Ronald E. Mizia

Diffusion-Welded Microchannel Heat Exchanger for Industrial Processes

The goal of next generation reactors is to increase energy efficiency in the production of electricity and provide high-temperature heat for industrial processes. The efficient transfer of energy for industrial applications depends on the ability to incorporate effective heat exchangers between the nuclear heat transport system and the industrial process. The need for efficiency, compactness, and safety challenge the boundaries of existing heat exchanger technology. Various studies have been performed in attempts to update the secondary heat exchanger that is downstream of the primary heat exchanger, mostly because its performance is strongly tied to the ability to employ more efficient industrial processes. Modern compact heat exchangers can provide high compactness, a measure of the ratio of surface area-to-volume of a heat exchange. The microchannel heat exchanger studied here is a plate-type, robust heat exchanger that combines compactness, low pressure drop, high effectiveness, and the ability to operate with a very large pressure differential between hot and cold sides. The plates are etched and thereafter joined by diffusion welding, resulting in extremely strong all-metal heat exchanger cores. After bonding, any number of core blocks can be welded together to provide the required flow capacity. This study explores the microchannel heat exchanger and draws conclusions about diffusion welding/bonding for joining heat exchanger plates, with both experimental and computational modeling, along with existing challenges and gaps. Also, presented is a thermal design method for determining overall design specifications for a microchannel printed circuit heat exchanger for both supercritical (24 MPa) and subcritical (17 MPa) Rankine power cycles.

Development and testing of an advanced neutron-absorbing gadolinium alloy for spent nuclear fuel storage

The U.S. Department of Energy requires nuclear criticality control measures for storage of its highly enriched spent nuclear fuel. A new alloy based on the Ni-Cr-Mo alloy system with a gadolinium addition has been developed. Gadolinium has been chosen as the neutron absorption alloying element because of its high thermal neutron absorption cross section. The metallurgical development, mechanical and physical properties, thermal neutron absorption properties, and accelerated corrosion-testing performance of this Ni-Cr-Mo-Gd alloy is described. A brief comparison is also included of the corrosion performance of this alloy as compared to borated stainless steel, which is commonly used as a neutron-absorbing, structural alloy.

Studies of the Corrosion Properties of Ni-Cr-Mo-Gd Neutron-Absorbing Alloys

Abstract The corrosion properties of Ni-Cr-Mo-Gd alloys that are being developed for use as a neutron-absorbing structural material were examined. The corrosion work was part of a larger alloy development program. The corrosion properties were examined by both electrochemical and longer-term immersion testing in standard test solutions and in simulated solutions used in corrosion testing by the Yucca Mountain Project. The addition of Gd to a Ni-Cr-Mo alloy results in the formation of a gadolinide (Ni5Gd) secondary phase. This phase was observed to preferentially dissolve under electrochemical testing at anodic potentials. The reaction appears to be mostly limited to the secondary phase exposed to the surface. A brief comparison with another neutron-absorbing alloy, borated stainless steel, is made.

Electrochemical Corrosion Testing of Borated Stainless Steel Alloys

The Department of Energy Office of Civilian Radioactive Waste Management has specified borated stainless steel manufactured to the requirements of ASTM A 887-89, Grade A, UNS S30464, to be the material used for the fabrication of the fuel basket internals of the preliminary transportation, aging, and disposal canister system preliminary design. The long-term corrosion resistance performance of this class of borated materials must be verified when exposed to expected YMP repository conditions after a waste package breach. Electrochemical corrosion tests were performed on crevice corrosion coupons of Type 304 B4 and Type 304 B5 borated stainless steels exposed to single postulated in-package chemistry at 60°C. The results show low corrosion rates for the test period