Session: MF-12-01 Leak Before Break

Paper Number: 106122

106122 - Regulatory Review Experience on the Leak-Before-Break Application of Apr1400 Reactors in Korea 

  In general, the concept of leak-before-break (LBB) is to prevent severe accidents such as a double-ended guillotine break by recognizing reactor coolant leaking at the through-wall crack of pressure boundary using a leak detection system and taking appropriate measures like reactor shutdown, etc. In order to apply the LBB concept to nuclear piping systems, it is necessary to prove experimentally or analytically that the probability of pipe rupture is extremely low. There is no necessity to install physical devices that minimize the effect of a pipe break, such as a pipe whip restraint, in the piping systems if the LBB concept is applied. It gives some flexibility to designing the installation layout of major components and relevant piping systems.

  The suitability for the application of the LBB concept is reviewed based on Article 15 (Environmental Effects Design Bases, etc.) of the regulations of the Nuclear Safety and Security Commission (Commission No. 30, 2021) and the standard review guidance 3.6.3 (Leak-Before-Break Evaluation Procedures) of the Korea Institute of Nuclear Safety. In the case of the OPR1000 reactor, the LBB concept was applied to the nuclear steam supply system, pressurizer surging line, and safety injection/shutdown cooling system. Unlike the OPR1000 reactor, a new direct vessel injection (DVI) system as a part of the emergency core cooling system is introduced in the design of the APR1400 reactor and provides a flow path from the in-containment refueling water storage tank to the reactor vessel.   

  The DVI pipe has a smaller size than other LBB-applied pipes in the APR1400 reactor so that a detectable leakage crack is relatively large and the local stiffness of the pipe is low, which is unfavorable to the stability evaluation of LBB. Therefore, when LBB is applied to a small pipe such as a DVI pipe, it is necessary to consider a high leak detection capability and an appropriate pipe material. In addition, although the probability of a pipe break is very low due to the small applied load such as low pressure, mid- to long-term regulatory studies are needed to improve the LBB acceptance criteria for small-sized pipes that require an unrealistically large detectable leakage crack for detecting a coolant leak. In this paper, the regulatory review experience on the LBB application of APR1400 reactors in Korea was discussed.

Presenting Author: Sangmin Lee Korea Institute of Nuclear Safety

Presenting Author Biography: Dr. Sangmin Lee is a principal researcher at the Korea Institute of Nuclear Safety. With over 20 years in component integrity evaluation aspects of nuclear facilities, Sangmin has experience in regulatory reviews and inspections as well as academic research. Sangmin served as the Working Group on Codes and Standards (WGCS) chair under the Committee of Nuclear Regulatory Activities (CNRA) of the OECD/NEA from 2018 to 2022. Sangmin earned a Ph.D. in mechanical engineering from Sungkyunkwan University in Korea.

Authors:

Sangmin Lee Korea Institute of Nuclear Safety
Yeji Kim Korea Institute of Nuclear Safety
Sunhye Kim Korea Institute of Nuclear Safety
Young-Hwan Choi Korea Institute of Nuclear Safety