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

2007 International RERTR Meeting

Abstracts and Available Papers Presented at the Meeting

MNSR Transient Analyses and Thermal Hydraulic Safety Margins for HEU and LEU Cores Using the RELAP5-3D Code

F.E. Dunn, J. Thomas, J. Liaw and J.E. Matos
RERTR Program
Argonne National Laboratory Argonne, IL 60439 USA


For safety analyses to support conversion of MNSR reactors from HEU fuel to LEU fuel, a RELAP5-3D model was set up to simulate the entire MNSR system. This model includes the core, the beryllium reflectors, the water in the tank and the water in the surrounding pool. The MCNP code was used to obtain the power distributions in the core and to obtain reactivity feedback coefficients for the transient analyses. The RELAP5-3D model was validated by comparing measured and calculated data for the NIRR-1 reactor in Nigeria. Comparisons include normal operation at constant power and a 3.77 mk rod withdrawal transient. Excellent agreement was obtained for core coolant inlet and outlet temperatures for operation at constant power, and for power level, coolant inlet temperature, and coolant outlet temperature for the rod withdrawal transient. In addition to the negative reactivity feedbacks from increasing core moderator and fuel temperatures, it was necessary to calculate and include positive reactivity feedback from temperature changes in the radial beryllium reflector and changes in the temperature and density of the water in the tank above the core and at the side of the core. The validated RELAP5-3D model was then used to analyze 3.77 mk rod withdrawal transients for LEU cores with two UO2 fuel pin designs. The impact of cracking of oxide LEU fuel is discussed. In addition, steady-state power operation at elevated power levels was evaluated to determine steady-state safety margins for onset of nucleate boiling and for onset of significant voiding.


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Dr. Jordi Roglans-Ribas
Technical Director, RERTR Department
Nuclear Engineering Division 362
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439
Fax:  +1 630-252-5161

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 16:02 +0200