ML20086E859
| ML20086E859 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 09/22/1972 |
| From: | Walker R PUBLIC SERVICE CO. OF COLORADO |
| To: | Kruesi F US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086E799 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8312080155 | |
| Download: ML20086E859 (9) | |
Text
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O PUBLIC SERVICE COMPANY OF COLORADO P.O.
BOX S4O e
OENVER.
COLORAOO e0201 Er F. E. Krussi Directorate of Regulatory Operations United States Atomic Energy Commission Washington, D. C.
20545
Subject:
Deficiency Report 10 CFR 50 Helium Circulators Fort St. Vrain Station
Dear Er. Kruesi:
Pursuant to the reporting requirements of 10 CFR 50, Part 50 55, we are submitting herewith as an interim report, twenty copies of the subject report involving the helium circulators at the Fort Saint Vrain Station.
The helium circulators are presently at the Gulf General Atomic facilities in San Diego. Public Service Company has monitored most of the disassembly work to date through our Nuclear Power Consultant and other personnel. We will, of course, be continuing our inspection efforts during the refurbishment and re assembly work. The results of our inspection efforts will be made available to the local Directorate of Regulatory Operations as the work is completed.
A. final report will be submitted as soon as possible after the final corrective actions have been decided upon.
We trust the attached report will provide you with sufficient infor-mation and will fulfill the requirements of an interim report under 10 CFR 50 regulations.
Very truly yours, k,Y. ?s (H-R. F. Walker, Vice President Engineering and Planning Electrie g gtment, m, g cc: Mr. John. Flora Director, Region IV Denver pY 03A1333';
0312080155 731101 PDR ADOCK 03000267 S
PDR 2 M44 L
DEFICIE!!CY REFORT I
i 10 CFR 50 Part 50.55 Fa$111ty:
Fort Saint Vrain Nuclear Generating Station
Subject:
Helium Circulators Date:
August 1972 1.
General Descrintion of Plant Conditions The hot flow test (HFT) having officially startud on June 28, 1972, had progressed to the heat-up phase with the overall test being about 42% complete at the time of shutdown due to helium circulator problems. Because of the temperature requirements to be reached during HFT the helium circulator water drive systems, and to some extent the auxiliary systems, had to be temporarily modified from what would be a normal design configuration. The_ helium circulators, for example, are driven by a prenuclear pelton wheel using high pressure feed water at somewhat higher than ncrral design pressures and flows. The pronuclear pelton wheel is of a larger diameter than -
the permanent nuclear pelton wheel, and was designed-only for limited use during the HFT to attain the highest possible temperature in the primary coolant due to the work of compression of the circulators (the prenuclear wheel being designed for 2500 hp versus 600 hp for the nuclear pelton wheel).
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Prior to shutdown of the system the circulators had been through various modes of operation, start-up and shut-down, some dictated by the HFT procedures and some_resulting from.overall system problems-
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that were uncovered during the test. The hours lof. circulator pelton wheel operation prior to shutdown varied for each circulator ranging from 257 hours0.00297 days <br />0.0714 hours <br />4.249339e-4 weeks <br />9.77885e-5 months <br /> on IB (C-2102) circulator to 506' hours on 1C (C.2103)-
circulator.
On7-31-72thespeed/wobbleprobesonheliumcirculatorID(C-2104) indicated excessive deflection and shaft orbiting which was believed at first to be faulty instrumentation problems..The 1D (C-2104).
circulator was shut-down, and the HFT was continued utilizing the other circulators.pending an investigation-of the apparent wobble of C-2104. A detail description of the instrumentation investiga-l tion is contained in-Appendix 1 of this report.. In the events that; i
followed, the 1C (C-2103) was-shutdown due to system requirements, and attempts to restart this circulator on 8-10-72'and again ~on -
8-11-72 failed. The machine appeared to be bound up as rotation
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could not be established. The HFT continued using 1A_and 1B'circu-lators (C-2101 and 2102 respectively) even though the marimum attainable speed _of C-2102 was restricted due to partial-plugging of the pelton wheel water drive nozzles._ On 8-12-72 minor wobble indications within acceptable limits were noted. Later that same, day the 1A circulator tripped from an indicated overspeed which in
< turn resulted in a trip of the 1B circulator. ' Attempts to restart -
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V Doficicncy Roport 10 CFR 50, H211um Circulators Pega 2 1.
General Description of Pinnt Conditions (Cont'd)
I the 1A circulator resulted in excessive wobble incications from thospoed/wobbloinstrumentation. All testing was discontinued on 8-13-72 pending investigation of the helium circulators.
