ML20062J974
| ML20062J974 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 08/18/1993 |
| From: | AFFILIATION NOT ASSIGNED |
| To: | |
| References | |
| OLA-2-I-MFP-047, OLA-2-I-MFP-47, NUDOCS 9311190361 | |
| Download: ML20062J974 (15) | |
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'93 tr.T- 28 ? 6 29 l i NCR DC2-93-TS-N017 FRETTING AND CORROSION ON CCW HEAT EXCHANGER TUBES <
MANAGEMENT
SUMMARY
]
On March 18, 1993, eddy current testing conducted during 2RS on 30% of component cooling water (CCW) heatiexchanger tubes l indicated fretting on the outside diameter of the tubes at the "
i baffle plutes.
l The immediate cause of this event was determined to be tube whirl.
The root cause of this event as been determined as vibrations caused by high flow when operating two RHR heat exchangers and one CCW heat exchanger early during refueling outages.
The contributory causes were determined as: (1) Tube fretting l against the baffles and tube supports; (2) Valves caused high vibrations in line; (3) One heat exchanger required for '
miscellaneous maintenance and' operational needs; (4) Flow much greater than original operating conditions tap to 25,000 gpm refueling vs. 12,500 gpm design).
The immediate corrective actions included 100% eddy current testing on both CCW heat exchanger 2-1 and 2-2, and~ plugging ,
tubes identified by TES to have excessive wear.
Eddy current testing was performed.on 30% of the CCW heat >
exchanger tubes in Unit 1 during 1R5 and no damage of this type was noted. 100% testing will be performed during 1R6.
The Operations department will revise their procedure to incorporate the maximum flow limits on the.CCW heat exchanger.
The need to perform mid-cycle Eddy Current testing is being determined by NECS Engineering.
This draft, dated June 15, 1993, provides the minutes from the TRG meeting held on June 10, 1993. The TRG will not reconvene.
The NCR write-up will be sent for comments, signed off and sent to PSRC.
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N NCR DC2-93-TS-N017:Rev. 00 ,
June 15,l1993 i
NCR DC2-93-TS-N017 FRETTING AND CORROSION OF CCW' HEAT EXCHANGER TUBES :
I. Plant Conditions I Unit 2 was in Mode 6 (Defueled) Et Ot power.
II. Description of Event A. Summary:
On March 18, 1993, during 2R5 eddy' current examination !
30% of component cooling water (CCW) heat. exchanger ,
i tubes indicated fretting on the outside diameter of the tubes at the baffle plates.
B.
Background:
During the normal, cooldown, and post-accident operations at the_Diablo Canyon Power Plant, . equipment- '
l associated with the primary system and.its auxillliaries produce heat. .This heat must be removed l in order to control equipment temperatures. However,
! much of this equipment.contains radioactiveLfluids that must not be released to the environment. .The. Component Cooling Water (CCW} System provides this' buffer-in that' ; .;
it is a closed. system that removes the heat generated- .
by the various' plant systems without. releasing m radioactive material to-the environment. " 4 The equipment that.is. cooled by-the CCW system may be l divided into two types,'the vital 11oads and the l miscellaneous loads. The vital loads are the l
components needed by the plant during; emergency and i
accident conditions to remove heat'from the core ^or-the I
containment structure atmosphere. The miscellaneous or !
non-vital loads cooled by the_CCW system are those-components that are not vital or immediately required during emergency or accident situations.
As component cooling water flows through-the vitalland.
miscellaneous loads, it absorbs heat. This heat is.then removed from the CCW System through the CCW' heat-exchangers by the Auxiliary Saltwater (ASW) System. ;
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NCR DC2-93-TS-N017 Rev. 00 June 15, 1993 The Component Cooling Water (CCW). System is a' closed-loop system consisting of.three pumps, two heat exchangers, a surge tank, and three parallel' cooling-loops.
Water flows from the' discharge of the CCW. pumps into.
one or two parallel discharge headers. Each discharge headers leads to the shell side of a CCW heat exchanger. Cooling water from the Auxiliary Saltwater-(ASW) System passes through the tube side.of.the heat.
exchanger. Only one of the CCW heat exchangers will be in service during normal operations.
