LR-N11-0163, Response to Draft NRC Request for Additional Information Regarding Relief Request Nos. S1-I4R-102 and S2-I3R-104 for ASME Code Pressure Test for Service Water Supply Buried Piping
| ML112030205 | |
| Person / Time | |
|---|---|
| Site: | Salem  |
| Issue date: | 07/21/2011 |
| From: | Duke P Public Service Enterprise Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| LR-N11-0163, TAC ME4861, TAC ME4862 | |
| Download: ML112030205 (10) | |
Text
PSEG Nuclear LLC P.O. Box 236, Hancocks Bridge, NJ 08038-0236 OPSEG Nuclear LLC 10 CFR 50.55a LR-N11-0163 JUL 11 2011 u.s. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001
Subject:
Salem Generating Station, Units 1 and 2 Renewed Facility Operating License Nos. DPR-70 and DPR-75 NRC Docket Nos. 50-272 and 50-311 Response to Draft NRC Request for Additional Information Regarding Relief Request Nos. S1-14R-102 and S2-13R-104 for ASME Code Pressure Test for Service Water Supply Buried Piping
References:
- 1.
Letter from Jeffrie J. Keenan, PSEG Nuclear LLC, to U.S. Nuclear Regulatory Commission, "Request for Relief from ASME Code Pressure Test for Service Water Supply Buried Piping," dated October 12, 2010 (ADAMS Accession No. ML102920464)
- 2.
Email from R. Ennis, USNRC to PSEG, "Salem Nuclear Generating Station, Unit Nos. 1 and 2, Draft Request for Additional Information (TAC NOS. ME4861 AND ME4862)," dated April 19, 2011 (ADAMS Accession No. ML111091118)
In Reference 1, PSEG Nuclear LLC (PSEG) submitted relief requests for Salem Generating Station, Units 1 and 2. The relief requests would allow PSEG to use an alternative examination for buried piping in the service water system in lieu of pressure tests required by American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code,Section XI, IWA-5244(b).
In Reference 2 the NRC requested additional information regarding PSEG's relief requests. The information requested by the NRC and PSEG's responses are provided in Attachment 1.
LR-N11-0163 Page 2 There are no new commitments contained in this letter. If you have any questions or require additional information, please contact Paul Duke at (856) 339-1466.
Sincerely,
~ke:.Y Licensing Manager - PSEG Nuclear Attachment cc:
W. Dean, Administrator, Region I, NRC R. Ennis, Project Manager - USNRC NRC Senior Resident Inspector, Salem P. Mulligan, Manager IV, NJBNE L. Marabella, Corporate Commitment Tracking Coordinator H. Berrick, Salem Commitment Tracking Coordinator LR-N11-0163 Response to Draft NRC Request for Additional Information Regarding Relief Request Nos. S1-14R-102 and S2-13R-104 for ASME Code Pressure Test for Service Water Supply Buried Piping Salem Nuclear Generating Station - Units 1 and 2 NRC Docket Nos. 50-272 and 50*311 By letter dated October 12, 2010 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML102920464), PSEG Nuclear LLC (PSEG, the licensee), submitted relief requests S1-14R-1 02 and S2-13R-104 for Salem Nuclear Generating Station (Salem), Unit Nos. 1 and 2. The proposed relief requests would allow PSEG to use an alternative examination for buried piping in the service water system in lieu of pressure tests required by American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (Code),Section XI, IWA-5244(b).
The Nuclear Regulatory Commission (NRC) staff has reviewed the information the licensee provided that supports the proposed relief requests and would like to discuss the following issues to clarify the submittal.
- 1.
Provide the following details about the buried service water prestressed concrete cylinder pipe (PCCP):
- a. Diameter and length Response to Question 1.a 24" inside Diameter The approximate lengths of the buried PCCP SW supply nuclear headers are as follows:
642 feet 12 SW Header Supply -
629 feet 21 SW Header Supply -
635 feet 22 SW Header Supply -
578 feet These lengths consist primarily of PCCP, but also include non-PCCP end pieces and fittings. Section 5 of PSEG's relief requests S1-14R-1 02 and S2-13R-104, submitted by letter dated October 12, 2010 (ADAMS Accession No. ML102920464), describe the Generic Letter (GL) 89-13 visual inspections of the SW headers as covering "approximately 300 feet for each buried header.". The lengths provided above are included in the scope of the subject relief requests and internal visual inspection of this piping is included in the GL 89-13 inspection program.
