ML21053A047
| ML21053A047 | |
| Person / Time | |
|---|---|
| Site: | Robinson  |
| Issue date: | 02/25/2021 |
| From: | Robinson H Duke Energy Progress, Plant Licensing Branch II |
| To: | John Klos Plant Licensing Branch II |
| Hood T | |
| References | |
| Download: ML21053A047 (15) | |
Text
Duke Energy Pre-Submittal Meeting - February 25, 2021 H. B. Robinson 3rd Interval Containment ISI Relief Request
Proposed Request in Accordance with 10 CFR 50.55a(z)(1)
H. B. Robinson Containment ISI Relief Request Third Interval H. B. Robinson, Unit 2 Containment Inservice Inspection (CISI) Proposed Relief Request Third Interval September 9, 2019 through September 8, 2029 2
Participants Mark Pyne, Manager Fleet ISI Engineering Programs - Duke Energy Angela Staller, ISI Program Manager - Duke Energy Austin Keller, ISI Program Manager - Duke Energy Winston Stewart, Manager Nuclear Engineering - Duke Energy Megan Watkins, Containment Program RE/RI - Duke Energy Art Zaremba, Fleet Licensing Manager - Duke Energy Chet Sigmon, Fleet Licensing - Duke Energy 3
Objectives for This Meeting:
Brief NRC on Dukes reason for proposed request, proposed alternative, basis for use, and proposed timeline Ensure common understanding for Duke Energys request, technical scope, and regulatory expectations Obtain NRC feedback prior to formal submittal 4
Agenda I. Components Affected II. ASME Code and Regulatory Requirements III. Reason for Request IV. Proposed Alternatives V. Basis for Relief VI. Precedents VII. Conclusion 5
I. Components Affected Components Affected:
H. B. Robinson (RNP), Unit 2 is one of two units in the US with the Containment shell metallic liner covered by thermal insulation and stainless steel sheathing.
Related sealant materials and moisture barriers
- Silicone rubber sealant is installed at the interface between approximately 2,200 adjacent stainless steel sheathing panels that cover the containment liner plate thermal insulation.
- Caulking and sealant materials are also installed between the containment concrete floor and the base of the stainless steel sheathing at Elevation 228-0, and at the top of the insulation panel sheathing at Elevation 367-10.
- Moisture barriers are installed between the joints and the concrete floor slab above the liner.
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I. Components Affected- Containment Liner Configuration Note: The containment liner is 1/2 thick from EL. 226 to EL 253, 3/8 thick from EL 253 to 352, and 1/2 thick above EL 352.
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II. ASME Code and Regulatory Requirements Code of record is the 2013 Edition.
ASME Section XI, Subsection IWE 10 CFR 50.55a(z)(1) 8
III. Reason for Request Duke Energy believes that some aspects of currently published and endorsed Editions of the ASME Section XI IWE requirements are focused on containment vessels rather than metallic liners.
The interior surface of the containment shell metallic liner is covered by approximately 2,200 thermal insulation panels. Approximately 400 of the panels have been removed to facilitate examinations of the liner plates behind them with coatings reapplied to the liner upon completion of examinations. As such, examinations of the liner behind the remaining 1,800 insulation panels would be subject to examination in accordance with Section XI requirements for Code Category E-C, Item Number E4.11, and would be required to be inspected during each inspection period.
Silicone rubber sealant is installed at the interface between adjacent stainless steel sheathing panels that cover the containment liner plate thermal insulation and would be required to be examined in accordance with Code Category E-A, Item Number E1.30 each inspection period.
Caulking and sealant materials are also installed between the containment concrete floor and the base of the stainless steel sheathing at Elevation 228-0, and at the top of the insulation panel sheathing at Elevation 367-10 and would be required to be examined in accordance with Category E-A, Item Number E1.30 each inspection period. Due to the difficulty of safely reaching the material at Elevation 367-10 for inspection, maintenance, and repair, Duke Energy considers visual examinations unusually difficult and does not intend to perform visual examinations of the caulking and sealant materials at this upper elevation.
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IV. Proposed Alternatives VT-1 visual examinations are proposed on 10% of the containment liner plates behind insulation panels at the interface between the concrete and the containment base mat (228-foot Elevation) in accordance with Section XI requirements once per ten-year interval.
