Document: NRC Regulatory Guide
Document ID: 769c53ca-7692-4fdf-9301-9fd64e37aa8f
Document Type: regulatory_guide
Title: Evaluations of Explosions Postulated To Occur on Transportation Routes Near Nuclear Power Plants (Rev. 3)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2110/ML21105A439.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.91
CFR Part: 
CFR Title: 

Content:
energy (British thermal units (BTU) or kilojoules (kJ)) α = yield (i.e., the fraction of available combustion energy participating in blast wave generation) ΔHc = theoretical net heat of combustion (BTU/lbm or kJ/kg) mF = mass of flammable vapor released (lbm or kg) The corresponding TNT equivalent mass in lbm or kg, WTNT (see Ref. 8) is ்ܹே்= ா ଵଽ଴଴ ஻்௎/௟௕೘ or ா ସହ଴଴ ௞௃/௞௚ (4) Values for heat of combustion and yield are available in NUREG-1805 and Factory Mutual (FM) Global’s Property Loss Prevention Data Sheets 7–42, “Guidelines for Evaluating the Effects of Vapor Cloud Explosions Using a TNT Equivalency Method,” May 2008 (Ref. 9). For example, the FM Data Sheet 7–42 assigns explosion efficiency factors (i.e., yields) based on the class of material. A detailed analysis of possible accident scenarios for particular sites, including consideration of the actual amount of potentially explosive material, potential release, site topography, and prevailing meteorological conditions, should be used to justify a value for the yield. However, for establishing safe standoff distances independent of site conditions, the use of a conservative estimate for the yield is prudent. To estimate the mass of flammable vapor, several methods are available, including those described in FM Data Sheet 7–42 and the methodology in “Estimating the Flammable Mass of a Vapor Cloud” by J.L. Woodward, 1998 (Ref. 10). For releases of vapor clouds at offsite locations or pipelines, plume modeling based on site topography and meteorological conditions should be evaluated. The atmospheric transport of released vapor clouds should be calculated using a dispersion or diffusion model that permits temporal as well as spatial variations for plume modeling. Information can be found in Chapter 5 of NUREG/CR-6410, “Nuclear Fuel Cycle Facility Accident Analysis Handbook,” issued March 1998 (Ref. 11). Determining the maximum probable