The Waste Isolation Pilot Plant (WIPP) transuranic repository remains a cornerstone of the U.S. Department of Energy's (DOE) nuclear waste management effort. The EPA recertified the WIPP for the third time in July 2017 (designated CRA-2014). Full recovery from the February 2014 operational incidents will not be complete until a second shaft is installed to allow for additional panels in the WIPP underground (tentatively planned for ~ 2021) but the WIPP has re-opened and shipments to the WIPP resumed in January 2017. These operational issues did not affect the long-term safety case for the permanent disposal of transuranic (TRU) waste and the use of a salt repository concept for the permanent disposal of nuclear waste remains intact. The operational issues, however, did lead to a higher focus on the scientific basis of the overall safety case and, in particular, the underlying brine and actinide chemistry models. This understanding is needed to address the low-probability scenario that brine inundation and release could occur due to human intrusions and is driven by regulatory requirements for the repository license case.<br/>For these reasons, research to strengthen and assess the degree of conservatism in the WIPP-relevant actinide/brine chemistry models continues. The overall ranking of actinides, from the perspective of potential contribution to release from the WIPP, is: Pu ~ Am &gt; U &gt;&gt; Th and Np and remains unchallenged from past recertification. Research emphasis in the past couple of years has focused on issues raised during the regulatory review process of the 2014 recertification application. The most important of these are: 1) oxidation state distribution of plutonium and the overall redox conditions expected; 2) role and importance of site-specific solubility studies in assessing the overall source term modeling in PA; and 3) effects of organic complexation on the An(III) and An(IV) oxidation states; and 4) further progress in understanding microbial effects. A status of ongoing research in these four areas will be provided.

Actinide solubility and speciation in the WIPP

256th National Meeting (2018)

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