ML21055A886

Response to Request for Additional Information Regarding Steam Generator Inspection 180-Day Report

ML21055A886
Person / Time
Site:	Beaver Valley
Issue date:	02/24/2021
From:	Grabnar J Energy Harbor Nuclear Corp
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
EPID L-2020-LRO-0063, L-21-036
Download: ML21055A886 (5)

Text

energy harbor Energy Harbor Nuclear Corp.

Beaver Valley Power Station P.O. Box 4 Shippingport, PA 15077 John J. Grabnar 724-682-5234 Site Vice President, Beaver Valley Nuclear February 24, 2021 L-21-036 ATTN: Document Control Desk U.S. Nuclear Regulatory Commission Washington, DC 20555-0001

Subject:

Beaver Valley Power Station, Unit No. 2 Docket No. 50-412, License No. NPF-73 Response to Request for Additional Information Regarding Steam Generator Inspection 180-Day Report (EPID L-2020-LRO-0063)

By correspondence dated October 13, 2020 (Accession No. ML20287A373), Energy Harbor Nuclear Corp. submitted to the Nuclear Regulatory Commission (NRC) information related to steam generator inspections performed during the Beaver Valley Power Station, Unit No. 2, spring of 2020 refueling outage (2R21 ). By email dated January 14, 2021 (Accession No. ML21015A576), the NRC staff requested additional information regarding the steam generator inspections. The Energy Harbor Nuclear Corp. response to the NRC request is attached.

There are no regulatory commitments contained in this submittal. If there are any questions or if additional information is required, please contact Mr. Phil H. Lashley, Manager - Fleet Licensing, at (330) 696-7208.

Sincerely, Grab-nar,J ohn 1907 2 Docu ~ .

John J. Grabnar

Attachment:

Response to Request for Additional Information

Beaver Valley Power Station, Unit No. 2 L-21-036 Page 2 cc: NRC Region I Administrator NRC Resident Inspector NRR Project Manager Director BRP/DEP Site BRP/DEP Representative

Attachment L-21-036 Response to Request for Additional Information Page 1 of 3 NRC staff requests for additional information are provided below in bold text and are followed by the Energy Harbor Nuclear Corp. response.

1. If there are sleeved tubes on the hot leg in rows 1 and 2, please clarify the inspections performed in the straight-leg portion of these tubes.

Response

There are no sleeves installed in the hot or cold legs of the row 1 or 2 tubes in the Beaver Valley Power Station, Unit No. 2 (BVPS-2) steam generators (SGs). Row 1 and 2 tube locations are located outside the sleeving boundary.

2. Please provide the following information about the detection for the first time of cold leg thinning at the second cold-leg support plate:

2.a. Describe how the form of the tube thinning compares to fleet operating experience for cold leg thinning in terms of the apparent mechanism.

Response

Cold leg thinning (CLT) is a documented degradation mechanism that occurred throughout the fleet of original Westinghouse Model 51 SGs. CLT is predominately located at lower cold leg tube support plates (TSPs) in the outer peripheral tubes of the tube bundle. CLT is caused by a corrosion (wastage) mechanism due to the crevice environment and accelerated or assisted by tube vibration. CLT refers to a volumetric type of degradation mechanism, centered within the cold leg TSP, but may extend axially to the full thickness of the TSP. Degradation of the outside tube wall surface occurs in a fairly uniform manner and exhibits both axial and circumferential extents. It was determined that the indication reported at the second cold leg TSP during the spring of 2020 refueling outage (2R21) in Row 40 Column 71 of SG A was caused by CLT.

2.b. Describe how the initial detection of this degradation mechanism in a Beaver Valley Unit 2 SG compares with fleet operating experience with respect to factors such as SG age, location, operating conditions, and type and amount of deposits.

Response

Cold leg thinning is predominately located at lower elevation cold leg tube support plates (TSPs) in the outer peripheral tubes of the tube bundle. CLT was detected throughout the fleet of original Westinghouse Model 51 SGs early in the operating life of the component. CLT was identified in the Beaver Valley Power Station, Unit No. 1 (BVPS-1) SGs as early as the spring of 1983 refueling outage (1R03) at approximately 2.67 effective full power years (EFPY) of operation.

Attachment L-21-036 Page 2 of 3 At BVPS-2, CLT was first detected in SG A during 2R21 at the second cold leg TSP in Row 40 Column 71 (located on the periphery of the tube bundle). The BVPS-2 SGs had amassed approximately 27.84 EFPY of operation at the end of Cycle 21.

