Evolution of Static Physical Properties in Plutonium by Self-irradiation Damage Page: 3 of 6
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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.
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.
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.
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 alpha-
decay 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 . In addition, naturally aged plutonium alloys of various ages are
characterized to validate the accelerated aging approach.
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Chung, B W; Lema, K E & Hiromoto, D S. Evolution of Static Physical Properties in Plutonium by Self-irradiation Damage, article, April 13, 2010; Livermore, California. (digital.library.unt.edu/ark:/67531/metadc840587/m1/3/: accessed November 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.