The irradiation behavior of small pin specimens of chill-cast U-10 wt.% Pu and U-15 wt.% Pu specimens projecting from heat transfer cushions is described. The specimens were coated with a thin layer of carbonyl-deposited nickel. The 15 wt.% Pu pins showed excellent dimensional stability at 1/3 wt.% total burnup. The 10 wt.% Pu specimens were somewhat inferior, failure of one of them indicating that the improvement in performance over unalloyed uranium may be due to the restraint imposed by the cladding.
Irradiations were made on a number of uranium-plutonium alloy specimens made from both cast and extruded materials. The cast alloys included alloys of uranium with 3.7, 5.6, and 13.0 wt. % plutonium, and the extruded alloys included alloys of uranium with 9.5, 14.1, and 15.7 wt.% plutonium. One-half of the extruded specimens were given a heat treatment consisting of heating to 545 deg C and cooling to and holding at 500 deg C for one hour in an attempt to remove the preferred orientation that was anticipated from extrusion. The specimens were irradiated to burnups ranging up to 0.54 at. % with central temperatures ranging up to 490 deg C. The cast specimens were all found to have developed severe surface roughening as a result of the irradiation they received, presumably because of excessively large grain sizes present before irradiation. Identically fabricated unalloyed uranium specimens showed similar behavior. The as-extruded alloy specimens maintained good surface smoothness under irradiation, but showed elongations which were dependent on plutonium content. For example, in samples with 0.4 at.% burnup, a 14.1 wt.% plutonium alloy specimen elongated 96%, whereas an 18.7 wt. % plutonium alloy specimen elongated only 5.4%. The heat-treated extruded specimens did not elongate anisotropically, indicating that the heat treatment used was effective in randomizing the grain orientation. However, the heat-treated specimens developed excessive surface roughening, apparently because the heat treatment caused an undesirably large grain size. (auth).
A total of 35 specimens of U-Pu-fissium alloy and 2 specimens of U-10 wt% Pu-5 wt% Mo alloy were irradiated as a part of the fuel-alloy development program for fast breeder reactors at Argonne National Laboratory. Total atom burnups ranged from 1.0 to 1.8% at maximum fuel temperatures ranging from 230 to 470 deg C. Emphasis was placed on the EBR-II Core-III reference fuel material, which is an injection-cast, U-20 wt% Pu-10 wt% fissium alloy. It was found that this material begins to swell catastrophically at irradiation temperatures above 370 deg C. The ability of the fuel to resist swelling did not appear to vary appreciably with minor changes in zirconium or fissium content. Decreasing the Pu to 10 wt%, however, significantly improved the swelling behavior of the alloy. Both pour-cast and thermally cycled material and pour-cast, extruded, and thermally cycled material appeared to be more stable under irradiation than injection-cast material. Under comparable irradiation conditions, the specimens of U-20 wt% Pu- 5 wt% Mo alloy were less dimensionally stable than the U-Pu-fissium alloys investigated.
ABS>An irradiation test of 1/16 in. diameter x 3/16 in. long U/sup 235/ and U/sup 235/-Zr alloy specimens, in the range 2 to 20 wt.% Zr, is described. The small pins were mounted in heat transfer blocks, or ''cushions, '' in such a way that suriace roughening and length changes could be observed, recorded, and compared for five stabilizing heat treatments up to exposure levels of approximately 1% total atom burnup. Addition of 2% Zr was found to be very beneficial, but the behavior of the alloys underwent distinct changes in going from 2 to 4 wt.% Zr. Material, both as-cast and subsequently isothermally treated, changed from minus to plus elongation, whereas wrought materials, either gamma-slow cooled or isothermally treated, changed from plus to minus behavior. Data-quenched wrought material varied unpredictably. Addition of Zr up to 20% showed further improvement in stability for all treatments. Factors which may have contributed to this behavior are discussed. (auth).
