**RSICC CODE PACKAGE PSR-198**

**1. NAME AND TITLE**

SPIRT-NRC: Computerized Mathematical Models of Spray Washout of Airborne Contaminants (Radioactivity) in Containment Vessels.

**2. CONTRIBUTORS**

United States Nuclear Regulatory Commission, Washington, DC and Benton City Technology, Benton City, Washington, through the Energy Science and Technology Software Center in Oak Ridge, Tennessee.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV; IBM303 (P00198I303301).

**4. NATURE OF PROBLEM SOLVED**

SPIRT predicts the washout of airborne contaminants in containment vessels under postulated loss-of-coolant accident (LOCA) conditions. SPIRT calculates iodine removal constants (lambdas) for post-LOCA containment spray systems. It evaluates the effect of the spectrum of drop sizes emitted by the spray nozzles, the effect of drop coalescence, and the precise solution of the time-dependent diffusion equation. STEAM-67 routines are included for calculating the properties of steam and water according to the 1967 ASME Steam Tables.

**5. METHOD OF SOLUTION**

The spectrum of drop sizes emitted from the spray nozzles is represented as a two-parameter log-normal distribution that is defined via input parameters. In SPIRT, this distribution is represented by a finite number of discrete drop-size groups. All calculations involving drop-size are then repeated for each group. The coalescence calculations are based on the assumption that each drop collision results in a coalescence. The number of drop collisions is derived from geometrical considerations based on an assumed maximum entropy spatial distribution of all drop sizes. The time-dependent diffusion equation is solved for each of the drop-size groups in the distribution. The first twenty terms of Dankwerts infinite series solution are used. In addition to these models several auxiliary routines are used to obtain the thermodynamic and diffusion characteristics of the constituents in the post-accident containment, i.e., steam, air, water, and iodine. SPIRT uses explicit functions throughout with the single exception of a numerical bisection routine incorporated to determine the roots of a transcendental function for the solution of the diffusion equation.

**6. RESTRICTIONS OR LIMITATIONS**

Maximum of 100 groups of drop sizes. The maximum drop diameter is set at 0.33 cm, chosen to represent approximately three standard deviations of a log normal distribution with a mean drop diameter of 0.1 cm and standard deviation of 1.5.

**7. TYPICAL RUNNING TIME**

NESC executed the sample problem in 2.5 CPU minutes on an IBM4331.

**8. COMPUTER HARDWARE REQUIREMENTS**

SPIRT-NRC requires 485 Kbytes of memory on an IBM4331. It also ran on an IBM 3033.

**9. COMPUTER SOFTWARE REQUIREMENTS**

SPIRT-NRC was compiled with a Fortran IV compiler under VM/CMS on an IBM 4331 at NESC in January 1988. It has also run on an IBM 3033 under MVS. It was not tested or modified when it was transferred through the ESTSC to RSICC and released in May 2003.

**10. REFERENCES**

**a) included in documentation**:

A.K. Postma, R.R. Sherry, and P.S. Tam, "Technological Bases for Models of Spray Washout of Airborne Contaminants in Containment Vessels", NUREG/CR-0009 (October 1978).

** b) background references**:

M.P. Burgess, G.L. Fuller, and A.H. Kaiser, "Thermodynamic Properties of Steam and Water Adapted for the IBM 360/195 Computer," DPSPU 76-11-3 (September 1976).

C.A. Meyer, R.B. McClintock, G.J. Silvestri, and R.C. Spencer, Jr., "Thermodynamic and Transport Properties of Steam, Comprising Tables and Charts for Steam and Water," New York (1967).

R.B. McClintock and G.J. Silvestri, "Some Improved Steam Property Calculation Procedures," Transactions of the ASME, Vol. 92, pp. 123-134 (April 1970).

R.B. McClintock and G.J. Silvestri, "Formulations and Iterative Procedures for the Calculation of Properties of Steam," ASME Publication (H- 17) (1968).

P.V. Dankwerts, "Absorption by Simultaneous Diffusion and Chemical Reaction into Particles of Various Shapes and into Falling Drops," Transactions of the Faraday Society, Vol. 47, pp. 1014-1023 (1951).

**11. CONTENTS OF CODE PACKAGE**

The package is transmitted on a CD which contains the referenced document in 10.a in an electronic PDF file plus the source files and sample problem written in a self-extracting, compressed Windows file.

**12. DATE OF ABSTRACT**

May 2003.

** KEYWORDS:** FISSION PRODUCTS; NUCLEAR SAFETY; RADIATION SOURCE
GENERATOR