IR 05000237/1988013

Insp Rept 50-237/88-13 on 880517-24.No Violations Noted. Major Areas Inspected:Plant 880516 & 17 MSIV Failure to Close During Loss of Air Testing

ML17201J329
Person / Time
Site:	Dresden
Issue date:	06/29/1988
From:	Ring M NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III)
To:
Shared Package
ML17201J328	List: IR 05000237/1988013 ML17201J327 ML17201J330
References
50-237-88-13, NUDOCS 8807120022
Download: ML17201J329 (30)

Text

U. S. NUCLEAR REGULATORY COMMISSION REGION II I Report No. 50-237/88013(DRP)

Docket No. 50-237 Licensee:

Commonwealth Edison Company P. 0. Box 767 Chicago, IL 60690 Facility Name:

Dresden Nuclear Power Station, Unit 2 Inspection At:

Dresden Site, Morris, I Inspection Conducted:

May 17 thru 24, 1988 Inspectors:

Approved By:

S. G. Du Pont P. D. Kaufman R. D. Lanksbury J. F. Schapker M. P. Huber H. L. Ornstein

~cl~2-~

M. A. Ring, Chief~7

..

-

/

Reactor Projects Section lB Inspection Summary License No. DPR-19 Inspection during the period of May 17 thru 24, 1988 (Report No. 50-237/88013(DRP))

Areas Inspected:

Augmented Inspection Team (AIT) inspection of the May 16 and 17, 1988, Unit 2 Main Steam Isolation Valves* failure to close during loss of air testin Results:

No violations or deviations were identifie The routine Technical Specification required surveillance does not identify Main Steam Isolation Valve (MSIV) degradation due to excessive stem packing frictio The Automatic Valve Company (AVCo) 4-Way solenoid-valves will hangup in an intermediate position during gradual loss of system air pressure, rendering the MSIV accumulators inoperabl The root cause of the eight Unit 2 MSIVs 1 failure to achieve full closure during the special loss of air test on May 16 and 17, 1988, was due to excessive MSIV stem packing frictio Unit 3 MSIVs did not experience excessive MSIV stem.packing friction and were operabl * PDR ADOCK 05000237 Q

PDC

• -

Augmented Inspection Team Report 50-237/88013 Page N Introduction 1 Synopsis of Event 1 AIT Fonnati on 1 AIT Charter 2 Persons Contacted

I I. Description - MSIVs Failure to Fully Close on Loss of Air Event of May 16 and 17, 1988 2 Narrative Description 2 Sequence of Events

III. System Description 4 Main Steam Isolation Valves (MSIVs)

4 Drywell Pneumatic System 5 Instrument Air System 6 Integrated Operation of Pneumatic and Instrument Air Systems

I Investigative Efforts 7 Synopsis of AIT Activities 7 Licensee Actions 9 Details of Testing and Inspection Activities 13 Lessons Learned and Corrective Actions 17 Historical Reviews 18 MSIV Maintenance 18 Industry Events 19 Procedure Reviews

V Safety Significance 22 Immediate 22 Under Operational Conditions

VI I. AIT Conclusion

VI I I. Concerns

I AIT Recommendations 24 IST Activities 25 Procedures 25 Evaluations 26 Testing 27 Information Notice

• Inspection

'..

,,

Attachment N A

8A Attachments Description Confirmatory Action Letter (CAL~RIII-88-12)

AIT Charter Main Steam Isolation Valve - Control Diagram Main Steam Isolation Valve Pneumatic Manifold - Closed Configuration Pneumatic Manifold - Open Configuration Pump Back System Primary Containment Atmospheric Control System Instrument Air System Service Air System

..

L

• Introduction Synopsis of Event On Thursday,December.24.,.1987, at 2:30 a.m., with Dresden Unit 2 at 93% power, the lB inboard Main Steam Isolation Valve (MSIV) was observed to have a dual position indication in the control roo Steam flow through the B steam line was observed to be approximately 75% of the flow through each of the A, C, and D steam line The licensee decreased power and attempted to cycle the lB MSIV with no success {the MSIV would neither open or close). The licensee's investigation into the event determined that the air supply line had pulled out of the pneumatic manifold on the valve operato The air supply line was repaired, tested, and subsequently declared operabl Because the valve had failed to fully close in response to the loss of air, the licensee scheduled further inspection and testing to be performed at the next outag On Monday, May 16, 1988, at approximately 8:00 a.m., with Dresden Unit 2 shutdown, the licensee was performing the special testing (SP 88-3-15) in response to the December 24, 1987, even The test being performed involved using the exercise control solenoid (MSIVs spring force alone without air assistance) to slowly close the MSIV This test was performed for all four inboard and four outboard MSIVs and none of them fully close On Tuesday, May 17, 1988, at approximately 8:00 a.m., the licensee was continuing the special testing of the MSIV The testing consisted of isolating the pneumatic air supply to the inboard MSIVs and the instrument air supply to the outboard MSIVs and monitoring the MSIVs to see if they would fully close on loss of air. The test results revealed that all eight MSIVs failed to *

