Argonne National Laboratory
RERTR
Reduced Enrichment for Research and Test Reactors
Nuclear Engineering Division at Argonne
U.S. Department of Energy

RERTR Publications:
Analysis Methods for Thermal Research and Test Reactors

ANL/RERTR/TM-29

COMPUTING CONTROL ROD WORTHS
IN THERMAL RESEARCH REACTORS

1. INTRODUCTION

Research reactor control rods are composed of materials which strongly absorb thermal neutrons. In such materials the low-energy neutron flux varies rapidly as a function of position, which causes steep flux gradients near the absorber surface. Under these conditions Fick's law of diffusion is invalid, and so, without special methods, diffusion theory cannot be used to calculate control rod worths in thermal research reactors. Higher order methods, such as Monte Carlo techniques, are commonly used for this purpose. However, reasonably accurate control rod worths can be computed within the framework of diffusion theory by characterizing the absorber material by means of a group-dependent set of effective diffusion parameters (Deff and Sa-eff) or by specifying group-dependent neutron current-to-flux ratios (i.e. internal boundary conditions) on the absorber surface.

The purpose of this paper is to show how effective diffusion parameters and internal boundary conditions can be calculated. Using these techniques, control rod worths are computed and compared with results of detailed Monte Carlo calculations and with measured values.

2016 RERTR Meeting

The 2016 International RERTR Meeting (RERTR-2016) will take place in Belgium. Stay tuned for further details.

2015 RERTR Meeting

The 2015 International RERTR Meeting (RERTR-2015) took place in Seoul, Korea on Oct. 11-14, 2015.
For more information visit RERTR-2015.


ARGONNE NATIONAL LABORATORY, Nuclear Engineering Division, RERTR Department
9700 South Cass Ave., Argonne, IL 60439-4814
A U.S. Department of Energy laboratory managed by UChicago Argonne, LLC
 

Last modified on July 29, 2008 11:34 +0200