Subsequent investigation revealed that two buckets had been thrown from~the 1D circulator prenuclear pelton wheel, four buckets had been thrown from the 1A circulator prenuclear pelton wheel and the pronuclear polton whool of the 1C circulator had sustained some damage. Based on these investigations it was decided initially that 1A, 10, and 1D circulators should be removed from the PCRV and be shipped back to GGA San Diego for disassembly and evaluation.
The results of initial circulator disassembly led to a later decision that an circulators including the spare (C-2105) should be returned to San Diego for disassembly, evaluation and modification.
2.
Disasse:rbly and Conditions Found The following is a brief description of the major items found in the disassembly of the circulators.
1A Circulator (C-2101) j 1.
Damage to the prenuclear pelton wheel (cavitation, loss of buckets) 2.
Scoring of shaft by lands of lower labyrinth 3
Lower labyrinth lands damaged 4.
Damage to shaft and bearings, chrome oxide flame spray coating wiped off bearing and shaft surfaces including the lower bearing and thrust faces due to shaft orbiting.
5 Damage to shutdown seal surfaces (static ss j '
6.
Brake shoe wear (wear of silver plating surface) 7.
Cavitation in the bearing water orifices (internal) 8, Foreign material in the bearing water system 1B Circulator (C-2102) 1.
Only slight pelton wheel damage (no loss of buckets, some cavitation evident) 2.
Damage to flame spray on upper thrust face 3
Brake shoe wear (wear of silver plated surface) 4.
Damage to compressor blading and struts on the primary coolant side due to foreign material (washer) in the compressor section.
5 Cavitation of the bearing water orifices 6.
Foreign material in the bearing water system
- 7.. Divorced from t e circulator-the pelton wheel water supply nozzles were partially plugged with foreign material
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Doficiency Ropor h CFR 50, Helium Circulat:rs C Pag 2 3 2.'
Disassenbly and Conditions Found sCont'd) 1C Circulator (C2103) t i
1.
Pelton wheel damage (Cavitation and Sevoro Cracking) 2.
Damage to shaft and bearing surfaces ( Flamo spray chrome oxide) 3 Somo scoring of the shaft in the water seal area due to disassembly.
4 Brake shoe wear (Silver plating) 5 Foreign body lodged between the shaft and housing in the area of the water seal proventing rotation.
6.
Fractured boit on the compressor dise (primary coolant side) 7.
Foroign material in the bearing water system 8.
Cavitation of bearing water orifices 9.
Some evidence of rust on the speed probes
- 10. Rust on the outside of the main bearing housing 1D Cirenlator (C2104) 1.
Pelton wheel damage (cavitation and loss of b'uckets) 2.
Scoring of shaft by lands of lower labyrinth 3
Lower labyrinth lands damaged 4.
Damage to shaft and bearings, chrome oxide flame spray coating wiped off bearing and shaft surfaces due to shaft orbiting.
5.
Damage to shutdown seal surfaces (static seal) 6.
141nor scoring of speed probe faces 7.
Brake shoe wear ( silver plating) 8.
Cavitation of bearing water orifices 9.
Foreign material in the bearing water system Snare Circulator (C2105)
{
Some minor wear was not' d, but such wear is) considered to be 1.
e normal resulting from the operation of this machino at the -
Valmont Test Facility. The circulator is considered to be completely operational. It should be noted that some minor cavitation or the beginning of such cavitation was evident l
in the bearing water orifices.
3.
Evaluation The entire matter is still under extensive review, and any evaluation at this timo must necessarily be considered preliminary and subject to change. Various parts that were damaged are being repaired whore possible, and new parts are being ordered or made where repair is not possible.
1.
Basically it is felt that all damage to the shafts, bearings and labyrinths of the 1A 'and 1D circulators was the result of excessive shaft orbiting brought on by the imblance introduced by the loss of material from the prenuclear pelton wheels. The shaft and bearing system design did perform as expected under these conditions with the chrome oxido layers rubbing off. There was no evidence of
,self volding or excessive heat build-up thus confirming the design conditions to tolerate rubbing. It should be noted that even aftor the shaft rub, the circulators wore capable of limited operation.
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Deficioney Repor CFR 50, Helium Circulators Page 4
- 3., Evnim tion (Cont'd) 2.
