Development of a biofilm formation method for waste forms stability evaluation

Area of Science:

• Environmental Science
• Microbiology
• Materials Science

Background:

• Accurate assessment protocols are crucial for predicting the long-term performance of waste disposal systems.
• Microbially induced degradation (MID) poses a significant challenge to the stability of waste forms.
• Existing methods, like the Nuclear Regulatory Commission (NRC) approach, have limitations in fully evaluating microbial degradation.

Purpose of the Study:

• To develop an improved biofilm formation method for evaluating waste form stability against MID.
• To address limitations in existing assessment protocols, particularly the NRC approach.
• To enhance the accuracy of predicting the long-term performance of waste disposal systems.

Main Methods:

• Developed a novel biofilm formation method with modifications to the NRC approach.
• Implemented a two-stage process: first for biofilm formation, then for evaluation.
• Controlled media and fermenter broths to have similar pH, unlike the NRC approach.
• Utilized two waste forms: 100% Tuskegee cement and 21% cobalt chloride/79% cement.

Main Results:

• The new method demonstrated effective biofilm formation on both tested waste forms.
• The two-stage process eliminated substrate limitation, yielding degradation indices approximately twice as high as the NRC method.
• Biofilm formation on the cobalt-containing waste form indicated cobalt does not possess antimicrobial properties.

Conclusions:

• The developed biofilm formation method provides a more accurate assessment of waste form stability to MID.
• The two-stage process and controlled pH offer a superior evaluation of microbial degradation compared to the single-stage NRC approach.
• The findings suggest that cobalt-containing waste forms are susceptible to microbial degradation, impacting long-term disposal system performance.