production, minimize corrosion of components, and minimize activity buildup. Corrosion-related phenomena and development of coolant and moderator corrosion control for both power and defense fission reactors has been studied extensively over the past 50 years. Less is known, however, about cooling systems for accelerators where a variety of transient chemical species and spallation products may be formed. The following provides a discussion on the issues that need to be addressed for proper water chemistry control for the APT system.

Silver encased high temperature superconductor ribbons produced by rolling

Ribbons of silver/yttrium-barium-copper oxide/silver (Ag/YBCO/Ag), nominally 0.01 in. (0.25 mm) thick, have been fabricated by unidirectional rolling and their resulting microstructures and superconducting properties evaluated. The influence of a postfabrication sinter/oxygen replenishment anneal on their properties has been determined. Grain alignment/preferred orientation of the YBCO core was observed. Typical transport critical-current densities measured in zero field at 4.2 and 77 K were 600 and 125 A/cm/sup 2/, respectively. Preliminary experiments on the bismuth-containing high-temperature superconductors have indicated that codeformation of a silver composite billet by rolling to thin strip is easily accomplished. >

Defects at Interfaces in Co-Extruded Metals

Summary The strength of the interface between core and clad in hydrostatically co-extruded copper-clad aluminum has been measured as a function of the total extrusion ratio. It is found that the interface strength exhibits a minimum at a particular extrusion ratio. This phenomenon is investigated analytically by modeling the co-extrusion process using a finite element code, ABAQUS, to determine the stresses at the interface in the deforming region of the die and in the extruded product. These calculations show that the state of stress at this interface depends on the die geometry and on the extrusion ratio. The implications of this observation on the design of dies for co-extrusion are discussed.