**RSIC CODE PACKAGE CCC-492**

**1. NAME AND TITLE**

MULTI-KENO2: A Monte Carlo Code System for Criticality Safety Analysis.

**2. CONTRIBUTOR**

Japan Atomic Energy Research Institute, Ibaraki-Ken, Japan.

**3. CODING LANGUAGE AND COMPUTER**

Fortran IV; FACOM-M380.

**4. NATURE OF PROBLEM SOLVED**

MULTI-KENO2 solves the Boltzman neutron transport equation by assuming the media to be
isotropic, ignoring the time dependence of the cross sections, and converting the equation to multigroup
form.

**5. METHOD OF SOLUTION**

Modifying the Monte Carlo code KENO-IV, the MULTI-KENO code was developed for criticality safety analysis. A function added KENO-IV to divide a system into many subsystems SUPER BOXes where the size of BOX TYPEs in each SUPER BOX can be selected independently. SUPER BOX TYPE is an extension of BOX TYPE. MULTI-KENO2, an improvement on MULTI-KENO, allows multibox intersections.

The scattering treatment used in MULTI-KENO2 assumes that the differential neutron scattering
cross section can be represented by a Pl Legendre polynomial. The weight of the neutron is reduced
by the absorption probability at each collision point of a neutron tracking history. When the neutron
weight has been reduced below a specified point for the region in which the collision occurs, Russian
roulette is played to determine if the neutron's history is to be terminated at that and if the neutron is
to survive with an increased weight. Splitting of high weight neutrons is allowed in order to minimize
the variance in Keff for a system with regions of widely varying average weight.

**6. RESTRICTIONS OR LIMITATIONS**

MULTI-KENO2 is flexibly dimensioned so that the allowed size of a problem is limited only by
the total data storage available.

**7. TYPICAL RUNNING TIME**

MULTI-KENO2 running times are highly problem dependent. Typical problems run between 2
and 50 minutes on the FACOM-M200, depending upon the number of histories requested, the
statistical weighting used, the presence or absence of reflectors, the complexity of the geometry, the
number of energy groups and the type of materials in the problem. An infinite cylinder of highly
enriched 235U-H2O was executed on a FACOM-M380 in 11.08 minutes; neutron histories were
30,000 and the number of energy groups were 137.

**8. COMPUTER HARDWARE REQUIREMENTS**

MULTI-KENO2 requires the use of a CALCOMP plotter. An output file for graphic processing,
called GDFILE, is determined for each computer system.

**9. COMPUTER SOFTWARE REQUIREMENTS**

MULTI-KENO2 was written in Fortran-IV (HE).

**10. REFERENCES**

**a. Included in documentation:**

Y. Naito, M. Yokota, and K. Nakano, "MULTI-KENO: A Monte Carlo Code for Criticality Safety Analysis," JAERI-M83-049 (March 1983).

Y. Komuro, "MULTI-KENO2: A Modified Version of MULTI-KENO," Informal Notes (July
1986).

**b. Background information:**

L. M. Peirie, N. F. Cross, "KENO IV: An Improved Monte Carlo Criticality Program," ORNL-4938 (November 1975).

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents (10.a) and one (1.2MB) DOS diskette which contains the
source codes and sample problem input and the library data.

**12. DATE OF ABSTRACT**

May 1986; update August 1986.

**KEYWORDS: ** MONTE CARLO; CRITICALITY CALCULATIONS; NEUTRON; REACTOR
PHYSICS; COMPLEX GEOMETRY; MULTIGROUP