(224d) Review of Fire Safety Analyses Conducted at the Savannah River Site

Fire safety analyses are required for operation of the Department of Energy Savannah River Site facilities, as specified by the site safety basis documents. Analyses required to ensure that flammable mixtures of gases and vapors are not formed are reviewed. Also covered are evaluations of the consequences of postulated vapor deflagrations and detonations and of exposure of radioactive materials to postulated external fires.

Fire prevention measures follow guidelines from the National Fire Protection Association (NFPA). Evaluations of the lower flammability limits for flammable gases and vapors are reviewed, as are methods used to determine the concentration of flammable vapors from evaporation of liquids in open top containers and from spills.

Flammable gas deflagrations and detonations are evaluated to determine if they could breach the containers holding these gases. The maximum deflagration pressure is estimated using the NASA code CEA, which incorporates thermodynamic combustion models. This code also can estimate the pressure for a simple detonation. An in-house code, DPAC, can be used to estimate transient deflagration pressures in unvented and partially vented containers. Peak detonation pressures for normally reflected detonation waves can be estimated by applying a multiplier to the simple detonation pressure. Lastly, detonations require an open gas space with a minimum cell size; rules of thumb to estimate cell size requirements are reviewed.

The consequences of the exposure of radioactive materials to external fires are based on the airborne release fractions (ARFs) and respirable fractions (RFs) for particles released if a container ruptures due to pressurization from heating by the fire. The heating rate for a container exposed to an external fire is evaluated using heat transfer computations, where the container is heated by gas at a specified external temperature. ASTM specifies the temperature transient based on measurements for open pool hydrocarbon fires. A Department of Energy standard gives the ARF as a function of the release pressure and the RF as a function of particle size.