Session: 02-10: Physics and Transport Theory - II

Paper Number: 134116

134116 - Validation of Doppler Reactivity Feedback in Spert-Iii E-Core With the Best-Estimate Transient Code Trac Toshiba Version 

Abstract: 

    We have developed a best-estimate transient code TRAC Toshiba version, which is Toshiba’s advanced version of the TRAC code for BWR. This code is expected to simulate thermal hydraulic and neutron kinetics phenomena three-dimensionally with high accuracy for BWR transient events.

    For the validation of the TRAC code, reactivity accident tests in cold-startup of SPERT-III E-core were calculated and compared with experiment results. Two lattice code NEUPHYS and TGBLA were used for the calculation. NEUPHYS developed by Nuclear Fuel Industries, Ltd. is a neutron transport calculation code with Method of Characteristics. TGBLA is a current licensing code of Toshiba. To consider effect of Doppler broadened rejection correction, Doppler coefficient calculated by the lattice codes were multiplied by 1.094 for TRAC code, because the lattice code do not consider the effect.

    For the confirmation of properly simulation of initial core condition of the tests, static nuclear characteristics of the core were calculated. As a result, neutron multiplication factor, spatial peak-to average power density, prompt-neutron generation time / effective delayed neutron fraction, differential control rod worths and transient rod worths were compared with experiment results, and good agreements were confirmed. However, calculation results of transient rod worths were under estimation with several cents in low worth cases especially.

    For the calculation of the transient tests, initial positions of control rod and transient rod were set by experiment results. Specifically, axial positions of control rod “z” were calculated with the following equation.

z = 14.55in + [rho - (T - 70) * (-0.4 cent/deg-F)/100] / (1.55$/in)

where

14.55in:   the position at near critical state without transient of boron-SUS region insertion,

rho:         inserted reactivity by transient rod for a test,

T:            initial temperature of a test,

-0.4 cent/deg-F:  temperature coefficient and

1.55$/in:  differential control rod worth at near critical state without transient of boron-SUS region insertion.

    Initial positions of transient rod were determined by plot data of experiment data of transient rod worths.

    Peak power of the transient tests, whose calculation results of transient rod worth agree well with experiment value, almost agree within uncertainty of experiment data. However, for the tests whose calculation results of transient rod worth were under estimation with several cents compared to experiment value, peak powers were obviously under estimation compared to experiment value.

    In the transient tests, the sensitivity of a cent of transient rod worth to peak power is more than 10%. Therefore, small amount simulation error in transient rod worth propagates large peak power error. In this study, to eliminate the effect of simulation error in transient rod worth, correlation curve between simulated transient rod worth and simulated peak power were compared to experiment data plot. As a result, estimated C/E - 1 of peak power without simulation error in transient rod worth were -3% ±4% for NEUPHYS/TRAC and -1% ±4% for TGBLA/TRAC in high reactivity insertion case more than 1$ (±4% were evaluated from uncertainty of experiment). In the transient tests, temperature of UO₂ pellet behaves adiabatically by the time of power peak in high reactivity insertion case more than 1$. Therefore, temperatures of UO₂ pellet at the power peak are expected to contain small amount simulation error, it is expected that doppler reactivity simulation error are dominant simulation error in peak power simulation error. Therefore, aforementioned simulation error -3% ±4% for NEUPHYS/TRAC and -1% ±4% for TGBLA/TRAC are expected as doppler reactivity simulation error.

Presenting Author: Tohru Egawa TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION

Presenting Author Biography: Obtaining a master's degree from Department of Quantum Science and Energy Engineering, Graduate School of Engineering, Tohoku University in 2013. Joined Nuclear Fuel Industries, Ltd. in 2013. Seconded to TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION since 2019. Specialty field is reactor physics and accident analysis of BWR.

Authors:

Tohru Egawa TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION
Mikio TOKASHIKI TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION
Takamasa Miyaji TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION
Takanori Fukunaga TOSHIBA ENERGY SYSTEMS & SOLUTIONS CORPORATION