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Test Facility Tour and Seminar at the National Physical Laboratory
(January 16–17, 2019)

The International Research Institute for Nuclear Decommissioning (IRID) has developed technologies for criticality control and re-criticality prevention, which can be used to promptly detect and terminate criticality, although re-criticality occurs. Accordingly, IRID has promoted activities for technology development in collaboration with international research institutes and specialists.

Here, we review the visit to the National Physical Laboratory (NPL) to tour the test facility tour and hold a seminar. As part of the “Upgrading Approach and System for Retrieval of Fuel Debris and Internal Structures (Development of Criticality Control Technology of Fuel Debris)” project for the development of calibration technology for the primary containment vessel (PCV), IRID has proceeded with the development of calibration technology for a gas radiation detector for re-criticality determination.

Visit to

National Physical Laboratory (NPL), Teddington (suburbs of London), United Kingdom (UK)


Currently, the PCV gas radiation-monitoring method is used to detect re-criticality by monitoring X-135 gamma rays. This method facilitates a detection of gamma rays in the early stage and has been developed to detect Kr-88 gamma rays. However, it is necessary to determine the gamma dose measured by the detector and Kr-88 concentration to measure the Kr-88 concentration with high accuracy using the high-energy gamma dose generated by Kr-88. This is called “calibration.” The NPL is currently the only organization that can generate Kr-88 gamma rays and develop a calibration. At this time, calibration technology has been established. Additionally, the NPL is considered to be the world authority with respect to measurement standards. Many researchers have been involved in this project. We had the opportunity to hold a seminar to introduce research results useful for the Fukushima Daiichi Nuclear Power Station and exchange valuable information.

  • Click [photos] to enlarge images.


  • Participants of the test facility tour

  • Van de Graaff accelerator

  • Graphite pile for neutron irradiation

  • Introduction of test devices

  • Lecture by Mr. Hideaki Kiyoura, General Manager of the R&D Management Department, IRID

  • Lecture by Professor Ken Nakajima, Kyoto University

Reports of Activities