Simulated Test of Reactor Shielding

REACTOR_SIMULATION is a FORTRAN90 program which simulates the shielding effect of a slab intended to absorb or reflect most of the radiation from a neutron source. This program is intended as a simple demonstration of Monte Carlo simulation as applied to the analysis of complicated probabilistic systems.

REACTOR_SIMULATION is an example program that was developed in the book "Numerical Methods and Software".

REACTOR_SIMULATION is a Monte Carlo simulation, using uniform random numbers, which investigates the effectiveness of a shield intended to absorb the neutrons emitted from a nuclear reactor.

The reactor is modeled as a point source, located at (0,0,0).

A particle emitted from the reactor has a random initial direction, and an energy selected from [Emin,Emax] with a 1/Sqrt(E) distribution.

The shield is modeled as a wall of thickness THICK, extending from 0 to THICK in the X direction, and extending forever in the Y and Z directions.

Based on the particle energy, a distance D is computed which measures how far the particle could travel through the shield before colliding.

Based on the particle direction, the position is updated by D units.

If the particle is now to the left of the shield, it is counted as being REFLECTED.

If the particle is to the right of the shield, it is counted as being ABSORBED.

If the particle is inside the shield, it has COLLIDED. A particle that collides is either absorbed (end of story) or SCATTERED with a new random direction and a new (lower) energy.

Every particle is followed from origin to its final fate, which is reflection, transmission, or absorption. At the end, a summary is printed, giving the number of particles with each fate, and the average energy of each group of particles.

Increasing NTOT, the number of particles used, will improve the expected reliability of the results.

Increasing THICK, the thickness of the shield, should result in more absorptions and reflections.


The computer code and data files described and made available on this web page are distributed under the GNU LGPL license.


REACTOR_SIMULATION is available in a C version and a C++ version and a FORTRAN77 version and a FORTRAN90 version and a MATLAB version.

Related Data and Programs:

BROWNIAN_MOTION_SIMULATION, a FORTRAN90 program which simulates Brownian motion in an M-dimensional region.

DUEL_SIMULATION, a FORTRAN90 program which simulates N repetitions of a duel between two players, each of whom has a known firing accuracy.

FAIR_DICE_SIMULATION, a FORTRAN90 program which simulates N tosses of 2 dice, making a histogram of the results.

HIGH_CARD_SIMULATION, a FORTRAN90 program which simulates a situation in which you see the cards in a deck one by one, and must select the one you think is the highest and stop; the program uses GNUPLOT for graphics.

ISING_2D_SIMULATION, a FORTRAN90 program which carries out a Monte Carlo simulation of an Ising model, a 2D array of positive and negative charges, each of which is likely to "flip" to be in agreement with neighbors.

ISING_3D_SIMULATION, a FORTRAN90 library which carries out a Monte Carlo simulation of a 3D Ising model.

MD1, a FORTRAN90 program which carries out a simple molecular dynamics simulation;

NMS, a FORTRAN90 library which accompanies the book "Numerical Methods and Software", from which the REACTOR_SIMULATION program was extracted.

POISSON_SIMULATION, a FORTRAN90 library which simulates a Poisson process in which events randomly occur with an average waiting time of Lambda.

THREE_BODY_SIMULATION, a FORTRAN90 program which simulates the behavior of three planets, constrained to lie in a plane, and moving under the influence of gravity, by Walter Gander and Jiri Hrebicek.

UNIFORM, a FORTRAN90 library which generates pseudorandom uniform numbers.


  1. David Kahaner, Cleve Moler, Steven Nash,
    Numerical Methods and Software,
    Prentice Hall, 1989,
    ISBN: 0-13-627258-4,
    LC: TA345.K34.

Source Code:

List of Routines:

You can go up one level to the FORTRAN90 source codes.

Last revised on 02 September 2012.