- b. Design and operating pressures Response to Question 1.b Design Pressure: 200 psi Operating Pressure: 150 psi
- c. Installation year Response to Question 1.c 1972-1973
- d. Pipe fabrication standard (e.g., AWWA C301-84)
Response to Question 1.d American Water Works Association (AWWA) C-301-64
- e. Manufacturer Response to Question 1.e Interpace Corporation LR-N11-0163
- f.
PCCP type - embedded-cylinder (EC-PCCP) or lined-cylinder (LC-PCCP):
Response to Question 1.f LC-PCCP
- 2. Discuss the history of failures or degradation, if any, of the Salem, Unit Nos. 1 and 2, buried PCCP service water piping.
Response to Question 2 The buried sections of Salem Units 1 and 2 Service Water (SW) supply nuclear headers are primarily constructed of 24-inch Pre-stressed Concrete Cylinder Pipe (PCCP), but also include end pieces and fittings that are non-PCCP, called "specials." These specials are non-prestressed 1/2"-thick steel pipe with a non-structural interior and exterior mortar coating for corrosion protection. The 16-foot sections (sticks) of PCCP with bell and spigot ends are connected with bell-bolt joints and external harness assemblies. The external harness assemblies are located at 3 o'clock and 9 o'clock along the length of the pipe sections to help resist axial loads. The PCCP sticks are designed with a 10 gage upgraded cylinder (compared to 16 gage cylinder for regular commercial grade PCCP).
LR-N11-0163 Salem Units 1 and 2 buried PCCP have no known history of failure or degradation e.g., due to prestressing wire breaks or cylinder degradation.
There has been no degradation of external concrete coating discovered during excavations to date and only superficial degradation of internal concrete lining identified during GL 89-13 inspections. However, non-PCCP-related (or "special" as noted above) conditions involving bell and spigot joints and external harnesses between pipe specials are described below for Salem Units 1 and 2:
November 2001 - The bell and spigot joint closest to the Service Water Intake Structure (SWIS) on the 12 SW Nuclear Header developed a leak which was discovered via visual observation of surface water adjacent to the SWIS. This condition was the subject of Salem Unit 1 License Amendment No. 248 and its Safety Evaluation Report (Reference 2-1), which facilitated PSEG's completion of investigation and repair. During initial investigation and corrective actions, PSEG evaluated the potential loss of pcep prestressing as a bounding credible failure mechanism of the piping system, and concluded that deterioration of PCCP reinforcing wires would not cause immediate catastrophic failure of the piping (as summarized in Reference 2-1). The leak was determined to be caused by failure of the steel bell ring in the bell and spigot joint of the special, and was not PCCP-related. Corrective measures were taken to repair the joint and install a double WEKO-Seal with steel backing. This issue drove corrective actions to install WEKO-Seals in the bell and spigot joints in all four SW supply nuclear headers, which have been completed.
April 2010 - During inspection and cleaning of 11 SW nuclear header in preparation for WEKO-Seal installation, the bell and spigot joint in the special closest to the SWIS was found to have a corroded steel bell ring. The joint was cleaned, coated and repaired with a double WEKO-Seal with steel backing.
Also, a 3/4-inch shear bolt head was found to have sheared off from a breakaway coupling on one of the two external harness assemblies. PSEG plans to repair the harness assembly during the next scheduled header outage in accordance with our corrective action program.
April 2011 -Two external harness assemblies for the 21 SW Nuclear Header at the two joints closest to the SWIS were found to have broken 3/4-inch shear bolts in the breakaway couplings. The breakaway couplings were replaced.
Metallurgical analyses of the breakaway coupling sheared bolt material for the 11 and 21 SW nuclear headers identified lower than expected material hardness, suggesting the most probable cause is inadequate bolting material. However, based on the capability of the bell bolts to maintain joint configuration, the sheared bolts do not affect piping integrity during design basis seismic conditions.
LR-N11-0163 Reference 2-1 Letter from U.S. Nuclear Regulatory Commission to PSEG Nuclear LLC "Salem Nuclear Generating Station, Unit No.1, Issuance of Amendment Re: Emergency Request for Change to Technical Specification (TS) 3/4.7.4, Service Water System (TAC No. MB3528)," dated December 27, 2001 (ADAMS Accession No. ML013540096)
- 3.
