ML20023D165

Reactor Mode Switch Failure Modes & Mechanisms, Final Rept

ML20023D165
Person / Time
Site:	Susquehanna
Issue date:	04/29/1983
From:	FRANKLIN INSTITUTE
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ML20023D164	List: ML20023D163 ML20023D165
References
F-A5818-1, NUDOCS 8305190322
Download: ML20023D165 (30)

Text

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SUSQUEHANNA UNIT 1 REACTOR MODE SWITCH FAILURE MODES AND MECHANISMS FIRL Final Report F- A5818-1 l

Prepared for Pennsylvania Power and Light Allentown, Pennsylvania April 29, 1983 The contract governing the work reported horein provides that the name or the logotype of The Franklin institute, or any of its divisions, and references to or quotes from this report shall not be used in advertisements, brochures, or other promotional material without prior written approval of The Franklin Institute.

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i s f SUSQUEHANNA UNIT 1 REACTOR MODE SWITCH FAILURE MODES AND MECHANISMS i

I FIRL Final Report F-A5818-1 Prepared for Pennsylvania Power and Light Allentown, Pennsylvania April 29,1983 The contract governing the work reported herein provides that the name or the logotyne of The Franklin Institute, or any of its divisions, and references to or quotes from this report shall not be used in advertisements, brochures. or other promotional material without prior written approval of The Franklin Institute.

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_s F-A5818-1 CONTENTS

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. 1 SlMMARY . . . . . . . . . . . . . . 1 2 BACKGROUND . . . . . . . . . . . . . . 2 3 OBJECTIVE . . . . . . . . . . . . . . 3 4 DESCRIPTION OF TESTED SPECIMENS . . . . . . . . 4 5 TEST PROCEDURES . . . . . . . . . . . . 10 T

5.1 Functional Testing . . . . . . . . . . 10 5.2 Internal Inspection . . . . . . . . . . 10 6 TEST RESULTS . . . . . . . . . . . . . 15 6.1 Functional Testing . . . . . . . . . . 15 6.2 Internal Inspection . . . . . . . . . . 16 7 CONCLUSIONS . . . . . . . . . . . . . 23 APPENDIX A - Pennsylvania Power & Light Licensee Event Report and Nonconformance Report

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' e F-A5818-1 FIGURES Nu mber Title Page 1 Mode Switch Outline . . . . . . . . . . . 7 2 Mode Switch . . . . . . . . . . . . . 8 3 Contact Block . . . . . . . . . . . . . 9 4 Functional Test Setup for Mode Switch . . . . . . . 12 5 Switch Key Position . . . . . . . . . . . 13 j 6 Outlines of Cam 1 and Cam 3 . . . . . . . .- . 19 7 Outlines of Cam 2 and Cam 4 . . . . . . . . . 20 8 Comparison of Cam 1 and Cam 3 . . . . . . . . . 21 9 Comparison of Cam 2 and Cam 4 . . . . . . . . . 22 TABLES Number Title Pag e 1 Mode Switch Identification Information . . . . . . 6 2 Acceptance Criteria for Functional Test . . . . . . 14 iv 000 Franklin Institute Research Laboratory,Inc..

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SUMMARY

FIRL Report No. Report

Title:

F-A5818-1 Susquehanna Unit 1 Reactor Mode Switch Failure Modes and Mechanisms conducted and Reported by: Conducted fort Franklin Institute Research Pennsylvania Power and Light Laboratory, Inc. Allentown, Pennsylvania i

Twentieth and Race Streets Philadelphia, PA 19103-Report Dates Period of Test Program:

April 29, 1983 April 4 through April 22, 1983 i

objective:

The objective was to determine the failure modes of the Susquehanna Unit I reactor mode switch and provide a detailed evaluation of the failure mechanisms.

l Equipment Tested:

I Susquehanna Unit 14-position reactor mode switch, specified by General Electric Co. (GE) Drawing No. 19589497P005, manufactured by Gould (no model number given),

e modular construction, and key handle.

