1CAN012301, Responses to Request for Additional Information for Request for Relief ANO1-ISI-035
| ML23030B329 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 01/30/2023 |
| From: | Couture P Entergy Operations |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 1CAN012301 | |
| Download: ML23030B329 (1) | |
Text
Entergy Operations, Inc. 1340 Echelon Parkway, Jackson, MS 39213 1CAN012301 10 CFR 50.55a(z)(2)
January 30, 2023 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555
Subject:
Responses to Request for Additional Information for Request for Relief ANO1-ISI-035 Arkansas Nuclear One, Unit 1 NRC Docket No. 50-313 Renewed Facility Operating License No. DPR-51
References:
- 1. Entergy Operations, Inc. (Entergy) letter to the U. S. Nuclear Regulatory Commission (NRC), "Request for Relief Related to American Society of Mechanical Engineers (ASME) Code Case N-729-6 Augmented Examination Requirements ANO1-ISI-035", (1CAN052201), (ML22151A322), dated May 31, 2022
- 2. NRC email to Riley Keele (Entergy) "Final RAI RE: Relief Request ANO1-ISI-035 (EPID L-2022-LLR-0050)," (1CNA122204), (ML22349A011), dated December 14, 2022 By Reference 1, Entergy Operations, Inc., (Entergy) requested the U.S. Nuclear Regulatory Commission (NRC) to approve a request for a one-time extension of the schedule for inservice examination of Control Rod Drive Mechanism (CRDM) Penetration No. 1 in the Arkansas Nuclear One, Unit 1 (ANO-1) reactor vessel closure head (RVCH). The augmented examination requirements of 10 CFR 50.55a(g)(6)(ii)(D) specify that periodic inservice volumetric or surface examinations be performed of RVCH penetrations in accordance with ASME Code Case N-729-6.
The NRC staff has reviewed the request and determined that additional information was required to complete their review (Reference 2).
The Requests for Additional Information (RAIs) and the associated responses are provided in the Enclosure.
Phil Couture Senior Manager Fleet Regulatory Assurance - Licensing Tel 601-368-5102
1CAN012301 Page 2 of 2 This letter contains no new regulatory commitments.
If there are any questions or if additional information is needed, please contact Riley Keele, Manager, Regulatory Assurance, at (479) 858-7826.
Respectfully, Phil Couture PC/rwc
Enclosure:
Responses to Request for Additional Information for Request for Relief ANO1-ISI-035 cc:
NRC Region IV Regional Administrator NRC Senior Resident Inspector - Arkansas Nuclear One NRC Project Manager - Arkansas Nuclear One Philip Couture Digitally signed by Philip Couture Date: 2023.01.30 09:52:42 -06'00'
ENCLOSURE 1CAN012301 RESPONSES TO REQUEST FOR ADDITIONAL INFORMATION FOR REQUEST FOR RELIEF ANO1-ISI-035
1CAN012301 Enclosure Page 1 of 5 RESPONSES TO REQUEST FOR ADDITIONAL INFORMATION FOR REQUEST FOR RELIEF ANO1-ISI-035 By Reference 1, Entergy Operations, Inc., (Entergy) requested the U.S. Nuclear Regulatory Commission (NRC) to approve a request for a one-time extension of the schedule for inservice examination of Control Rod Drive Mechanism (CRDM) Penetration No. 1 in the Arkansas Nuclear One, Unit 1 (ANO-1) reactor vessel closure head (RVCH). The augmented examination requirements of 10 CFR 50.55a(g)(6)(ii)(D) specify that periodic inservice volumetric or surface examinations be performed of RVCH penetrations in accordance with American Society of Mechanical Engineers (ASME) Code Case N-729-6.
The NRC staff has reviewed the request and determined that additional information was required to complete their review (Reference 2).
Below are the Requests for Additional Information (RAIs) and the associated responses.