The outlet lines leading from each heat exchanger join to form a common header. The three CCW cooling loops branch off from this Header. The A and B-loop ~ provide cooling to-the vital-(ESF) equipment. This equipment consists of the Centrifugal Charging Pumps (CCPs), the.
Residual Heat Removal (RHR) pump: and heat exchangers, the Safety Injection (SI) pumps, the' Containment Fan Cooling Units (CFCUs) and their motors, the Post-Accident Sampling System, and.the CCW Pumps themselves (the lube oil and seal water coolers)..
Each Unit has two YUBA CCW heat exchangers which have straight tubes about 35 feet long.- Auxiliary salt-walter (ASW) flows inside the 90-10 copper' nickel tubes, with component cooling water on the shell side.
Six 5/8 inch thick support plates are spaced about every four feet. The 1,237 tubes:in'eachEheat exchanger are about'one inch'in diameter.
C. Event'
Description:
On March 18, 1993, eddy current testing of-approximately 10% of-CCW heat exchanger 2-1 tubes-indicated fretting on the outside diameter of the tubes at the baffle plates. ' Eddy current testing continued' until approximately 30%'of the tubes had been tested.
On March 23, 1993, a representative tube was removed' from CCW heat exchanger 2-1 for; examination; (The resulting holes were plugged.) Examination revealed a maximum' wall thinning of.approximately.25%.
On March 29, 1993,. engineering performed'100% eddy current testing on CCW heat exchanger 2-2 using'a recalibrated probe. The results of the testing 93NCRWP\93TSN017.PGD Page 3 of 13
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NCR DC2-93-TS-N017 Rev. 00 '
June 15, 1993 l
indicated fretting similar to.the-wear found'in heat.
exchanger 2-1, and several tubes'were. identified for plugging. .
On March 31, 1993, engineering performedL100% Eddy Current. testing on CCW heat-exchanger 2-1 using'a e recalibrated probe. The;results'of the testing. >
identified nine additional tubes for plugging. .
i The depth of'the damage varied with-the deepest damage; #
about 25 percent of the tube wall' thickness of-50 mils. '
10 tubes with damage greater than 20 percentEthrough' wall were plugged. .
It has been determined that the_CCW' heat exchanger: ,
tubes fretting was due to vibrations caused by high.
l flow when cperating two RHR heat exchangers and one CCW heat early in the-refueling outage.
! The Operations department will revise their procedure ;
to incorporate the maximum flow limits on the CCW heat l
exchanger.
The need to perform mid-cycle. Eddy Curren't testing is :
being determined by NECS Engineering.
D. Inoperable Structures,. Components, or Systems that~
Contributed to the Event: l None.
E. Dates and Approximate Times.for. Major. Occurrences:
March 18, 1992: Event / Discovery:date. during 2R5'. ~
~ analysis of the results of Eddy.
Current' testing.on 30%.of the CCW .
Heat Exchanger tubes indicates fretting-on the outside diameter of the tubes at the baffle plates.
F. Other Systems or Secondary Functions Affected:
None.
G. Method of Discovery:
During the performance of Eddy Current examination various indications on the CCW Heat Exchanger tubes were identified.
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j, NCR DC2-93-TS-N017 nov. 00 June 15, 1993 H. Operator Actions:
None.
I. Safety System Responses:
None.
III. Cause of the Event A. Immediate Cause:
Itbe whirl.
B. Determination of Cause:
See root cause analysis.
C. Root Cause:
The root cause of this event is due to vibrations caused by high flow when operating two RHR heat exchangers and one CCW heat exchanger early in the refueling outage.
j D. Contributory Cause:
I 1. Tube fretting against the ba#fles and tube ,
supports.
- 2. Valves caused high vibrations in line.
- 3. One heat exchanger required for miscellaneous maintenance and operational needs.
