Dynamic Simulation of Hanford Tank Waste Remediation System

Cleaning up and disposing of approximately 50 years of nuclear waste is the main mission at the U.S. Department of Energy’s Hanford Nuclear Reservation, located in the southeastern part of the state of Washington. A major element of the total cleanup effort involves retrieving, processing, and disposing of radioactive and hazardous waste stored in 177 underground storage tanks. referred to as the Tank Waste Remediation System (WRSJ, is expected to cost billions of do//ars and take approximately 25 years to complete. Several computer simulations of this project are being created, focusing on both programmatic and detailed engineering issues. This paper describes one such simulation activity, using the ithinkml computer simulation software. This effort, The ithink” simulation includes a representation of the complete JWRS cleanup system. from retrieval of waste through intermediate processing and final vitrification of waste for disposal. addressed to date by the simulation effort include the need for new underground storage tanks to support TWRS activities, and the estimated design capacities for various processing facilities that are required to support legally mandated program commitment dates. This paper discusses how the simulation was used to investigate these questions. Major issues ithinkm is a registered trademark of High Performance Systems. Inc. of Hanover, New Hampshire. INTRODUCTION The Tank Waste Remediation System (TWRS) is responsible for retrieving radioactive and hazardous waste from 177 underground storage tanks, and processing and converting this waste lo high-level radioactive waste (HLW) and low-level radioactive waste (LLW) glass for safe long-term storage. This clean up system must satisfy commitments among the US. Department of Energy, the US. Environmental Protection Agency (EPA), and the Washington State Department of Ecology (Ecology) as documented in the /fan ford Federal Facility Agreement and Consent Order (Tri-Party Agreement) (Ecology et al. 1996). The dynamic simulation includes retrieval of waste from tanks, sodium molarity and dilution adjustments, chemical pretreatment (or separations). evaporative concentration, in-process storage, and vitrification (conversion to glass). The model investigates proper facility sizing, as well as timing and sequencing of operational activities for multiple scenarios. Predetermined waste retrieval sequences from 149 single-shell tanks (SST), including special programs such as interim stabilization liquid pumping sequences (required for near-term removal of liquids from SSTs known or suspected lo be leaking) are followed. Waste is received from the SSTs into 28 double-shell tanks (DST) for later retrieval for processing on an established schedule. The 28 DSTs are used for all short-term storage and process support needs. SSTs are used only for long-term storage. Major constraints include various Tri-Party Agreement commitment dates for retrieval and processing, limited in-process storage space from the 28 DSTs, and resource commitments lo the waste treatment privatization program.