Elements of Prog:am:

1 First, the reactor mode switch was wired to a lamp peray. Using a smooth motion, the switch was rotated, and lamp status and can follower position were recorded at each switch position. The testing was repeated while rotaring the switch handle unevenly to determine the effects of over- and undertravel of the switch handle. If an abnormal condition was observed at any point during the course of the testing, a description of the condition was noted on the data sheet. Testing was continued until the abnormal f conditions had been thoroughly examined. Next, the reactor mode switch was disasssabled one segment at a time. During disassembly, a descriptive record was kept of any l abnormalities found in the parts, operation, and construction. Contact block cam

l. segments were compared, and any indication of wear was noted. Critical measurements l were made of the failed contact blocks. These measurements included the gap between the I can follower and guide, the diameters of the can shaf t and shaf t guide aperture, and the degree of the re. dial twisting of the can shaft.

l Conclusionar .

Functional testing of the reactor mode switch reproduced the failure that occurred on March 22 at Susquehanna Unit 1 and identified other failure modes that had not been previously discovered.

Significant irregularities were found among the can shaf t parts, and large design clearances resulted in imprecise operation of the can followers. The shaft was found to have angular differences of +10 degrees from the handle end to the opposite end. At l critical operating points of certain switch segments, a change in state of the contacts

! would occur with a rotation of 10 degrees. Therefore, these contacts could be either

open or closed at the same nominal switch handle position.

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2. BACKGROIDD On March 22, 1983, while the reactor was in hot shutdown, the reactor mode switch at Susquehanna Unit 1 was placed in the startup position to allow a surveillance test to be performed. Following the completion of the sur-veillance test, the Inode switch handle was turned to the shutdown position which should have actuated all four channels of the reactor protection system (RPS). However, when the switch was placed in the shutdown position, RPS channel "B" failed to actuate. This failure prompted a Licensee Event Report (LER) and a Nonconformance Report (NCR), which are included in Appendix A of this report.

On April 4,1983, Franklin Institute Research Laboratory (FIRL) was contracted by Pennsylvania Power and Light Company (PP&L) to test the failed reactor mode switch and determine the cause of the failure.

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3. OBJECTIVE The objective of this test program was to determine the failure modes of the Susquehanna Unit i reactor mode switch and provide a detailed evalus tion of the failure mechanisms. In the evaluation, particular emphasis was given to examining the cause of the failure which occurred at the plant on March 22.

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4. DESCRIPTION OF TESTED SPECIMEN The reactor mode switch, which was tested by FIRL, was the same component that failed on March 22 at Susquehanna Unit 1.

The switch was specified by General Electric Company (GE) and was manufactured by Gould, Inc. No model number could be identified for this component. Table 1, however, lists identification information that was found on the switch. In lieu of a model number, the GE " drawing" number (195B9497P005) is used as a unique identifier. This number identifies the GE design drawing (195B9497) and a unique part number (P005) given on the GE drawing. (The operating handle for the switch is a removable key. The key number is 401, which is stamped on the shank of the key. Part number 5, as stated on the drawing, is the switch which is operated by key number 401.)

When the reactor mode switch was received at FIRL, it was receipt inspected, and photographs were taken of the switch in the as-received condition. No damage was visible on the exterior of the switch; however, movement of internal parts was heard when the switch was turned over. It was noted that the case was constructed of plastic which was later identified as self-extinguishing polycarbonate per GE drawing 195B9497. During receipt inspection, the switch was operated a very limited number of times so as to not disturb its condition before it could be tested.

l The reactor mode switch uses modular construction; see Figures 1 and 2.

At the front of the switch is a four-position key operating handle that contains the detent mechanism and stop plate, which prevents turning the handle past the two extreme positions. 'Ib the rear of the operator are 8 l

contact blocks interspaced with 14 spacer blocks. The contact blocks contain the electrical contacts. The spacer blocks contain no contacts and are used

, for additional separation of four groups of contact blocks. Each block has a l

nominal depth of 0.475 inch. Attached to the final block is a plastic l

l backplate.

l The blocks are divided into four sections by six metal separator plates.

