**1. NAME AND TITLE**

ALARM-B2: A Computer Code System for Analysis of a Large Break LOCA of a BWR.

**2. CONTRIBUTOR**

Japan Atomic Energy Research Institute (JAERI), Tokyo, Japan, through the OECD Nuclear
Energy Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV and Assembler; IBM 360/370, 3084.

**4. NATURE OF PROBLEM SOLVED**

ALARM-B2 is a modified version of ALARM-B1 and is a tool to analyze thermo-hydraulic
phenomena of a BWR during a postulated large break LOCA.

**5. METHOD OF SOLUTION**

ALARM-B1 does not calculate the heat transfer to the coolant during the transient but specifies it by input data. ALARM-B2 provides a one-dimensional heat conduction equation, a heat transfer correlation package, and a point reactor kinetics equation to analyze the heat transfer phenomenon in the core region during a LOCA. It also calculates thermal hydraulics in the pressure vessel and the primary coolant loop during the transient of a large break of the recirculation line.

The system of partial differential equations describing fluid conservation for stream-tube are
integrated over a number of control volumes. The resulting set of simultaneous equations that is based
on the assumptions of one-dimensional, homogeneous, thermal-equilibrium flow is linearized and
advanced for a small time increment by a simple explicit numerical technique. The one-dimensional
heat conduction equations describing temperature profiles within solid material are written in finite
difference forms which are linearized and solved by the Crank-Nicolson implicit method.

**6. RESTRICTIONS OR LIMITATIONS**

None noted.

**7. TYPICAL RUNNING TIME**

No study has been made by RSIC of typical running times for ALARM-B2.

**8. COMPUTER HARDWARE REQUIREMENTS**

ALARM-B2 is operable on the IBM 360/370 and the IBM 3084 computers.

**9. COMPUTER SOFTWARE REQUIREMENTS**

Fortran IV and Assembler compilers are required.

**10. REFERENCE**

F. Araya, "ALARM-B2: A Computer Program for Analysis of Large Break LOCA of BWR,"
JAERI-M 9665 (Revised September 1984).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced document and two (1.2MB) DOS diskettes which contain the source
code and sample problem input.

**12. DATE OF ABSTRACT**

June 1986.

**KEYWORDS: ** NUCLEAR SAFETY