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Category:Report
MONTHYEARML24166A1982024-06-0707 June 2024 NIST - Independent Third-Party Second Nuclear Safety Culture Assessment, Revision 1 ML24064A1992024-03-0101 March 2024 Us Dept. of Commerce, National Institute of Standards & Technology (NIST) - Change to the Nbsr Requalification Plan in Response to an NRC Request for Additional Information (ADAMS Accession No. ML22223A146) ML24064A0282024-02-29029 February 2024 Requalification Program for the Nbsr ML24023A6212023-12-0606 December 2023 Us Dept. of Commerce, National Institute of Standards & Technology - Problem Identification and Resolution (Pi&R) Performance Area Assessment Report ML24023A6192023-10-23023 October 2023 NIST Center for Neutron Research Reactor Operations and Engineering (NCNR-ROE) Assessment of NCNR-ROE Procedures Program ML24023A6222023-09-0505 September 2023 Final Report - Safety Evaluation Committee (Sec)/Safety Assessment Committee (Sac) ML24023A6232023-09-0101 September 2023 Independent Nuclear Safety Consultant Assessment of Training at the NIST Center for Neutron Research (NCNR) - Final ML24023A6202023-07-11011 July 2023 Independent Nuclear Safety Consultant Assessment of the Root Cause Analysis Performed by NCNR Into the February 3, 2021 Event at the NIST Center for Neutron Research, Revision 1 ML23207A0412023-06-0202 June 2023 Us Dept. of Commerce, National Institute of Standards & Technology, Independent Third-Party Nuclear Safety Culture Assessment of the NIST Center for Neutron Research ML23040A3402023-03-0909 March 2023 NIST Restart Authorization Technical Evaluation Report ML22293B8082022-10-19019 October 2022 National Institute of Standards & Technology (NIST) - License Amendment Request ML22350A0692022-08-19019 August 2022 Us Dept. of Commerce, National Institute of Standards & Technology (Nist), Response to Request for Additional Information on License Amendment Request - Gamma Spectrum Analysis Report ML22227A1502022-08-15015 August 2022 Us Dept of Commerce, National Institute of Standards & Technology (Nist), Request NRC Permission to Restart the Reactor Upon Completion of Listed Corrective Actions and Recovery Efforts ML22223A1462022-08-11011 August 2022 Docket Number 50-184 and the Nbsr Requalification Plan ML21340A0072021-12-0303 December 2021 Analysis of Cooling Flow Through 29 Fuel Elements with Fuel Element 1175 Dislodged ML21294A3722021-10-21021 October 2021 National Institute of Standards and Technology - Supplement to October 1, 2021 Report and Restart Request ML21288A5532021-10-15015 October 2021 NIST Center for Neutron Research - Problem Identification and Resolution ML21274A0252021-09-30030 September 2021 Corrective Action Plan Corrective Actions Required Prior to Reactor Startup ML21274A0262021-09-30030 September 2021 Corrective Action Plan Corrective Actions Required Post-startup ML21274A0232021-09-21021 September 2021 Latch Improvement Safety Analysis ML21274A0222021-09-20020 September 2021 Root Cause Response, Revision 1 ML21274A0192021-09-13013 September 2021 Ncnr Twg Report Root Cause Investigation of February 2021 Fuel Failure, Revision 2 ML21274A0212021-08-12012 August 2021 Final Report Sec Subcommittee Report: Review of the Ncnr Event Response and Technical Working Root Cause Analysis and Corrective Action Plan ML21274A0202021-06-0303 June 2021 Ncnr Twg Report Addendum to Root Cause Investigation of February 2021 Fuel Failure ML21153A3972021-06-0202 June 2021 Requalification Program for the Nbsr ML21340A0082021-05-17017 May 2021 Heat Transfer in a Disc Wedged Between Two Fuel Element Plates ML18157A1382018-05-31031 May 2018 Technical Evaluation of the Preliminary Safety Evaluation Report Supporting the Conversion to Low-Enriched Uranium Fuel for the National Bureau of Standards Reactors ML0907001322009-03-0303 March 2009 Us Dept. of Commerce, NIST, Response to Request for Additional Information on Operator Requalification Program 2024-06-07
[Table view] Category:Technical
MONTHYEARML24166A1982024-06-0707 June 2024 NIST - Independent Third-Party Second Nuclear Safety Culture Assessment, Revision 1 ML24064A1992024-03-0101 March 2024 Us Dept. of Commerce, National Institute of Standards & Technology (NIST) - Change to the Nbsr Requalification Plan in Response to an NRC Request for Additional Information (ADAMS Accession No. ML22223A146) ML24064A0282024-02-29029 February 2024 Requalification Program for the Nbsr ML24023A6212023-12-0606 December 2023 Us Dept. of Commerce, National Institute of Standards & Technology - Problem Identification and Resolution (Pi&R) Performance Area Assessment Report ML24023A6192023-10-23023 October 2023 NIST Center for Neutron Research Reactor Operations and Engineering (NCNR-ROE) Assessment of NCNR-ROE Procedures Program ML24023A6222023-09-0505 September 2023 Final Report - Safety Evaluation Committee (Sec)/Safety Assessment Committee (Sac) ML24023A6232023-09-0101 September 2023 Independent Nuclear Safety Consultant Assessment of Training at the NIST Center for Neutron Research (NCNR) - Final ML24023A6202023-07-11011 July 2023 Independent