Corrosion Considerations in the Use of Boral in Spent Fuel Storage Pool Racks

Abstract

Boral is a cermet of Boron Carbide 'B{sub 4}C' in aluminum clad in aluminum. It is manufactured in rolled sheets using techniques similar to those used in the production of uranium aluminum fuel elements. The core of the standard Boral contains 35% boron carbide by weight. Cladding material is typical 1100 aluminum. Where it is exposed to water in service, the edges of the Boral are recommended by the manufacturer to be clad with aluminum by welding. In Spent Fuel Pool (SFP) racks, the Boral is usually not a structural member but is inserted in cavities between the spent fuel storage positions in the racks. In these locations it is sealed by welding to prevent access of water. Inherently, however, the corrosion of the Boral, both the boron carbide-aluminum cermet and the aluminum cladding, should be minimal in a spent fuel storage pool. The cavities into which the Boral is sealed are typically fabricated of aluminum alloys, i.e. type 6061, or stainless steel. In either case, these are the structural members of the SFP racks. In an SFP, water chemistry tends to be strictly controlled because the SFP water mixes with the reactor coolant during refueling procedures. In SFP's atmore » BWR sites, water chemistry is typical of that of a BWR i.e. high resistivity neutral water. In SFP's at PWR sites water chemistry typically contains 2 to 3,000 parts per million ppm boron as boric acid, which is there primarily to prevent dilution of the reactor primary coolant during refueling and is not relied on for criticality considerations. The water chemistries and anticipated corrosion of SFP materials were reviewed in an earlier report. BNL-NUREG 23021, July, 1977.« less