ML20086L449
| ML20086L449 | |
| Person / Time | |
|---|---|
| Site: | Peach Bottom  |
| Issue date: | 05/24/1974 |
| From: | Boyer V PECO ENERGY CO., (FORMERLY PHILADELPHIA ELECTRIC |
| To: | Knuth D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086L448 | List: |
| References | |
| NUDOCS 8402080238 | |
| Download: ML20086L449 (6) | |
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PHILADELPHIA ELECTRIC COMPANY 2301 MARKET STREET PHILADELPHIA. PA.19101 (215)841-45oo VICE PRESIDENT May 2h, 197h Dr. D. F. Knuth, Director Director of Regulatory Operations United States Atomic Energy Commission Washington, D. C.
20545
Subject:
Significant Deficiency Final Report Hydraulic Shock Suppressor Performance Peach Bottom Atomic Power Station, Unit No. 3 AEC Construction Permit No. CPPR-38 File: QUAL 2-10-2 SDR No. 8
References:
- 1. M. J. Cooney letter to A. Giambusso and J. P. O'Reilly dated January 22, 1974
- 2. E. J. Bradley letter to R. C. DeYoung dated March 14, 1974
Dear Dr. Knuth:
In compliance with 100FR50 55 paragraph (e), we are submitting the attached Significant Deficiency Final Report concerning the subject hydraulic shock suppressor performance for Unit No. 3 We would like to point out that our reference no. 1.
formally notified the AEC DRO I and DOL of the subject for Peach Bottom Atomic Power Station - Unit No. 2 in accordance with Section 6.7.2.B.1 of Technical Specification Appendix A of DPR-44 In addition, our reference no. 2. formally notified DOL of the subject, _
its evaluation and corrective action for Unit No. 2 and Unit No. 3 Although the attached Significant Deficiency Report discusses both Unit No. 2 and Unit No. 3, this report is intended to satisfy the requirements of 10CFR50 55(e) for Peach Bottom Atomic Power Station -
Unit No. 3 h,
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Dr. D. F. Knuth, Director United States Atomic Energy Commission Page twn We trust that this satisfactorily resolves the item.
If further information is required, please do not hesitate to contact us.
Sinc erely,
- .$ F l w,l. V 'I hjr Attachment Copy to
J. P. O'Reilly, USAEC
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SIGIIFICANT DEFICIENCY R3 PORT - SDR NO. 8 ElIT UO. 3 HYDRAULIC SHOCK SUPPRESSOR PERFORMANCE PEACH BOTTOM ATOMIC POWER STATION - UNIT 3 AEC CONSTRUCTION PERMIT TO CPPR-38 DESCRIPTION OF DEFICIENCY During early stages of plant operational testing of Unit 2 instances of Grinnell hydraulic shock suppressors (snubbers) acting as restraints to themal motion after a ctrncmic event were observed.
Opening of a nain stean line relief valve resulted in developnent of dynanic and sustained pressure in a snubber hydraulic cylinder attached to the relief valve discharge line and which was instmmented for test purposes. The dynamic pressure is caused by the sudden steam flow and the sustained cylinder pressure is related to a force acting to restrain themal expansion of the pipe. A subsequent turbine by-pass system test resulted in a similar observation that five of the nine by-pass lines were restrained from themal expansion after by-pass valve opening or contraction af ter the turbine by-pass valve closure and resulting cooling of the pipe. Of these five snubbers one was observed to act as a re-straint holding the cold pipe h the hot position over a period of days.
Review of the Grinnell snubber nechanism resulted in the conclusion that the snubbers, when operating as designed, would act as a restraint to themal motion if systen operation caused snubber check v tlve actuation and a centinued force in the same direction as the actuating force was applied. Thus, opening nf the relief valve could cause a dynamic motion of the pipe suffident to close the snubber check valve and the immediate themal expansion of the discharge line would exert a continued force on the snubber which would prevent the check valve from opening.
In the case of the turbine by-pass valves the snubber check valves either per-fomed in a sinilar manner as described above or closed when the by-pass valves closed and the subsequent contraction applied the continued force.
It should be noted that the snubber valve assemblies hclude variable crifices in parallel with the check valve. These orifices are intended to allow some snubber motion with closed check valves.
This notion is slow and requires substantial cylinder pressures to develop before the orifices pemit deeign motion. It was determined that these orifices are nomally set to allow a 1/8 inches / minute motion at 7000 psig cylinder pressure. Since one of the five restrained turbine by-pass lines was completely restrained it was concluded that the variable orifice was completely closed or plugged.
Subsequent ' shop inspection revealed that the variable orifice was closed.
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, Stress analysis of the relief valve discharge piping and by-pass lines indicate that, although the stresses msulting from the stated occurrences exceeded original intent, the stresses did not exceed the Code allowable stresses.
CORRECTIVE: ACTI0jl To eliminate the continued circumstance of potentially closed snubber valve block variable orifices, instructions were given to replace all Grinnell snubber valve blocks with new factory set and marked replacements.