- 4. Flow much greater than original operating-conditions (up to 25,000 gpm refueling vs. '12,500 1 gpm design). l l
IV. Analysis of the Event l
A. Safety Analysis:
i There are three forms of vibration commonly found, I which are fretting, collision and cracking. Fretting 93NCRWP\93TSN017.PGD Page 5 of 13 i
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e NCR DC2-93-TS-N017 Rev. 00 June 15, 1993
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which is also called chatter is the most common form of.
tube damage. It occurs.at' support! plates or baffles. 1 Tubes may wear either 180 degree or 360 degrees around d their circumference. Thelmost' common occurrence?is the 180 degree wear,'is especially.found:in'the: bundle; ;
periphery.- The support plate or baffle may.also wear,' H causing. increased hole size. .The hole and~ tube wear j increase the clearance between the tube,and~ support' plate / baffle. This condition reduces damping and increases the tube vibration. 'Therefore rate, of l fretting degradation increases exponentially.
However, regularly scheduled Eddy Current testing is- j designed to detect this condition so it can be 1 corrected before the failure of:the tubes. j Subsequently.these tubes can be plugged as required' :
before any leakage occurs, j T.herefore the-health-andfsafety of the public ha've not been affected by this condition.
I B. Reportability:
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( 1. Reviewed under QAP-15.B'and: determined to be l non-conforming in accordance with Section 2.l.5.-
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l 2. Reviewed under 10 CFR 50.72 andL10 CFR 50.73 per- -
NUREG 1022 and determined'not to'be reportable. ;
- 3. Reviewed under 10 CFR Part 21 and determinedLt hat I this problem will not require a:10 CFR'21-report, j since (a) it'is being evalu qed.under*10 CFR. '~-
- 50.72/73, and (b). it does ' not involve defects =in vendor-supplied services / spare parts in stock.
- 4. This problem will be reported via an INPO' Nuclear Network entry.- )
- 5. Reviewed under 10 CFR 50.9 and determined to be
, not. reportable since this event does not have a-significant implication;for'public health and.
safety or common defense and security. '
- 6. Reviewed under the criteriaLof APLC-29: requiring.
the issue and approval of an OE and determined that an OE may be required.
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NCR DC2-93-TS-N017 Rev.o00 l June 15, 1993 i
V. Corrective Actions .
A. Immediate Corrective Actions:
- 1. Engineering performed 100% eddy current testing ,
with a recalibrated probe on both Unit 2 CCW heat exchangers.
I
- 2. PG&E is currently plugging all tubes that had' '
either more thanL20% wall thinning or tangential-wes.r from the baffle' plate.
- 3. Management issued a memo to' Operations personnel" with instructions to' switch over from one CCW. heat 'i exchanger to the other in the event of unusual ,
chemical makeup.
! B. Investigative Actions:
- 1. Write and submit an INPO Network. Entry to' inquire '
if other utilities are experiencing' fretting -
problems with Yuba heat exchangers. If so, what l are.they doing to address:them.- ;
l RESPONSIBILITY: .P. Dahan DEPARTMENT: Regulatory Compliance. ~
Tracking AR: A0299486, AE # Ol' STATUS: COMPLETE.
l NOTE: .This INPO network has been1 cancelled by.
the TRG chairman.
- 2. Evaluate the results of Eddy Current-on CCW' Heat Exchanger 2-2.
RESPONSIBILITY: M. Da Re DEPARTMENT: System Engineering'_
Tracking AR: A0299486, AE #'02 STATUS: COMPLETE Redo a complete inspection-of CCW heat exchanger
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3.
2-1. Calibrate the probe to this type of defect.
RESPONSIBILITY: M.~Da Re DEPARTMENT: System Engineering !
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NCR DC2-93-TS-N017 Rev. 00 l June 15, 1993 Tracking AR: A0299486, AE # 03 STATUS: COMPLETE j
- 4. Evaluate the effects of reduce flow rate. .
RESPONSIBILITY: I. Alexandrow l DEPARTMENT: System Engineering Tracking AR: A0299486, AE # 04 STATUS: RETURN
- 5. Document the discussions held with the heat exchanger manufacturer.
