LAPUR 6.0 Benchmark Against Data from the GENESIS Facility (NUREG/CR-7047)

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Publication Information

Manuscript Completed: March 2012
Date Published: March 2012

Prepared by:
Oak Ridge National Laboratory
P. O Box 2008
Oak Ridge, TN 37831-6010

Authors:
Martin Rohde
Jose March-Leuba

Dr. Tai L. Huang, NRC Project Manager
NRC Job Code J4430

Office of Nuclear Reactor Regulation
U.S. Nuclear Regulatory Commission
Washington DC 20555-0001

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Abstract

This report contains an evaluation of the LAPUR6 code against stability data measured in the GENESIS facility in Delft University of Technology, Netherlands. LAPUR6, a computer program in FORTRAN, is a mathematical description of the core of a boiling water reactor (BWR). Its two linked modules, LAPURX and LAPURW, respectively solve the steady-state governing equations for the coolant and fuel and the dynamic equations for the coolant, fuel, and neutron field in the frequency domain. The result of these calculations is a closed-loop transfer function that relates power oscillations to external perturbations in core reactivity. The stability parameters of merit, decay ratio (DR) and frequency of oscillation are estimated from the calculated transfer function. The LAPUR code has been validated in the past against a reasonable array of BWR test data.

The GENESIS facility is located in the Reactor Institute of Delft University of Technology, Netherlands. It is a boiling, natural circulation facility where flows, void fraction, and density wave instabilities can be studied over a wide range of conditions. The facility was initially constructed to simulate the conditions of the ESBWR design and was scaled so that, using Freon 134a at low power, the results could be extrapolated to water at full ESBWR power and pressure. Previous publications describe the GENESIS scaling laws in detail. The GENESIS facility may be run on purely thermal-hydraulic mode, by keeping the thermal power constant, or with a simulated reactor neutronic feedback. For the later purpose, the core pressure drop is measured and the core-average void fraction is estimated based on a one-channel model. The reactivity feedback and the fuel response are modeled on a control computer, and the thermal power is modulated according to the predicted reactor response. All data used for this benchmark includes the simulated reactivity feedback.

Twenty-seven GENESIS measurements at different operating conditions were simulated by LAPUR6. All geometry and measurements were scaled to water properties for use in LAPUR6. Ninety-two axial nodes were used to model GENEIS (17 for the core and 75 for the chimney). The results of these benchmark calculations show that LAPUR6 predicts an oscillation frequency of ∼0.7 Hz, which agrees with the measured frequency, and indicates that the chimney has little or no effect on the dynamic oscillations. The DRs calculated by LAPUR6 are in agreement with those measured in GENESIS.