ML18153C856
| ML18153C856 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 12/20/1991 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 91-750, NUDOCS 9201020209 | |
| Download: ML18153C856 (6) | |
Text
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VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 2 3 2 61 December 20, l99l United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, D. C. 20555 Gentlemen:
VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 THREADED CONNECTIONS IN NUCLEAR PIPE Serial No.
NO/ETSR2 Docket Nos.
License Nos.91-750 50-280 50-281 DPR-32 DPR-37 On December 13, 1991, we identified a condition where the current as-built configuration of certain piping systems do not conform to the Code specified in the UFSAR.
The original construction code, ASA 831.1-1955, Pressure Piping, as clarified by Code Case N-3, "Proposed Case on Screwed Connections," does not permit the use of screwed connections in nuclear piping systems where the threads provide the only seal.
Flanges for flow elements in the Reactor Coolant System (RCS), Chemical and Volume Control System (CVCS), High Head Safety Injection System (HHSI), Low Head Safety Injection System (LHSI), Outside Recirculation Spray System (ORS), and Residual Heat Removal System (RHR) have been identified with threaded connections.
During a telephone discussion between Mr. P. E. Fredrickson of your staff and Mr. M.
L. Bowling of Virginia Power on December 16, 1991, it was requested that we submit relief requests for the nonconforming condition. Therefore, in accordance with 1 o CFR 50.55a, paragraph g(5), relief is requested from the requirements described in ASME Section XI, 1980 Edition, Winter 1980 Addendum, associated with the use of threaded fittings in nuclear piping systems.
Background
Unit 2 was shutdown due to a leak in the Reactor Coolant System. The leak was located at a threaded connection in a flange for the flow element (2-RC-FE-2492) on the 'C' RTD bypass line that was not seal welded.
After identifying that this configuration was in nonconformance with the original construction code, walkdowns of accessible portions of safety systems were performed in the Unit 2 containment and outside containment for both Units 1 and 2 to identify any additional threaded connections that were not seal welded.
After identifying additional threaded
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connections, the nonconforming condition was evaluated in accordance with the guidance of Generic Letter 91-18, "Information to Licensees Regarding Two NRC Inspection Manual Sections on Resolution of Degraded and Nonconforming Conditions and on Operability," and dispositioned in accordance with our station deviation process. This process included a determination of operability, a safety evaluation, and NRC notification of the nonconforming condition. A list of the threaded connections and fittings is shown in Attachment 1.
The leaking threaded connection and the other threaded connection in the 'C' loop RTD bypass line flow element (2-RC-FE-2492) as well as threaded connections on the
'8' loop RTD bypass line flow element in the Reactor Coolant System were replaced with a structural weld in accordance with ASME Section XI prior to the restart of Unit 2.
The remainder of the identified threaded connections were evaluated and determined not to affect safety system operability nor pose any immediate threat to the public health and safety. Furthermore, repair with the unit on line would require entering action statements for safety systems to perform the necessary modification. Therefore, Unit 2 was returned to service and the repair of the remaining threaded connections in Unit 1 and 2 was deferred to the next refueling outages.
Relief Reguest Article IWA 4000 of Section XI of the ASME Boiler and Pressure Vessel Code requires that repairs to Class 1, 2, and 3 pressure-retaining components be performed in accordance with Design Specification and Construction Code of the component.
The Construction Code for Surry 1 and 2 is ASA 831.1, 1955 Edition (Code for Pressure Piping), specifies the rules and requirements for making branch connections in nuclear piping systems.
Nuclear piping is defined as that piping designed to contain a fluid whose loss from the system could result in a radiation hazard to either the plant personnel or the general public. The use of threaded connections and fittings in nuclear piping is allowed. However, Code Case N-3 of ASA 831.1, 1955 Edition, prohibits the use of threaded connections in which threads provide the only seal.
Pursuant to your request, relief is requested from IWA-4120 of ASME Section XI, which states that repairs shall be performed in accordance with the Construction Code, and IWB-7313 of ASME Section XI, which prohibits the use, in Class 1 piping systems, of threaded joints in which the threads provide the only seal. Code Case N-3 of ASA B31.1, 1955 Edition, prohibits the use of threaded connections in nuclear piping in which the threads provide the only seal. However, the Code Case addresses only the concern with leakage, and does not question the structural integrity of threaded fittings.
Although the threaded joint which was leaking was repaired in accordance with IWA-4120, the remaining threaded joints listed in Attachment 1, which were not repaired, do not conform with the intent of IWA-4000 and 7000 of ASME Section XI.
e Operation of the Surry units with threaded fittings is not considered to be a nuclear safety concern.
The threaded fittings at Surry have tapered threads as required by ASA B31.1, and are designed for service conditions well in excess of the maximum temperature/pressure conditions expected in the nuclear piping systems.
Leakage in threaded fittings begins as weepage and increases slowly over a period of time. This failure mode was evident in the leakage observed on flow element 2-RC-FE-2492, and was identified during routine daily RCS leak rate calculations. The leakage was within the RCS makeup capability.