RESPONSIBILITY: M. Da Re ECD: 04/30/93 DEPAFTMENT: Systems Engineering Tracking AR: A0299486, AL # 05 STATUS: COMPLETE
- 6. Write and submit an INPO Network Entry to inquire if other utilities are experiencing fretting problems with Yuba heat exchangers. If so, what are they doing to address them.
RESPONSIBILITT: P. Dahan DEPARTMENT: Regulatory Compliance.
Tracking AR: A0299486, AE # 07 STATUS: COMPLETE.
NOTE: This INPO network has been submitted on July 30, 1993.
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C. Corrective Actions to Prevent Recurrence:
- 1. Operations to revise their procedure to incorporate the maximum flow limits on the CCW heat exchanger.
RESPONSIBILITY: M. Da Re ECD: 09/31/93 DEPARTMENT: Systems Engineering-Tracking AR: A0299486, AE #09 STATUS: ASIGNED l Outage Related? No
! OE Related? No NRC Commitment? No CMD Commitment? Yes l
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- 1, l NCR DC2-93-TS-N01' Nev. 00 June 15, 1993 i
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- 2. The: manager technical services:to talk to NECS1 Engineering to make.a determination for the need to perform mid-cycleLEddy Current 1 testing,-
RESPONSIBILITY: R. FosterL . ECD: _08/01/93 ';
DEPARTMENT: ~ Systems Engineering ,
Tracking AR: A0299486, AE.# 08 '
STATUS: ASIGNED Outage'Related? No.
OE Related? No NRC Commitment? No I CMD Commitment?. No
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D. Prudent Actions;(not' required for NCR closure)' >
- 1. Incorporate in DCM S-14 a method of warning-for '!
maximum flow condition that:could occur'and the.
resulting ~ danage . 1 RESPONSIBILITY: D.'Howland. ECD:'12/31/93' DEPARTMENT: NECS PG '
l Tracking AR: A0 ['
STATUS: ASSIGNED VI. Additional Information l
A. Failed Components:
i i None.
l I B. Previous Similar Events:
1 None.
l-C. Operating Experience Review:
- 1. NPRDS:
Not applicable.
- 2. NRC'Information Notices, Bulletins,; Generic
' Letters:
None.
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L NCR DC2-93-TS-N017 Rev.:00 June 15, 1993
i None. '
D. Trend Code:
4 Responsible department EN, and cause code C1'and C5. I E. Corrective Action. Tracking:
- 1. The' tracking action request is'A0299486. i
- 2. Are the corrective' actions' outage rel'ated? :
No.
F. Footnotes and Special. Comments:.
'None.
G.
References:
- 1. Initiating Action Request A0298919.
- 2. Tracking Action Request A0299486.
l 3. AR A0300624 H. TRG Meeting Minutes:
- 1. On March 26,.1993,'tne TRGLeonvened-and considered' d the following: "M "**
l The chairman establishsd'the.following proposed-
-agenda: ' ~
t
- a. Introduction. !
- b. Background.
- c. Sampl-a . tube .
- d. Fretting location. ..
- e. Vendor's ( Yuba ) 1 r e c ommenda t i ons /p os~i t i on .
- f. NES position / recommendations. .'
- g. Root cause (probability at'this' time).
Background:
Report of Eddy Current' testing oflUnit 2. heat exchanger tubesLrevealed. fretting on the'outside-93NCRWP\93TSN017.PGD' Page 10, of 13 3
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NCR DC2-93-TS-N017 Rev. 00 June 15, 1993 circumference of some tubes.
A sample of a damaged tube with fretting was examined by members of the TRG.
l Drawings of the fretting locations were reviewed and a discussion on the possible causes followed.
The vendor (Yuba) recommendations / position were reviewed. The minimum wall thickness is about
.030", (40% wear). Their stress calculations can allow as much as 50% of the wall thickness which is .025".
Discussion on how long the CCW heat exchanger can run with this degraded condition.
The design of our heat exchangers is an old static design rather than the present dynamic design of the modern heat exchangers.