Nuclear Safety Consultant Assessment of the Root Cause Analysis Performed by NCNR Into the February 3, 2021 Event at the NIST Center for Neutron Research, Revision 1 ML23207A0412023-06-0202 June 2023 Us Dept. of Commerce, National Institute of Standards & Technology, Independent Third-Party Nuclear Safety Culture Assessment of the NIST Center for Neutron Research ML23040A3402023-03-0909 March 2023 NIST Restart Authorization Technical Evaluation Report ML22293B8082022-10-19019 October 2022 National Institute of Standards & Technology (NIST) - License Amendment Request ML22350A0692022-08-19019 August 2022 Us Dept. of Commerce, National Institute of Standards & Technology (Nist), Response to Request for Additional Information on License Amendment Request - Gamma Spectrum Analysis Report ML22223A1462022-08-11011 August 2022 Docket Number 50-184 and the Nbsr Requalification Plan ML21340A0072021-12-0303 December 2021 Analysis of Cooling Flow Through 29 Fuel Elements with Fuel Element 1175 Dislodged ML21288A5532021-10-15015 October 2021 NIST Center for Neutron Research - Problem Identification and Resolution ML21274A0252021-09-30030 September 2021 Corrective Action Plan Corrective Actions Required Prior to Reactor Startup ML21274A0262021-09-30030 September 2021 Corrective Action Plan Corrective Actions Required Post-startup ML21274A0232021-09-21021 September 2021 Latch Improvement Safety Analysis ML21274A0222021-09-20020 September 2021 Root Cause Response, Revision 1 ML21274A0192021-09-13013 September 2021 Ncnr Twg Report Root Cause Investigation of February 2021 Fuel Failure, Revision 2 ML21274A0212021-08-12012 August 2021 Final Report Sec Subcommittee Report: Review of the Ncnr Event Response and Technical Working Root Cause Analysis and Corrective Action Plan ML21274A0202021-06-0303 June 2021 Ncnr Twg Report Addendum to Root Cause Investigation of February 2021 Fuel Failure ML21153A3972021-06-0202 June 2021 Requalification Program for the Nbsr ML21340A0082021-05-17017 May 2021 Heat Transfer in a Disc Wedged Between Two Fuel Element Plates ML18157A1382018-05-31031 May 2018 Technical Evaluation of the Preliminary Safety Evaluation Report Supporting the Conversion to Low-Enriched Uranium Fuel for the National Bureau of Standards Reactors 2024-06-07
[Table view] |
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Addendum to Root Cause Investigation of February 2021 Fuel Failure NCNR Technical Working Group (TWG)
June 3, 2021 As part of the ongoing investigations of the February 2021 NCNR fuel failure, additional discoveries continue to be made beyond those which are described in the narrative given in the TWG Root Cause investigation (revision 1 dated May 13, 2021).
Video surveillances of latching and latch checks have revealed the possibility of inadvertently unlatching a fuel element by a relatively small impulse force from dropping the pickup tool onto the element head without any rotational force being applied. This was repeatedly demonstrated after discovery and was recorded on video.
Analysis of this phenomenon has shown that when the latch is moved to the fully latched position, the spring on the element head, in addition to elastic compression, stores further elastic energy in the form of elastic windup, or elastic torsion.* Thus, if the downward impulse from dropping the pickup tool is sufficient to push the latch out of the notch in the upper gird plate, the residual torque will move the latch towards the unlatched position (i.e. from where it came during the latching process) and, potentially all the way to fully unlatched (if all of the tool rotation remains stored in the spring as residual torque).
It is impossible to state categorically whether this caused the unlatched element leading to the February 3 event, but given the tool rubbing noted in the J-7 position during the January 4 refueling, it is likely that such an impulse may have occurred. This, combined with the improperly performed latch checks, offers a credible explanation of events.
Corrective Actions An investigation (now assigned to CARRI team 5a) will be made as to the necessity and feasibility of a redesign of the element head spring mechanism. One concern is that adding complexity to the mechanism may create unintended consequences, so such a redesign must be carefully considered.
Root Cause Determination Although this discovery offers a plausible explanation as to the direct cause of the event on February 3, the fundamental root causes discussed in the TWG Root Cause investigation remain unchanged.
- This elastic windup is made possible by the friction between the end-surfaces of the spring and the respective machine parts against which the spring develops a friction moment, that is proportional to the spring compression. It should be noted that here the descriptors compression and torsion are used with respect to the macroscopic outline of the spring, i.e., as if it were a tube (which it is not; it is a helix). So, these are not descriptors of the actual loading of the material of which the spring is made, which would be torsion and bending respectively.