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APPENDIX D ACCIDENT ANALYSIS

This appendix presents, as required by NEPA, the estimated consequences of accidents that could occur at the LLNL Livermore site, LLNL Site 300, and SNL, Livermore. Figure D-1 illustrates the relationship of Appendix D to other EIS/EIR appendices, sections of the document, and DOE requirements.

The scenarios described here are those that define the bounding envelope of accidents—that is, any other reasonably foreseeable accident at the LLNL Livermore site, the LLNL Site 300, or SNL, Livermore would be expected to have smaller consequences. The analyses of accidents are conservative, being based on assumptions that deliberately maximize environmental consequences, with little or no credit taken for existing preventative and mitigating features in each building or operation analyzed or the safety procedures that are mandatory at LLNL and SNL, Livermore.

Three types of accidents are discussed: those with a potential for releases of radioactive material, those with a potential for release of toxic chemicals, and those involving high explosives. For accidents involving radioactive materials and toxic chemicals, the appendix describes how locations or operations were selected for analysis, the computer codes used to estimate consequences, the development of the scenario and assumptions about source terms, the selection of computer modeling and a description of the results, and predicted health effects. For accidents involving high explosives, the appendix discusses the use of high explosives at the sites, the potential accidents associated with these uses, the effects of potential accidents, and measures that can mitigate these accidents.

D.1 APPROACH TO THE ANALYSIS OF POTENTIAL ACCIDENTS

Accident scenarios have been developed to reflect the broad range of accidents that might occur at the LLNL Livermore site, LLNL Site 300, and SNL, Livermore. These scenarios include low-probability, high-consequence accidents and the more probable low-consequence accidents. Where appropriate, the scenarios are specific to particular buildings and operations and for specific transportation situations.

The following terms are used to define the scenarios:

• A reasonably foreseeable accident is an accident with "impacts which have catastrophic consequences, even if their probability of occurrence is low, provided that the analysis of the impacts is supported by credible scientific evidence, is not based on pure conjecture, and is within the rule of reason" (40 C.F.R. section 1502.22). "Credible" means having reasonable grounds for believability, and the "rule of reason" means that the analysis is based on scientifically sound judgment.
• An accident is bounding if no reasonably foreseeable accident with greater consequences can be identified. A bounding envelope is a set of individual bounding accidents covering the range of probabilities and possible consequences.
• An analysis is conservative if the net result of the assumptions entering into it maximizes the environmental consequences of the accident being analyzed.

A deterministic, nonprobabilistic approach was used to develop the accident scenarios, including those scenarios without a specific initiating cause. The wide range of postulated accidents characterizes the range of risks associated with the operation of the LLNL Livermore site, LLNL Site 300, and SNL, Livermore. To keep the analyses of these accidents within the rule of reason, the scenarios use conservative assumptions, such as stable meteorological conditions that reduce the downwind dilution of hazardous-material releases, or ignore the tendency of reactive chemicals to be depleted by reaction; and in addition, the analyses of these accidents do not violate physical principles or take credit for mitigating factors when the initiating circumstances would render those factors inoperable.

Bounding scenarios were developed for specific hazards (i.e., radioactive material, toxic chemicals, or high explosives for an operation in a building or during transportation). The postulated accident scenario for radioactive material, toxic chemicals, or high explosives, can be reasonably evaluated in terms of the effective dose equivalent, specific toxic effects of individual chemicals, or the radius of impact; and from this, the bounding scenario can be determined. In all cases, bounding scenarios are based on the most limiting consideration: radiation exposure, chemical concentration, or peak overpressure.

The radiological exposures are discussed in the individual scenario descriptions reported in section D.2.8, and the health effects from these exposures are presented in section D.2.9. The chemical exposures are discussed in the individual scenario descriptions reported in section D.3.3. The health effects associated with chemical releases are analyzed separately and presented in section D.3.2.4. The consequences of high explosive accidents are addressed in the individual scenario descriptions in section D.4.3.