ML19332F940
| ML19332F940 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 12/07/1989 |
| From: | Shelton D TOLEDO EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 1742, IEB-88-008, IEB-88-8, TAC-69622, NUDOCS 8912190349 | |
| Download: ML19332F940 (5) | |
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EDISON A Cnero Dev Cwmnv j
l DONALD C. SHELTON Docket Number 50-346 gg=
License Number NPF-3 Serial Number 1742 December 7, 1989 United States Nuclear Regulatory Commission Document Control Desk Vashington, D. C. 20E 5
Subject:
Response to NRC Compliance Bulletin No. 88-08, Supplement 3 Gentlemen Toledo Edison (TE) hereby submits the information requested by NRC Compliance Bulletin No. 88-08, Supplement 3, " Thermal Stresses in Piping Connected to Reactor Coolant Systems" dated, April 11, 1989 (Log Number 1-2072). The subject bulletin supplement in conjunction with Bulletin 88-08, dated June 22, 1988, requested that licensees review their Reactor Coolant Systems (RCS) to identify any connected unisolable piping that cou3d be subjected to temperature distributions which result in unacceinable thermal stresses. NRC Compliance Bulletin 88-08 further requested licensees to take appropriate action, where such piping is identified.
The results of the review are included in the attached evaluation performed by Toledo Edison. This evaluation also includes a schedule for completion of the remaining action requested in Bulletin 88-08.
Completion of this activity vill satisfy the requirements of Bulletin 88-08, supplement 3.
Should further information be requested, please contact R. V. Schrauder, Manager-- Nuclear Licensing, at (419) 249-2366.
Very truly yours, RWG/ssg attachment cci P. M. Byron, DB-1 NRC Senior Resident Inspector A. B. Davis, Regional Administrator, NRC Region III T. V. Vambach, DB-1 NRC Senior Project Manager 93/6 THE TOLEDO EDISON COMPANY EDISON PLAZA 300 MADISON AVENUE TOLEDO, OH:043652 t
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t Response to NRC Bulletin No. 88-08, Supplement 3 l
For Davis-Besse Nuclear Power Station i
i Unit Number 1 This letter is submitted in conformance with Atomic Energy Act of 1%4 Section 182a, in response to NRC Bulletin 88-08, Supplement 3 (Log Number 1-2072)
" Thermal Stresses in Piping Connected to Reactor Coolant Systems".
By:
D. C. Shelton, Vice President, Nuclear Sworn and subscribed before me this 7th day of December 1989.
bu fad W ted Notary Public, State of Ohio EVELYt1L DRESS NOTARYPU3tC,5 TATE OF0H10 MyCassiaabpesMy23,1934
i Dock 3t Nu;ber 50-346 License Number NPF-3 Serial Number 1742 Page 1 Response to NRC Compliance Bulletin Number 88-08, Supplement. 3 BACKGROUND:
NRC Bulletin No. 88-08, Thermal Stresses in Piping Connected to Reactor Coolant Systems (RCS) was issued on June 22, 1988 with Supplements 1 and 2 issued on June 24, 1988, and August 4, 1988 respectively.
The concern identified in Bulletin Supplement 3 was that thermal fatigue of unisolable piping connected to the RCS can occur as a result of small leaks. The actions requested are intended to provide assurance that unisolable sections of piping connected to the RCS will not be subjected to stresses that could cause fatigue failure.
Toledo Edison provided response to the NRC Bulletin on October 8, 1988 (Serial No. 1585).
In that response all penetrations / connections vere reviewed for possible in-leakaEe to RCS and it was concluded that the concern identified in Bulletin 88-08 lu not applicable to the Davis-Besse plant.
Supplement 3 to this Bulletin was issued on April 11, 1989. This supplement addresses the concern related to leakage out of the RCS.
EVALUATION:
The following connections / penetrations were reviewed to determine whether unisolable sections of piping connected to the RCS could be subjected to fatigue failure as a result of temperature stratification or temperature oscillations that could be induced by small leaks:
1.
Core Flood / Low Pressure Injection (2) 2.
High Pressure Injection (4) 3.
Letdown (1) 4.
Reactor Coolant Drains / Vents (several) 5.
Decay Heat Drop Line (1) 6.
Sample Line (1) 7.
Pilot Operated Relief Valve, PORV (1)
NOTE:
Numbers in parenthesis are the numoer of penetrations in the RCS.