VT-1 visual examinations in accordance with Section XI requirements are proposed on additional containment liner plates that were not examined during the First or Second Containment Inservice Inspection Intervals. A minimum of 90 liner plates shall be selected from the accessible population of liner plates to be examined.
These examinations will occur on a once per ten-year interval basis. This sample size satisfies the criteria in NRC Draft Regulatory Guide DG-1070, Table 1 for a lot size greater than 1000.
In addition, when any insulation panel at any elevation is removed for maintenance activities, VT-1 visual examinations shall be performed on the exposed containment liner plate surfaces in accordance with Section XI requirements.
If successive examinations are required in accordance with IWE-2420, they may be limited to surfaces whose coatings have not been restored to protect against potential future degradation.
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IV. Proposed Alternatives A general visual examination shall be performed in accordance with Table IWE-2500-1, Examination Category E-A, Item E1.30 on moisture barriers installed between the containment liner plate and the interior concrete floor embedment zone on the liner plates that are examined at the containment base mat.
A general visual examination shall be performed on all sealant and caulking materials installed at the base of the bottom row of insulation panel stainless steel covers at Elevation 228 (approx.) with exception to very high radiological areas such as the Regen Heat Exchanger, as well as sealant and caulking material between vertical joints in the bottom row of insulation panel stainless steel covers in accordance with Section XI requirements.
In lieu of the Acceptance Standards required by IWE-3521(a) which states, pressure-retaining component corrosion or erosion that exceeds 10% of the nominal wall thickness, Duke Energy proposes that corrosion or erosion that exceeds 120% of the minimum wall thickness required by design shall require correction or evaluation to meet the requirements of IWE-3122 prior to continued service.
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V. Basis for Relief Over the last two intervals more than 400 insulation panels have been removed at various locations and elevations to facilitate inspections resulting in all liner plate wall thicknesses greater than the minimum thickness required by design.
All areas examined were recoated and as-left examinations performed prior to re-insulating and sheathing replacement. Duke Energy believes that these surfaces are no longer priority examination locations and that re-applying the coating following the evaluation provides reasonable assurance that degradation is being mitigated.
Sealant and caulking materials installed at the base mat of the containment insulation and in the vertical joints between insulation panel stainless steel covers at EL 228 will be examined in accordance with Section XI requirements during each inspection period to ensure that any potential standing water that could accumulate on the concrete floor does not contact the liner plate.
IWE-3521(a) defines degradation exceeding 10% of nominal wall thickness a relevant condition. This criteria is more appropriate for vessels. Use of this acceptance criteria for metallic liners is considered overly conservative given the Robinson liner has ample wall thickness margin.
The RNP Unit 2 containment is a post-tensioned concrete containment vessel with a A36 metallic liner. Significantly less than 90% of the liner thickness is required in order to maintain the liner design function of providing a leak tight barrier.
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VI. Precedents Similar relief requests were approved for the first and second containment inspection intervals at Robinson.
Relief request IWE/IWL-RR-01 was approved for Category E-A, Item Number E1.11 for the containment metallic liner for the second inspection interval.
Relief request IWE/IWL-RR-02 was approved for Category E-A, Item Number E1.30 for the moisture barriers for the second containment inspection interval.
The primary difference in the relief request being submitted for the third containment inspection interval and the requests submitted for previous intervals is related to the code category for the containment liner. Previously, relief was requested for code category E-A, item E1.11. Based on Code Interpretation XI-1-13-25, the containment liner is now considered to be inaccessible. Therefore, the code category and item number for which relief is being requested for the metallic liner is now E-C, E4.11.
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VII. Conclusion Performing inspections of 100% of the liner and moisture barrier materials during each inspection period is unusually difficult.
Approximately 2,200 Insulation panels Difficulty safely reaching all areas Panel obstructions Radiological concerns with the regen heat exchanger area. Dose rates during the fall 2018 outage were 2800c/1600@30 cm, and 9 Rem was received.
For the reasons discussed in this presentation, Duke Energy believes that the proposed alternative provides an acceptable level of quality and safety.
Duke Energy plans to submit this request during the Spring of 2021.
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