Review and perspectives on spallings release models in the 1996 performance assessment for the Waste Isolation Pilot Plant

Abstract

The Waste Isolation Pilot Plant was licensed for disposal of tnnsuranic wastes generated by the U.S. Department of Energy. The facility consists of a repository mined in a bedded salt formation, approximately 650 m below the surface. Regulations promulgated by the U.S. Environmental Protection Agency require that performance assessment calculations for the repository include the possibility that an exploratory drilling operation could penetrate the waste disposal areas at some time in the fbture. Release of contaminated solids could reach the surface during a drilling intrusion. One of the mechanisms for release, lmown as spallings, can occur if gas pressures in the repository exceed the hydrostatic pressure of a column of drilling mud. Calculation of solids releases for spallings depends critically on the conceptual models for the waste, for the spallings process, and assumptions regarding driller pa.mmeters and pmctices. Thk paper presents a review of the evolution of these models during regulatory review of the Compliance Certification Application for the repository. A summary and perspectives on the implementation of conservative assumptions in model development are also provided.