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Authorization of Relief Request No. RR-ISI-05-20 Regarding Mitigation of Buried Saltwater System Piping Degradation
	ML22202A514
Person / Time
Site:	Calvert Cliffs
Issue date:	07/28/2022
From:	Hipolito Gonzalez; NRC/NRR/DORL/LPL1
To:	Rhoades D; Constellation Energy Company, Constellation Nuclear
	Gonzales H, NRR/DORL/LPL1
References
	EPID L-2022-LLR-0013
	Download: ML22202A514 (10)
	v • d • e

July 28, 2022 Mr. David P. Rhoades Senior Vice President Constellation Energy Generation, LLC President and Chief Nuclear Officer Constellation Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 -

AUTHORIZATION OF RELIEF REQUEST NO. RR-ISI-05-20 REGARDING MITIGATION OF BURIED SALTWATER SYSTEM PIPING DEGRADATION (EPID L-2022-LLR-0013)

Dear Mr. Rhoades:

By letter dated February 3, 2022, Constellation Energy Generation, LLC (the licensee) proposed an alternative to certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Article IWA-4000 for Calvert Cliffs Nuclear Power Plant (Calvert Cliffs), Units 1 and 2.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1),

licensee proposed to use a mechanical sleeve assembly to repair inside surface degradation of mortar-lined, ductile iron piping in the saltwater system for the Calvert Cliffs fifth 10-year inservice inspection (ISI) interval.

The NRC staff finds the licensee has demonstrated that its proposed alternative provides an acceptable level of quality and safety in lieu of complying with the ASME Section XI requirements and inspection items specified and referenced in Relief Request No.

RR-ISI-05-20. Accordingly, the NRC staff concludes that the licensee has adequately addressed all of the regulatory requirements set forth in 10 CFR 50.55a(z)(1).

Therefore, the NRC authorizes the use of the proposed alternative for Calvert Cliffs, Units 1 and 2, for the current fifth 10-year ISI interval which began on July 1, 2019, and is currently scheduled to end June 30, 2029.

All other ASME BPV Code,Section XI, requirements for which relief was not specifically requested and approved in this relief request remain applicable, including third-party review by the Authorized Nuclear Inservice Inspector.

If you have any questions, please contact Michael Mahoney at 301-415-3867 or via email at Michael.Mahoney@nrc.gov.

Sincerely, Hipolito J. Gonzalez, Chief Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-317 and 50-318

Enclosure:

Safety Evaluation cc: Listserv Hipolito J.

Gonzalez Digitally signed by Hipolito J. Gonzalez Date: 2022.07.28 12:47:35 -04'00'

Enclosure SAFETY EVALUATION BY THE OFFICE NUCLEAR REACTOR REGULATION RELIEF REQUEST NO. RR-ISI-05-20 REGARDING MITIGATION OF BURIED SALTWATER PIPING DEGRADATION CALVERT CLIFFS NUCLEAR POWER PLANT, LLC CONSTELLATION ENERGY GENERATION, LLC CALVERT CLIFFS NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-317 AND 50-318

1.0 INTRODUCTION

By letter dated February 3, 2022, (Agencywide Documents Access and Management System, Accession No. ML22034A008) Constellation Energy Generation, LLC (the licensee) proposed an alternative (Relief Request No. RR-ISI-05-20) to certain requirements of the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code),Section XI, Article IWA-4000 for Calvert Cliffs Nuclear Power Plant (Calvert Cliffs), Units 1 and 2.

Specifically, pursuant to Title 10 of the Code of Federal Regulations (10 CFR) 50.55a(z)(1),

licensee proposed to use a mechanical sleeve assembly to repair inside surface degradation of mortar-lined, ductile iron piping in the saltwater system for the Calvert Cliffs fifth 10-year inservice inspection (ISI) interval.

Pursuant to 10 CFR, Section 50.55a(a)(z)(1), the licensee requested approval of this proposed alternative repair method on the basis that the proposed repair provides an acceptable level of quality and safety.