NRC REQUEST (RAI-1)
Given the limited hypothetical flaw analysis case is the time for an outside diameter (OD) axial crack centered at the toe of the weld to grow through the nozzle wall, the NRC staff requests additional information on the options for OD surface examination and the hardship associated with any such options.
(a)
Provide additional information (e.g., schematic drawings, diagrams, photographs, description) regarding how the configuration of the RADCAL instrument installed on CRDM Penetration No. 1 prevents volumetric and surface examinations from the inside diameter (ID) and OD of the nozzle penetration and wetted surface of the J-groove weld, as appropriate.
ENTERGYS RESPONSE (RAI-1a)
During the incident at Three Mile Island, Unit 1 in March 1979, reactor coolant system (RCS) water in the area above the core turned into steam. Since the plant did not contain the instrumentation to measure the water level inside the reactor vessel in this area, the water level above the core could not be determined at any time during this incident. The NRC issued NUREG-0737 that requires the capability of determining the water level throughout the reactor vessel. Entergy chose to install the RADCAL probe to satisfy the requirements of Item II.F.2 of NUREG-0737, Inadequate Core Cooling.
The hardware for the RADCAL is divided into three main sub-assemblies and several lesser assemblies. These three subassemblies are Control Rod Brazement Instrument Guide Assembly - This assembly is a guide structure which is permanently bolted into the control rod tube. It provides alignment and flow induced vibration protection for the instruments.
1CAN012301 Enclosure Page 2 of 5 CRDM Adaptor Flange / Closure Guide Assembly - This assembly is permanently bolted to the center control rod drive mechanism (CRDM) flange, replacing the CRDM. It provides guidance and protection for the manometer tubes, protection for the instrument leads and a portion of the pressure boundary.
Manometer Tube / Closure Assembly - Contains the actual probes. It provides controlled volumes for the instrument and forms a portion of the pressure boundary.
Figure 1 provides a drawing of the arrangement of the RADCAL assembly and the CRDM Penetration No.1 nozzle.
Figure 1 As shown in the photograph of Figure 2, the CRDM Adaptor Flange / Closure Guide Assembly passes through CRDM Penetration No. 1. The Inside Diameter (ID) of CRDM Penetration No. 1 is 2.765 inches +0, -0.030. The Outside Diameter (OD) of the Closure Guide Assembly is 2.625 inches. Therefore the radial gap is within the range of 0.055 to 0.070 inches between the nozzle and the RADCAL assembly. As this assembly is bolted to the CRDM flange, it cannot be flexed from side to side. The RADCAL assembly extends approximately 46 inches below the bottom of CRDM Penetration No. 1 during refueling outages when the head is located on its storage stand. Figure 3 is a photograph showing the general orientation of the CRDM penetrations with installed CRDM drives (leadscrews and leadscrew support tubes) from under the ANO-1 RVCH. Please see the response below to Part (b) of RAI-1 with regards to how the installed RADCAL assembly affects access for nondestructive examination (NDE).
1CAN012301 Enclosure Page 3 of 5 Figure 2 Figure 3
1CAN012301 Enclosure Page 4 of 5 NRC REQUEST (RAI-1)
Given the limited hypothetical flaw analysis case is the time for an outside diameter (OD) axial crack centered at the toe of the weld to grow through the nozzle wall, the NRC staff requests additional information on the options for OD surface examination and the hardship associated with any such options.
(b)
Discuss the maximum extent to which the volumetric and surface examinations can be performed without removal of the RADCAL instrument and provide any assessment of the hardship associated with examinations of the portion of CRDM Penetration No. 1 that is not directly obstructed by the RADCAL instrument.
ENTERGYS RESPONSE (RAI-1b)
Volumetric and Surface Examination from the ID To perform a volumetric examination of the penetration requires access to the ID of the penetration. Similarly, access to the ID of the penetration is needed to perform a surface examination of the inside of the penetration. With the RADCAL assembly installed in the penetration, the only available access to the penetration ID is from below through the radial gap between the penetration and RADCAL assembly. A radial gap of 0.125 inches is the typical radial gap in the industry between the inside of CRDM penetrations and thermal sleeves or leadscrew support tubes installed inside the penetration.
