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Neptuniumnn(V) sorption and diffusion in opalinus clay.
Tao Wu1, Samer Amayri, Jakob Drebert
1Intitue of Nuclear Chemistry, Jhannes Gutenberg-Universität Mains, 55099 Mains, Germany. twu@hutc.zj.cn
Environmental Science & Technology
|September 22, 2009
Summary
We studied neptunium (Np(V)) sorption and diffusion in Opalinus Clay (OPA). Np(V) showed strong sorption, with a Kd of 0.10 m3/kg, impacting its migration in clay formations.
Area of Science:
- Geochemistry
- Environmental Science
- Nuclear Waste Management
Background:
- Understanding radionuclide behavior in geological formations is crucial for safe nuclear waste disposal.
- Opalinus Clay (OPA) is a potential host rock for radioactive waste repositories.
- Neptunium (Np(V)) is a key actinide of concern in nuclear waste.
Purpose of the Study:
- To investigate the sorption and diffusion characteristics of neptunium(V) in Opalinus Clay.
- To determine key parameters governing Np(V) migration in a clay formation under realistic conditions.
- To assess the suitability of Opalinus Clay as a barrier for Np(V) containment.
Main Methods:
- Batch experiments were conducted to determine the sorption coefficient (Kd) of Np(V) in OPA suspensions.
- Through- and out-diffusion experiments using tritiated water (HTO) were performed to measure diffusion-accessible porosity.
- In-diffusion experiments were utilized to study the diffusion of Np(V) in intact OPA, considering its strong sorption.
Main Results:
- The sorption coefficient (Kd) for Np(V) in OPA suspensions was determined to be 0.025 +/- 0.005 m3/kg.
- The diffusion-accessible porosity of intact OPA was measured as 0.15 +/- 0.01.
- For Np(V) diffusion in intact OPA, the effective diffusion coefficient (De) was found to be (6.9 +/- 1.1) x 10(-12) m2/s, with a rock capacity factor (alpha) of 243 +/- 4.
- The Kd for Np(V) in intact OPA, derived from diffusion experiments, was 0.10 +/- 0.01 m3/kg, indicating strong sorption.
Conclusions:
- Neptunium(V) exhibits strong sorption behavior in Opalinus Clay, significantly retarding its diffusion.
- The determined diffusion parameters (De and alpha) and sorption coefficient (Kd) provide essential data for modeling Np(V) migration in clay formations.
- Opalinus Clay demonstrates a high potential as a natural barrier for containing neptunium in radioactive waste disposal scenarios.
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