WSRC-MS-2000-00432

Evaluating Compliance With DOE-STD-3009-94
Appendix A Requirements

K. R. O’Kula and J. M. East
Westinghouse Safety Management Solutions LLC
Aiken, SC 29804-5388

This document was prepared in conjunction with work accomplished under Contract No. DE-AC09-96SR18500 with the U.S. Department of Energy.

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Introduction

Appendix A, Evaluation Guideline, is a newly-published guidance document to DOE-STD-3009-94, Preparation Guide for U.S. Department of Energy Nonreactor Nuclear Facility Safety Reports (January 2000). In addition to specifying a numerical radiological criterion to be used in the safety-class (SC) System, Structure, and Component (SSC) selection process for existing Department of Energy (DOE) facilities, Appendix A also describes methods and assumptions for calculating doses. Included are standardized dispersion specifications for quantifying doses to the site boundary from postulated accidental releases from the affected facility. While calculations of this nature must be performed at numerous DOE sites and for many facility types, few computer models rigorously comply with the requirements of Appendix A. Moreover, site-specific characteristics must be evaluated that take into account directional distance to the boundary, height of and the duration of the release.

The analysis highlighted here focuses on the application of MACCS Version 1.5.11.1 for meeting the intent of Appendix A for Savannah River Site (SRS) facilities. The dispersion and subsequent consequences are those due to several evaluation basis accident (EBA) source terms described in the authorization basis documentation. A primary goal is to demonstrate that a direction-independent consequence analysis numerically bounds the intent of Appendix A.

Appendix A and the Savannah River Site

Appendix A to DOE-STD-3009-94 prescribes a standardized approach for quantifying the 95th percentile of dose distribution accounting for variations in distance to the maximally exposed offsite individual (MOI) as a function of distance. The dose calculation references Regulatory Guide 1.145 of the Nuclear Regulatory Commission (NRC) for determination of the five percent overall site relative concentration (c/Q) value at the exclusion area boundary (EAB). A straightline Gaussian model is to be applied with one-hour averaged c/Q values for the entire course of plume duration for a period not to exceed eight hours. Other aspects of the 95th percentile calculation are covered, including

SRS is a 310-square mile DOE Complex reservation containing nuclear and chemical processing, stabilization, and storage facilities located in western South Carolina, bordered by the Savannah River. SRS is heavily forested outside of major facility areas with minimal terrain variation. Since the majority of active facilities are clustered near the Site center, the evaluation described here considers three prototypic source terms assuming release the central Site region and SRS-characteristic meteorology.

MACCS-Based Methodology

The principal intent of this study is to demonstrate that the current MACCS-based, direction-independent 95th percentile protocol is bounding relative to the intent of the Appendix A specification. The MACCS protocol is based on Version 1.5.11.1 because of Software Quality Assurance concerns with later releases of the code. In this approach, MACCS is used in a Latin Hypercube Sampling (LHS) mode to sample hourly, SRS-specific meteorological records from a five-year quality-assured database. The meteorological data file and a spatial grid, configured for sufficient resolution and containing evaluation points at specific distances of interest, are evaluated as inputs. The calculated dose is the 95th percentile, direction-independent dose at the closest boundary distance from the closest point in a group of facilities, to the site boundary. In contrast, the Appendix A protocol allows the 95th percentile dose to be dervied taking into account direction-specific distances from the facility to the site boundary and wind-rose effects.

Results for Three Prototypic Source Terms

The evaluation performed used a Joint Frequency Distribution (JFD) mode shell to execute MACCS to determine direction-independent (MACCS) and direction-dependent (Appendix A) doses, assuming center-of-site and ground release conditions. The three accident source terms are due to impacts to, and subsequent releases from: 1) tritium; 2) spent fuel; and 3) weapons grade plutonium material-at-risk. Table 1 compares the MACCS direction-independent protocol Total Effective Dose Equivalent (TEDE) obtained for each of these source terms with the direction-dependent Appendix A counterpart. The results indicate that the current protocol is conservative by four to eight percent.

Table 1. Individual Dose at Site Boundary for Three Source Term Types



Source Term Type

MACCS

Direction-Independent TEDE
(mSv)

Appendix A

Direction-Dependent
TEDE
(mSv)

[MACCS]/

[Appendix A]

Tritium

6.24E-07

5.98E-07

1.04

End-of-Life Fuel Element

6.37E-01

5.91E-01

1.08

Weapons Grade Plutonium

3.17E-01

2.95E-01

1.07

 

While the results indicate the current protocol for calculating consequences to support safety analysis documentation is conservative relative to the intent of Appendix A to DOE STD-3009-94, it is emphasized that this is not a generic finding. The interaction of specific distances to the boundary, terrain variations, source term type, and computer methodology must be evaluated on a case-by-case basis.

Acknowledgment

This extended summary was prepared by Westinghouse Safety Management Solutions LLC (WSMS) under contract with Westinghouse Savannah River Company (WSRC), subject to the warranty and other obligations of that contract and in furtherance of WSRC’s contract with the United States Department of Energy (DOE).

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