Evolution of Static Physical Properties in Plutonium by Self-irradiation Damage
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1264-Z08-10
Evolution of Static Physical Properties in Plutonium by Self-irradiation Damage Brandon W. Chung, Kenneth E. Lema and David S. Hiromoto Lawrence Livermore National Laboratory, Livermore, CA 94551, U.S.A. ABSTRACT The alpha-decay of plutonium leads to the age-related change in physical properties. This paper presents updated results of age-related effects on enriched and reference alloys measured from immersion density, dilatometry, and mechanical tests. After nearly 100 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys are decreasing in density by less than 0.002% per year and now exhibit a near linear density decrease, without void swelling. The tensile tests show that the aging process increases the strength of plutonium alloys, followed by possible saturation past 70 equivalent years of age. The ultimate goal of this work is to develop capabilities to predict physical properties changed by aging effects. INTRODUCTION Plutonium exhibits notoriously complicated metallurgical behaviors, depending sensitively on phase as well as on chemical content and microstructure [1, 2]. Current studies in plutonium metallurgy are motivated by the need to better understand the influence of the metallurgical phenomena on the physical properties for stockpile stewardship, nonproliferation, environmental issues, and nuclear power. One of the key areas of research is developing capabilities to predict physical properties changed by the radioactive decay of plutonium that incessantly creates lattice damage and in-growth of radiogenic helium. Because these integrated aging effects would normally require decades to measure, studies are underway to assess the effects of extended aging on the physical and static mechanical properties of plutonium alloys by incorporating roughly 7.3 atomic % of highly specific activity isotope 238Pu into the 239Pu metal to accelerate the aging process. By monitoring the properties of the 238Pu enriched alloy and naturally aged plutonium alloys, the aging properties of plutonium from the self-irradiation damage can be predicted. EXPERIMENT Radiation damage from alpha decay in plutonium occurs at a rate of ~0.1 dpa (displacement per atom) per year. Because the effects of interest occur over decades, our approach is to accelerate the effects of radiation damage in plutonium metal by incorporating 7.3 atomic % of the higher specific activity isotope 238Pu into the 239Pu lattice. The rate of alphadecay of 238Pu is nearly 300 times that of 239Pu so the rate of radiation damage accumulation can be increased. Using this method, the radiation damage in plutonium equivalent to sixty years of natural aging can be simulated in only a few years. Additional details of sample preparation are presented elsewhere [3]. In addition, naturally aged plutonium alloys of various ages are characterized to validate the accelerated aging approach.
Details of operation of the dilatometer system, immersion density, and static tensile test techniques are presented elsewh
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