Analysis of Loss of Feedwater Heater Transients for Lungmen ABWR by TRACE/PARCS (NUREG/IA-0429)

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Publication Information

Manuscript Completed: March 2013
Date Published: September 2013

Prepared by:
Jong-Rong Wang, Tsung-Sheng Feng*, Hao-Tzu Lin, Chunkuan Shih*

Institute of Nuclear Energy Research, Atomic Energy Council, R.O.C. 1000, Wenhua Rd., Chiaan Village, Lungtan, Taoyuan, 325, TAIWAN

*Institute of Nuclear Engineering and Science, National Tsing Hua University, 101 Section 2, Kuang Fu Rd., Hsinchu, TAIWAN

K. Tien, NRC Project Manager

Division of Systems Analysis
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

Prepared as part of:
The Agreement on Research Participation and Technical Exchange
Under the Thermal-Hydraulic Code Applications and Maintenance Program (CAMP)

Published by:
Office of Nuclear Regulatory Research
U.S. Nuclear Regulatory Commission
Washington, DC 20555-0001

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Abstract

The TRACE/PARCS model of Lungmen ABWR was used to evaluate the loss of feedwater heater (LOFH) transient of the Lungmen startup tests. The Loss of Feedwater heater transient is an anticipated operational occurrence (AOO) event. Identifications of the responses of the Lungmen models and verification of the plant vendor's analysis results are crucial in the plant licensing analysis. PARCS, a three-dimensional neutronics simulator, is capable of performing detail transient three-dimensional core power distributions and can be coupled with TRACE for thermal hydraulic feedback analysis. The feedwater enthalpy entering the RPV in this event is modeled as a 30 seconds time constant decay curve. When feedwater temperature drops approximately 37°C, the feedwater control system (FWCS) triggers reactor internal pump (RIP) runback and selected control rod run in (SCRRI) immediately. The colder feedwater temperature collapses the voids, which leads to the void reactivity increase and decreases RPV water level. SCRRI can reduce the core reactivity and core temperature which then increase the Doppler reactivity. The water level would fluctuate between L3 and L8, having enough safety margins to avoid either low or high water level scram setpoints. On the other hand, we have also simulated another case without RIP runback and SCRRI. The sensitivity studies of this transient include different time constants, SCRRI delay times, RIP runback rates and RIP runback delay times. Furthermore, the study of 18 CHANs model and 206 CHANs model performance with TRACE/PARCS has been evaluated. The SNAP animation model can show three dimensional visualized results of different core parameters.