1. NAME AND TITLE

BWR-LTAS: Code System for Boiling Water Reactor Long-Term Accident Simulation.

2. CONTRIBUTOR

Oak Ridge National Laboratory, Oak Ridge, Tennessee through Energy Science and Technology Software Center, Oak Ridge, Tennessee.

3. CODING LANGUAGE AND COMPUTER

Fortran 77; IBM 3033 (C00485/I3033/01).

4. NATURE OF PROBLEM SOLVED

BWR-LTAS was developed by the Severe Accident Sequence Analysis program at ORNL to perform studies of specific accident sequences at Brown's Ferry Unit One: station blackout, small break LOCA primary injection, loss of decay heat removal, loss of vessel water injection, and anticipated transient without scram. The primary use has been to estimate the effects of operator actions on the timing and course of events leading up to but not including severe fuel damage. The original version of the code was written in IBM CSMP-III (Continuous System Modeling Program) and called BWR-LCAP. The present version BWR-LTAS (BWR-Long Term Accident Simulation) is coded in Fortran. Modifications of the code since the publication of Ref. 1 is documented in Ref. 2. These were done to complete the ORNL studies of the Browns Ferry Loss of Control Air accident and to add an option to simulate Mark II primary containment.

5. METHOD OF SOLUTION

The code consists of differential and algebraic equations of mass and energy conservation and equations of state for the reactor vessel and containment. Some important parameters calculated are reactor vessel water levels, pressure, and injection flow, average fuel temperature, safety-relief valve flow, containment pressures and temperatures, and suppression pool water level and temperature. These variables may be calculated for arbitrary time periods following initiation of the accident sequence.

6. RESTRICTIONS OR LIMITATIONS

Limited to specific reactor types. BWT-LTAS is applicable only for Brown's Ferry.

7. TYPICAL RUNNING TIME

On the IBM 3033, the sample problem ran in 3 minutes.

8. COMPUTER HARDWARE REQUIREMENTS

BWR-LTAS is operable on the IBM 3033 computers.

9. COMPUTER SOFTWARE REQUIREMENTS

A VS Fortran (Level 1.3.1) compiler is required under MVS. This package was initially distributed by RSICC in September 1985. It was later transferred to the NESC then to the ESTSC then back to RSICC and released February 2002. RSICC tested it in 1985 but did not test or modify it later.

10. REFERENCES

R.M. Harrington and L.C. Fuller, "BWR-LTAS: A Boiling Water Reactor Long-Term Accident Simulation Code," ORNL/TM-9163, NUREG/CR-3764 (February 1985).

R.M. Harrington, "Modifications the BWR-LTAS Since December 1984," Memo (June 20, 1985).

11. CONTENTS OF CODE PACKAGE

Included are the referenced documents and a CD which contains the source code and sample problem input and output. Files are transferred in both self-extracting Windows and GNU compressed tar files for convenience. The code was tested only on mainframe computers and was not ported to PC or workstation.

12. DATE OF ABSTRACT

September 1985; revised November 1987, February 2002.

KEYWORDS: HEAT TRANSFER; REACTOR ACCIDENT