CORROSION SCIENCE SECTION 364 CORROSION—APRIL 2005 Submitted for publication August 2004; in revised form, October 2004. ‡ Corresponding author. E-mail: aroy@unlv.nevada.edu. * Department of Mechanical Engineering, University of Nevada, Las Vegas (UNLV), 4505 Maryland Parkway, Las Vegas, NV 89154-4027. (1) UNS numbers are listed in Metals and Alloys in the Unified Num- bering System, published by the Society of Automotive Engineers (SAE International) and cosponsored by ASTM International. Environment-Assisted Cracking of Structural Materials Under Different Loading Conditions A.K. Roy, ‡, * M.K. Hossain,* R. Prabhakaran,* and S. Sama* ABSTRACT Significant efforts are ongoing, nationally and internationally, to reduce the radioactivity of spent nuclear fuel (SNF) and high-level waste (HLW) for their disposal in a potential reposi- tory by transmutation. Martensitic alloys EP-823, HT-9, and 422 (UNS S42200) are currently being considered as candi- date target structural materials for transmutation applications. This paper presents the results of stress corrosion cracking studies of these three alloys in aqueous environments of dif- ferent pH values under constant load and slow strain rate testing conditions at ambient and elevated temperatures. Metallographic and fractographic evaluations of all broken specimens by optical microscopy and scanning electron microscopy have also been performed. KEY WORDS: high-level waste, martensitic alloys, optical microscopy, scanning electron microscopy, slow strain rate testing, spent nuclear fuel, stress corrosion cracking INTRODUCTION The disposal of nuclear waste poses a severe chal- lenge to all nuclear power generating nations. Efforts are in progress to dispose of high-level radioactive waste (HLW) and spent nuclear fuel (SNF) in a geo- logic repository located at the Yucca Mountain site near Las Vegas, Nevada. Since HLW and SNF each have a long half-life, they must be stored inside the proposed repository for an unusually long time. Significant attention is currently being focused on reducing the half-life of these nuclear wastes by transmutation. This process involves bombarding a target material by proton beams generated by an accelerator or a reactor, thereby producing neutrons. Neutrons are impinged upon HLW/SNF to trans- mutate highly radioactive and/or long half-life to short half-life, less radioactive species. 1 Thus, the average half-life of these radioactive materials can be substantially reduced, which will reduce the critical storage period. The target material used during this process will be contained inside a subsystem structural container made of suitable martensitic materials, e.g., Alloys EP-823, HT-9, and 422 (UNS S42200) (1) . Extensive work has been performed to evaluate the susceptibil- ity of these alloys to stress corrosion cracking (SCC) in aqueous environments of different pH values at ambi- ent and elevated temperatures. The SCC behavior of all three alloys has been evaluated under constant load (CL) and slow strain rate (SSR) testing condi- tions. Metallographic and fractographic evaluations have been performed by optical microscopy and scan- ning electron microscopy (SEM), respectively. EXPERIMENTAL PROCEDURES Experimental heats of Alloys EP-823, HT-9, and 422 were melted using a vacuum-induction melt- ing practice. Their chemical compositions are given 0010-9312/05/000075/$5.00+$0.50/0 © 2005, NACE International