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The human factor in licensing and operating the next generation of nuclear plants
As human factors specialists working at the intersection of human performance and nuclear operations, we are witnessing one of the nuclear sector’s most significant transitions in decades. The emergence of small modular reactors, microreactors, and other advanced designs is reshaping the industry’s landscape. Digital instrumentation and controls, passive safety systems, and increased automation are creating opportunities for greater safety margins and more flexible operation. These same features also fundamentally redefine what it means to “operate” a nuclear plant. Interactions among human roles, automation, and passive systems shape how people maintain awareness, exercise judgment, and intervene when necessary. These developments affect both operational realities and the regulatory foundations on which nuclear safety is built.
Hee-Jin Shim, Chang-Kyun Oh, Hyun-Su Kim, Myung-Hwan Boo, Jong-Jooh Kwon
Nuclear Technology | Volume 190 | Number 1 | April 2015 | Pages 88-96
Technical Paper | Materials for Nuclear Systems | doi.org/10.13182/NT13-150
Articles are hosted by Taylor and Francis Online.
Metal fatigue is a well-known phenomenon whereby material characteristics are deteriorated when even a small load is applied repeatedly. Therefore, an accurate fatigue evaluation is very important in terms of component integrity and reliability. In the design stage, the fatigue evaluation of nuclear class 1 components has to be performed in accordance with Sec. III of the ASME Boiler and Pressure Vessel Code. However, operating experience shows that the design transients are very conservative compared to the actual ones in terms of the heating/cooling rates and the number of transient occurrences. Considering that these two factors affect the thermal stress and thereafter the fatigue usage factor (FUF), the actual fatigue damage can differ from the design fatigue evaluation result. In order to evaluate and monitor the FUF exactly, therefore, various methods have been proposed and widely implemented. Among these, the cycle-based approach (CBA) utilizes the stresses for the design transients and reflects only the actual number of transient occurrences. For this reason, the CBA provides a conservative FUF, although it is very simple and easy to implement. Therefore, a simple and accurate fatigue monitoring method is still needed.
The purpose of this paper is to develop a new approach for effective fatigue damage monitoring. To do this, a thorough review is conducted for the design transients and actual transients for the Westinghouse-type pressurized water reactors in Korea. In addition, a wide range of finite element analyses are carried out varying the heating/cooling rates and the pattern of the transients. Based on this result, a new CBA is proposed incorporating the simple correction factors for both the heating/cooling rates and the transient patterns. A case study is also carried out for the reactor pressure vessel outlet nozzle to verify the validity and applicability of the proposed method. The result indicates that the proposed method can provide a realistic FUF, and more importantly, it is very easy to implement. From these, it is anticipated that the new approach can be widely used in practical fatigue monitoring of nuclear components and piping.