(Two separators candwiching a spacer block are used to divide each set of adjacent contact sections.) In the center of each section, there are two M Franklin Institute Research Laboratory,Inc.,

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Additional descriptive information on the reactor mode switch is presented in Section 6.2, which describes the results of the internal inspection of the switch.

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F-A5818-1 Table 1. Mode Switch Identification Information Description of Identifier Identifier Gould Identification H33553X1 Sticker 180-010 Case Identifier 879-12 GE Inspection Insp. Date: 8038 Sticker PO i s MP644 Item: 01 Rev.: 01 Drawing: 195B9497P00 5 Rev.: 03 Key Itamber 401

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TEST PROCEDURES The test program was designed to document "as-found" functional 4

abnormalities and then, through internal inspection and measurement, determine

- the reason for the abnormal conditions.

5.l' FUICTIONAL TESTING The reactor mode switch was wired to a lamp array as shown in Figure 4.

With the switch in position 1 (see Figure 5) , the circuit was energized. The 4

status (on or off) of the indicating lamps and the positions (in or out) of the can followers were recorded. Using a smooth motion that minimized any overtravel or undertravel, the switch was rotated counterclockwise. Lamp status and cam follower position were recorded at each switch position. After data were obtained for position 4, another set of data was recorded as the switch was rotated clockwise. The testing was repeated while rotating the switch handle unevenly to determine the effects of over- and undertravel of the switch handle.

Acceptance criteria for the functional test are identified in Table 2.

This information was derived from PPEL drawing number 8856-M1-C72-5 (3)-9 of the RPS . If an abnormal condition (such as datum that differs from the

( acceptance criteria) was observed at any point during the courne of the testing, a description of the condition was noted on the data sheet. Testing was continued until the abnormal conditions had been thoroughly examined.

5.2 INTERNAL INSPECTION The reactor mode switch was disassembled one segment at a time, and measures were taken to identify 111 parts so that the switch could be l- reassembled later if necessary. During disassembly, a descriptive record was

.kept of any abnormalities found in the parts, operation, and construction.

Contact block cam segments were compared, and differences and irregularities in the segments were recorded. Any indication of wear was also noted.

-Photographs were taken of the internal parts and structure of the switch, showing both normal and abnormal conditions.

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Critical measurements were made of the failed iontact blocks. These measurements included the gap between the cam follower and guide, the diameters of the cam shaf t and shaf t guide aperture, and the degree of the

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radial twisting of the cani shaft.

Because of its construction, the reactor mode switch had to be dis-assembled from back to front. Data were first taken during the disassembly of the two contact block sections farthest from the key operating handle. At this point, disassembly was halted so that PP&L personnel could witness the disassembly of the remaining two sections.

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5. TEST RESULTS 6.1 FUNCTIONAL TESTING In the first trial of the functional test, data were taken as the switch was rotated evenly from position 1 to position 4. With the switch in position 1 (the run mode) , the statur, of the indicating lamps agreed with the acceptance criteria. However, the cam follower at contact terminals 29, 30 did not appear to be correctly positioned, being in an intermediate state that was neither in nor out. This suggested that the 29, 30 contact was partially closed.

No abnormalities were seen when the switch was in positions 2 or 3.

When the switch was rotated to position 4 (the shutdown mode), several problems were found. First, it was noted that six lamps were on in this position. Lamps for contact terminals 13,14 aad 29, 30 were lit in addition to the four lamps which should have been lit. Also, it was noted that cam followers at contact terminals 21, 22 as well as 13,14 and 29, 30 appeared to be in rather than out. The cam follower at terminals 5, 6 was in an' intermediate state.

In the second trial, data were taken as the switch was raoved from position 4 back to position 1. 'Ihe results of this trial were identical to the results of trial 1.