2.0 REGULATORY EVALUATION

Adherence to Section XI of the ASME Code is mandated by 10 CFR 50.55a(g)(4) which states, in part, that ASME Code Class 1, 2, and 3 components will meet the requirements, except that design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI.

Paragraph 10 CFR 50.55a(z) states, in part, that alternatives to the requirements of paragraphs (b) through (h) of 10 CFR 50.55a or portions thereof may be used when authorized by the Director, Office of Nuclear Reactor Regulation. A proposed alternative must be submitted and authorized prior to implementation. The licensee must demonstrate:

1. The proposed alternative would provide an acceptable level of quality and safety, or

2. Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Based on the above, and subject to the following technical evaluation, the NRC staff finds that regulatory authority exists for the licensee to request the use of an alternative and the NRC to grant relief and the use of the proposed alternative.

3.0 TECHNICAL EVALUATION

3.1 ASME Code Components Affected

ASME Code Class 3 Buried Saltwater System ductile cast iron 30- and 36-inch piping for Calvert Cliffs, Units 1 and 2.

3.2 Applicable Code Edition, Addenda, and Requirements The current code of record for Calvert Cliffs, Units 1 and 2, is the ASME Code,Section XI, 2013 Edition, no Addenda. Calvert Cliffs, Units 1 and 2, are in their fifth 10-year ISI interval which began on July 1, 2019, and will end on June 30, 2029.

ASME B&PV Code,Section XI, Article IWA-4000 is applicable to repairs/replacements of the affected components.

3.3

Reason for Request

In accordance with 10 CFR 50.55a(z)(1), the licensee is requesting approval of this proposed alternative repair method on the basis that the proposed repair provides an acceptable level of quality and safety.

The reason for the proposed alternative repair is to allow the use of a mechanical repair system to restore pressure boundary integrity for degraded conditions found during inspections. The proposed mechanical repair system will be utilized only for localized degradation in the piping.

The licensee stated that the direct replacement of this piping to correct relatively minor localized conditions would not result in a compensating increase in the systems overall level of quality and safety when compared to the proposed mechanical repair alternative.

The licensee stated that there are no approved methods or new technologies that provide an adequate method to weld ductile cast iron piping without adversely affecting the integrity of the base metal. The ductile cast iron Buried Saltwater System underground piping contains bell and spigot pipe with fittings that connect to compress the joint gasket. This consists of a loose flange or gland that is slid over the spigot section of the pipe prior to insertion into the bell. Once inserted into the joint, bolting is installed between the gland and the integrally cast flange on the bell section of piping. The bolting is then tightened to seat the V wedge type gasket and thus provide a leak tight joint.

The licensee stated that repairs and modifications to ductile cast iron pipe must use similar methods of mechanical compression for connectivity and in some cases threaded joints may also be utilized.

The planned comprehensive inspection of the Buried Saltwater System piping is being performed to assess and ensure the long-term integrity of the pipe.

The licensee stated that previous internal inspections of the piping revealed areas of missing or deteriorated cement mortar liner and the mortar lining was repaired. Areas where base metal deterioration has been noted have been minor and have not fallen below minimum wall thickness criteria. The licensee stated that at this time there is no reason to believe that the integrity or reliability of the buried piping has been compromised. The licensee stated that they are not aware of any specific areas that may be subject to accelerated degradation due to saltwater corrosion or areas of high stress concentration that could be prone to cracking or fracture. There is also a protective coating on the outer diameter of the piping that provides a barrier from external corrosion.

A visual inspection of the concrete liner and base metal, if exposed, will be performed. Any suspect indication will be subject to nondestructive examination methods.

The licensee stated that the construction cost, impact on outage duration, and operational challenges to replace a portion of the Buried Saltwater System piping during an outage are substantial. The physical proximity of the Buried Saltwater System piping and the constraints encumbered by interferences located in the Turbine Building make replacement very challenging. Furthermore, the licensee stated that the Saltwater System is the ultimate heat sink, and replacement could affect both trains of that system, a full reactor core offload would be required. In addition, it would be required to align the unaffected unit to provide cooling to the spent fuel pool, thus establishing abnormal plant configurations for an extended period of time.

