Citation:

SANTILLAN, E. U. The Geochemistry of the Waste Isolation Pilot Plant. U.S. Environmental Protection Agency, Washington, DC, 2021.

Impact/Purpose:

This report discusses the geochemical concepts and methods used to estimate potential releases in the Performance Assessment as they relate to the specific conditions at the WIPP. It can also be used as an introduction to different models contained in the Performance Assessment.

Description:

The Waste Isolation Pilot Plant (WIPP), located near Carlsbad, New Mexico, is a deep geologic repository for the disposal of defense-related transuranic radioactive waste operated by the U.S. Department of Energy (DOE). The repository is located in a bedded salt deposit, approximately 660 meters below the subsurface. Regulatory oversight for the radioactive waste at the facility is provided by the U.S. Environmental Protection Agency (EPA) as established by the WIPP Land Withdrawal Act. As a part of a demonstration of compliance with radioactive waste disposal standards that EPA has established, DOE submits a Performance Assessment (PA) model calculation for the repository’s 10,000- year regulatory timeframe. This PA calculation projects potential quantities of actinides released into the accessible environment as a result of various potential intrusions into the repository. EPA initially certified the WIPP’s compliance in 1998, and since the facility first received waste in 1999, DOE has submitted a recertification application with an updated PA every 5 years. The PA incorporates multiple different models and concepts, ranging from the rock mechanics of the surrounding salt matrix to the geochemistry of the actinides’ interacting with brine pockets. This document provides an overview of the various geochemical concepts in the PA used to estimate actinide releases and relates them to the specific conditions at the WIPP and the PA methods. The various sections in the document are meant to be modular and can be used separately or in conjunction with the rest of the document as a primer to give context and background to different models present in the PA.

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