**1. NAME AND TITLE**

JN-METD: Neutron Transport Code System with Isotropic Scattering, Bare Slabs and
Homogeneous Slabs (JN Method 1), Multilayer Slabs (JN Method 2).

**2. CONTRIBUTOR**

Nuclear Studies Division, CCR EURATOM, Ispra (Varese), Italy, through the OECD NEA
Data Bank, Gif-sur-Yvette, France.

**3. CODING LANGUAGE AND COMPUTER**

FORTRAN IV; IBM 360/370, IBM 360/65/91.

**4. NATURE OF PROBLEM SOLVED**

JN-METD solves stationary neutron transport problems in bare spherical reactors to obtain the
asymptotic time constant, the effective multiplication factor or the critical radius, and the flux
distribution as a function of space and energy. It also solves stationary problems in homogeneous
slabs to obtain the space, angle, and energy-dependent flux due to a plane isotropic, point isotropic,
or monodirectional boundary source. The first and second time moments are calculated for the
time-dependent flux in the slab with a point isotropic or monodirectional delta function source on
one boundary. JN-METD solves time-dependent problems in a non-multiplying bare sphere
without up-scattering of neutrons to evaluate the space, energy, and time-dependent flux resulting
from the incidence of an external source at the center; and solves time-dependent problems in a
non-multiplying homogeneous slab without upscattering of neutrons to evaluate the space, angle,
energy, and time-dependent flux in the slab without upscattering of neutrons to evaluate the space,
angle, energy, and time-dependent flux in the slab with a point isotropic or monodirectional source
on one boundary.

**5. METHOD OF SOLUTION**

The JN method, an analytical approach to neutron transport in a finite system is used within the
context of the multigroup and (up to) J7 approximation by assuming that the scattering of neutrons
is spherically symmetric in the laboratory system. This method uses the expansion into spherical
Bessel functions of the Laplace-Fourier transformed emission density of neutrons and the kernel of
the integral equation (resulting from the Laplace and Fourier transformation of an integral transport
equation with respect to time and space, respectively).

**6. RESTRICTIONS OR LIMITATIONS**

The present size of the floating common for all subscript variables is set to be 72,000 bytes.
The core storage requirement is less than 305 K bytes in the FORTRAN IV, version G on the IBM
360/65.

**7. TYPICAL RUNNING TIME**

Typical running time on the IBM 360/65 is nearly 4 minutes to obtain the time-dependent
lowest group angular and total flux in a slab with a delta function source on one boundary (in a 7-group J7 approximation with 2 space, 3 angle, and 56 time points), including the time required for
obtaining the stationary flux as well as the time-dependent flux due to a Gaussian pulse source.
The calculation of the stationary angular, total and leakage flux in a slab takes 1 to 2 minutes in a
7-group J7 approximation with 11 space and angle points.

**8. COMPUTER HARDWARE REQUIREMENTS**

JN-METD was designed for the IBM 370 computer. Test runs were made on the IBM 360/91.

**9. COMPUTER SOFTWARE REQUIREMENTS**

A FORTRAN IV compiler is required.

**10. REFERENCES**

T. Asaoka, "JN-METD1, A FORTRAN-IV Programme for Solving Neutron Transport
Problems with Isotropic Scattering in Bare Spheres and Homogeneous Slabs by the J_{N} Method,"
EUR 4601e (1971).

T. Asaoka and E. Caglioti Bonanni, "JN-METD2A FORTRAN-IV Programme for Solving
Neutron Transport Problems with Isotropic Scattering in Multilayer Slabs by the J_{N} Method," EUR
4839e (1972).

**11. CONTENTS OF CODE PACKAGE**

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

**12. DATE OF ABSTRACT**

December 1972; updated May 1975.

**KEYWORDS: ** NEUTRON; JN METHOD; SLAB; ONE-DIMENSION