Additional Investigations Concerning the Hydration of Magnesium Oxide in the Waste Isolation Pilot Plant

Nathalia L. Chadwick and Anna C. Snider

Sandia National Laboratories¹

Carlsbad Programs Group

Carlsbad, NM 88220

WIPP is a U.S. Department of Energy repository for the disposal of defense-related, transuranic waste. The repository is located in southeast New Mexico at a depth of 655 m in the Salado Formation, a Permian bedded salt formation. MgO is currently being emplaced in the repository to reduce actinide solubilities by consuming CO₂ produced by possible microbial activity, buffering the repository at about pH 9, and by consuming water. Magnesium oxide (MgO) is the only engineered barrier that is recognized as such for the WIPP by the U.S. Environmental Protection Agency. Premier Chemicals is presently the supplier of MgO to the WIPP project.

Initial results from our inundated hydration experiments indicate that Premier MgO does not appear to be fully hydrated and some sets of data are irreproducible. To address these issues additional experiments have been initiated with different conditions, such as grain size, different MgO lots, etc., to ascertain the determining factors involved. Sets of experiments, containing 5 g of Premier MgO in 100 mL solutions, are placed in ovens at varying temperatures and shaken frequently. The pH is measured and weight loss on ignition (LOI) is calculated on the samples. The new data will aid in the interpretation of the complex MgO hydration system.

Acknowledgement: This research is funded by WIPP administrated by the Department of Energy.

1. Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy’s National Nuclear Security Administration under Contract DE-AC04-94AL85000.