증기분사기의 형상 인자에 따른 증기 및 공기 방출특성 연구 = Study on Steam and Air Clearing Characteristics according to Shape Factors of Sparger

다국어 초록 (Multilingual Abstract)

Steam-water direct contact condensation (DCC) phenomena has been studied extensively because of its important in a variety of industrial operations such as underwater propulsion system, steam jet injector, direct contact feedwater heater, and nuclear reactor system. Especially, in a water cooled reactor, no matter what kind of design it is, it is almost inevitable that one will encounter the DCC during some transient or accident conditions.
APR1400 (Advanced Power Reactor of 1400 MW) adopts several safety features to enhance its safety and mitigate a severity of accident consequences. One of the key features of the APR1400 is in-containment refueling water Storage tank (IRWST) integrated with Safety Depressurization and Vent System (SDVS). The typical SDVS of APR1400 consists of the POSRVs followed by a length of piping and several spargers installed in the IRWST. In case of accidents, Pilot Operated Safety Relief Valves (POSRVs) in the SDVS open in order to prevent the reactor from over-pressurization. Actuation of the POSRVs results in a transient high energy and momentum flow of water, air and steam from a pressurizer into the IRWST through the spargers.
These consecutive discharge processes of water, air and steam are usually called water jet, air clearing and steam condensation, respectively. Such a transient imposes the dynamic loads both on the IRWST boundaries and the structures submerged in the IRWST. Especially, during the air clearing period, the maximum pressure loads are taken place by the oscillation of discharged air bubble cloud. The period of the steam condensation, however, is much longer compared with that of the water jet and the air clearing, which are continued within a few seconds. The steam condensation produces a high frequency and low amplitude oscillatory loading on the pool.
In order to properly design a sparger with high discharging efficiency and low dynamic load, it is essential to understand the phenomena of the DCC of steam and the air clearing within operating conditions of PWR using multi-hole discharging device: sparger. Sparger, however, is a multi-hole device. It is expected that the characteristics of sparger is different from those of single-hole nozzle due to the interaction of neighboring steam jets. Therefore, the condensation characteristics of a multi-hole sparger must be understood. In order to expand the single-hole relations to a multi-hole sparger, the interaction of the discharging steam with its neighboring steam jets and the sparger shape factor, which can be represented by the pitch-to-diameter ratio, P/d, and the hole distribution pattern must be considered.
The objectives of the present study are to provide the sound understanding on the effect of multi-hole of a sparger. One of the objectives of the present study is to investigate the dynamics of pressure oscillation in terms of the pressure amplitude and the dominant frequency when steam is fed through various kinds of multi-hole I-type spargers in a subcooled water. The second objective is not only to investigate the performance of each sparger tested here with respect to the pressure behavior and thermal mixing effect in a pool, but also to compare multi-hole sparger data with those of a single-hole nozzle to clarify the multi-hole effect.
As a first step of the study, single-hole nozzle test was conducted to improve the understanding of the characteristics of the DCC of steam jet, whose results would provide basic information for a multi-hole sparger. With the results of the single-hole test, the new condensation regime map was proposed with respect to the pool water temperature and the steam mass flux. The steam jet length to diameter ratio and heat transfer coefficient relation were also investigated from the experimental data. The single-hole nozzle test was described in Chapter 2.
Based on the results of the single-hole nozzle test, multi-hole sparger test was carried out to investigate the effects of multiple holes of sparger. In Chapter 3, dedicated to describe the multi-hole sparger test, detailed dynamic behavior such as pressure amplitude and dominant frequency during the steam discharging phase described, and the new frequency correlation including the P/d ratio and related thermal hydraulic parameters was proposed to consider the interaction effect of neighboring steam jets. The geometric effect of sparger on the thermal mixing performance in the pool was investigated.
Finally, to verify the air clearing performance of the prototypical sparger of the APR1400, Unit Cell Sparger test was performed, and described in Chapter 5. From the Unit Cell Sparger test, the pressure forcing function, which can be used as a reference maximum pressure for the design verification of related system to improve the safety of the reactor system.
In the design and/or selection of an optimal sparger related to the DCC phenomena, the thermal mixing effects as well as the characteristics of the pressure pulse, such as amplitude and frequency, should be considered. It is noted that the dominant frequencies observed in this study are dependent on the dimension of the system such as the hole and the bore size of the spargers. Accordingly, it is strongly recommended that more systematic studies with various sizes of spargers must be carried out and the mechanism regarding steam bubble oscillation in water has to be studied more precisely.

목차 (Table of Contents)

• 제 1 장 서론 1
• 1.1 연구목적 및 필요성 1
• 1.2 연구동향 분석 4
• 1.3 연구내용 및 방법 9
• 제 2 장 단공 노즐에 의한 직접접촉응축특성 17
• 2.1 개요 17
• 2.2 실험장치 및 조건 18
• 2.2.1 실험장치 18
• 2.2.2 유량계 보정 19
• 2.2.3 실험조건 및 방법 21
• 2.3 실험결과 및 분석 22
• 2.3.1 증기제트형상 22
• 2.3.2 증기제트 길이 26
• 2.3.3 평균 응축 열전달계수 29
• 2.3.4 증기제트 내부 온도분포 33
• 2.3.5 응축영역도 35
• 2.3.6 응축압력진동특성 37
• 2.4 요약 39
• 제 3 장 다공 증기분사기 형상에 따른 직접접촉응축특성 63
• 3.1 개요 63
• 3.2 실험장치 및 조건 64
• 3.2.1 실험장치 64
• 3.2.2 실험방법 64
• 3.3 응축진동 주파수 해석방법 65
• 3.3.1 Fourier 급수 65
• 3.3.2 Fourier 변환 68
• 3.3.3 유한 Fourier 변환 69
• 3.3.4 Fast Fourier Transform 71
• 3.4 실험결과 및 분석 71
• 3.4.1 실험범위 설정 72
• 3.4.2 응축진동에 의한 압력파 73
• 3.4.3 응축진동하중의 크기 74
• 3.4.4 수조 내 열혼합 성능 76
• 3.4.5 응축 진동주파수 78
• 3.5 요약 84
• 제 4 장 APR1400 원형 증기분사기에 의한 공기방출특성 106
• 4.1 개요 106
• 4.2 실험장치 및 조건 107
• 4.2.1 기계계통 107
• 4.2.2 계측계통 110
• 4.2.3 자료처리계통 111
• 4.2.4 실험조건 114
• 4.3 증기분사기를 통한 유체방출시 유동현상 115
• 4.4 실험결과 및 분석 118
• 4.4.1 방출시 증기공급배관 내 열수력거동 118
• 4.4.2 방출시 수조 내 압력하중 119
• 4.4.3 실험변수가 수조하중에 미치는 영향 121
• 4.5 압력하중함수 개발 124
• 4.5.1 기포 최대 압력 및 대표주파수 125
• 4.5.2 압력하중함수 128
• 4.6 요약 130
• 제 5 장 결론 및 제언 158
• REFERENCES 162
• APPENDIX A 171
• APPENDIX B 174
• APPENDIX C 181
• APPENDIX D 190
• ABSTRACT 194