Yuba position on tube plugging:
There is a 2% margin in the heat transfer coefficient. Therefore, 2% of the heat exchanger tubes can be plugged without creating much reduction in efficiency.
Engineering can evaluate the data gathered on these tubes and give the results of their evaluation, 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> after receiving the data.
There is no POA on the CCW heat exchangers.
Operability evaluation.
t If some tubes failed and leaked, Operations will notice it in the make-up-of the surge tank.
Flow balance is another issue which will need to be addressed outside of this TRG.
Proposed root cause: Static design rather than dynamic design of heat exchanger. Wear caused by the tube's vibration cn1 the shell side.
Three investigative actions issued. For more details see paragraph V.B.
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NCR DC2-93-TS-N017 Rev. 00 June 15, 1993 l
l 2. On April 9, 1993, the TRG reconvened and l considered the following:
The TRG reviewed the event and immediate corrective actions. Please see paragraph II.C.
Immediate corrective actions included (1) performing 100% eddy current testing with a j recalibrated probe on both Unit 2 CCW heat i
exchangers, (2) plugging all tubes that had eit':r more than 20% wall thinning or tangential wear from the baffle plate, and (3) issuing a memo to operations with instructions to switch over from one CCW heat exchanger to the other in the event of unusual chemical makeup. (Note: Tube plugging
! on heat exchanger 2- 2 was still in progress at the time of this meeting.). Although 20% eddy l
current testing during 1R5 indic ted no fretting, 100% testing will be performed on Unit 1 heat exchangers during 1R6.
93NCRWP\93TSN017.PGD Page 12 of 13
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NCR DC2-93-TS-N017 Rev. 00 ;
June 15, 1993 The.TRG discussed-the 10 CFR 50.59 safety.
evaluation. The heat exchangers are not degraded ~ >
below the point at.which they would remove the heat resulting from a design basis LOCA.
The TRG noted that 1R5 and 2R5 were the first:
times that the:CCW heat exchangers had been. eddy current tested.
The TRG discussed the current high flow conditions. With two RHR heat exchangers on line,.
the flow rate through one CCW heat exchanger is. .
22,000 GPM. .
The TRG noted that the potential exists for the i heat exchangers to have different baffle positions.
The TRG discussed a DCN.Rev'A which. states that up.
- to.12 tubes may be plugged in_each exchanger (2%
margin). Only 10 tubes were plugged in exchanger- ;
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2-1, including the tube that was removed for examination.
The TRG reviewed reportability and determined this I event not to be reportable to the NRC. ,
The TRG agreed that yes, an INPO. network entry I will be made. (It..had previously been canceled.)
The TRG discussed the Bechtel report, the basis
, for exceeding the original design flow 3 ate.
l A root cause analysis will be provided at the next TRG meeting. The immediate cause.of.this event is '
tube whirl.
Possible corrective actions to prevent recurrence include adjusting.the-maxi-flow valves,.rebundling '
the tubes, and replacing.the heat exchangers.
, The TRG reviewed and revised the NCR write-up.
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The TRG is tentatively scheduled to reconvene on May 10. 1993.
- 3. On June 10,.1993, the-TRG. reconvened and considered the'followingi 93NCRWP\93TSN017.PGD- Page' 13' of- 13 i'
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NCR DC2-93-TS-N017 Rev. 00 June 15,.1993 Another NCR covering CCW heat load. Unresolved action.
Discussion on why the vibration occurred. ,
Needed more flow in 1983 Bechtel came back and said we did not have any problem.
Administrative requirements being put in place.to put in place two RHR heat exchangers.
One corrective action to prevent recurrence was added (for more details see para.-V C2)
Engineering is expected to have the Eddy Current testing complete within 6 months.
THE TRG WILL NOT RECONVENE. THE WRITE UP WILL BE SENT FOR COMMENTS AND TRG VOTING MEMBERS WILL BE ADVISED TO COME AND SIGN THE NCR.
I. Remarks:
None.
J. Attachments.
None.
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