Neptunium and Plutonium Solubilities in a Yucca Mountain Groundwater
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- 作者：D. Wes Efurd ; Wolfgang Runde ; Joe C. Banar ; David R. Janecky ; John P. Kaszuba ; Phillip D. Palmer ; Fred R. Roensch ; and C. Drew Tait
- 刊名：Environmental Science & Technology
- 出版年：1998
- 出版时间：December 15, 1998
- 年：1998
- 卷：32
- 期：24
- 页码：3893 - 3900
- 全文大小：187K
- 年卷期：v.32,no.24(December 15, 1998)
- ISSN：1520-5851
文摘
Solubilities of neptunium and plutonium were studied inJ-13 groundwater (ionic strength of about 3.7 mmol; totaldissolved carbonate of 2.8 mmol) from the proposed YuccaMountain Nuclear Waste Repository site, Nevada, atthree different temperatures (25, 60, and 90 
C) and pHvalues (6.0, 7.0, and 8.5). Experiments were performed fromboth over- and undersaturation at defined CO2 partialpressures. The solubility of 237Np from oversaturationranged from a high of (9.40 ± 1.22) × 10-4 M at pH 6.0and 60 C to a low of (5.50 ± 1.97) × 10-6 M at pH 8.5 and90 C. The analytical results of solubility experimentsfrom undersaturation (temperatures of 25 and 90 C andpH values 6, 7, and 8.5) converged on these values. The239/240Pu solubilities ranged from (4.70 ± 1.13) × 10-8 M at pH6.0 and 25 C to (3.62 ± 1.14) × 10-9 M at pH 8.5 and 90C. In general, both neptunium and plutonium solubilitiesdecreased with increasing pH and temperature. Greenish-brown crystalline Np2O5·xH2O was identified as thesolubility-limiting solid using X-ray diffraction. A meanthermodynamic solubility product for Np2O5·xH2O of log Ksp= 5.2 ± 0.8 for the reaction Np2O5·xH2O + 2 H+ 
2NpO2+ + (x+1)H2O at 25 C was calculated. Sparinglysoluble Pu(IV) solids, PuO2·xH2O and/or amorphousplutonium(IV) hydroxide/colloids, control the solubility ofplutonium in J-13 water.
C) and pHvalues (6.0, 7.0, and 8.5). Experiments were performed fromboth over- and undersaturation at defined CO2 partialpressures. The solubility of 237Np from oversaturationranged from a high of (9.40 ± 1.22) × 10-4 M at pH 6.0and 60 C to a low of (5.50 ± 1.97) × 10-6 M at pH 8.5 and90 C. The analytical results of solubility experimentsfrom undersaturation (temperatures of 25 and 90 C andpH values 6, 7, and 8.5) converged on these values. The239/240Pu solubilities ranged from (4.70 ± 1.13) × 10-8 M at pH6.0 and 25 C to (3.62 ± 1.14) × 10-9 M at pH 8.5 and 90C. In general, both neptunium and plutonium solubilitiesdecreased with increasing pH and temperature. Greenish-brown crystalline Np2O5·xH2O was identified as thesolubility-limiting solid using X-ray diffraction. A meanthermodynamic solubility product for Np2O5·xH2O of log Ksp= 5.2 ± 0.8 for the reaction Np2O5·xH2O + 2 H+ 2NpO2+ + (x+1)H2O at 25 C was calculated. Sparinglysoluble Pu(IV) solids, PuO2·xH2O and/or amorphousplutonium(IV) hydroxide/colloids, control the solubility ofplutonium in J-13 water.