In this study, the impact load resulting from collision with the fuel rods of surrogate spent nuclear fuel (SNF) assemblies was measured during a rolling test based on an analysis of the data from surrogate SNF-loaded sea transportation tests. Unfortunately, during the sea transportation tests, excessive rolling motion occurred on the ship during the test, causing the assemblies to slip and collide with the canister. Hence, we designed and conducted a separate test to simulate rolling in sea transportation to determine whether such impact loads can occur under normal conditions of SNF transport, with the test conditions for the fuel assembly to slide within the basket experimentally determined. Rolling tests were conducted while varying the rolling angle and frequency to determine the angles and frequencies at which the assemblies experienced slippage. The test results show that slippage of SNF assemblies can occur at angles of approximately 14° or greater because of rolling motion, which can generate impact loads. However, this result exceeds the conditions under which a vessel can depart for coastal navigation, thus deviating from the normal conditions required for SNF transport. Consequently, it is not necessary to consider such loads when evaluating the integrity of SNFs under normal transportation conditions.

Currently, the development of evaluation technology for vibration and shock loads transmitted to spent nuclear fuel and structural integrity of spent nuclear fuel under normal conditions of transport is progressing in Korea by the present authors. Road transportation tests using surrogate spent nuclear fuel were performed in September, 2020 using a test model of KORAD-21 transportation cask and sea transportation tests were conducted from September 30 to October 4, 2021. Finally, the shake table tests and rolling test were conducted from October 31 to November 2, 2022. As a result of the sea transportation test data analysis, an impact load resulting from the collision of objects was measured on fuel rods of a surrogate spent nuclear fuel assemblies during the rolling test was observed. Excessive rolling motion occurred on the ship during the rolling test, causing the surrogate spent nuclear fuel assemblies to slip and collide with the canister. To analyze under which conditions such impact loads occur and whether this event is possible under normal conditions of transport of spent nuclear fuel, a test was designed to simulate the rolling test in sea transportation and was performed. The rolling test was conducted on ACE7 and PLUS7 assemblies, respectively, varying the rolling angle and rolling frequency to determine at which angles and frequencies the assemblies experienced slippage. According to the test results, slippage of the used nuclear fuel assemblies can occur due to rolling motion at angles of approximately 14° or higher, leading to the possibility of generating impact loads. It was observed that the rolling angle is a more major factor for slippage than the rolling frequency. This exceeds the conditions under which a vessel can be permitted to depart for coastal navigation, thus it is considered to deviate from the normal conditions of transport of spent nuclear fuel. Therefore, it is not necessary to consider such loads for evaluating the integrity of spent nuclear fuel during normal transportation conditions.

Currently, the development of evaluation technology for vibration and shock loads transmitted to spent nuclear fuel and structural integrity of spent nuclear fuel under normal conditions of transport is progressing in Korea by the present authors. Road transportation tests using surrogate spent nuclear fuel were performed in September, 2020 using a test model of KORAD-21 transportation cask and sea transportation tests were conducted from September 30 to October 4, 2021. Finally, the shake table tests and rolling test were conducted from October 31 to November 2, 2022. The shake table test was performed with the input load produced conservatively from the data obtained from the road and sea transportation tests. The test input was produced based on the power spectral densities and shock response spectrums from the transportation tests. In addition to the test inputs from the road and sea tests, sine sweep input and half sine input were used to verify the vibration characteristics of assemblies under boundary conditions during normal conditions of transport. Because the input load of the shake table test was produced conservatively, a slightly larger strain than the strain value measured in road and sea transportation tests was measured from the shake table tests. In the case of the sea test, it is considered that the process of enveloping the data in the 20 to 80 Hz range generated by the engine propeller system was performed excessively conservatively. As a result of analyzing the test results for the difference in boundary conditions, it was confirmed that the test conditions of loading the basket generated a relatively large strain compared to the conditions of loading the disk assembly for the same input load. Therefore, it is concluded that a transportation cask having a structure in which a basket and a disk are separated, such as KORAD-21, is more advantageous in terms of vibration shock load characteristics under normal conditions of transport than a transportation cask having an integral internal structure in which a basket and a disk are a single unit. However, this effect will be insignificant because the load itself transmitted to the disk assembly is very small.