In the unlikely event that a complete failure of an orifice flange connection were to occur, leakage would be limited to within the capabilities of the normal makeup systems due to the small diameter of the sensing bores in the orifice flanges.
Leakage from remaining threaded fittings in the Reactor Coolant System would be identified by daily leak rate monitoring, and detected by radiation monitoring equipment. Leakage in the other affected systems would be noticed during routine walkdowns and periodic tests.
The potential for leakage from threaded fittings in normally idle systems is considered negligible, since these fittings are not continually subjected to service temperature/pressure conditions. In the unlikely event of leak initiation upon the start of a normally idle system, the leakage rate would be significantly less than that observed on flow element 2-RC-FE-2492 due to lower temperature and pressure.
The existing threaded connections have been in service for up to 19 years and have undergone numerous hydrostatic tests and operational cycles with no apparent degradation of sealing capability.
Interim Measures to Ensure Structural Integrity To ensure structural integrity of the RCS and other nuclear piping systems containing threaded connections, accessible fittings will be monitored during performance of normally scheduled tests and walkdowns.
Safety Assessment An evaluation of continued operation with the existing threaded connections has been performed for a LOCA. The minor leakage resulting from a leaking fitting is bounded by other accident analyses.
e Corrective Measures The leaking threaded fitting for 'C' loop RTD bypass line flow element 2-RC-FE-2492 has been repaired with a structural code weld, as were other nonleaking threaded fittings in the 'B' and 'C' loop RTD bypass lines in the Unit 2 Reactor Coolant System.
Since operation with the other existing threaded connections does not present a safety hazard, no further repair will be performed at this time. Instead, the remaining threaded connections in both Units 1 and 2 will be inspected and repaired during the next refueling outages.
Conclusions The existing threaded connections in the nuclear piping system in Surry 1 and 2 do not adversely affect safe operation of the units and therefore pose no threat to the health and safety of the public.
Please contact us if you have any questions or require additional information.
Very 1
t~l~your, J~
W. L. Stewart Senior Vice President - Nuclear Attachment cc:
U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, N.W.
Atlanta, Georgia 30323 Mr. Morris Branch NRC Senior Resident Inspector Surry Power Station
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ATTACHMENT 1 THREADED CONNECTIONS SURRY POWER STATION UNITS 1 AND 2
ATTACHMENT I THREADED CONNECTIONS IN ORIFICE FLANGES SYSTEM 1 ln*trument No.
I Commenb I
Pressure Temperature eves FE-1150*
Flanges not accessible for examination on 12/13/91. (Assumed to have threaded connections) 2700 PSIG FE-2150*
125°F FE-1147*
Flanges not accessible for examination on 12/13/91. (Assumed to have threaded connections)
FE-2147*
CH-FE-1122*
Pipe plugs are not welded.
CH-FE-2122*
Unit 1 instrument tap connections are threaded and are not seal welded. Unit 2 instrument tap CH-FE-1160*
connections m seal welded.
CH-FE-2160*
CH-FE-1124*
CH-FE-2124*
CH-FE-1127*
CH-FE-2127*
CH-FE-1130*
CH-FE-2130*
HHSI FE-1940 (Fl-1940/Fl-1940A)
Threaded connections into FE from both associated Fl's. The connections from FI-1940 & -
2700 PSIG 1940A m seal welded. The connections from Fl-1943 & -1943A !nL seal welded. The 220°F FE-1943 (Fl-1943/Fl-1943A) connections from Fl-2940 & -2943 are not seal welded.
FE-2940* (Fl-2940/FI-2940A)
FE-2943* (Fl-2943/Fl-2943A)
LHSI FE-1941
- Unit 1 and 2 instrument tap connections are threaded and m seal welded. Unit 1 pipe plugs~
!!Q! seal welded. Unit 2 pipe plugs m seal welded.
220°F FE-1945*
FE-2945 FE-1946*
Unit 1 flanges not accessible for examination on 12/13/91. (Assumed to have threaded 2235 PSIG FE-1491
- connections) 650°F FE-1492*
No problems noted for FE-2490. The instrument taps apparently are socket weld connections and FE-2490 m properly welded. The pipe plugs were threaded and m seal welded in place.
FE-2491 For FE-2491, the instrument connections m properly welded. The pipe plugs were threaded and FE-2492 were not seal welded in place when originally inspected, however these connections~ welded prior to unit startup.
RHR NO PROBLEMS Flow element is venturi type. All piping connections are welded in Unit 2 and assumed to be 350 PSIG welded in Unit 1 400°F ORS FE-157A*
The instrument taps and pipe plugs for all flow elements except FI-157 A are threaded and ~
116 PSIG FE-157B*
seal welded. The downstream flange instrument tap for Fl-157A i§ welded but the other 280°F FE-257A*
instrument tap and the pipe plugs are not welded.
FE-257B*
)
NOTE: Flow elements marked with an asterisk(*) contain, or are suspected to contain threaded connections at the orifice flange taps that are not seal welded in accordance with the requirements of ASA B31.l - 1955 Code Case N-3.