ML20086E659
| ML20086E659 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 10/15/1973 |
| From: | Walker R PUBLIC SERVICE CO. OF COLORADO |
| To: | Knuth D US ATOMIC ENERGY COMMISSION (AEC) |
| Shared Package | |
| ML20086E663 | List: |
| References | |
| 10CFR-050.55E, 10CFR-50.55E, NUDOCS 8312070474 | |
| Download: ML20086E659 (13) | |
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P.O. BOX 840 OENVER, COLORADO 80201 3
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October 15, 1973 Dr. Donald Knuth Directorate Regulatory Operations Office of Regulation Washington, D. C.
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Subject:
Deficiency Report,10 CFR 50 Helima Circulators Fort St. Vrain Station Ref.:
Interim Report Filed August, 1972
Dear Dr. Knuth,
In accordance with the reporting requirements of 10 CFR 50, Part 50 55, we are submitting herewith twenty (20) copies _of our final report involving the helium circulators.and associated systems.
i This report is filed to finalize the interim report referenced above, and to report additional findings which were uncovered by follow-up-action and subsequent testing.
All of the original damage-to the circulators as reported-by the referenced interim report was corrected, and the circulators were. subsequently tested. The "D" circulator (C-210h), is presently' in GGA shops in San' Diego for _ inspection of possible blockage of the-internal bearing water piping. Theproblemwiththie'"D"circulatorL
-is an isolated.one-, and one that should be corrected' vith minimal concern.
' We have kept-abreast of all' problems -and _ developments byj extensive-use of ?
. our own consultants and through the : efforts,of four own personnel.
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Puruc Str.vice Cn PANYOF cot.Q !Q Om 10/15/T3-It should be noted that while it appears that the problems have been adequately resolved, we do have additional testing that will be conducted as a part of our start-up testing series which we intend to monitor closely for assurance that the applied solutions are adequate.
We will keep the local Directorate infomed and abreast of all significant developments. We trust that the_ attached report will provide you with sufficient information to. evaluate the defi-ciency reported and the subsequent resolutions.
Very truly yours, k.3'luaAfw.
R. F.' Walker Vice President Engineering and Planning Electric Department RFW/DW:ga Attachment cc:
E. Howard Morris, Directorate, Region IV-l Y
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l DEFICIENCY REPORT
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- 10 CFR 50-Part 50 55.
l FACILITY: FORT ST. VRAIN NUCLEAR GENERATING STATION 1
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SUBJECT:
HELIUM CIRCULATORS AND AUXILIARIES
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REPORT.DATE: OCTOBER 10', 1973 -
REFERENCE:
INTERIM REPORT,-ABOVE' SUBJECT, AUGUST, 1972 ATTACHMENTS: GULF. GENERAL ATOMIC REPORT GA-A1271h w
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PSC PRE-NUCLEAR PELTON WHEEL'. CAVITATION, REPORT =
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b 1.0- SCOPE-Thist report is issued to finalize the interim report referenced
. above, and to supplement the referenced report with the additional infomation resulting from follow-up action and subsequent system testing.
The attached GGA report confirms the findings of the interim report that the original circulator damage resulted from the shaft orbiting brought on by the imbalance introduced by the loss of material from the pelton wheels. GGA's report also confirms the initial findings that the damage to the pelton wheels was caused by excessive civitation, and such cavitation can be controlled by a nitrogen suppression system.
In addition the GGA report addresses the failure analysis of the pelton i
l wheels, cavitation mechanisma, the cavitation suppression test program,.
the nitrogen suppression system and pelton wheel operation with nitrogen suppression. The subjects' are treated in detail in the GGA report and I
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therefore the contents of the report have been-frequently referenced herein without further qualification or explanation.. It is the intent 4
of this final report to correlate in generalithose items of the interim-report with GGA's report and to provide additional information that developed as a result of subsequent system testing that.vas not pre-,
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viously reported.
. 2.0 GENERAL'DESCRIiTION 2.1 Follow-Up Repair Work The damage to the circulators, as reported previously,-
was repaired and design modifications were effected for'five (5)' circulators.
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2.0 GENERAL DESCRIPTION - Cont'd.
a) Shaft, labyrinth and bearing' damage was repaired in GGA shops, San Diego.
b) The brake shoes were replaced with solid silver shoes rather than silver plated.
c) The bearing water orifice was redesigned and replaced.with a three stage breakdown orifice to avoid cavitation.
d) The housing of each circulator was modified to correct the funnel effect of the bearing water entrance to assist in preventing ingestion of foreign material between the bearing and the housing. Improved flushing and. vater chemistry control vere also incorporated into procedures to ' control circulating foreign material.
e) All compressor disc bolts were replaced with bolts made of Inconel T18.
f) The primary compressor. blades for the "B" circulator"(G2102).
vere replaced. This was a long lead item, and in the' interest of. time the spare ' circulator (C-2105) was modified'~ and rein-
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stalled as the "B" circulator.
g) All pelton. wheels were replaced using the same design and materials.
