DOI QR코드

DOI QR Code

Evaluation of Long-term Performance of Metal Seal Through Accelerated Test

가속화 시험을 통한 금속 밀봉재 장기성능 평가

  • Received : 2020.05.28
  • Accepted : 2020.08.06
  • Published : 2020.08.30

Abstract

Metal seals are the main components that establish the containment boundary in bolted casks, which store spent nuclear fuel. These seals are degraded by heat and radiation. In addition, creep occurs when the seals are exposed to intense heat for an extended period. This creep results in the stress relaxation of the seals, which consequently impairs the seal integrity. The stress relaxation can reduce the sealing performance of the metal seal, which can further cause leakage in the storage cask. Moreover, the reduction of bolt tension leads to sealing performance degradation. In this study, the results of high-temperature-accelerated tests were obtained to evaluate the containment integrity of metal seals and the decrease in bolt tension. During the tests, the leakage rate, bolt strain, and ambient temperature of the metal seals were measured and analyzed. The metal seals were found to maintain containment integrity for 50 years of storage. The validity of the acceleration test was also investigated.

사용후핵연료를 저장하는 볼트체결 저장용기의 격납경계를 형성하는 주된 구성요소는 금속 밀봉재이다. 이러한 금속 밀봉재는 열과 방사선에 의해 그 성질이 저하된다. 또한, 금속 밀봉재가 강한 열에 장기간 노출되면 크리프 현상이 발생한다. 이러한 크리프는 밀봉시스템에 응력 이완을 가져와서, 결국 밀봉재의 건전성을 해치게 된다. 이러한 응력 이완은 금속 밀봉재의 밀봉성능 저하로 이어지며, 저하의 정도에 따라 저장용기의 누설을 야기할 수 있다. 또한, 볼트 체결력의 감소도 밀봉성능 저하에 영향을 미친다. 본 논문에서는 금속 밀봉재의 격납건전성과 볼트체결력 감소를 평가하기 위해 수행한 가속화 시험의 결과에 대하여 기술한다. 전 시험기간 동안 각 시편에서의 누설률, 볼트 변형률, 금속 밀봉재 주변 온도를 계측하여 분석하였고, 금속 밀봉재는 저장기간 50년 동안 격납건전성을 유지함을 입증하였다. 또한, 가속화 시험의 타당성에 대해서 기술하였다.

Keywords

Acknowledgement

본 연구는 산업통상자원부(MOTIE)와 한국에너지기술평가원(KETEP)의 지원을 받아 수행한 연구 과제입니다. (No. 20201710200010)

References

  1. S. Schubert, F. Koch, U. Probst, and H.P. Winkler, "Behavior of Metallic Seals in CASTOR(R)-Casks under Normal and Accident Conditions of Transport: Qualification Requirements", The 15th Int. Symp. on the Packaging and Transportation of Radioactive Materials (PATRAM 2007), October 21-26, Miami (2007).
  2. H. Volzke, "Research activities at BAM related to extended spent fuel and HLW storage", The 28th Annual regulatory information conference, March 8-10, Bethesda (2016).
  3. L. Qiao, S. Nagelschmidt, and U. Herbrich, "Application of a modified Arrhenius equation to describe the time-temperature equivalence in relaxation analysis of metal seals", J. Civ. Eng. Archt., 11, 853-861 (2017).
  4. M. Wataru, K. Shirai, T. Saegusa, and C. Ito, "Longterm Containment Test using Two Full-Scale Lid Models of Metal Cask with Metal Gaskets for Interim Storage", The 3rd East Asia Forum on Radwaste Management, November 1-4, Gyeongju (2010).
  5. T. Saegusa, K. Shirai, M. Wataru, H. Takeda, and K. Namba, "Basis and Safety Case of Spent Fuel Storage", IAEA International Workshop on the Development and Application of a Safety Case for Dual Purpose Casks for Spent Nuclear Fuel, IAEA, May 19-21, Vienna (2014).
  6. F. Ledrappier, J.F. Juliaa, A. Beziat, K. Vulliez, L. Mirabel, M. Wataru, K. Shirai, H.P. Winkler, and R. Hueggenberg, "Numerical simulation of HELICOFLEX metallic gasket ageing mechanism for spent fuel cask", Proc. of the 18th Int. Symp. on the Packaging and Transportation of Radioactive Materials (PATRAM 2016), cea-02439458, September 18-23, 2016, Kobe.
  7. American National Standard Institute, American National Standard for Radioactive Materials - Leakage Tests on Packages for Shipment, ANSI N14.5 (2014).
  8. D. Wolff, "Metal and Elastomer Seal Investigation", Proc. of 2015 Used Fuel-High Level Waste Extended Storage Collaboration Program, 153-174, December 1-3, 2015, Charlotte.
  9. K. Namba, K. Shirai, and M. Wataru, "Long-Term Leak-tightness Test using the Full-Scale Lid Model of the Metal cask, (5) Evaluation of Residual Gasket Load considering Compressive Creep Characteristics of Aluminum Outer Jacket", Japan Nuclear Society Conference (2012). (in Japanese)
  10. Ministry of Trade, Industry and Energy, Development of a comprehensive safety test technology for the transport/storage system of spent nuclear fuel, MOTIE Final Report No. 201471020173B (2016).