RSICC CODE PACKAGE PSR-614

**1. NAME AND TITLE**

COBRA-SFS CYCLE 4A: Code System for Thermal Hydraulic Analysis of Spent Fuel Casks.

**2. CONTRIBUTORS**

Pacific Northwest Laboratory, Richland, Washington, USA.

**3. CODING LANGUAGE AND
COMPUTER**

Fortran; Linux, MacOS and Windows. (P00614MNYCP01).

**4. NATURE OF PROBLEM
SOLVED**

COBRA-SFS (Spent Fuel Storage), a code for thermal-hydraulic analysis of multi-assembly spent fuel storage and transportation systems. COBRA-SFS is a computer program that performs thermal-hydraulic analyses of multi-assembly spent-fuel storage and transportation systems. It uses a lumped-parameter, finite-difference approach to predict flow and temperature distributions in spent fuel storage systems and fuel assemblies, under forced and natural convection heat transfer conditions, in both steady-state and transients. Derived from the COBRA family of codes, which have been extensively evaluated against in-pile and out-of-pile data, COBRA-SFS retains all the important features of the COBRA codes for single-phase analysis and extends the range of application to problems with two-dimensional radiative and three-dimensional conductive heat transfer. With these added capabilities, COBRA-SFS has been used to analyze various single- and multi-assembly spent fuel storage systems containing unconsolidated and consolidated fuel, with a variety of fill media.

**5. METHOD OF SOLUTION**

The finite difference equations for mass continuity, momentum, and energy for the fluid are solved using the RECIRC solution method, adapted from the COBRA-WC code. In this method, the set of equations is solved iteratively to obtain the flow and pressure fields. The primary advantage of the RECIRC method is that it is applicable to reverse and recirculating flows, such as those occurring in storage systems where the geometry allows natural circulation flow paths. RECIRC uses a Newton-Raphson technique similar to the one developed by Hirt to solve the conservation equations, but it has been made implicit in time, as was done in the SABRE code.

The RECIRC flow field solution is divided into two parts: a tentative flow solution and a pressure solution. The tentative flow solution is achieved by iteratively sweeping the subchannel array from inlet to exit. In each sweep, tentative axial flows and crossflows are computed for the channels by evaluating the two linearized momentum equations with current values for pressure and other independent variables. After all tentative flows and crossflows have been computed at all axial levels, the flows and pressures are adjusted to satisfy continuity by a Newton-Raphson method.

**6. RESTRICTIONS OR
LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

CPU time requirements are very problem-dependent.

**8. COMPUTER HARDWARE
REQUIREMENTS**

Linux, MacOS and Windows systems.

**9. COMPUTER SOFTWARE
REQUIREMENTS**

No special requirements. Source should compile on Linux, MacOS and Windows systems with a functioning FORTRAN compiler. No executables are included.

**10. REFERENCES**

**10.a included in distribution files and in P613.pdf:**

Michener, T.E.; Rector, D.R.; Cuta, J.M; Adkins, Jr. H.E. COBRA-SFS: A THERMAL-HYDRAULIC ANALYSIS CODE FOR SPENT FUEL STORAGE AND TRANSPORTATION CASKS Cycle 4a, PNNL-24841 PNNL (October 2017).

**11. CONTENTS OF CODE
PACKAGE**

The package is transmitted on one CD with the reference cited above, source and sample problems. No Executables are included.

**12. DATE OF ABSTRACT**

November 2017

** KEYWORDS: ** HEAT TRANSFER; THERMAL HYDRAULICS; WASTE MANAGEMENT