2.2 Testing Program Concurrently with the repair work on the circulators,.vork
. began on the nitrogen pressurization system. arid the suppression.
T head test' program as ' described in GA-A12714. g The nitrogen -
system was' completed prior to resumption (5/30/73) of the HotL
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2.2 Testing Program - Cont'd.
Flow Test (HFI'). The test program for the suppression system continued. The results of the test program indicate that approximately 30 paid suppfession head provides a conservative margin to prevent pelton wheel cavitation.
2 3 Resumption of Hot Flow Testing "With all circulators repaired and reinstalled, initial-
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testing resumed on 5/7/73, and the hot now test was resumed on 5/30/73 with the nitrogen suppression system in operation.
As might be expected from any new system several operating problems were experienced with the suppression system. Due.to improper pressure balancing between circulators and lacit of level indication the pelton wheels were submerged on one or more occasions due to the failure of the. turbine water ' drain cavity 1
to properly drain. Also due to inappropriate location of pressure gages it was learned that the pressure suppression-in the pelton wheel. cavity was not being maintained at 30 paid.
The system was modified to correct these problem areas.
These problems were not recognized soon enough,'hbvever, and as a result some> additional pelton wheel cavitation occurred during the HFT as described in GA-A12714.
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The HFT continued until 6/27/73 when'a drop.in circulator performance was noted.in "C'.' circulator ~ (C-2103).
Subsequent investigation revealed severe erosion on the elbov just up a
stream of the' nozzle supplying water to the pelton wheel'.
Th$ erosion was caused by. impingement' of water..from the.
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2.3 Resumption of Hot Flow Testing - Cont'd.
Investigation revealed erosion in the nozzle throat.
Failure of the nozzle o-ring seal resulted in flow divergence from the nozzle and hence the impingement on adjacent nozzle elbows. The results and action taken are more particularly described on Pages 29 thru 39 of GA-A1271h.
Necessary repairs were made and the HFT vas continued to completion on 8/13/73.
3.0 OTHER RELATED PROBLDIS 3.1 Speed valves During initial phases of the hPf cavitation problems and control instability were experienced with water speed control valves that serve the ' helium circulator pelton wheel drives (SV-2109, 2110, 2115 & 2116). These valves ara 2-1/2 inch trim, a
20,000 series Masoneilan globe valves with double "D" Domotor actuators. For the HFT these valves vera operated with temporary h" trim installed for the increased flow required.
Initial operation of these valves resulted in severe cavitation and control instability which in turn led to severe system pressure oscillations.
Subsequent investigation revealed that the cavitation problem could be handled by changing to a balanced valve trim.
Also isolation valves were installed upstream of the speed valves to relieve these valves of the need to also' function as block valves. Valve instability problems were _directly related to the stiffness of the actuator.
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3.0 OTHER RELATED PROBLEMS - Cont'd.
The plug and seat design were modified and an upstream pressure control system was installed to program pressure from 1000 psig at low flow to 2900 psig at maximum flov, thus minimizing pressure drop across these valves. The valve actuator was changed to a stiffer hydraulic actuator, ITT General Control hydramotor actuator Model AH91. These valves are now operating satisfactorily.
3.2 Back-Up and Emergency Bearing Water The helium circulators, having water lubricated bearings, are normally supplied bearing water via a closed loop bearing water system. To provide adequate protection to the circulator bearings in the event of loss of normal bearing water a ns back-up bearing water system consisting of an emergency feed water supply tied to tb? normal bearing water system through interlocked control valves is provided as a back-up source. In the event of failure of the back-up bearing water source an emergency bearing water system is provided, consisting of a gas pressurizer and an accumulator, to provide at least 30 seconds of bearing water supply to allow the circulator to coast down after trip without damage to the bearings.
During initial testing we experienced a considerable number of pmblems with this system. The response times necessary to get the back-up system in service prior to a circulator trip and to get the emergency system to fire to protect the circulator bearings were extremely fast. For most of the HPf the system
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was operated only with emergency back-up until necessary modi-fications could be designed and tested to obtain the response I
times required. Modifications and testing vere extensive. Piping changes were made.
Final testing has been completed the results of indicate that these systems are now perfoming satisfactorily.