Hence, the current probe used at ANO Unit 1 is designed to operate in a nominal radial gap of 0.125 inches. Testing shows that the probe can be driven into a gap as small as 0.085 inches.
As stated above, the radial gap between the nozzle and the CRDM Adaptor Flange / Closure Guide Assembly is nominally 0.070 inches (0.055 inches minimum). Furthermore, the RADCAL assembly is too stiff to be flexed to significantly increase the gap size. Therefore, the existing probe design cannot be used to inspect this penetration with the RADCAL assembly installed.
Similarly, the other gap scanner probes available through the two NDE vendors in the U.S. who offer NDE services for under-head examinations are designed to work with a nominal radial gap of 0.125 inches or greater. In summary, tooling to perform an examination from the inside of Penetration No. 1 with the RADCAL assembly installed is not commercially available.
Surface Examination from the OD Neither of the two vendors that offer under-head NDE services has tooling available that can be used to perform a fully remote examination of the outer surfaces (i.e., nozzle OD below the weld and wetted surface of J-groove weld and butter) of a CRDM penetration. Therefore, performing a surface examination of the outer surface of Penetration No. 1 would necessarily entail significant worker dose. A liquid penetrant test (PT) of the outer penetration surfaces would be fully manual. One vendor does have tooling to facilitate manual eddy current testing (ET) of the penetration outer surfaces. This ET tooling is manually deployed and as such would require a technician to position and manipulate the probe. For either the PT or ET option, removal of drive leadscrews and leadscrew support tubes (three or more) from adjacent CRDM
1CAN012301 Enclosure Page 5 of 5 penetrations would be needed for access and to reduce the dose to the examiner (See Figure 3). Removal of leadscrew support tubes, which are integral with the control rod drive mechanisms, requires disassembly of the bolted flange joint at the upper end of each respective CRDM penetration nozzle, entailing some risk of reactor coolant leakage at this mechanical joint just above the head upon plant startup. In addition, a head stand extension would have to be installed and a platform built to gain access to the center of the RVCH.
Entergy does not have data for the radiation field under the ANO-1 head since head replacement. As an approximation, the data from ANO-2 when a manual inspection was performed of Nozzle 46 is used to estimate the dose for a surface examination of the outer surfaces of Penetration No. 1 on the ANO-1 head. Using estimated time to set the equipment up, perform the examination, and remove the equipment, the estimated dose is in excess of 3 rem. This estimate conservatively does not include any dose for removing the adjacent drives or preparing the surface for examination.
Summary In summary, without removal of the RADCAL instrument, tooling is not available to perform a volumetric examination of CRDM Penetration No. 1 nor an examination of the inside surface of CRDM Penetration No. 1. For the reasons presented in Reference 1, removal and replacement of the RADCAL instrument would constitute a hardship without a compensating increase in the level of quality and safety. Performing a surface examination of the outer surfaces of CRDM Penetration No. 1 would necessarily entail substantial worker dose and some risk of introducing a reactor coolant leak at a bolted flange joint that was disassembled and reassembled to facilitate the examination. Hence, performing a volumetric or surface examination of all or portions of the examination volume/surface specified by ASME Code Case N-729-6 would constitute a hardship without a compensating increase in the level of quality and safety considering the basis for the alternative proposed in Reference 1.
References
- 1. Entergy Operations, Inc. (Entergy) letter to the U. S. Nuclear Regulatory Commission (NRC), "Request for Relief Related to American Society of Mechanical Engineers (ASME)
Code Case N-729-6 Augmented Examination Requirements ANO1-ISI-035",
(1CAN052201), (ML22151A322), dated May 31, 2022
- 2. NRC email to Riley Keele (Entergy) "Final RAI RE: Relief Request ANO1-ISI-035 (EPID L-2022-LLR-0050)," (1CNA122204), (ML22349A011), dated December 14, 2022