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Vegetation-Derived Insights on the Mobilization and Potential:Transport of Radionuclides from the Nopal I Natural Analog Site, Mexico

Published online by Cambridge University Press:  10 February 2011

Bret W. Leslie ,
David A. Pickett  and
English C. Pearcy
Bret W. Leslie
Affiliation:
U.S. Nuclear Regulatory Commission, MS T-7C6, Washington, D.C. 20555–0001
David A. Pickett
Affiliation:
Center for Nuclear Waste Regulatory Analyses, 6220 Culebra Road, San Antonio, Texas 78238–5166
English C. Pearcy
Affiliation:
Center for Nuclear Waste Regulatory Analyses, 6220 Culebra Road, San Antonio, Texas 78238–5166
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Abstract

The Nopal I uranium (U) deposit, Peñia Blanca, Mexico is a source term and contaminant transport natural analog to the proposed high-level nuclear waste repository at Yucca Mountain, Nevada. In an attempt to characterize the mobilization and potential transport of adionuclides in the unsaturated zone at the Nopal I deposit, vegetation growing on ore piles was analyzed for 238U, 235U, and 232Th decay-series isotopes. Specimens of Phacelia robusta growing on highgrade piles of U ore were collected and analyzed by alpha autoradiography, and by alpha and gamma spectrometry. Activities for U, thorium (Th), and radium (Ra) isotopes (Bq/kg dried plant) were 300, 1000, and 7000 for 238U, 230Th, and 226Ra, respectively. The 226Ra activities in these specimens are among the highest ever measured for plants; furthermore, the plant-to-soil 226Ra concentration ratio is higher than expected. These results demonstrate the large mobility and bio-availability of Ra in the Nopal I environment, and support previous indications of recent loss of 226Ra from the ore body. Comparison between the activities of 238U and 232Th decay-chain Th isotopes in the plants and in the ore substrate indicate that relative mobilization into pore solutions of 228Th > 230Th > 232Th, in a ratio of about 50 – 25:4:1, respectively. The similarity of the plant's 234U/238U activity ratio (˜1.2) to that of a caliche deposit that formed adjacent to the Nopal ore body around 54 ka suggests the 234U/238U activity ratio of U released from the ore is approximately 1.2. The U and 236Ra isotope activities of the plants and ore substrate, and solubility considerations, are used to assess a source term model of the potential Yucca Mountain repository. These results suggest the use of a natural analog source term model in performance assessments may be non-conservative.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 556: Symposium QQ – Scientific Basis for Nuclear Waste Management XXII , 1999 , 833
Copyright
Copyright © Materials Research Society 1999

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References

REFERENCES

1. Murphy, W.M. and Pearcy, E.C., in Scientific Basis for Nuclear Waste Management XV, edited by Sombret, C.G. (Materials Research Society, Pittsburgh, PA, 1992), pp. 521–527.Google Scholar
2. Pearcy, E.C., Prikryl, J.D., Murphy, W.M., and Leslie, B.W., Appl. Geochem. 9, 713 (1994).Google Scholar
3. Murphy, W.M., Pearcy, E.C., and Pickett, D.A., Seventh EC Natural Analog Working Group Meeting, edited by Maravic, H. Von and Smellie, J. (EUR 17851 EN, Luxembourg, 1997), pp. 105–112.Google Scholar
4. Leslie, B.W., Pearcy, E.C., and Prikryl, J.D., in Scientific Basis.for Nuclear Waste Management XVI, edited by Interrante, C.G. and Pabalan, R.T. (Materials Research Society, Pittsburgh, PA, 1993), pp. 505–512.Google Scholar
5. Pearcy, E.C., Prikryl, J.D., and Leslie, B.W., Appl. Geochem. 10, 685 (1995).Google Scholar
6. Murphy, W.M. and Codell, R.B., in Scientific Basis for Nuclear Waste Management, edited by Lee, J. and Wronkiewicz, D.J. (Materials Research Society, Pittsburgh, PA, 1998), this volume.Google Scholar
7. Pickett, D.A. and Murphy, W.M., in Scientific Basis for Nuclear Waste Management, edited by Lee, J. and Wronkiewicz, D.J. (Materials Research Society, Pittsburgh, PA, 1998), this volume.Google Scholar
8. Luo, S. and Ku, T.-L., Geochim. Cosmochim. Acta. 55, 555 (1991).Google Scholar
9. Linsalata, P., Morse, R.S., Ford, H., Eisenbud, M., Franca, E.P., Castro, M.B. de, Lobao, N., Sachett, I., and Carlos, M., Health Physics 56, 33 (1989).Google Scholar
10. Cox, P. (private communication).Google Scholar
11. Johnston, I.M., J. Arnold Arbor. 24, 90 (1943).Google Scholar
12. Basham, I.R., Econ. Geol. 76, 974 (1981).Google Scholar
13. Cutshall, N.H., Larsen, I.L., and Olsen, C.R., Nucl. Instr. Meth. 206, 309 (1983).Google Scholar
14. Leslie, B.W. and Pearcy, E.C., Geol. Soc. Amer. Abstr. Prog. 25(6), A- 184 (1993).Google Scholar
15. Ajuria-Garza, S. and Jamrack, W.D. in Uranium Ore Processing (International Atomic Energy Agency, Vienna, Austria, 1976), pp. 1 0 7 -1 18.Google Scholar
16. Prikryl, J.D., Pickett, D.A., Murphy, W.M., and Pearcy, E.C., J. Contam. Hydr. 26, 61 (1997).Google Scholar
17. Pickett, D.A. and Murphy, W.M., Seventh EC Natural Analog Working Group Meeting, edited by Maravic, H. Von and Smellie, J. (EUR 17851 EN, Luxembourg,1997), pp. 113–122.Google Scholar
18. Pickett, D.A., Prikryl, J.D., Murphy, W.M., and Pearcy, E.C., submitted to Appl. Geochem. (1998).Google Scholar
19. Simon, S.L. and Ibrahim, S.A., in The Environmental Behaviour of Radium, (International Atomic Energy Agency, Vienna, Austria, 1990), pp. 545–599.Google Scholar
20. Whitehead, N.E., Brooks, R.R., and Coote, G.E., New Zealand J. Sci. 14, 66 (1971).Google Scholar
21. Wong, V., MS thesis, University of Texas at El Paso, 1994.Google Scholar
22. Murrell, M.T., Goldstein, S.J., and Dixon, P.R., EOS Trans. Amer. Geophys. Un. 78(46), F788 (1997).Google Scholar
23. Osmond, J.K. and Ivanovich, M., in Uranium-Series Disequilibrium: Applications to Earth, Marine, and Environmental Sciences 2nd ed., edited by Ivanovich, M. and Harmon, R.S. (Clarendon Press, Oxford, 1992), pp. 259–289.Google Scholar
24. Osmond, J.K. and Cowart, J.B., in Uranium-Series Disequilibrium: Applications to Earth, Marine, and Environmental Sciences 2nd ed., edited by Ivanovich, M. and Harmon, R.S. (Clarendon Press, Oxford, 1992), pp. 290–333.Google Scholar
25. Krishnaswami, S., Graustein, W.C., and Turekian, K.K., Water Res. Res. 18, 1663 (1982).Google Scholar
26. Bish, D.L., Carey, J.W., Carlos, B.A., Chipera, S.J., Guthrie, G.D. Jr., Levy, S.S., Vaniman, D.T., and WoldeGabriel, G., Yucca Mountain Site Characterization Project Milestone 3665, 1996.Google Scholar