Working Group on Fuel Safety (WGFS)

    Introduction

    The Working Group on Fuel Safety has been set up by the Committee on the Safety of Nuclear Installations (CSNI) and it has been working in accordance with the CSNI Strategic Plan to address cross-cutting issues related to fuel behaviour in accident conditions, including work on associated aspects of thermal-hydraulics, oxidation, chemistry, mechanical behaviour and reactor physics. This group was originally the Special Expert Group on Fuel Safety management (SEGFSM), later evolving into the Working Group on Fuel Safety Margins (WGFSM) before becoming the WGFS.

    Mandate

    The main mission of the Working Group on Fuel Safety is to advance the current understanding and address safety issues related to fuel safety.

    The specific mandate is as follows:

    1. The Group will report to the Committee on the Safety of Nuclear Installations (CSNI), assist the Committee with its work and carry out the programme of work approved by the CSNI.
    2. Assess the technical basis for current safety criteria and their applicability to high burn-up (above 50 MWd/kg) and to new fuel designs and materials. The assessment will focus on anticipated transients and postulated accident conditions. Information relevant to fuel performance under normal operating conditions will be considered only to the extent necessary to assess the safety behaviour.
    3. Determine needs and priorities for future research programmes in the area of fuel safety behaviour, with the aim of understanding and adequately modelling key phenomena and of quantifying safety margins.
    4. Review from the safety point of view, the adequacy of fuel codes and methodologies used for different core assessments as related to high burn-up fuel. Cores with different fuel assembly designs and with MOX fuel are to be considered. Neutronic, thermal-hydraulic and materials aspects are considered as they relate to core safety assessment.
    5. Provide a forum where safety-relevant fuel issues emerging from operating experience and research work can be addressed and resolved in an effective manner.

    The group will aim at facilitating international convergence in fuel safety issues, including experimental approaches, interpretation and use of the experimental data or of other relevant information.

    The group will perform its activities mainly through organising topical meetings on specific subjects or through small task forces dedicated to covering specific programme items.

    Programme of work

    Work in progress or recently finished

    Update of the state-of-the-art report on fuel behaviour during loss-of-coolant accident (LOCA) conditions

    This activity aims to update the CSNI report published by NEA in 2009 on fuel behaviour during LOCA conditions. After a preliminary review of the 2009 report, it was concluded that information provided on experimental programmes was incomplete or missing altogether. Significant parts of this missing information have become available since the 2009 report was produced. Since this activity started in early 2017, very substantial additional information has been identified.

    Phenomena identification and ranking table (PIRT) for spent-fuel pool (SFP) accidents

    This activity, jointly undertaken with the WGAMA, aims to apply the PIRT approach to SFP accidents in order to identify phenomena that are expected to have a high impact on accident consequences or mitigation and for which the level of understanding or knowledge is poor. This generates valuable insights in a context where decisions on research priorities may be made. The activity follows on from a previous joint WGFS-WGAMA activity that produced a status report on SFP loss-of-coolant and loss-of-cooling accidents (see “Recent reports” below).

    Workshops

    In a collaborative venture with several groups of the Nuclear Science Committee, WGFS helped organise a workshop on advanced fuel modelling for safety and performance enhancement. The workshop was held in March 2017 in Paris over two and a half days and attracted 80 participants from NEA member countries. The proceedings are being prepared.

    WGFS organised a two-day workshop for organisations participating in NEA Working Groups on the issue of pellet-clad interaction. This was stimulated in particular by the increasing practice of reactor-power adjustments in order to follow the load on the electrical grid. The workshop programme comprised 31 presentations and nearly 80 people participated. The proceedings (including the papers) are being prepared.

    Future activities

    Planned activities for the WGFS include:

    • reviewing design-basis accidents, especially loss-of-coolant accidents and reactivity-initiated accidents;
    • periodically assessing and reviewing fuel safety criteria;
    • investigating advanced fuel designs and the possible effect of such designs on safety margins (both for existing and advanced reactor designs).

    Recent reports

    Reactivity Initiated Accident (RIA) Fuel Codes Benchmark Phase-II – Volume 1: Simplified Cases Results Summary and Analysis
    NEA/CSNI/R(2016)6/VOL1

    Reactivity Initiated Accident (RIA) Fuel Codes Benchmark Phase-II – Volume 2: Task No. 1 Specifications
    NEA/CSNI/R(2016)6/VOL2

    Reactivity-initiated Accident Fuel-rod-code Benchmark Phase II: Uncertainty and Sensitivity Analyses
    NEA/CSNI/R(2017)1

    Fuel fragmentation, relocation and dispersal during loss-of-coolant-accidents
    NEA/CSNI/R(2016)16

    Spent fuel pools in loss-of-cooling/coolant accident conditions
    NEA/CSNI/R(2015)2

    Leaking fuel impacts and practices
    NEA/CSNI/R(2014)10

    RIA Fuel Codes Benchmark – Volume 1
    NEA/CSNI/R(2013)7/VOL1

    RIA Fuel Codes Benchmark – Volume 2
    NEA/CSNI/R(2013)7/VOL2 (104 Mb)

    Nuclear Fuel Safety Criteria technical review (second edition)
    NEA/CSNI/R(2012)3

    CSNI Technical Opinion Papers No. 13 LOCA Criteria Basis and Test Methodology
    NEA/CSNI/R(2011)7

    Proceedings of the Workshop on Nuclear Fuel Behaviour during RIA
    NEA/CSNI/R(2010)7

    Benchmark calculations on Halden IFA-650 LOCA test results
    NEA/CSNI/R(2010)6

    Safety significance of the Halden IFA-650 LOCA test results
    NEA/CSNI/R(2010)5

    State-of-the-art Report on Nuclear Fuel Behaviour under Reactivity Initiated Accident (RIA) Conditions
    NEA/CSNI/R(2010)1, NEA No. 6847, ISBN 978-92-64-99113-2

    Nuclear Fuel Behaviour in Loss-of-coolant Accident (LOCA) Conditions
    NEA/CSNI/R(2009)15, NEA No. 6846, ISBN 978-92-64-99091-3

    The predecessor of the SEGFSM, the Task Force on Fuel Safety Criteria, prepared the following report, that sets out the results of OECD/CSNI/PWG2 Task Force's work on fuel safety criteria:

    Fuel Safety Criteria Technical Review
    NEA/CSNI/R(99)25

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    Last reviewed: 4 July 2017