In the third trial, the switch handle was rotated unevenly to determine the effects of over- and undertravel. For switch positions 1, 2, and 3, the results were the same as those in trial 1. Significant findings were made when the switch was in position 4.

At first, contacts 13,14 and 29, 30 were incorrectly closed as they were for trial 1. When the handle was turned slightly in a clockwise direction toward position 3, contact 21, 22 also closed and remained closed af ter the j handle was released. Only when the handle was turned counterclockwise until the stop was reached did the correct contact and configuration result. The

switch was manipulated several times, and these results were repeated consistently.

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In the last trial, _ abnormal conditions resulted for position 2. At first, the correct contact configuration was seen. Then, when the handle was turned slightly clockwise toward position 1, contacts 9,10 and 25, 26 closed and remained closed af ter the handle was released. As in trial 3, these results were consistent and repeatable. Also, during this trial, a wiring terminal was touched which resulted in the closing of another. contact that should have remained open. From this result, it was later deduced that one side of the contact crossbar was already closed when the terminal was touched. %e slight movement of the associated opposite terminal, which is directly connected to the stationary contact, was sufficient to close the air gap between the contact of the crossbar and that of the terrainal, completing the circuit.

In general, it was noted that the switch exhibited make-before-break operation. It was verified that this was in accordance with GE drawing 195B9497 which specified this type of operation for all contacts.

6.2 INTERNAL INSPECTION When the reactor mode switch was disassembled, a number of facts were discovered about its design and construction Each block of the switch was attached to the block in front of it by two screws that passed through the mounting holes shown in Figure 3. The can shaf t was made of plastic, and each block of the switch contained an individual section of the shaf t which plugged into other sections of the shaf t contained in adjacent blocks. Thus, the cam shaft consisted of 22 sections (one in each block) . Each cam shaft section consisted of a molded plastic shaf t onto which a disk was fitted. In the contact blocks, the disks were shaped to serve as cams that would open and close the contacts, i

Differences were noticed among tne cams. To better examine these differ-ences, an opt.ical comparator was used to produce an enlarged image of each cam, and then a tracing was made of the image. The results can be seen in Figures 6 and 7. Cam 1 operates contacts 29, 30 and 31, 32, and cam 3 oper-

.ates contacts 21, 22 and 23, 24. Both cams perform identical functions in ,

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F-A7818-1 significant differences in their shape. These differences are highlighted in black in Figure 8. (In this figure, the cams have been aligned and then superimposed.) Cam 2 (contacts 25, 26 and 27, 28) and cam 4 (contacts 17,18

-and 19, 20) are also different, as shown in Figure 9.

While operating the switch, an abnormality was observed in the movement of the can follower. As the can was rotated and it reached a transition point where it opened or closed the contacts, the can follower would no longer move vertically as shown in Figure 3, but would become cocked at an angle. When the contacts were closing, the cocking of the can follower allowed it a greater amount of downward movement than if it had remained vertical. Two abnormal conditions were observed as a result: (1) contacts closed on one side of the moving contact crossbar and not on the other or (2) contacts on both sides of the crossbar closed prematurely. Measurements were made of the clearance between the cam follower and the cam follower guide. These measurements ranged from 0.025 to 0.029 inch.

The can shaft and shaft guide aperture diameters were measured to ,

determine the amount of cam shaf t clearance. Clearance values ranged from 0.009 to 0.015 inch.

It was observed that the can shaf t had a tendency to twist. For instance, with the switch in position 1, the orientation of cam 1 (farthest from the handle) was recorded. When the switch was rotated to another position and then returned to position 1, the can had a different orientation, which differed from the original position by 20*. Measurements to determine i

the maximum angular differences were made at cams 1 through 4 with the switch

' in each of.the four positions. Results ranged from 10

• to 25*. These results are significant because a contact can be brought from full open to full closed l with only 10* of can rotation.