The replacements were specified to have faster snubber check valve act-uating speeds; a minimum of 10 or 15 inches / minute rather than the originally furnished 8 inches / minute and variable orifices which would accommodate 1/8 or 1/2 or 1 inch / minute velocities at 1500 psig cylinder pressure rather than 1/8 inch / minute at 7000 psig cylinder pressure.
With Grinnell's approval and until such time as the replacement valve blocks were available, it was decided to field adjust the variable orifices by turning them full closed and then opening as required to assure the prnper setting. It was decided that based on available test data such a field adjustment would be adequate for the snubbers provided by the USSS vendor and that replacement of those units would not be re-quired.
Review of the eight snubbers on each unit furnished by another supplier indicated that the variable orifice settings were certified and encapsulated to prevent resetting thus no corrective action was con-sidered necessary for these snubbers.
The above described occurrences related to the nain steam relief valve discharge piping and turbine by-pass lines, however, all snubbers would dispicy the same operating characteristics. Accordingly all systems which include snubbers have been reviewed to establish if:
a) under any design transients the pipe velocity due to thermal expansion would exceed the check valve actuating velocity and ff.it does, will the resulting themal expansion as restrained by the variable orifice cause unacceptable stresses or nozzle loads.
b) operation would result in an anticipated dynamic transient sufficient to cause snubber check valve clnaure followed by thermal expansion and if it dnes, will the themal expansion as restrained by the variable orifice cause unacceptable stresses or nozzle loads.
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operation subsequent to a seismic event which caused snubber check valvo closure and results in thermal transient and if it does, will the thermal expansion as restrained by the variable orifice cause unacceptable stresses or nozzle loads.
The systems reviewed and conclusions for each system are as follows:
1)
Hain Steam Relief Valves Discharge Piping -
Opening of the valves is expected to cause a dynamic transient sufficient to close the snubber check valves. This occurrence will be followed by restrained thermal expansion as limited by the snubber variable orifice. No unacceptable stresses or nozzle reactions will result from this routine occurrence.
2)
Turbine By-Pass Valve Discharge Lines -
(Sans discussion as 1 above) 3)
HPCI/RCIC Turbine Steam Lines -
These lines are nomally maintained hot and snubber check valve closure during normal plant operation would not be followed by themal expansion. For the case of a cold shutdown steam line being placed in service, analysis indicates that no themal or dynamic action should be anticipated which would cause snubber check valve closure. However, such closure was conservatively assumed and analysis indicated that the RCIC system as built would not experience any overstress or nozzle overload conditions; the HPCI as built would experience a turbine steam inlet nozzle overload condition. Accordingly, plans are being made to provide a by-pass amund ti.e HPCI system outboard steam isolation valve which will be used for system heat-up and which will limit heatup rate so that the restrained themal growth will not result in nozzle overload. Until this change is made heat-up rate will be administratively controlled by throttling the inboard isolation valves.
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HPCI/RCIC Turbines Exhaust Lines -
Available HPCI test data does not indicate restrained thermal growth on system operation. If a seismic event is postulated to cause snubber check valve closure simultaneous with a HPCI/RCIC system start, the observed exhaust line cyclic vibration will serve to alternately open and close the snubber check valves and avoid restrained thermal growth. Further the snubber variable ori-fices in these systems have been adjusted to accept the total thermal growth without resulting in aioverstress or nozzle over-load condition.
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CORRECTIVE ACTION (Continued) 5)
HPCI/RCICSuetion Lines -
The maximun thermal transient possible based on suction water temperature can be accommodated by the variable orifices without resulting in an overstress or nozzle overload condition.
6)
RHR and Core Spray Suction and Discharge Lines -
(Same as 5 above) 7)
For the case of a seismic event causing snubber check valve closure and simultaneously initiating a HPCI injection into the feedwater line, stress analysis 11dicates that the snubber variable orifice bleed rate will accommodate feedwater pipe motion without exceeding code allowable piping stress levels or causing a nozzle overload condition.
8)
Mainsteam -
Assuming a dynamic event causing snubber check valve closure, controlled heat-up and cool-down of the insulated mainsteam lines will result in thermal motions which can be accommodated by the snubber variable orifices.
9)
CRD Withdraw and Insert Iines -
Analysis reveals that completely restrained thermel growth can be accommodated without causing overstress or causing a nozzle t
overload condition.
- 10) Reactor Recirculation System -
l There is no mechanism for snubber check valve closure which would be followed by a' thermal transient thus no restrained themal J
growth will be experienced.
j Of the total of 136 snubber valve blocks comitted for change on Unit #3, -
119_ have been enmpleted, material expected to allow completion of the i
remaining 17 units by 6-8-7h.
SAFEIT IMPLICATICNS The field setting and marking of the snubber variable orifices and the i
snubber valve block replacement program assures that proper snubber variable orifice settings will avoid over stress or excessive nozzle reactions in systems for which snubber check valve closure followed by a themal trans-ient should be anticipated. Increasing the snubber check valve velocities -
for the replacement snubber valve blocks will result in minimizing _in-stances of closed check valves resulting in restrained thermal motion.
Accordingly the initially observed snubber perfomance is not considered -
to have any safety implication.
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