Concerning internal visual inspection:
- a. What fraction of the length can be internally inspected using the crawler?
Response to Question 3.a The entire length of the piping in the scope of the relief requests can be internally inspected using the crawler.
- b. Will the pipe be cleaned prior to internal visual inspection?
Response to Question 3.b If necessary, cleaning is performed before inspection. Based on experience during periodic GL 89-13 inspections, cleaning is typically not required.
- c. What are the acceptance criteria for visual inspection?
Response to Question 3.c Each SW supply nuclear header is internally inspected every three years (Le.,
one of the two headers is inspected each refueling outage). Internal surfaces are either concrete or, to a much lesser extent (Le., in wall penetration areas), epoxy-lined. Concrete should be free from degradation, e.g. spalling, cracking, and loss.
Epoxy liners should be free from degradation, e.g., holidays, blistering, loss, cracking and pinholes. Degraded conditions are repaired as required and any underlying metal degradation that exists due to coating or concrete lining failure is evaluated for weld repairs. WEKO-Seals, which have been installed in the bell and spigot joints of all 4 SW supply nuclear headers, are inspected for nicks, tears, or any other damage indicative of deterioration. In addition, WEKO-Seals are periodically pressure tested to ensure leak tightness during normal plant operation is maintained.
PSEG's response to Question 5.a includes additional details regarding evaluation of visual inspection results.
LR-N11-0163
- 4.
Discuss any corrosion controls (e.g., cathodic protection) or soil corrosivity evaluations (e.g., soil resistivity, pH, chloride, sulfate measurements) that have been performed to ensure the integrity of the subject piping.
Response to Question 4 There is no cathodic protection currently installed on the SW buried PCCP.
PSEG work orders for excavation at Salem Units 1 and 2 include activities for soil samples during the excavation work. Typical analysis of the samples is performed to determine the following:
- 1.
Pipe-to-soil potentials, measured in accordance with NACE Standard TM0497 Soil Resistivity;
- 2.
Soil classification in accordance with the Unified Soil Classification System (USCS) or equivalent;
- 3.
Moisture content;
- 4.
Sulfide Ion Concentration;
- 5.
Conductivity;
- 6.
pH;
- 7.
Sulfate Ion Concentration; and
- 8.
During the recent (Spring 2011) Salem 2R18 refueling outage, soil analysis was performed adjacent to the carbon steel wall penetration spools of the 21 SW supply nuclear header at two buried pipe program locations that were excavated.
The conclusions resulting from these two soil analyses are summarized below and indicate the soil has very low corrosiveness.
Location 1 - #21 SW nuclear header excavation at SWIS (Location D-10 on PSEG Drawing # 219563 Sheet 1, submitted as Attachment 5 to the October 12, 2010 relief requests)
Two Resistivity readings (ohm-cm) - 7,200 and 14,000 ohm-cm Two pH readings - 7.45 and 7.86 Two Sulfide readings - 3.1 and 3.1 are both below Method Detection Limits (MDL)
% Moisture recorded at 9.48% and 10.3%.
The soil resistivity values alone indicate the soil has low / mild corrosiveness.
However, based on review of the AWWA C1 05 Soil Test Evaluation of the pH, Sulfide, and % Moisture readings, this is indicative of very low corrosiveness soil.
Visual examination of the external surfaces of the carbon steel pipe wall penetration spool identified that the piping was in very good condition. This was confirmed with ultrasonic testing (UT) of the piping, using a 2-inch by 2-inch grid.
Nominal pipe wall thickness for the 24" wall penetrations is 0.500". The manufacturer's minimum wall thickness (87.5% of Nominal Thickness) is 0.438".
LR-N11-0163 A total of 152 UT readings were taken, with the lowest reading being 0.531 inches, (Le. 106% of nominal wall thickness).
Location 2 - #21 SW nuclear header excavation at the Pipe Tunnel (Location E1-E2 on PSEG Drawing # 219563 Sheet 1)
One Resistivity reading (ohm-cm) - 8,733 ohm-cm One pH reading - 7.57 One Sulfide reading - 3.3 (below MDL)
% Moisture recorded at 23.3%.