When the switch was completely disassembled, the operator (detent segment) was inspected. The operator detent mechanism did not hold the shaf t completely stationary, but allowed 5' of play. The connection between the metal shaf t of the operator and the plastic connector of the can shaf t allowed another 5* of play. When the p1rstic connector was removed, rotated 45*, and 4

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Q e F-A5818-1 placed back on the metal shaft, the connection was snug, allowing less angular play. The connector was examined under a microscope, and wear was visible on interior surfaces of the connector. Surfaces that were not in contact with the metal shaf t showed no signs of wear. When the connector was mated with both operator shaf t and cam shaft, the connection was found to have more angular play than when the connector was on the operator shaf t only. This was

, because the connector provided a female connection for both shafts but was not long enough to accommodate their combined lengths. Therefore, in the fully assembled state, the plastic connector between the metal operator shaf t and the cam shaf t would tend to have more than 5* of play, and this would increase with operational cycling of the switch.

No significant signs of wear were noticed on other switch surfaces.

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Figure 8. Comparison of Cam 1 and Cam 3 (with differences highlighted in black)

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7. COtCLUSIONS Functional testing of the reactor mode switch reproduced the failure that occurred on March 22 at Susquehanna Unit 1. It also identified other failure modes that had not baen previously discovered.

When the switch was internally inspected, significant irragularities were found among the can shaf t parts. Large design clearances resulted in imprecise operation of the cam followers, and the general construction of the switch allowed nonuniform rotation of the cam shaf t. The cumulative effects of these factors resulted in erroneous operation of the switch.

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I APPENDIX A PENNSYLVANIA POWER AND LIGHT j LICENSEE EVENT REPORT AND

) NONCONFORMAICE REPORP 4

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20th and Race Streets. Phila., Pa. 19103 (215) 448-1000

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s II. O -f3 PennsYIvania Power & Light Company s=_ san =ms Two Nonn N.nin sue.: . uentown, PA 18'o1 e 215 m>51st arch 23, 1983 s

Mr. R.C. Haynes.

Regicnal Administrator, Region I. .

'J.S. Nuclear Regulatory Commission "

631' Park Avenue

, King of Prussia, PA 19406 -

SL'SQ'.'EHANNA STEAM ELECTRIC STAT 10ii

• 0ENSEE

. EVENT REPORT 83-043/01P-0

• 22 '00450 FILE 841-23 PLA- It?O Cear *'e. "3 ynes :

'hi; transmission confirms the verbal notifi~ cation of . March 22, '933,*2y 2.J.

Steffenauer to J.G. McCann of your staff, concerning ne failure of the " "

cran 9e! c' Ne react:r protection system to actuate wnen the recc::r - de switen was urned frem startup to shutdown. The reactor was in Operating Con-cition 3. het snutdown, wnen this occurred. The mcde switch had been riscee

'a  : e star:a: ;osition to allow a surveillance to et perfor ed or One scre

isc ar;e volur.e ven: valves.

This condition is considered reportable in accordance with Technical S:e[ificati:-

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• 2 PP&L NONCONFORMANCE REPORT

1. NCR NO. 2. NO. TAGS NOTE: INSTRUCTICNS FCR COMPLETINC 83-234 1 NCR ARE CN REVERSE SIDE

3. ITEMS DESCRIPTION / LOCATION 4. CHG/ SPEC /PART/REV. No.

Reactor Mode Selector Switch 8856-M1-C72-22(10)-3 (51) on 1C551 S. SYSTEM NO. 6. UNIT NO.

58 1 Tar 1.oeatien t on svitch (svitch 7. SUPPLIER / CONTRACTOR /SECTICN

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8. NCNCONFCRMING CONDITICN Contacts 13 & 14 and contacts 29 t. 30 on switch S1' operate intermittently when si te elaced inte the shutdevn mede resultine in a half scram in lieu of a full scram. This renders the cuality of switch 51 en IC551 as indeterminate.

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