HABIT 2.2 Description of Models and Methods (NUREG-2244)

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Publication Information

Manuscript Completed: January 2021
Date Published: May 2021

Prepared by:
J.J. Tomon
L.C. Sun
S.I. Haider1
T.O. Spicer2

1Office of Nuclear Reactor Regulation
U.S. Nuclear Regulatory
Commission Washington, D.C.

2University of Arkansas
Fayetteville, AR 72701

Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Availability Notice


To ensure the safe operation of commercial nuclear power plants, control room (CR) operators must be protected from dangers arising from possible exposure to hazardous chemicals that may be discharged as a result of equipment failure, operator errors, or events external to plant operation. General Design Criterion (GDC) 4, “Environmental and dynamic effects design bases,” of Appendix A, “General Design Criteria for Nuclear Power Plants,” to Title 10 of the Code of Federal Regulations Part 50, “Domestic licensing of production and utilization facilities,” requires, in part, that structures, systems, and components important to safety be designed to accommodate the effects of and to be compatible with the environmental conditions associated with normal operation, maintenance, testing, and postulated accidents. GDC 19, “Control room,” requires that a CR be provided from which actions can be taken to operate the nuclear power unit safely under normal conditions and to maintain it in a safe environment under accident conditions. Additionally, Regulatory Guide 1.78, “Evaluating the Habitability of a Nuclear Power Plant Control Room During a Postulated Hazardous Chemical Release,” provides guidance and endorses the use of the HABIT computer code for examining CR habitability following a postulated release of toxic chemicals. The original version of HABIT was a package of computer codes designed to be used for the evaluation of CR habitability in the event of an
accidental release of toxic chemicals and radioactive materials. Given information about the design of a nuclear power plant, a scenario for the release of toxic chemicals, and information about the air flows and protection systems of the CR, HABIT could be used to quick estimate the chemical exposure or radiological dose to CR personnel. This report describes current code updates and changes to the technical basis of HABIT. 

HABIT is based on the external transport (EXTRAN) computer code for estimating transient concentrations at a specific downwind location (i.e., CR air intake) for four release scenarios: liquid burst, liquid leak, gas burst, and gas leak. EXTRAN combines procedures for estimating the amount of airborne material, a Gaussian puff dispersion model, and building-wake diffusion algorithms. This report describes the latest version, HABIT 2.2, which is an update to HABIT 2.0. It works in Microsoft© (MS) 64-bit operating systems such as MS Windows 10. HABIT 2.2 has fully integrated both the DEGADIS and SLAB codes and incorporated the Britter-McQuaid Workbook criteria for automatic screening the importance of denser-than-air effects. Finally, unlike previous versions, HABIT 2.2 has removed all the radiological dose calculation computer applications.

Page Last Reviewed/Updated Wednesday, May 05, 2021