GGA's initial investigation of the pelton wheels indicates that the excessivo cavitation and resulting uheol failurcs are the result or direct consequence of running the pelton wheels with water at or abovo saturation temperatures with no cavitation suppression head. The cavitation and resulting damago to the polton wheols is still under review at this time. In the interim work is underway on the dosign of a nitrogen pressure suppression system to climinate formation of bubbles in the nozzle discharge streamand/orflashingduetosaturationconditions.
3 The brake shoe wear is attributed to normal wear. The circulators have essentially been through the number of starts and stops that woro initially anticipated for the life of the machines. The brako shoos are to be replaced tith solid silver shoes rather than the silver plated shoos.
4.
The cavitation of the boaring water orifices will require a new orifice design. In some cases more than one orifice in series may have to be used for the required pressure breakdown. Design is underway, and tests will be performod as necessary. The orifices on all circulators will be replaced.
5 Foreign material in the bearing water systemicould have resulted from inlot scroon break-through and inadequate system flushing.
Present plans call for chemically cleaning the bearing water system extognal to the circulators and careful water chemistry control. Some bypass piping changes are also under consideration.
Concerning the picco of foreign material lodged in the water seal of the 1C circulator, present plans call for cutting a slot in the housing just upstream of the water sea'l inlet to provide a pocket for collection of any foreign materi'a1. This slot will be put in all circulators.
I 6.
The fractured bolt found (compressor disc bolt) on the 1C circu-lator has initially been attributed by GGA to a stress corrosion problem. The matter is still under review; howev'er, in the intorim present plans call for either a bolt material change or plating of the bolts to provide corrosion protection. All bolts in this service on each circulator compressor wheel will bo replaced or plated.
7.
The foreign body (assumed to be a washer as a piece of a washer was found in the compressor section) that entered the compressor section of the 1B circulator resulted in damage in the form of material deformation and material removal in the form of knicks and gouges of the struts on the inlet to the compressor wheol and on the leading edges of several of the coepressor wheel blades. The origin of the washer is unknown at this timo. It is felt that the blados could be repaired if absoluto1y necessary, but present' plans call for blade replacement.
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Defici ncy Roport CFR 50, Holium circulat:rs p g3 5 t
4 Correctivo Action As stated abovo various immodiato actions have been taken to repair 4
or replace danaged parts, and some rodosign work is underway. The ontiro mattor, however, is still under review and final ovaluations, final decisions and final corrective actions are yet to bo made.
A completo ovaluation report including corrective actions taken will be submittod at a lator dato.
Appondix 1 is attached to provido a detail report of checks and tests mado in the field leading up to the decision to remove the holium circulators and return them to San Diego.
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Defici:ncyReporg0CFR50,HeliumCirculattra
' APPENDIX I DISCOVERY OF CIRCULATOR PROBLEMS Fiold Activities 7-31-72 to 8-18-72 "D" CIRCULATOR On 7/31/72 excess wobble was noted on "D" circulator while running at 7000 RPM.
The circulator was shutdown to scif-turbining.
The wobble magnitude decreased as speed was decreased but did not disappear at self-turbining speed as would be expected if the wobble were caused by an unbalance condition.
Several quick checks were run at self-turbininr; speed in an effort to establish instrumentation integrity.
One-speed signal from "D" was routed through a "C" circulator speed module. No apparent change in wobble was noted; however actual values were not recorded.
The speed simulator was then used as a signal sub-ctitute from the circulator end of one of the speed probe cables. The indication was read on the wobble scope through a "D" circulator speed module. The signal received was considered a normal signal from the speed simulator.
The speed pulses from the simulator did not coincide with the peaks and valleys of the wobble sine wave as was the case when the "D" circulator speed probes were supplying the signal.
No record of these initial checks were made inasmuch as they were immediate checks made to search not ponnible inntrumentation mal-function. No instrumentation problem could be found. Direction was subsequently given to CGA Operations to limit "D" circulator operation to self-turbining speed u.ntil a test could be outlined which would better define the problem.
On 8/2 through 8/4 wobble magnitude measurements were obtained from all 12 speed probes from "D" circulator at self-turbining speed.
In addition, measurements from four cf the 12 probes were obtained through a "C" circulator speed module.
Measurements obtained through the "C" module agreed renoncbly well with those obtained through "D" module on three of the four probes. On the fourth probe the measurement through "C" module was approximately 50% that obtained through "D" module. The data indicated shaf t wobbic with the greatest magnitude at the lower journal bearing.
On 8/7/72 Engineering requested further tests which would define the problem more clearly.
This test obtained wobble measuremeuts at several shaft' speeds above self-turbining.
