[ RadSafe ] Yucca Mountain - neptunium

[Strickert, Rick]

>From "Dissolved Concentration Limits of Radioactive Elements" (Y. Chen, E.R. Thomas, F.J. Pearson, P.L. Cloke, T.L. Steinborn, and P.V. Brady, ANL-WIS-MD-000010 REV 02, June 2003;                         http://www.ocrwm.doe.gov/documents/amr/34715/34715.pdf), the issue may be  between two neptunium solubility models, one with neptunyl(V) oxide as the controlling solid, and the other model, which uses neptunium(IV) oxide.

The report states that its preference for the neptunyl(V) oxide model is based on work by Efurd, D.W.; Runde, W.; Banar, J.C.; Janecky, D.R.; Kaszuba, J.P.; Palmer, P.D.; Roensch, F.R.; and Tait, C.D. 1998. "Neptunium and Plutonium Solubilities in a Yucca Mountain Groundwater." Environmental Science & Technology, 32, (24), 3893-3900. Easton, Pennsylvania: American Chemical Society. TIC: 243857 (I haven't read the paper of Efurd, et al..) 

The solubility-limited neptunyl(V) aqueous concentrations are over an order of magnitude higher for the neptunyl(V) oxide model than for the neptunium(IV) oxide model in the neutral to acidic pH range.  Carbonate complexing may also begin to increase the aqueous neptunium concentration at pH values > approx. 8.

There's also a question of the importance of the crystalline oxide vs. an amorphous hydrous oxide (e.g., Np2O5*xH2O or NpO2*xH2O).  The hydrous oxide is more soluble, but ages to a less soluble crystalline form.  

Rick Strickert
Austin, TX


-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On Behalf Of Franz Schönhofer
Sent: Thursday, March 17, 2005 6:15 PM
To: RADSAFE
Subject: [ RadSafe ] Yucca Mountain - neptunium

RADSAFErs,
 
I met a few days ago a US scientist, who is involved with the Yucca
Mountain project. He agreed with me that Yucca Mountain is a political
question, but he also told me that the only scientific concern which has
to be still investigated is the behaviour of neptunium in the
repository, because it has turned out that it is much more soluble than
it was estimated.
 
Anybody who can comment on this?
 
Best regards,
 
Franz
 
Franz Schoenhofer
PhD, MR iR
Habicherg. 31/7
A-1160 Vienna
AUSTRIA
phone (international) -43-699-1168-1319
phone (national) 0699-1168-1319
 
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