EPA-Provided Comment: Stakeholder comment received at the May 12, 2010 

Stakeholder meeting in Albuquerque 

Comment: Is DOE aware of these experiments (Plutonium nanocolloids) and have the 

results been taken into account (if applicable) in the WIPP radionuclide 

release scenarios? 

Documentation provided at the Stakeholder meeting: 

Argonne National Laboratory News Release: “Scientists discover how the structure of 

plutonium nanocluster contaminants increases risk of spreading,” 2008. 

DOE Response 

The DOE is aware of the plutonium nanocolloid experiments as outlined in the Argonne National 

Laboratory news release. A more extensive description of the experimental work has also been 

published in Soderholm et al. (2008). The Pu nanocolloid reported in Soderholm et al. (2008) is 

a specific example of an intrinsic colloid of Pu. Recent information on the formation and 

transport of Pu(IV) intrinsic colloids is presented in Section SOTERM-3.8.1 of CRA-2009 

(DOE, 2009), which notes that the intrinsic colloids tend to be very low in concentration and 

have a limited capability for radionuclide transport in the WIPP environment. The experimental 

results in Soderholm et al. (2008) therefore have limited applicability to long-term performance 

under the anticipated conditions in the WIPP. Despite this, the potential for plutonium 

nanocolloids to be present in the WIPP is included within the concentration of Pu(IV) intrinsic 

colloids in WIPP performance assessment. 

The detailed discussion of the Pu(IV) intrinsic colloids in Section SOTERM-6.3.2.1 of the first 

Compliance Recertification Application (CRA-2004)(DOE, 2004) is directly relevant to the 

nanocolloids of plutonium. As explained in Sections SOTERM-6.3.2.3 and SOTERM-6.3.2.4 of 

CRA-2004, Pu(IV) intrinsic colloids are included in performance assessment at a concentration 

of 10-9 M, which is conservative because the 10-9 M concentration is an upper bound based on an 

equipment detection limit. 

Another feature of the results reported in Soderholm et al. (2008) is that Pu nanocolloids passed 

through an anion-exchange column in strong acidic conditions (7.5 M nitric acid) without 

retardation. These experimental conditions are not relevant to the conditions expected in the 

WIPP repository. Pu nanoclusters reported in Soderholm et al. (2008) are highly charged (-14) 

particles. Such highly charged nanoclusters would be efficiently sorbed on mineral surfaces in 

the WIPP repository. 

In summary, the DOE is aware of the research on Pu nanocolloids and believes that this type of 

colloid is unlikely to form in significant concentrations under WIPP relevant conditions. In 

addition, if this type of colloid could form in the WIPP, its presence is encompassed in the 10-9

1
2

M concentration for Pu(IV) intrinsic colloids assumed in the WIPP long-term performance 

assessment. 

DOE References 

Soderholm, L., Almond, P.M., Skanthakumar, S., Wilson, R. E., and P.C. Burns, “The Structure 

of the plutonium oxide nanocluster [Pu38O56Cl54(H2O)8]

14-“, Angew. Chem. Int. Ed., 47 (2008) 

298-302. 

U.S. Department of Energy (DOE). 2004. Title 40 CFR Part 191 Compliance Recertification 

Application for the Waste Isolation Pilot Plant (March). 10 vols. DOE/WIPP 2004-3231. 

Carlsbad, NM: Carlsbad Field Office. 

U.S. DOE. 2009. Title 40 CFR Part 191 Subparts B and C 

Compliance Recertification Application for the Waste Isolation Pilot Plant. 

DOE/WIPP 09-3424. Carlsbad, NM: U.S. Department of Energy Carlsbad Field Office.