**1. NAME AND TITLE OF CODE**

TRISTAN: Multigroup Three-Dimensional Direct Integration Method Radiation Transport
Analysis Code System.

**AUXILIARY DATA LIBRARIES**

NDX42: 42-group neutron cross section set (group structure same as DLC-92/GICX40).

NDX50: 50-group neutron cross section set (0.1 lethargy intervals).

**2. CONTRIBUTOR**

Department of Nuclear Engineering, University of Tokyo, Japan.

**3. CODING LANGUAGE AND COMPUTER**

Fortran 77; HITAC M-280.

**4. NATURE OF PROBLEM SOLVED**

TRISTAN solves the three-dimensional, fixed-source, Boltzmann transport equation for neutrons
or gamma rays in rectangular geometry. The code can solve an adjoint problem as well as a usual
transport problem. TRISTAN is a suitable tool to analyze radiation shielding problems such as
streaming and deep penetration problems.

**5. METHOD OF SOLUTION**

The solution technique is the method of direct integration. It is a method of characteristics based on analytical integration along the radiation trajectories in several directions. This method, originated by K. Takeuchi, is suitable for radiation shielding problems because of its exactness in the treatment of the streaming term of the transport equation.

TRISTAN was developed to solve the Boltzmann transport equation in the group theory in (x,y,z)
coordinates. A numerical integration of double-differential cross sections is applied to represent
precisely the anisotropic scattering instead of using the Legendre polynomial expansion. TRISTAN
includes several techniques such as a separation of the flux into the scattered and unscattered
components and a conservation of radiation flux restored by a balance equation. The principal feature
that enhances the applicability of TRISTAN is the utilization of a stratification of angular mesh and an
adjoint solution to reduce the required computational time.

**6. RESTRICTIONS OR LIMITATIONS**

TRISTAN cannot be used for criticality calculations. It does not utilize variable (flexible) dimensioning to facilitate efficient core data storage allocation yet. Each user must reset each array size according to the spatial and angular mesh sizes he wants to use by changing parameter statements in TRISTAN.

TRISTAN underestimates the low energy (below 1 MeV) neutron distribution in the material such
as the iron shield. At low energies scattering within the group dominates.

**7. TYPICAL RUNNING TIME**

The 252 spatial mesh, 168 angular mesh,5 neutron group, sample problem, included in the code
package, required about 6 minutes on the HITAC M-280. Several hours of CPU time will be required
for a practical shielding analysis, although CPU time required depends on the problem size and the
numerical option.

**8. COMPUTER HARDWARE REQUIREMENTS**

HITACI M-200H, M-280 (IBM-like).

**9. COMPUTER SOFTWARE REQUIREMENTS**

A system subroutine CLOCK is called to sample CPU time. The local system equivalent will be
needed.

**10. REFERENCES**

Y. Oka, Alert (April 23, 1991).

T. Ida, Y. Oka, S. Kondo, and Y. Togo, "TRISTAN: A Three-Dimensional Radiation Transport
Calculation Code by the Direct Integration Method," UTNL-R 204 (March 1987). [Includes the journal
article by T. Ida, Y. Oka, S. Kondo, and Y. Togo, "Development of Radiation Transport Code in
Three-Dimensional (x,y,z) Geometry for Shielding Analyses by Direct Integration Method," *J. Nucl.
Sci. Technol.* 24, 181-193 (1987)].

**11. CONTENTS OF CODE PACKAGE**

Included are the referenced documents and one (1.2MB) DOS diskette which contains the source
code, sample input and data library, plus output from the sample problem.

**12. DATE OF ABSTRACT**

October 1987, revised May 1991.

**KEYWORDS:** COMPLEX GEOMETRY; INTEGRAL BOLTZMANN EQUATION;
MULTIGROUP; STREAMING