The high-level nuclear waste (HLW) repository disposes of high-level nuclear waste at a depth of 500 m to 1,000 m underground. Structural health monitoring must be accompanied by the complex environmental conditions of high temperature, high humidity, radiation, and mechanical stress. A thermocouple for measuring temperature, total stress meter and pore pressure meter for measuring stress and water pressure, relative hygrometer and electrical resistivity sensor (TDR or SUS) for measuring humidity, accelerometer for measuring crack signals, and strain gauge for measuring displacement are used. For safety, after disposing of HLW in the HLW repository, access to the disposal tunnel gets blocked, making it impossible to replace or remove the monitoring sensors. So, it is necessary to evaluate the effect of the HLW repository’s environmental conditions on the monitoring sensors and enhance their durability through quantitative life evaluation and shielding. Before evaluating the life of accelerometers and strain gauges used in the HLW repository, an experimental study is conducted to determine failure modes and failure mechanisms under radiation conditions, which are unique environmental conditions of the HLW repository.

The high-level nuclear waste (HLW) repository is a 500-1,000 m deep underground structure to dispose high-level nuclear waste. The waste has a very long half-time and is exposed to a number of stresses, including high temperatures, high humidity, high pressure These stresses cause the structure to deteriorate and create cracks. Therefore, structural health monitoring with monitoring sensors is required for safety. However, sensors could also fail due to the stresses, especially high temperature. Given that the sensors are installed in the bentonite buffer and the backfill tunnel, it is impossible to replace them if they fail. That’s why it is necessary to assess the sensors’ durability under the repository’s environmental conditions before installing them. Accelerated life test (ALT) can be used to assess durability or life of the sensors, and it is important to obtain the same failure mode for reliability tests including ALT. Before conducting the test, the proper stress level must be designed first to get reliable data in a short time. After that, acceleration of life reduction with increasing temperature and temperature-life model should be determined with some statistical methods. In this study, a methodology for designing stress levels and predicting the life of the sensor were described.

The high-level nuclear waste (HLW) repository is a 500-1,000 m deep geological disposal system with a very long life expectancy for disposing of high-level waste, which is known to have a half-life of several thousand years. This repository is subject to harsh environmental conditions, such as high temperature and radiation from high-level waste, that can cause deterioration and crack. When radiation escapes through cracks, it can injure persons on the ground. Therefore, it is essential to install a sensor that can detect problems such as cracks. But, since the high-level nuclear waste (HLW) repository is sealed with bentonite and backfill, the sensor cannot be removed or replaced once it has been installed. Therefore, it is necessary to develop a highly durable monitoring sensor that can withstand harsh environmental conditions. Before attempting to improve durability, it is first required to assess durability quantitatively. And an accelerated life test is a widely used method for assessing durability. However, it is important to obtain the same failure mode when conducting a reliability test, such as an accelerated life test. If the accelerated life test is conducted using different failure modes, the dependability of the results is inevitably diminished. Therefore, in this study, a representative failure mode for the piezoelectric sensor used in the accelerated life test was derived through experiments and literature research.

The high-level waste disposal system is an underground structure exposed to complex environmental conditions such as high temperature, radiation, and groundwater. The high-level waste disposal causes structural cracks and deterioration over time. However, since the high-level waste disposal system is a structure that should be operated for a very long time, developing a high-durability monitoring sensor to detect cracks and deterioration is essential. The durability of the sensor can be evaluated by predicting the expected life through the accelerated life test, one of the reliability qualification tests. The most important factor in the accelerated life test design is setting the harsh stress level. This study figured out the harsh stress level of the piezoelectric sensor, which is commonly used for underground structure monitoring. It is possible to determine the appropriate stress level for the accelerated life test by investigating the harsh stress level for the temperature factor. It will contribute to more accurate life expectancy prediction.

The high-level nuclear waste disposal system is a structure with a very long life expectancy, and deterioration and cracking of the structure may occur over time. In addition, the high-level nuclear waste disposal system is in complex extreme conditions such as high temperature, groundwater, and radiation. Therefore, we need to develop a highly durable monitoring sensor that can detect the deterioration and crack of structures in extreme conditions. Since the durability of a sensor is closely related to the sensor lifetime, it is essential to predict the sensor lifetime accurately. The sensor lifetime can be predicted through the reliability qualification test. Among them, the accelerated life test conducted under harsh conditions is widely used as a method to shorten the test period. The major factor in carrying out the accelerated life test is to set the appropriate harsh conditions. Therefore, this study experimentally derived the operating limit of the monitoring sensor. It is essential to set the proper harsh conditions when performing the accelerated life test. Through this study, it is judged that it will be helpful in determining the appropriate stress level when performing the accelerated life test for accurate lifetime prediction.

국가직무능력표준(National competency standards, NCS)은 산업현장에서 직무를 수행하기 위해 요구되는 지식, 기술, 태도 등의 내용을 국가가 체계화한 것이다. NCS기반 현장중심 교육과정을 적용한 방사선과 재학생 3학년을 대상으로 일반촬영에 대한 방사선사 직무수행도를 평가하였다. 평가 결과, 모든 촬영방식에서 우수 및 충족 비율이 93% 이상으로 현장중심 교육과정이 재학생의 직무수행도 향상에 긍정적인 영향을 끼친 것으로 판단된다. CR 방식은 전체적으로 가장 우수한 평가를 받았으나 대상자 간 편차가 크고 영상기기조작능력이 부족한 것으로 평가되었고 Film 방식은 노출조건 설정 및 현상작업이 문제점으로 평가되었다. DR 방식은 우수한 평가를 받았으나 영상기기조작능력, 부속기자재운영능력이 부족한 것으로 평가되었다. 각 촬영에서 성취수준 이하의 평가요소를 교과목 운영에 보완한다면 재학생의 학업성취도 향상뿐만 아니라 졸업 후 임상에서 방사선사 직무수행도 향상에 도움이 되리라 판단 한다.