fully clos Based on this, the licensee declared all of the MSIVs*

inoperable and made the required Emergency Notification System (ENS) phone call to notify the NR AIT Formation In response to the Maf.16 and 17 events, Region III formed a special inspection team on May 18, 1988, comprised of S. G. Du Pont, Dresden Senior Resident Inspector (SRI) and Team Leader, P. D. Kaufman, Dresden Resident Inspector (RI), R. D. Lanksbury, LaSalle SRI, and J. F. Schapker, Region III Reactor Safety Inspecto All four members were on site by the morning of May 1 Based upon informa-tion gathered on May 18 and upon further evaluation, the decision was made to form an Augmented Inspection Team (AIT).

The AIT was comprised of the above four individuals plus the addition of M. P. Huber, Region III Reactor Safety Inspector, and H. L. Ornstein, Senior Reactor Systems Engineer, Office of Analysis and Evaluation of Operational Data (AEOD).

All of ih~ AIT members had arrived on site by the morning of May 21, 198 Concurrent with the AIT activities, Region III issued a Confirmatory Ac~ion Letter

...

\\;

• (CAL-RIII-88-12) which was received by the.licensee on May 18, 1988, and is included as Attachment 1 to this repor The CAL confirmed certain actions to be taken by the licensee in support of the AIT and established that the restart of Unit 2 could only occur upon concurrence of the Region JII RegioDal Adminjstrator, or his designe AIT Charter On May 19, 1988, the AIT fonnulated and provided to Region III a draft charter for concurrenc On May 20, 1988, Region III transmitted the approved AIT charter (Attachment 2) to the AIT on site. The general areas to be investigated were:

0

0

Root cause of the MSIVs' failure to fully close on loss of ai Safety significanc Interaction of prior maintenance activities to the even Broader implication Event reportin Persons Contacted Commonwealth Edison Company (CECo)

• N. J. Kalivianakis, General Manager, CECo BWR Operations

• E. D. Eenigenburg, Station Manager, Dresden

• J. W. Wujciga, Production Superintendent, Dresden J. A. Silady, Nuclear Licensing Administrator, CECo

• E. R. Zebus, Engineering Superintendent, CECo BWRE

• R. Meadows, Maintenance Staff Supervisor, Dresden D. Van Pelt, Assistant Superintendent - Maintenance, Dresden W. R. Betourne, Quality Assurance Engineer, Dresden

• J. Achteberg, Technical Staff Supervisor, Dresden

• E. Armstrong, Regulatory Assurance Supervisor, Dresden M. Strait, Master Mechanic, Dresden J. Kotowski, Assistant Superintendent - Operations, Dresden General Electric Company (GE)

• C. T. Nieh, Design Engineer, GE - Valve Design

• J. Nash, Resident Engineer, GE

• Denotes those attending the exit meeting on May 24, 1988.

In addition, other members of the Dresden staff were contacted by tbe AI II. Description - MSIVs Failure to Fully Close on Loss of Air Event of May 16 and 17, 198 A *

Narrative Description With Dresden Unit 2 in cold shutdown for a short maintenance outage and Unit 3 in a refueling outage, all eight Unit 2 Main Steam

• *

Isolation Valves (MSIVs) failed to fully close during a special loss of air test which ~1as being conducted to further investigate a December 24, 1987, _failure of Unit 2 inboard MSIV 203-18 to fully close when its pneumatic supply air line pulled out of the manifold bloc To conduct this test, the drywell pneumatic supply and instrument air supply headers were isolated, permitting the headers to bleed down slowly, while monitoring the MSIVs to verify if full closure was achieved on a loss of air. Test results revealed that all eight MSIVs failed to fully close, thus the licensee declared all the MSIVs inoperabl Sequence of Events On December 24, 1987, Unit 2 inboard MSIV 203-18 failed to fully close when its pneumatic supply line separated from the manifold block on the valve operato In response to this event, a special loss of air test procedure was developed (SP 88-3ll5) to be per-formed during an upcoming short maintenance outage on Unit 2 to determine if incomplete MSIV closure was related to loss of main supply air to the valve while maintaining pilot ai On April 14, 1988, while Unit 2 was operating at about 30% power, a drywell inspection revealed an air leak on the coupling connecting the supply air to the inboard MSIV 203-18 pneumatic manifol There had not been any MSIV motion as a result of the air lea Review of the leak was unable to determine if the significance was large enough to cause the valve to clos On April 27, 1988, while Unit 2 was operating at about 80% power, inboard MSIV 203-18 partially close The cause of the partial closure was determined to be due to the air supply connection separating from the manifold block similar to the December 24, 1987 even The air supply line was reconnected after corrective maintenance to the manifold increased the thread distance for the connectio As previously noted, testing was scheduled during the May 1988 outage to determine the cause of the failure of the MSIV to fully close during loss of air condition On May 16, 1988, with Unit 2 in cold shutdown, the special loss of air test commenced at 8:00 The first section of the test involved installing a jumper to maintain the AC exercise control solenoid (Number 6 on Attachment 3) energized to allow full stroke testing of each MSIV when the test pushbutton was depressed in the control roo This test configuration enables the over-piston are to be vented and the air from under-piston area to bleed of The valves should then drift closed on MSIV spring force onl None of the eight valves fully close *

