NUREG-1364: Regulatory Analysis for the Resolution of Generic Safety Issue 106: Piping and the Use of Highly Combustible Gasses in Vital Areas

Highly combustible gases such as hydrogen, propane, and acetylene are used at all nuclear power plants. Hydrogen is of particular importance because it is stored in large quantities and is distributed and used continuously in buildings containing safety-related equipment. Large hydrogen releases at the hydrogen storage facilities or in these buildings could lead to fires or explosions that might result in loss of safety-related equipment. This report gives the regulatory analysis for the resolution of Generic Safety Issue 106, "Piping and the Use of Highly Combustible Gases in Vital Areas." Scopirig analyses showed that the risk associated with the storage and distribution of hydrogen for cooling electric generators at boiling-water reactors (BWRs), the off-gas system at BWRs, the waste gas system at pressurized-water reactors (PWRs), and station battery rooms and portable bottles of combustible gas used for maintenance at PWRs and BWRs is small. On the basis of generic evaluations, the NRC staff has concluded that several possible methods to reduce risk could provide cost-effective safety benefits at some plants. However, in view of the observed large differences in plant-specific characteristics affecting the risk associated with the use of hydrogen, and the marginal generic safety benefit that can be achieved in a cost-effective manner, it is recommended that this generic issue be resolved simply by making these results available in a generic letter. This information may help licensees in their plant evaluations recommended by Generic Letter 88-20, Supplement 4, "Individual Plant Examination of External Events for Severe Accident Vulnerabilities,"