원자력발전소 Class 1E 케이블 활성화에너지 분석에 관한 연구

Abstract

원자력법 시행규칙 제 19조 2항은 원자력발전소 운영자가 발전소의 안전성 관련 전기 및 계측기기에 대한 기기검증을 수행하고 검증상태를 유지 관리하도록 요구하고 있다. 내환경검증은 발전소의 설계기준사고 분석에서 제시하는 온도, 압력, 방사선 조사량, 화학물질 및 침수상태에 따라 시험, 분석, 경험 및 복합적인 방법에 의한 검증을 하는 것이다. 분석은 부분적 시험결과 및 이론적 계산식을 토대로 하므로 내환경검증의 대부분은 시험이 차지한다. 시험이란 압력용기에 기기를 넣은 뒤 발전소 설계기준사고 시의 환경조건을 모사한 LOCA/HELB 프로파일에 따라 온도 압력을 변화시키면서 기기의 정상작동 여부를 확인하는 것이다.

본 논문에서는 국내외에서 일반적으로 적용되고 있는 IEEE Std 323-2003년판의 내환경검증 시험방법에 따라 국내 원전 영광 1,2호기 내환경검증(EQ) 대상 케이블 5종의 케이블 절연체 및 자켓 시편을 채취하여 적외선 분광 분석(FT-IR; Fourier Transform Infrared Spectroscopy)으로 재질의 유사성을 분석하고, 열중량 분석(TGA; Thermogravimetric Analysis) 및 시차주사열량분석(DSC; Differential Scanning Calorimetry)으로 활성화 에너지를 분석하여 각 원전의 케이블 데이터 베이스와의 유사성을 비교 검토하는 것이다.

시험결과, 재질의 유사성이 없는 케이블에 대해서는 열․ 방사선노화․ LOCA시험 수행으로 케이블의 내구성이 원전에 40년 설계수명까지 계속 사용할 수 있는지를 검증함으로서 국내, 외 각 원전의 케이블 데이터베이스를 분석하여 상호간 공유할 수 있는 프로세스가 되도록 논 하고자 하였다.|Extending the lifetime of a NPP is one of the most important concerns in the global nuclear industry. Cables are one of the long - life items that have not been considered for replacement during the design life of a NPP. To extend the cable life beyond the design life, it is first necessary to prove that the design life is too conservative compared with actual aging. Condition monitoring is useful means of evaluating the aging condition of cable. In order to simulate natural aging in a nuclear power plant, a study on accelerated aging must first be conducted. In this study, evaluations of mechanical aging degradation for a neoprene cable jacket were performed after accelerated aging under continuous and intermittent heating conditions.

The equipment and cables used for nuclear power plants shall be maintained following the guidance of USNRC Regulatory Guide 1.89. In particular, strict management is required for the maintenance of cables. For the replacement of previously installed cables without qualification documentations, thorough review is required considering cost and the intent of environmental qualification (EQ). In this study, we are to take the specimens of EQ cables for Nuclear Power Plant, analyze them to identify their similarity, and make use of them as the reference material substituting qualification documentation. Polymer materials of EQ cables for Yonggwang Unit 1&2 were analyzed using FT-IR (Fourier Transform Infrared Spectroscopy), TGA (Thermo-Gravimetric Analysis), and DSC (Differential Scanning Calorimetry) to qualify the similarity with the cables having qualification documentations. The similarity of materials was analyzed through FT-IR and the activation energies of the cables were analyzed through TGA and DSC equipment to compare them with the cables having qualification documentations.

Examining the activation energies derived, it is possible to have different values based on the thermal characteristics according to cable materials and field condition of plants. For five cables of Yonggwang Unit 1&2 without qualification documentation, FR-IR, TGA, and DSC analysis were performed and their results were compared with the data in EQDB(EQ Data base) to derive the findings as below.

1. The criteria for the similarity is assumed to be 98% for FT-IR analysis of cable insulation and jacket. 2. Comparing the result of the cables collected from Yonggwang Unit 1&2 with EQDB, jacket showed conformance while insulation showed slight nonconformance. 3. Comparing the activation energy values measured from TGA and DSC analysis with those of EQDB, their values fell within the range of ± 3%, which shows the similarity with the cables having qualification documentations.

Subsequently, thermal, aging and LOCA testing were performed for replacement cable has satisfied all the performance requirements of the tests. So, it was validated that the replacement cable can maintain its integrity when DBE(HELB) occurs after its normal operation of 40 years at 40℃, which result in the reduction of enormous replacement cost for the cable.