Each of the two trains of Core Flood and Lov Pressure Injection (LPI) piping is isolated from the RCS by a common check valve and two independent check valves. These check valves are individually lenk tested following each refueling, whenever the plant has been in cold shutdown for greater than 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> and leak testing has not been performed within the previous 9 months, or after maintenance has been performed on the valves.
During operation, any leakage through these valves vould be evident by increasing Core Flood Tank level or high LPI piping pressures.
Both of these parameters have indicators and alarms.
Each of the four High Pressure Injection (HPI) lines are isolated from the RCS by two check valves and one normally closed motor operated globe valve in series. One of these injection lines is the normal makeup supply line and this line was addressed in the Company's October 8, 1988 response. The leak tightness of each series pair of check valves is tested as Reactor Coolant L
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.. Dockat Nu ber 50-346 License Number NPF-3 Serial Number 1742 Page 2 System pressure is increased following each refueling.
The piping has instrumentation including an alarm to identify high pressure as a result of leakage. Additionally, the motor-operated globe valves are in the auxiliary i
building and do not have packing leak-off lines, therefore packing leaks can be readily identified.
All portions of the lov temperature / low pressure Letdown and sampling piping can be isolated from the RCS. The RCS drain and vent piping is small diameter piping and is not expected to be subject to thermal stratification.
The decay heat removal drop line is a 12 inch line which connects the RCS hot-leg piping to the suction of the Decay Heat Removal Pumps. The pumps are isolated from the the reactor coolant loop by two isolation valves in series, DH12 and DH11.
Both these valves are closed when the RCS is at operating pressure.
Both isolation valves are located in a dedicated valve pit inside containment which has sump level switches and alarms.
High water 1cvel in this pit provides unambiguous indication of valve packing leaks from these isolation valves or leaks to containment atmosphere from small valves in a bypass around DH12 intended for thermal expansion relief.
An 8-inch bypass around the motor operated isolation valves, DH11 and DH12, renins isolated during normal plant operation by two locked-closed manual isolat. ion valves (DH 21 and DH23).
Packing leakage from these valves is direct to containment. The valve maintenance histories shov occasional packing repairs initiated from observations of boric acid crystallization and local corrosion.
These valves were repacked with " live-load" packing during the 5th refueling outage.
Recent surveys have shown no evidence of leakage.
Leakage past the series isolation valves into the low-pressure portion of the Decay Heat Removal Loop is unlikely.
Torque settings on the Limitorque valve operators in DH11 and DH12 assure seating, effectively closing off a leakage path through both valves into the low pressure portion of the line. Any leakage which might occur vould be be detected by an elevated pressure indication in the low pressure line during routine tours.
Considering the leakage path described for the foreign plant in Supplement 3 of the Bulletin, the first valve, DH12, isolating this line from the RCS vas determined to have packing leaks during the fifth operating cycle.
The original packing was replaced during the fifth refueling outage with " live load" packing to correct the identified leakage and prevent future leakage.
l No leakage has been Jetected subsequent to the packin;; modification.
CONCLUSIONS The decay heat loop isolation valves in Davis-Besse Unit 1 are located significantly further from the RCS than those at the foreign power plant described in Supplement 3 of the Bulletin. Heat loss through the thermal insulation along the 74 foot length of unisolable line upstream of valve DH12, results in extensive cooling of the leakage flow before reaching the valve.
The resultant lov temperature of the line at the isolation valve makes it improbable that the cyclic leakage phenomenon described for the foreign plant in the Bulletin would apply to Davis-Besse Unit 1.
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License Number NPF-3 Serial Number 1742 Page 3 Although some degree of thermal stratification may have existed in horizontal l
portions of the Decay Heat Line, examinations of the lines during the recent refueling outage (5RFO) inservice inspections identified no reportable flaw indications.
The small leakage flow has been determined not to create conditions conducive to' thermal striping in the decay heat line.
Hence, the leakage condition would not be expected to result in 11avs initiated from the interior of the piping.
To confirm that an adverse condition does not exist in the line, visual and dye-penetrant examinations of selected portions of the pipe vill be performed during the sixth refueling outage.
Stress effects due to thermal stratification are most likely discerned on the outside of the pipe.
Toledo Edison vill continue to monitor industry programs on thermal stratification, cycling and striping in piping. Recommendations from Babcock and Vilcox Owners Group and EPRI will continue to be evaluated for applicability to Davis-Besse.