As requested by Solid Waste Management (SWM), this report documents the Savannah River National Laboratory's (SRNL's) evaluation of updated Naval Reactor waste container and inventory projections and proposes a Naval Reactor Component Disposal Area (NRCDA) groundwater (GW) pathway modeling approach for the next E-Area Low-Level Waste Facility (LLWF) Performance Assessment (PA).Two areas within the E-Area LLWF are used as disposal sites for reactor components from the U.S. Navy. Currently, components arrive by rail and are moved by crane to the 643-26E at-grade gravel disposal pad. Prior to operational closure, reactor components were stored and ultimately disposed in-place on the 643-7E NRCDA (Wilhite and Flach 2004). Naval Reactor (NR) waste is comprised of highly radioactive components consisting of activated corrosion-resistant metal alloy contained within welded thick steel casks, and auxiliary equipment primarily contaminated with Activated Corrosion Products (sometimes referred to as "crud" by the U.S. Navy) at low levels and contained within thinner-walled bolted containers. The 643-7E disposal pad, which contains 41 casks and has an interim soil cover, is closed to future receipts. The latest NR waste projections for the 643-26E disposal pad are substantially different from the original estimates due to a change in reactor maintenance. The original estimate was for 50 heavily shielded, welded casks and 50 thinner-walled bolted containers (primarily shield blocks). Currently, NR Programs project 33 heavily shielded, welded casks, of which 31 are already in-place on the 643-26E pad, and 381 thinnerwalled bolted containers.In addition to new waste form projections, there have been changes in facility layout and closure plans as well as PA modeling improvements. This report documents these changes as well as key NRCDA recommendations from the 2015 PA Strategic Plan (Butcher 2016).
Key findings and recommendations are summarized inTable 0-1 below. SRNL-STI-2018-00633 Revision 0 vii Table 0-1. Comparison of Proposed Modeling Approach with 2008 E-Area LLWF PA. Model Feature-Aspect New Approach 2008 PA Approach Justification Number of NR Containers on 643-26E Open ended 100 cask limit Requested by SWM Type of Analysis Limits analysis -model unit curie of each rad for comparison with Performance Objectives Preliminary closure analysismodeled dose impact of projected inventory supplied by NR -scaled results for limits Requested by SWM 643-7E Perform closure analysis on final inventory from 41 containers Applied results of 643-26E model to 643-7E performance Changes in flow paths due to new aquifer model Limits Separate limits -ACP and activated metal, bolted and welded casks Single set of limits -combined all forms of inventory into a representative Knolls Atomic Power Laboratory core barrel/thermal shield cask Revision viii Revision 0 10 Table 4-2. 643-26E Projected Inventories by Waste Type Activated Metal (FY40) ACP (FY40) ISOTOPE Activity (Ci) ISOTOPE Activity (Ci)