3.4 Licensees Proposed Alternative and Basis for Use The scope of the repair alternative is limited to the buried sections of the 30- and 36-inch Saltwater System ductile cast iron piping. The proposed repair alternative is not applicable for use on any gray cast iron section of the Saltwater System piping.

The licensees supporting calculation states any repairs will be made in straight lengths of pipe.

This includes the bell and spigot joints that are part of straight lengths of pipe within the Saltwater System. The proposed repair alternative is not designed to be used in pipe fittings or across mitered joints.

The licensee stated that the Saltwater System piping has a design pressure of 50 psig. The Saltwater System temperature varies in accordance with Chesapeake Bay temperature throughout the year and load demands on the system. The Saltwater System is designed to temperatures from 30 degrees Fahrenheit (°F) up to the design temperature of 200°F.

The proposed repair/replacement alternative is a sleeve assembly primarily consisting of a pressure-retaining backing plate, internal rubber gasket, and four retaining bands.

The backing plate is made of ASME SB-688 (AL6XN) (UNS N08367), a single sheet of 16-gauge sheet metal 14 inches wide and designed to enclose the entire inside circumference of the 30-inch and 36-inch size pipe. It will be placed directly over the degraded area on the inner diameter of the pipe to restore pressure boundary integrity.

The rubber gasket is made of ethylene propylene diene monomer (EPDM). It is factory vulcanized to form one continuous piece and designed to fit the piping inner surface. The gasket is 0.3 inch thick and about 20 inches wide. The ends of the gasket have grooved ribs. The rubber gaskets are placed over the backing plate and completely enclose the entire backing plate and extend beyond each end of the backing plate.

The retaining bands are also made of AL6XN, 2 inches wide, 0.1875 inch thick and ring shaped.

Two retaining bands are placed on each end of the gasket and two near the middle where the backing plate is located. The retaining bands are radially expanded by a hydraulic expander to keep the backing plate and the gasket in place and held tightly against the pipe. The retaining bands are locked in place by wedges also made of AL6XN material. The two end retaining bands compress the groove ends of the gasket against the pipe inner circumference and provide a leak tight seal to prevent water intrusion past the gasket. The two middle retaining bands secure the backing plate in place.

The Saltwater System underground piping has a nominal 0.25-inch cement lining on the inside surface. The licensee stated that prior to installation of the sleeve, the cement lining for the entire length of the sleeve assembly should be removed and repaired with an approved coating.

To prevent galvanic corrosion, the outer surface of the backing plate will be wrapped with a 0.125-inch-thick rubber gasket so that the stainless steel backing plate does not come in direct contact with the ductile cast iron piping. The licensee stated that it is possible, although unlikely, to have crevice corrosion should the water leak under the outer stainless steel retaining bands.

Therefore, the licensee stated that periodic inspections will be performed by disassembling the sleeve assembly and checking for any deterioration of the retaining bands, signs of leakage past the gasket, or any other degradation.

The licensee supplied a design calculation for the repair sleeve assembly for the loads applied during installation and operation. The licensee stated that the calculation demonstrates that the repair provides a mechanism to restore pressure boundary integrity by utilizing the reinforcing plate as the new pressure boundary for a locally degraded section of the piping.

The proposed repair system will be applied in cases where degradation has resulted in saltwater piping wall thickness falling below minimum design wall thickness values and is the result of corrosion initiated on the interior diameter of the saltwater piping. The licensee stated that this proposed repair will not be used in cases of discovered crack-like flaws, through-wall degradation, or on corrosion that initiated on the external diameter of the saltwater piping.

Should any of those cases be discovered, the licensee stated that additional analysis would be performed, and a separate proposed repair alternative would have to be submitted.

3.5 Duration of Proposed Alternative The licensee is requesting approval of Relief Request No. RR-ISI-05-20 for the current fifth ISI interval which began on July 1, 2019, and is currently scheduled to end June 30, 2029.

