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 (WGFS) is to advance the current understanding and address safety issues related to fuel safety.

    The specific mandate is as follows:

    • The group will report to the Committee on the Safety of Nuclear Installations (CSNI), assist the committee with its work and carry out a programme of work approved by the CSNI.
    • 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.
    • 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.
    • Review from a 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.
    • 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 to facilitate international convergence on 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

    Leaking fuel impacts and practices
    Objectives of the task are:

    • to promote a better understanding on the handling of leaking fuel in power reactors, discuss and review the current practices in member countries;
    • to summarise results and draw conclusions to help in decisions on the specification of reactor operation conditions with leaking fuel rods and on the handling of leaking fuel after removal from reactor.

    The task started with a questionnaire where about 50 questions were answered in 23 sets from 14 countries. A report has been drafted and has been reviewed in the working group.

    RIA fuel rod codes benchmark
    The scope of activity was to organize a benchmark of RIA fuel rod codes based on a set of consistent, recent experiments performed in the NSRR and CABRI test reactors. In order to maximize the benefits from this exercise, a consistent set of 4 experiments on very similar highly irradiated fuel rods tested under different experimental conditions were used:

    • low temperature, low pressure, stagnant water coolant, very short power pulse,
    • high temperature, medium pressure, stagnant water coolant, very short power pulse,
    • high temperature, low pressure, flowing sodium coolant, larger power pulse,
    • high temperature, high pressure, flowing water coolant, medium width power pulse.

    The participation into the benchmark took 17 organizations representing 14 countries, which provided solutions for some or all the cases that were defined. In terms of computer codes used, the spectrum was also large as solutions were provided with FALCON, FEMAXI coupled to TRACE, FRAPTRAN, RANNS, RAPTA, SCANAIR, TESPAROD and TRANSURANUS.

    The final report has been prepared to be published.

    Mechanical testing of fuel cladding for RIA applications
    The task reviewed the test methodologies in use in NEA member countries for characterising the fuel cladding mechanical response under reactivity initiated accident (RIA) and provided recommendations how these methodologies can be used with respect to the parameters to be characterized. As a result of this task a CSNI technical report was drafted, and has been prepared to be published.

    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

    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

    Review of High Burn-up RIA and LOCA Database and Criteria
    NEA/CSNI/R(2006)5

    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


    Contact

    Olli Nevander,


    Last reviewed: 10 April 2014