Specialist Workshop on Advanced Measurement Method and Instrumentation for enhancing Severe Accident Management in an NPP addressing Emergency, Stabilization and Long-term Recovery Phases
    December 7-10, 2020. Fukushima, JAPAN

Background of SAMMI-2020

In the past severe accidents (SA) at Three Mile Island Unit 2 (TMI-2), Chernobyl Unit 4 (ChNPP4), and Fukushima Daiichi Units 1, 2, and 3 (1F1, 1F2, and 1F3), insufficient data or data from degraded measurement instruments caused fatal mistakes in accident countermeasures, hindering reactor recovery. Based on such bitter lessons, the role of measurement method and instrumentation has been recognized as an important subject. New measurement methods and instrumentation are under consideration for providing accurate information on reactor conditions before, during and even after a SA. In addition, there still exist various unresolved issues partially due to significant adverse conditions especially during and after a SA.

After a SA, most measurement instruments in nuclear power plant (NPP) are inaccessible because of harsh SA environments that include extremely high radiation fields. However, data from selected instruments are required prior to and during recovery and decommissioning work, such as temperature, pressure, and chemical and radiation conditions. Installation of various kinds of new instrumentation with novel techniques considering specific designs of NPPs that may encounter a SA is also envisaged to establish optimum and effective recovery and decommissioning work environments.

Concerning workshops (WS) on the measurement techniques and instrumentation, a OECD/NEA/CSNI WS was held first in 1997 at Santa Barbara, USA to provide data suitable for computer code model development, validation and improvement. This WS was dedicated for the measurement techniques for thermal-hydraulic phenomena experiments. SWINTH-2016 was held in 2016 at Livorno, Italy by the SILENCE network with a similar objective as that for the Sant Barbara WS. These two WSs greatly contributed to develop and validate reactor safety analysis codes dedicated mostly for design-basis accident (DBA) safety assessment by obtaining experimental data with high accuracy and less uncertainty. SWINTH-2019 is to be held as a WS under the NEA/CSNI/WGAMA and SILENCE network with a scope that includes measurement methods and instruments for experiments to study SA phenomenology. SWINTH-2019, however, does not deal with the measurement techniques and instrumentation for NPP SAM measures.

Concerning the OECD/NEA WSs and specialist meetings that deal with measurement methods and instrumentation for NPP severe accident management (SAM), a series of efforts were completed before the Fukushima Daiichi Accident (FDA) in 2011;

  1. First CSNI Specialist Meeting on Instrumentation to Manage Severe Accidents (1992), Cologne, F.R.G.
  2. OECD Specialist Meeting on Operator Aids for Severe Accident Management and Training (SAMOA) (1993), Halden, Norway
  3. Second OECD Specialist Meeting on Operator Aids for Severe Accident Management (SAMOA-2) (1997), Lyon, France
  4. WS on Operator Training for Severe Accident Management (SAM) and Instrumentation Capabilities during Severe Accidents (2001), Lyon, France

Very recently, after the FDA, the Canadian Nuclear Safety Commission (CNSC) and the Canadian Nuclear Laboratories (CNL) co-hosted the 2018 International Severe Accident Management Conference (ISAMC-2018) at Ottawa, Canada, following an initiative of the OECD/NEA/CSNI/WGAMA. The ISAMC-2018 participants shared knowledge and experience about Post-Fukushima enhancements of the SAM requirements, principles, strategies and procedures; equipment for AM; human factors considerations under accident conditions; use of research and development (R&D) results in strengthening AM effectiveness.

A number of presentations addressed the SAs’ instrumentation and equipment survivability, and habitability. One specific presentation of “A R&D cooperative program proposal to enhance Severe Accident Management in existing and future NPPs within the OECD/NEA NI2050 initiative” by D. Jacquemain (IRSN) highlighted the need to establish programs to address challenges and opportunities for “Reinforcement of SA instrumentation including harmonization in qualification, behaviour of existing instrumentation and development of innovative instrumentation”. Recommendations were made to further perform research on instrumentation behavior and survivability in SAs conditions, and on enhancing instrumentation for SAM and emergency response.

Other than the above efforts related to the OECD/NEA/CSNI initiatives, the IAEA published an IAEA Nuclear Energy Series report NP-T-3.16, “Accident Monitoring Systems for Nuclear Power Plants,” in 2015 in response to one of the action items of the IAEA Action Plan on Nuclear Safety (2011) which was established in response to the Fukushima Daiichi accident to define a programme of work to strengthen the global nuclear safety framework.

SAMMI-2020, to be held in the year of Olympic and Paralympic Games in Japan, tries to gather and summarize all the relevant information on new measurement methods and instrumentation suitable for NPP SAM, along with revised SA guidance based on instrumentation survivability insights, to prevent, mitigate and recover from SAs in existing and future NPPs. Expected outcomes are updates regarding recent advancements from developmental efforts for new methods and testing under NPP prototypical conditions of temperature, pressure, chemical and/or radiation. Numerical simulations and expectations will be discussed that identify the NPP system and local conditions during and after SAs to characterize needs for a key measurement method and instrumentation capable of surviving conditions under which appropriate SAM measures are required. In addition, ideas will be presented regarding future experiments to identify the SA phenomena and conditions and to provide data to validate numerical analysis methods, proposed new measurement methods and instrumentation. Presentations will also describe revised SA guidance for NPP SA management and emergency decision-making.