The reduced propensity for the occurrence of CLT in the BVPS-2 SGs may be related to the design of the SG itself. When compared to other Model 51 SGs, the BVPS-2 SGs contain a flow distribution baffle located approximately 20.0 inches above the secondary side face of the tubesheet as well as 7 tube support plates. The BVPS-2 SGs also contain 6 additional stay rods, 3 on the hot leg and 3 on the cold leg for a total of 11 stay rods. Other Model 51 SGs only have 5 stay rods. The addition of these internal components adds rigidity to the tube bundle and thereby helps to limit an element (vibration) needed for CLT to occur.

Another factor to consider in reducing the occurrence of CLT is the BVPS-2 secondary side chemistry regime. This regime limits a second element (aggressive crevice chemistry) needed for CLT. The primary and secondary side chemistry regime follow the latest revisions of the Electric Power Research Institute primary and secondary side chemistry guidelines.

The BVPS-2 SGs were chemically cleaned during the spring 2017 refueling outage (2R19). A full tube bundle cleaning technique called inhibited advanced scale conditioning agent (iASCA) was utilized. A total of 7,111 pounds of sludge was removed from the three SGs through the iASCA process and post iASCA sludge lancing. Post 2R19 sludge lancing has removed a combined average for all three SGs of 89 pounds per outage. The amount of sludge removed from the BVPS-2 SGs follows a similar pattern seen at other sites post chemical cleaning. The iron transport data for the three cycles following the tube bundle cleaning using iASCA are as follows: Cycle 20 (1.52 parts per billion or ppb), Cycle 21 (1.17 ppb) and the current operating cycle, Cycle 22 (1.52 ppb as of February 2, 2021).

A sludge characterization was performed on the sludge that was removed during the fall of 2018 refueling outage (2R20). The primary elemental constituent in the 2R20 SG bulk sludge samples was iron (67.2 to 70.9 percent [%]), as measured by the inductively coupled plasma (ICP) method. Minor constituents of chromium, manganese, nickel, titanium, and carbon were also present in the sludge. Magnetite was identified as the main fraction, with no hematite, copper oxide or maghemite identified. This indicates reducing conditions were maintained in the SGs during power operation. Copper concentrations increased compared to fall of 2012 refueling outage (2R16) sludge analysis (this effect was also observed at another United States plant following iASCA application). The copper most likely redistributed from tube scale, but remains well below industry averages, and is comparable to the industry median concentration for plants with no balance of plant copper present. The 2R20 average copper concentration in the three SGs was 1046 parts per million (ppm) versus the industry average of 8448 ppm. Flakes of the sludge were characterized for thickness, porosity, and density and were generally comparable to 2R16 refueling outage sludge results.

Attachment L-21-036 Page 3 of 3 2R16 was the last refueling outage where a SG sludge characterization was performed prior to 2R20.

2.c. Describe how an appropriate rate was determined for projecting degradation growth during the current operating cycle.

Response

Row 40 Column 71 of SG A was reported with a CLT indication during 2R21. The indication was located at the second cold leg TSP and measured 0.29 inch and 0.52 inch in axial and circumferential extent, respectively, with a bobbin coil depth measurement of 25% through wall (TW).

The BVPS-1 original Model 51 SGs experienced cold leg thinning. During the fall of 2004 refueling outage (1R16), which was the last SG inspection before SG replacement, a total of 386 cold leg thinning indications were reported. Historical lookups show precursor signals in many of these locations from the prior spring of 2003 refueling outage (1R15) inspection. Therefore, robust growth rate information was available.

Based on the BVPS-1 data, the growth rate for Row 40 Column 71 was projected to be (at the 95th percentile) 10.4% TW per EFPY or 14.9% TW for a Cycle 22 duration of 1.437 EFPY.

3. The discussion of tube plugging and repairs for SG21A indicates that sleeves were installed in two tubes following in-situ pressure testing, but the tubes were subsequently plugged based on engineering analysis. Please describe if the analysis would allow for future sleeving of in-situ pressure-tested tubes, and under what conditions, at Beaver Valley Unit 2.

Response

An analysis was requested during the outage to leave these two sleeved tube locations in-service but the timeframe in which the analysis had to be completed could not be met, therefore, the two tubes were plugged. It has since been determined that the cost and scope of such analyses outweighs the benefit of sleeving in-situ pressure-tested tubes and permitting them to remain in service. Therefore, at the time of this response, there is no plan to pursue an analysis of this type in the future.