As was the case with Location 1, the soil resistivity values alone indicate the soil has low I mild corrosiveness. However, based on review of the AWWA C105 Soil Test Evaluation of pH, Sulfide, and % Moisture readings, this is indicative of very low corrosiveness soil. Again, visual examination of the external surface of the carbon steel pipe wall penetration spool identified that the piping was in very good condition. This was confirmed with UT of the piping. The UT was recorded from a 2-inch by 2-inch grid. A total of 205 UT readings were taken, with the lowest reading being 0.495 inches, (Le. 99% of nominal wall thickness).
- 5.
A dominant PCCP failure mode is corrosion of the prestressing wires outside of the metal cylinder, resulting in fracture of the prestressing wires and catastrophic pipe rupture with little prior leakage (see References 1 - 3).
References
- 1.
Failure of Prestressed Concrete Cylinder Pipe, A. E. Romer, D.
Ellison, G.E.C. Bell, B. Clark, AWWA Research Foundation (2008)
- 2.
Inspecting systems for leaks, pits, and corrosion, J. M.Makar, N.
Chagnon, Journal American Water Works Association, 91, 7, pp.
36-46 (1999)
- 3.
Condition assessment of prestressed concrete cylindrical water pipes, R. AI Wardany, 60th Annual WCWWA Conference and Trade Show, Regina, SK. September 23-26, pp. 1-9 (2008)
- a. Explain how a visual examination of the pipe inside diameter can detect the degradation of the wires and ensure structural integrity of the pipe for the length of a period of the 1 O-year in-service inspection interval.
Response to 5.a PSEG's relief requests of October 12, 2010 propose to perform visual examination of the ground surfaces above the subject buried SW piping, and visual examination of the inside surface of the piping, in lieu of the ASME LR-N11-0163 Section XI, IWA-5244 (b)(1) periodic test. As stated in the relief requests, neither the change in flow test nor the unimpaired flow test allowed by IWA-5244(b) are particularly sensitive regarding their ability to detect small amounts of through-wall leakage.
The visual inspection is a basic and widely used method to inspect peep.
This method consists of accurately documenting visible deterioration along the pipe inside surface with the location of as-found anomalies marked, photographed or videoed for future surveys and tracking. Internal observation may include: degradation of the interior concrete core, spalling, out of round pipe cross-section, rust stains, longitudinal cracks, circumferential cracks or bell and spigot joint issues.
Longitudinal cracks detected during visual examination would be of particular concern because such cracks may be indicative of distress due to loading (e.g., as a result of prestressing wire failures). The buried pipe visual inspections at Salem Units 1 and 2 are focused on locating cracking of the inner concrete core. The presence of longitudinal cracks would suggest a potential location where damage to the pre-stressing wires or wire breakage has occurred. At a crack location, the underlying flawed area can be further assessed (e.g., by sounding). Therefore, it is reasonably assured that any degraded sections of piping will be identified, monitored and restored before any catastrophic failure.
The structural integrity of Salem Service Water Nuclear Supply Headers is further assured by the following factors:
- 1. Soil sampling and analysis are discussed in response to question 4, and indicate very low soil corrosiveness.
- 2. The nominal wall thickness of the steel liner at Salem Units 1 and 2 is significantly thicker than that of standard commercial peep and nearly meets the ANSIIASME 831.1 design minimum wall requirement for operating pressure of the SW piping, without considering the prestressing of the wires. Against burst pressure, there is a factor of safety of 2.24 (for 200 psi design pressure) and a factor of safety of 2.99 (for 150 psi operating pressure).
- 3. The SW peep materials of construction were tested, procured and installed with quality control requirements in accordance with procedures for safety related, nuclear class 3, seismic category I piping system.
- 4. Installation of WEKO-seals in the joints of each SW supply nuclear header protects against leakage. As noted above in response to Question 3, the subject WEKO-Seals are currently inspected at three year intervals during refueling outages.
LR-N11-0163
- b. Other examination and monitoring techniques, such as remote field eddy current/transformer coupling (RFEC/TC) and acoustic emission monitoring (AE), have been used to identify wire breaking before catastrophic failure occurs. Justify the adequacy of visual examination of the inside diameter of the pipe to detect wire degradation prior to the point that structural integrity of the pipe is challenged.
Response to S.b The response to Question 5.a also addresses this Question 5.b.