Year
2010
Abstract
A modern storage system or transport package for spent nuclear fuel requires a thermally efficient and structurally robust fuel basket. Development of thermally capable (high heat rejection capability) and a structurally competent fuel basket design that can meet the 10CFR71.73 “free drop” or USNRC’s nonmechanistic tipover requirements has been stymied for lack of a suitable basket material. Austenitic stainless steel, the staple material for fuel baskets, suffers from relatively poor thermal conductivity. Carbon steel, another material of choice for cost conscious users, is corrosion prone. Borated Aluminum, more common in Europe, has poor structural strength at typical operating temperatures in casks. Metamic®-HT, a nano-particle-strengthened aluminum containing Boron Carbide powder, developed by Holtec International, removes the above limitations that have hampered the progress in cask design. This paper provides a summary of the three-year test program carried out to quantify the minimum guaranteed properties of Metamic®-HT. The tests were carried out on coupons of Metamic®-HT in three physical states: i. Raw (as-extruded) ii. Thermally conditioned to simulate 40 years of cask thermal environment iii. Thermally conditioned and irradiated to simulate 40 years of fluence The key thermo-mechanical properties of Metamic®-HT (listed below) have been characterized by a testing program similar to the qualification regimen for an ASTM material. i. Creep Strength ii. Yield and Ultimate strengths iii. Young’s modulus iv. Elongation v. Area reduction vi. Charpy impact strength and lateral expansion vii. Fracture toughness viii. Thermal conductivity, expansion coefficient, and heat capacity ix. Emissivity A large number of coupons (well over 1,000) were tested to perform statistical correlations on the data obtained on each property. The results of the test program were shared with the USNRC in Docket No. 71-9325, which provided the basis for the certification of the fuel basket in HI-STAR 180. This paper contains a summary of the critical characteristics of the Metamic®-HT material and the “minimum guaranteed values” (MGVs) to which it is being produced for use in fuel baskets and fuel racks.