that we believe were caused by seawater that entered the helium release vents when the sphere wasfirst submerged. The defects appeared to be ruptures ad- jacent to the external closure weld. The inside of the cladding showed corrosive attack along grain boun- daries, sometimes penetrating to 30% of the wall thickness, presumably caused by the seawater, but metallography of typical specimens showed no evidence of sodium chloride. The plutonia sphere showed no sign of corrosion. Probably, sudden immersion of the hot FSA caused water penetration through the vents in the cladding and the water and the salt residue, together with the high temperature and intense alpha and gammairradiation caused chemical attack and disintegration of the iridium cladding from within. VI. BEHAVIOR OF CAPSULE MATERIALS IN AQUATIC ENVIRONMENTS _ (George M. Matlack, Gilbert B. Nelson, and James H. Patterson) Heat source capsule materials were immersed in simulated seawater at 23° for 1 to 3 yr, then examined for corrosion of the surfaces and of boundaries between dissimilar metals. The materials tested were molybdenum, T-111 alloy, Pt-20Rh, and Ta- 10W. Molybdenum sheet, after immersion for 1 yr showedno corrosion other than deposition of crystals containing elements present in seawaterand a slight increase of the molybdenum concentration in the water. Couples formed of T-111, Pt-20Rh, and Ta10W showed nogross corrosion after 3 yr of immer- sion, and none of the elements was found in the water. There were very thin layers of a dark amorphoussubstanceat the contact boundaries, and in all instances these layers were composed chiefly of manganese, also presentin the seawater. These capsule construction materials seem to remain uncorroded for up to 3 yr of immersion in seawater. VII. BEHAVIOR OF SIMULATED SEAWATER (Zr,U) FUEL IN (George M. Matlack) were immersed for over 2 yr in simulated seawater. One sample from a Hastelloy-N clad fuel rod was immersed for 20 months, and a similar sample, ex- cept that it was from an unclad rod, was immersed for 25 months. Neither underwentanyvisible change in the luster of its cut surface; fine burrs and saw marks were unchanged. The radioactivity in the water became twice normal background within a week after sample immersion and did not increase thereafter. The activity was mainly !°’Cs, with a minorfraction of ©°Co activity from the clad sample. The excellent stability of this fuel in seawater was also confirmed by ocean exposure tests conducted at San Clemente Island by the Naval Undersea Center. REFERENCES 1. W. W. Weir, Soil Science (J. B. Lippincott Co., Chicago, 1949), p. 132. 2. D. Rohr, LASL, private communication. 3. M. W. Nathans, LFE Environmental, Richmond, CA, private communication. 4. J. H. Patterson, G. B. Nelson, and G. M. Matlack, “The Dissolution of 78Pu_ in Environmental and Biological Systems,’’ Los AlamosScientific Laboratory report LA-5624 (1974). 5. O. G. Raabe, G. M. Kanapilly, and H.A. Boyd, “Studies of the In Vitro Solubility of Respirable Particles of 2°8Pu and 78°Pu Oxides and an Accidentally Released Aerosol Containing 78°Pu,” in “Lovelace Foundation for Medical Education and Research, Inhalation Toxicology Research Institute Annual Report” LF-46 (1973), pp. 24-30. 6. B. O. Stuart, “Comparative Distribution of “°8Pu and “9Py in Rats Following Inhalation of the Oxide,” Battelle Northwest Laboratories report BNWL-1050 (1979), pp. 3.19-3.20. 7. J. Hudson, “Analysis of Microsphere Debris,” in “Sandia Laboratory Quarterly Report, Aerospace Nuclear Safety Program, April 1, 1968,” report SCPR-68-451, pp. 34-36. Two irradiated, enriched uranium SNAP fuel samples, each a 6-mm-thick section of ZrH-10 U (93° enriched 2351), cut from a full-size fuel rod, 15