3.6

NRC Staff Evaluation

The NRC staff evaluated the design, examinations, analysis, pressure tests and the proposed repair method in relief request RR-ISI-05-20 dated February 3, 2022. The licensee provided a summary of the proposed repair systems:

1. The materials utilized in the repair system (ASME SB-688) are resistant to corrosion attack when exposed to saltwater in the Saltwater System.

2. The maximum size of the degraded area including projected growth will fit within a 3-inch diameter area.

3. No additional supports are required for the repair system. No welding is required for installation. The component to be utilized relies only on the ductile cast iron piping for structural and pressure integrity.

4. The repair system has been designed for pressure boundary integrity only. The remaining non-degraded ductile cast iron pipe maintains full design structural capacity of the piping system. The installation of the repaired system will be performed with controlled procedures.

5. The repair system utilized considers all design basis loading requirements including seismic and ensures that it will continue to perform its intended function during all those types of events. In addition, the repair system can be removed to allow inspection and monitoring of the deteriorated area.

6. The repair system to be utilized is designed in such a manner so as not to damage or adversely affect the existing ductile cast iron piping.

7. The intended use of the repair system is to repair localized degraded areas in the piping and is not designed to transmit longitudinal loads or a full circumferential severance of the piping.

8. When degradation is identified in the ductile cast iron pipe, it will be characterized to ascertain whether the degradation is inside diameter or outside diameter initiated and the characterization will be considered in the projected degradation growth.

9. The repair system will be installed in piping that is continuously supported and the additional weight does not increase bending in the ductile cast iron pipe.

10. Any degradation identified that is due to erosion or corrosion of the thickness of the material at the load transfer area will be determined and checked against design criteria.

11. The constraining effects of the repair system have also been considered and there are no adverse effects from the installation of the repair system on the ductile cast iron pipe.

The internal mechanical seal (i.e., EPDM rubber gasket, retaining bands) has been utilized as a corrosion barrier in numerous Class 3 systems throughout the nuclear industry for many years.

These seals have ensured that the host pipes are isolated from the effects of the process fluid corrosive effects The installation of this proposed alternative repair is considered to arrest the growth of the corrosion since it will completely seal the degraded area from the corrosive fluid (saltwater). To provide assurance of the proposed repair, the licensee provided a commitment after installing the sleeve assembly that they will disassemble the first repair system to inspect the degraded area after two cycles. The inspection will include:

A check of the retaining bands and backing ring for corrosion A check of the area under the sleeve for wetness A check for any damage of the liner A check for damage of the EPDM gasket The results of this inspection will then be used to determine if any change in the periodicity of this action is warranted. The licensee stated in case of multiple installations, only one of the proposed repair systems will be disassembled while the rest will be visually inspected every other refueling outage while performing their current preventive maintenance task to inspect Saltwater System piping.

All degradation that is identified will be assessed by the licensee on a case-by-case basis.

Depending on the defect size, the pressure plate may be altered to provide adequate strength to account for degradation outside of the design basis calculation. Appropriate changes will be made to the calculation to reconcile any changes to the pressure plate dimensions. Defects will be characterized to ensure that the defect will be contained within the specified limits of the repair system. Subsequent inspection frequencies of the encapsulated degraded area will also be determined. Monitoring of the size of the degradation will be performed as required.

3.6.1 NRC Staff Evaluation Summary The NRC staff finds the licensees commitment and proposed repair systems identified in section 3.6 of this safety evaluation to be acceptable because the additional inspections will reduce the possibility that degradation of the repair would not be identified during a scheduled inspection. The proposed alternative also provides reasonable assurance of structural integrity or leak tightness of the subject component since the proposed repair is considered to stop the growth of the corrosion by completely sealing the degraded area from the corrosive fluid which is saltwater.

4.0 CONCLUSION

The NRC staff concludes that the proposed alternative provides reasonable assurance of structural integrity of the 30- and 36-inch Class 3 Buried Saltwater System ductile cast iron piping for Calvert Cliffs, Units 1 and 2.

The NRC staff finds that the proposed alternative described above would provide an acceptable level of quality and safety. Accordingly, the NRC staff concludes that the licensee has adequately addressed all the regulatory requirements set forth in 10 CFR 50.55a(z)(1).