Letter Sequence Request |
---|
|
|
MONTHYEARML21274A0222021-09-20020 September 2021 Root Cause Response, Revision 1 Project stage: Request ML21274A0242021-09-21021 September 2021 Memorandum on Recovery Items Project stage: Request ML21274A0232021-09-21021 September 2021 Latch Improvement Safety Analysis Project stage: Request ML21274A0252021-09-30030 September 2021 Corrective Action Plan Corrective Actions Required Prior to Reactor Startup Project stage: Request ML21340A0102021-12-0303 December 2021 Ncnr Response to November 17, 2021 Request for Supplemental Information Project stage: Request ML21340A0072021-12-0303 December 2021 Analysis of Cooling Flow Through 29 Fuel Elements with Fuel Element 1175 Dislodged Project stage: Request ML21361A2462021-12-23023 December 2021 Nbsr License Amendment Request Project stage: Request ML21361A2472021-12-23023 December 2021 Nbsr License Amendment Request Project stage: Request ML22012A0902022-01-11011 January 2022 Nbsr License Amendment Request, Revised No Significant Hazard Consideration Determination Project stage: Request ML22011A0732022-01-20020 January 2022 NIST Acceptance of the Application for a License Amendment Re Fuel Element Latch Verification Technical Specification Revision Project stage: Acceptance Review ML22160A2852022-06-0808 June 2022 Nbsr License Amendment Request Supplement Project stage: Supplement ML22181A1282022-07-21021 July 2022 National Institute of Standards and Technology - Issuance of Amendment No. 13 to Renewed Facility Operating License No. TR-5 Project stage: Approval 2021-09-30
[Table View] |
|
---|
Category:Report
MONTHYEARML24023A6212023-12-0606 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 2023-09-05
[Table view] Category:Technical
MONTHYEARML24023A6212023-12-0606 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 2023-09-05
[Table view] |
Text
Latch Improvement Safety Analysis September 21, 2021 Introduction As noted in both the TWG and ERCAS reports, process improvements need to be made to ensure that all fuel elements are latched. Management, procedural, training, and oversight issues are addressed in the corrective actions outlined in the Root Cause Response report. In addition to the changes identified in the reports, this document provides a safety analysis of the proposed latch verification improvements and describes how they provide complete protection against an element remaining in an unlatched state as outlined in IE-CA-2 of the ERCAS report.
Issues The following is a list of issues that were identified with the previously existing procedures for verifying a fuel element was latched:
- 1. Because of the difficulties in providing a direct visual indication of the latch, latching was verified by the position (height and rotation) of the pickup tool while it was attached to the element.
- 2. The fidelity of height checks is inadequate to provide assurances of latching. Multiple measurements and checks determined that measurements of tool height were not a reliable indication of the latch state of an element. The tolerances in the measurements were not adequate to verify the latch state.
- 3. Rotational checks of the tool were made without adequate marks on the index plate for reference. The checks were made and the adequacy of the extent of rotation was determined by operator experience. There were no reference marks on the index plate for rotation latch checks as described in existing procedures.
- 4. During testing it was determined that it is possible to inadvertently unlatch an element by a transferring mechanical impulse from the pickup tool. Because of the stored force in the compressed and rotated spring of the latch, a small impulse from a tool was enough to unlatch an element partially or fully.
Proposed Improvements The latching of elements will be verified using two processes. The first will be a verification of the rotation of the latching tool to the proper position. The second and final verification will be a visual examination of each latch to verify that it is in the fully latched position. The following is a list of improvements that will be implemented:
- 1. Implementation of a Final Visual check. The use of a video system, currently under construction, will be implemented and mandated as the last check prior to a reactor startup and after all pickup tools are stowed. Each element will be visually verified to be latched, as required by TS 3.9.2.1(3) by review of the video, checking the element head or latching bar. Once the visual verification is performed further manipulation of fuel elements will not be permitted without an additional visual check.
Analysis: This will provide unambiguous evidence that all elements are fully latched. As this is the last check, and because no use of the pickup tools will be allowed after this check, there is no possibility that an element could subsequently become unlatched. Note: The likelihood of coolant flow unlatching a fully latched element is not credible.
- 2. Discontinuation of height checks. Height checks will no longer be part of the latch check procedure as they do not provide a clear indication of latch status.
Analysis: A detailed dimensional study and empirical measurements of the tooling and index plate has shown that there is inadequate fidelity in a height check to provide absolute assurance that an element is latched. Attempting to do so could give a false sense of security, particularly when the other improvements given here are much more robust.
- 3. Utilization of clear Index plate marking. Clear fiduciary marks will be made on the index plate to verify proper azimuthal rotation in the latched position. This will satisfy requirements of TS 3.9.2.1(2). Verification of this position will be made by a second individual, providing redundant verification.
Analysis: Markings will be made in such a way as to provide unambiguous indication that the element is latched into position. Any unlatched or partially latched elements would be immediately recognized.
Summary Going forward, there will be two verifications of fuel latching:
- 1) a rotation check (with redundant peer check) using clear fiduciary marks, and
- 2) a visual check using video equipment after all fuel movements are complete.
Each of these independently satisfies the latch check requirements in TS 3.9.2.1 and provides unambiguous verification that an element is latched and eliminates the possibility of a reactor startup with an element unlatched.