Numerical Analysis for Hydrogen Flame Acceleration during a Severe Accident in the APR1400 Containment Using a Multi-Dimensional Hydrogen Analysis System

Abstract

Korea Atomic Energy Research Institute (KAERI) established a multi-dimensional hydrogen analysis system to evaluate hydrogen release, distribution, and combustion in the containment of a Nuclear Power Plant (NPP), using MAAP, GASFLOW, and COM3D. In particular, KAERI developed an analysis methodology for a hydrogen flame acceleration, on the basis of the COM3D validation results against measured data of the hydrogen combustion tests in the ENACCEF and THAI facilities. The proposed analysis methodology accurately predicted the peak overpressure with an error range of approximately ±10%, using the Kawanabe model used for a turbulent flame speed in the COM3D. KAERI performed a hydrogen flame acceleration analysis using the multi-dimensional hydrogen analysis system for a severe accident initiated by a station blackout (SBO), under the assumption of 100% metal–water reaction in the Reactor Pressure Vessel (RPV), to evaluate an overpressure buildup in the containment of the Advanced Power Reactor 1400 MWe (APR1400). The magnitude of the overpressure buildup in the APR1400 containment might be used as a criterion to judge whether the containment integrity is maintained or not, when the hydrogen combustion occurs during a severe accident. The COM3D calculation results using the established analysis methodology showed that the calculated peak pressure in the containment was lower than the fracture pressure of the APR1400 containment. This calculation result might have resulted from a large air volume of the containment, a reduced hydrogen concentration owing to passive auto-catalytic recombiners installed in the containment during the hydrogen release from the RPV, and a lot of stem presence during the hydrogen combustion period in the containment. Therefore, we found that the current design of the APR1400 containment maintained its integrity when the flame acceleration occurred during the severe accident initiated by the SBO accident.

Numerical Analysis for Hydrogen Flame Acceleration during a Severe Accident Initiated by SBLOCA in the APR1400 Containment

“…The analysis methodology for the hydrogen flame acceleration using the COM3D version 4.10 was established such as Table 1 on the basis of the validation results against the test data of ENACCEF and THAI, as shown in Figure 2 [3]. This methodology accurately predicted the peak overpressure developed in the hydrogen flame acceleration with an error range of approximately ±10%.…”

“…As an effect of this accident, Korea Atomic Energy Research Institute (KAERI) evaluated an integrity of the containment of the Advanced Power Reactor 1400 MWe (APR1400) which is operating in the Republic of Korea. The evaluation was first performed by calculating an overpressure buildup owing to a hydrogen flame acceleration using a multi-dimensional hydrogen analysis system (MHAS) for a hypothetical severe accident initiated by the SBO accident [2,3]. The MHAS was developed by combining MAAP [4], GASFLOW [5], and COM3D [6] for simulating hydrogen release, distribution and combustion in the containment of a NPP during the severe accident.…”

“…The MHAS was developed by combining MAAP [4], GASFLOW [5], and COM3D [6] for simulating hydrogen release, distribution and combustion in the containment of a NPP during the severe accident. In particular, an analysis methodology for the COM3D code was established to accurately calculate the overpressure buildup on the basis of the validation results against several test data [3].…”

“…From the calculation results using the MHAS for the severe accident initiated by the SBO accident in the APR1400 containment, we judged that the integrity of the containment can be maintained because the calculated peak pressure of 510 kPa was lower than the containment fracture pressure of 1223 kPa [3,19]. In the evaluation, a 100% metal-water reaction in the reactor pressure vessel (RPV) was assumed in developing the severe accident scenario to induce a higher hydrogen concentration in the containment according to the safety review guidelines [20].…”

“…In the evaluation, a 100% metal-water reaction in the reactor pressure vessel (RPV) was assumed in developing the severe accident scenario to induce a higher hydrogen concentration in the containment according to the safety review guidelines [20]. This calculation result may have resulted from the design features of the APR1400 containment which are a large air free volumes of approximately 88,631 m 3 in the cylindrical dome geometry with diameter 45.72 m and height 69.69 m and an opening structure of the steam generator (SG) compartments where the hydrogen was discharged upward to the upper region by the safety depressurization system [3,19]. In addition, the thirty passive auto-catalytic recombiners (PARs) located at several positions in the containment, such as in Figure 1, effectively removed the released hydrogen as the severe accident proceeded [9,10,19].…”