**RSICC CODE PACKAGE PSR-444**

**1. NAME AND TITLE**

FIRAC: Nuclear Facilities Fire Accident Model.

**2. CONTRIBUTORS**

Los Alamos National Laboratory, Los Alamos, New Mexico through the Energy Science and Technology Software Center, Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN; CRAY 1 (P00444CY00000).

**4. NATURE OF PROBLEM SOLVED**

FIRAC predicts fire-induced flows, thermal and material transport, and radioactive and nonradioactive source terms in a ventilation system. It is designed to predict the radioactive and nonradioactive source terms that lead to gas dynamic, material transport, and heat transfer transients. FIRAC's capabilities are directed toward nuclear fuel cycle facilities and the primary release pathway, the ventilation system. However, it is applicable to other facilities and can be used to model other airflow pathways within a structure. The basic material transport capability of FIRAC includes estimates of entrainment, convection, deposition, and filtration of material. The interrelated effects of filter plugging, heat transfer, and gas dynamics are also simulated. A ventilation system model includes elements such as filters, dampers, ducts, and blowers connected at nodal points to form networks. A zone-type compartment fire model is incorporated to simulate fire-induced transients within a facility.

**5. METHOD OF SOLUTION**

FIRAC solves one-dimensional, lumped-parameter, compressible flow equations by an implicit numerical scheme. The lumped-parameter method is the basic formulation that describes the gas dynamics system. No spatial distribution of parameters is considered in this approach, but an effect of spatial distribution can be approximated by noding. Network theory, using the lumped parameter method, includes a number of system elements, called branches, joined at certain points, called nodes. Ventilation system components that exhibit flow resistance and inertia, such as dampers, ducts, valves, and filters, and those that exhibit flow potential, such as blowers, are located within the branches of the system. The connection points of branches are nodes for components that have finite volumes, such as rooms, gloveboxes, and plenums, and for boundaries where the volume is practically infinite. All internal nodes, therefore, possess some finite volume where fluid mass and energy storage are accounted for. The conservation of mass equation is applied at each internal node. The steady-state flow rate in incompressible flow is determined by the pressure drop. The usual one-dimensional approximation is assumed to treat the quasi-steady compressible flow inside a constant area duct. An iterative implicit numerical scheme is used to solve for pressure and density corrections at each node until the system is balanced.

**6. RESTRICTIONS OR LIMITATIONS**

Maxima of, 100 nodes, 100 rooms, 100 control dampers, 100 branches, 40 blowers, 25 plot frames with 4 curves per plot, 20 special filter types, 20 radioactive source terms that can be tracked, and 15 blower characteristic functions.

**7. TYPICAL RUNNING TIME**

NESC executed the sample problem in approximately 30 CP minutes on a CDC CYBER170/875 and in approximately 3 CPU minutes on a Cray Y-MP.

**8. COMPUTER HARDWARE REQUIREMENTS**

Approximately 305,000 (octal) words are required to run the sample problem on a CDC CYBER170/875 and 515,000 (octal) words on a Cray Y-MP.

**9. COMPUTER SOFTWARE REQUIREMENTS**

CTSS (Cray1), UNICOS 5.0 (Cray Y-MP).

**10. REFERENCES**

B.D. Nichols and W.S. Gregory, "FIRAC User's Manual: A Computer Code to Simulate Fire Accidents in Nuclear Facilities," NUREG/CR-4561 (LA-10678-M) (April 1986).

L. Reed, "FIRAC, NESC No. 1092. CRA1B, FIRAC Tape Description and Implementation Information," National Energy Software Center Note 91-27 (December 14, 1990).

**11. CONTENTS OF CODE PACKAGE**

Included in the package are the referenced documentation and a DOS-formatted 3.5" diskette including source code and a sample problem. No executable is included with the package.

**12. DATE OF ABSTRACT**

September 1999.

** KEYWORDS:** FIRES; HEAT TRANSFER; REACTOR SAFETY