3.3 Buffer Helium Recirculators Buffer helium is supplied to the circulator, and as the -
name implies this helium source acts as a buffer between the primary coolant on one sida and bearing water on the other.*;
The system requires that small differential precsures be' main-teined and if the small differentials are upset the ' circulator involved is tripped. While conducting the hot. flow test we experienced several circulator trips (buffer-mid-buffer),
primarily associated with back-up bearin6 vater testing.
It was subsequently determined that the supply of buffer helium.was not adequate to maintain differentials during a transfer 'from normal to back-up bearing water. By running with the-normal and i
standby buffer helium recirculntors ia each loop spurious trips _
were eliminated. Oc the basis of these tests it was-detemined that the buffer helium recirculators would have to be increased :
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in capacity.. New acirculators are on order with a capacity of' approximately twice that of the original units. ' Shipment of --the new recirculators is expected in late November.
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30 OTHER RELATED PROELDS - Cont'd.
3.h Surge Tank Level & Drains Several probl ms were experienced with the bearing water surge tank level and drain system.
Most of the problems were reco1ved by instrumentation and operational ad,justments. Some piping and other physical modifications were made during the course of the hot flow test and af+.er the hot flow test. These modifications have been tested and found to be acceptable.
35Ng Pressurization System The system was modified to include the nitrogen suppression system. These modifications were documented by Amendment 28 to the FSAR, and in addition are addressed in GA-A1271h.
h.0 EVALUATION h.1 Helium Circulator Operation The circulators were repaired satisfactorily as evidenced by the subsequent testing prior to the HFT, and by their performance during the HPf. The only problem experienced with.
the circulators themselves-was an. apparent blockage of the "D"
circulator (C-2104) ' check valves or internal piping' for,the back-up bearing water system.. This circulator. was removed and sent to GGA shops in San.Diego for' inspection.
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circulator (previously I,he "B"Echeulator) has been installed
. in place of the "D"' circulator, and~ preliminary operational _
checks exad tests 1. ave been accomplished to. verify performance. -
With reference to the pelton wheellcavitation problems,
and the nozzle erosion problems it is recognized that some kj y.
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h.0 EVALUATION - Cont'd.
cavitation was experienced subsequent:to the installation of the N2 pressurization system and that the nozzle erosion occurred in.
this same time frame.
In this respect it is difficult to come to' an unquestionable conclusion that the suppression system solved all of the cavitation problems. It is-known that the suppression system was not in proper operation during'some. periods of time during the hot flow test, and it is reasonable to assume thst the cavitation that '
did occur took place during these periods of time. The testing program was such, however, that subsequent testing time was-not sufficient to arrive at an absolute conclusion. Operating, time of the circulator after the second change out of pelton wheels was net sufficient to evcluate the Inconel material versus~
the 17-b ph material. In accordance with the analysis provided'.
by GA-A1271h the pelton wheel life has been 'shown to be adequate 'for.
the entire plant design life.
With reference to the nozzle' and elbow erosion problems, the nozzles are being changed from a Nitra11oy material ~to Inconel 718. The elbows of the nuclear' pising arej180* apart making impingement from one nozzle to the other ' impossible, and;
'the immediate. drain cavity area subject to flow impingement will be..
protected by an Inconel"718 splash 7 sheet.. It is felt that these '
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modifications will' be more than adequateLto prevent similar problems ' _
for the pemanent nuclear. piping.
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4.0 EVALUATION - Cont'd.
It is important to note that all cavitation and erosion problems that have occurred have been with temporary pre-nuclear pelton wheels and temporary pre-nuclear piping. It is also important to note that the conditions experienced during the HM are the most adverse conditions (high flow, maximum horsepower) that the circulator pelton wheel system will ever experience.
While there were some anomalies in the testing program and some problems during the HM, it is felt that these anomalics and problems are sufficiently defined, and that the HFT experience has been adequate, to indicate that problems have been resolved, especially when considering the conservative conditions that I!PT represents versus nomal nuclear operating requirements.
h.2 Other Related Problems The problems that have resulted 'during system tests' as outlined in Section 3.0 above are considered to be adequately resolved as evidenced by satisfactory testing following-system modification..
50 FURTHER CORI:ECTIVE ACTION OR EVALUATION No further corrective action other than. that outlined herein or in GA-12hl7 is contemplated at this time.
Further evaluation of the nitrogen suppression system and the Inconel pelton wheels will be made upon completion of the hot physics,
tests, as there will be extensive'. pelton wheel operation at:that jimeN9
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Careful attention will be given to proper ' operation-of the suppression-system during this portion.of:.the ~ testing program. ' Observation of the s
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pelton wheels upon cor:pletion of theae tests should provide con-clusive evidence of the adequacy of suppression system in minimizing cavitation.
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