The test results cicarly defined the problem as shaft unbalance existing in the steam turbine /Pelton wheel area of the circulator. The test results also indicated probable shaft and/or lower bearing damage within the circulator.
"D" circulator thus was verified as unavailable for the remainder of the hot flow test. The immediate hot flow te'st plans were to continue the hot flow test with the three remaining operable circulators; even though "B" circulator was incapable of maximum available speed because.of partially plugged Pelton whcci nozzles.
This decision was reached on 8/11/72.
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"A" CIRCULATOR On 8/12/72 "A" circulator wobbic was noted as being somewhat larger than had been noted on prior operations.
Speed was approximately 7000 RPM. The wobbic indica-
.tions were approximately 0.3 mill and 0.5 mill; higher than on previous operation but well below the~2 mill shutdown value. Pertinent circulator parameters were noted as being normal. Verbal direction was given to continue operation and to cbserve wobbic indications more frequently than had been practiced.
"A" and "B" circulators had been brought to speed in an cffort to continue hot flow test.
Approximately 5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> later "A" circulator tripped off on an indicated overspeed.
Speed at the time of the trip was 7500 RPM. Wobbic magnitude had not changed during that 5 hour5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> period.
Following the "A" circulator trip on overspeed "B" circulator tripped on low bearing water flow, completely shutting down both "A" and "B" circulators.
A logical explanation of this is that when "A" tripped the rapid speed change joggled the bearing supply to drain AP on "A" sufficiently to call for an accumulator firing.
The accumulator firing trips one bearing water pump and consequently "B" circulator then tripped on low bearing water flow.
"B" tripped approximately 4.5 seconds after "A" tripped.
Following this incident "A" would not scif-turbine.
"A" circulator was subsequently broken free by bumping with Pelton water at 430 psi nozzle pressure. The circulator continued to self-turbino after it was bumped, however the wobbic indication now was approximately-1 mill at the lower journal.
Because of this excessive wobbic indication at self-turbining speed "A" circulator was restricted to scif-tur'bining speed.
On 8/13/72 a test was run,on "A" circulator to obtain wobbic magnituden.- The test also substituted -input from the speed simulator in place of. "A" circulator speed probes. This was done in'an. effort to disperse' doubts about the integrity of the wobble instrumentation. The test obtained like datp from "B" circulator.
The test verified the instrumentation to everyone's satisfaction. - Following the test "A" circulator tripped during a blowdown of buffer sense. lines.
It would not again scif-turbine.
(It was later restarted by manuhl torquing; wobbic.
indications at scif-turbining. speed were such that "A" circulator was considered -
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unavailable.)
"C" CIRCULATOR On S/10/72 "C" circulator would not self-turbine. There h'ad been no reports 6f excessive wobbic on this circulator.
It had been' operated at self-turbining. speed' and at 5300 RPM on 8/8/72.
"C" was shutdown from the 5300 RPM above' because of relief valve probicms'on the emergency _feedwater header. - On 8/10/72.fo11owing
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repair of the relief valve, an unsucccasful attempt at self-turbining by bumping--
with Pelton: water was made. A.15% opra speed. valve position.was.used.
-On 8/11/72 another attempt at self-turbinin'g by.humpit. was made., Five hundred psi at~the Pelton nozzles,was used. The circulator would not-break free.
3 An additional problem noted on "C", circulator.was a helium ' leak from the ponctra-tion.1 It was first reported on 8/5/72' and ' described as/very large.1 1Nofattempts-t=
'wcre made.at the time to obtain a rate measurement...PCRV pressure atithe time:
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was between 400 and 450 psia.
On 8/7/72 a leak rate measurement was made and recorded at 8 scfm.
PCRV pressure was 304 psi-The penetration pressurization line then was isolated from the penetration pressurization valve llVlll?0. The penetration leak rate dropped to zero and remained so until the PCRV pressure was increased. At 352 psia leakage was still zero.
At 386 psia leakage from the penetration was 460 sec/ min.
At 440 psia leakage was 660 sec/ min.
This was the last reading taken. A leak at the primary seal or at the seal between the bearing cartridge and circulator support cone was indicated. There is no means of determining which seal is at fault.
"B" CIRCULATOR 1;o problems other than partially plugged Pelton supply nozzles were noted on "B" circulator.
Because of the plugged nozzles "B" circulator had been operated sparingly since 7/18/72 cven though there were no operational restrictions imposed.
"B" circulator still self-turbined freely with no indicated wchble on 8/15/72.
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