Various non-face-to-face services are being activated due to the influence of the Corona 19 virus around the world. However, unlike the rapid development of delivery services, social awareness of delivery services is causing many problems. Therefore, in this study, we analyze the quality attributes of delivery services from the consumer's point of view, and based on the results, we try to derive a direction for service improvement. In this study, quality factors were established through interviews and surveys with actual consumers, and quality attributes were classified through the Kano model and Timko’s customer satisfaction coefficient. “Attractive” is (‘Ease of ordering, Accurate delivery to the designated place’), “One Dimensional” is (‘Variety of payment methods, Accurate delivery on time, Accurate delivery of ordered food, Degree of non-deformation of packaging conditions, etc., Convenience of use time’), “Must be” is (‘Kindness of the delivery person’), “Reverse” is (‘provision of services, service response to order discrepancies’). This study has academic significance in that it compensated for the disadvantage of not being able to interpret the mathematical meaning of the Kano model with Teamco’s customer satisfaction coefficient. It also has practical implications in that it provides an indirect clue to future improvement directions.

2017년 미국 DOE 주도하에 수행된 국제공동 복합모드운반시험 중 도로트럭운반시험, 연안항해시험, 대서양항해시험에서 측정된 가속도 및 변형률 데이터를 분석하였다. 먼저 각 운반모드 별로 발생한 하중이 전달경로에 따라 하중이 증폭되는지 감쇄되는지가 조사되었다. 그 결과 운반모드 및 하중경로 내 어떤 부분이냐에 따라 발생한 하중이 모의핵연료집합체에 전달되는 특성이 다름을 확인하였다. 그리고 변형률 데이터를 분석하여 육상 및 해상운반동안 발생한 변형률이 사용후핵연료에 건전성에 미치는 영향을 파악하였다. 그 결과 측정된 변형률은 사용후핵연료의 건전성에는 영향을 미치지 못하는 정도로 작은 크기임을 확인하였다. 본 연구에서 분석된 가속도와 피로평가 결과는 예정된 국내 정상운반시험조건에서의 운반시험에 유용한 기초자료로 활용될 것이다.

최근 국내에서 육상 및 해상을 통한 소외 정상운반 시 진동 및 충격하중에 대한 사용후핵연료의 건전성 평가 기술 개발이 수행되고 있다. 이와 관련된 국내 연구사례는 전무하여 기존에 진행된 또는 현재 수행중인 해외연구사례를 조사하여 국내 연구에 참고하고자 한다. 2000년 이전 과거 미국의 사용후핵연료의 정상운반 시 진동 및 충격하중 측정 관련 연구현황을 조사 하였고 2009년부터 미국국립연구소 주관으로 실시한 단축가진시험, 콘크리트블럭 트럭운반시험, 다축가진시험에 대해서 조사하였으며 2017년 미국 SNL, 스페인의 ENSA, 한국이 공동으로 수행한 복합운반시험을 상세히 조사하였다. 시험 준비과정, 절차, 가속도 및 변형률 측정결과, 유한요소 및 다물체동역학 해석과정 등이 조사되었다. 각 시험 별로 측정된 변형률 자료를 바탕으로 사용후핵연료 피로곡선과 비교한 결과 손상을 일으키기에는 매우 미미한 정도의 변형률이 발생한다는 초기 결론을 얻었음을 확인하였다. 하지만 현재 결론은 일부 결과만을 검토한 예비 결론으로 상세한 검토가 현재 미국에서 진행 중이다. 미국에서 지금까지 수행한 사용후핵연료의 정상운반조건에서의 진동 및 충격하중 측정과 관련하여 조사된 내용은, 국내 운반환경에서 사용후핵연료의 정상운반시험을 수행할 때 참고할만한 유용한 자료라 판단된다.