Determining Dilute Condition Dissolution Rates with Stirred Reactor Coupon Analysis

With many countries deciding on deep geological disposal of high-level nuclear waste, the corrosion behaviour of the glassy waste matrix is of utmost importance. Multiple studies determined glass dissolution rates under various conditions, resulting in a general rate behaviour scheme of a high initial rate, followed by a low residual rate (plus a potential late-stage increase).

To simulate the impact of groundwater contact with the waste matrix, robust dissolution rate parameters are crucial, but thus far a protocol for interlaboratory comparability was missing.

As part of a waste form development program at Pacific Northwest National Laboratory, the Stirred Reactor Coupon Analysis (SRCA) test method was developed over the last years and used to determine the three dilute rate model parameters [rate constant, activation energy, and pH power law coefficient] for many glass compositions.

The SRCA reactor design is composed of a stirred solution contained in a large volume baffled reactor in which glass coupons are suspended. Dissolution rates are determined by height differences between masked and unmasked areas of each coupon measured post mortem with, e.g., profilometer analysis.

To evaluate the robustness of the method, a round-robin study was initiated with 12 international groups testing four glass composition under various pH/temperature conditions.

With the method proving useful for this application and showing strong potential for use as a bulk measure of glass corrosion, we are attempting to establish a consensus standard procedure recognized by ASTM International. Naturally, applications of the method to other fields of mineralogy and geochemistry are encouraged.