This document reports the circumstances surrounding the failure of sheathed thermocouples during a test being conducted in the KAPL-120 Loop. The report is prepared to provide a record of these events and to acquaint those who use these thermocouples for testing of other applications with the difficulties that are sometimes encountered.

Although the corrosion of resistance of Zircaloy--2 clad fuel elements in high temperature water is excellent, some concern has been expressed in regard to the resistance against fretting corrosion. Since this form of corrosion can proceed quite rapidly it could induce fuel element failure through penetration of the cladding. Fretting corrosion if it occurred, would take place either where the fuel element contacted the process tube or where portions of the fuel element contacted each other, e. g. wire-wrapping around a cluster of cylindrical fuel rods. This form of corrosion is defined as corrosion occurring at contact areas and as such, fretting of Zircaloy-2 could take place in many reactor concepts. This report details the results of testing performed to induce fretting corrosion of Zircaloy-2 and the direction of the future tests.

aluminum has been considered as a material for cladding fuel elements to be used in reactors cooled by high-temperature recirculating water. Aluminum is abundant, chap, has a relatively low cross section for thermal neutrons, and is readily fabricated into complex shapes. For these reasons, it appears that the use of aluminum rather than steel, Zircaloy or other candidate materials for fuel element cladding, would result in considerable savings in operating expense. The actual economics will of course depend on specific factors such as core materials and design of the reactor/. Aluminum appears particularly attractive for cladding the cores of aluminum-plutonium alloy proposed for the Plutonium Recycle Test Reactor since, in this case, the physical characteristics of the core and cladding would be practically identical.

This is the third of a series of reports describing the phases of a study of the wear and galling of autoclavedZircaloy-2 by various bearing surface materials. The first report (1) showed that increasing contact area between the autoclaved Zircaloy-2 surfaces will not prevent scratching. It also showed that metals softer than Zircaloy-2 in general do not scratch it. The second report (2) described how eight metals and alloys were wear-tested on autoclaved Zircaloy-2 as prospects for fuel element support-bearing surface materials.