On May 17, 1988, another section of the special test was performed on the inboard MSIV This section required complete isolation of the air supplied*by the drywell pneumatic supply header, permitting a-slow bleed down rat None of the valves fully close The same test was performed on the outboard MSIVs by isolating the instrumen air supply header and the same results occurre Thus, at 12:55 p.m., all eight MSIVs were declared inoperabl *

The licensee contacted the NRC Duty Officer via ENS at 3:26 p.m., on May 17, 1988, and informed him that all 8 Unit 2 MSIVs were declared inoperable since they failed to fully close on loss of air. The Re~id~nt Inspector ~as in the control room when the ENS call was mad *The NRC Region III, Reactor Projects Branch 1, Branch and Section Chiefs held a conference call with the Dresden Station Manager at approximately 5:30 p.m., on May 17, 1988, during which it was agreed that the MSIV problem had to be investigated and fully understood prior to restart of Dresden Units 2 and During this call, it was also agreed that two of the eight MISVs could be released for further testing while six valves would be quarantined in an as found conditio On May 18, 1988, a telephone conversation between the NRC Region III Director, Division of Reactor Projects and the Dresden Station Manager was held to discuss the MSIVs' failure to close during a loss of air test on Unit Additionally, a Confirmatory Action Letter (CAL-RIII-88-12) was issued following the conversation which prohibited the startup of Dresden Units 2 and 3 until a determination had been made that equipment performance (MSIVs) was satisfactory and concurrence of the Regional Administrator or designee had been.obtaine A special inspection into the MSIV event commenced on May 18, 1988, by a team comprised of the Dresden Resident Inspector staff, the Senior Resident Inspector - La Salle, and a Regional Specialis The special inspection progressed into an Augmented Inspection Team (AIT) on May 19, 198 The AIT was headed by the Dresden Senior Resident Inspecto III. System Descriptions Main Steam Isolation Valves (MSIVs)

The Main Steam Isolation Valves (MSIVs) are 20 inch air/spring operated, balanced "T" type, globe valve A typical MSIV is shown in Attachment The MSIV combines full port design with straight line flow to provide a good flow'patter The MSIV utilizes upstream pressure to aid in valve closure by tilting the actuator toward the upstream side of the valv The balancing feature of the MSIV makes it possible to take advantage of the upstream pressure to aid in holding it closed and to have the advantage of requiring a smaller actuator* cylinder to open it. This is accomplished by allowing the full upstream line pressure to bleed into the chamber above the plug through the balancing port to exert a force on the plug internals in a direction to hold it against the sea When the actuator starts to open the MSIV, the steam lifts the pilot off its seat to vent the steam inside the plug into the downsteam lin As the stem travel continues, the plug is lifted off the main valve seat to open the valve por The actuato~ is supported by four spring guide shafts designed to support the actuator without any outside suppor Eight coil springs located

around the spring guide shafts are used for closing the MSIV in case of air failur The MSIVs are opened; and held open, by compressed air but will close with either air or spring actio The valve closure time is controlled between 3 and 5 seconds by a hydraulic (oil) dash.pot.which is mounted below the main air cylinder and is equipped with an external bypass pipe and flow control valv The air for the MSIV actuator is supplied and controlled by a pneumatic manifold that is located on one side of the actuato The inboard MSIVs receive their air supply from the drywell pneumatic pumpback system and the outboard MSIVs receive their air supply from the instrument air syste Attachment 3 shows a schematic diagram of the MSIV pneumatic manifol The MSIV pneumatic manifold directs air to one side of the piston, located inside the actuator, and vents the other side to atmosphere, to control which direction the MSIV will mov The pneumatic actuator consists of three 3-Way solenoid operated valves (SOVs) (2 AC and 1 DC) and two 4-Way valve The three 3-Way SOVs act as pilot valves and control the positions of the 4-Way valves by directing air to, or venting air from, the These SOVs are shown on Attachments 5 and 6 as #1, #2, and # SOVs #1 and #2 are utilized for normal opening and fast closure of the MSIV SOV #3 is only utilized to allow exercising the MSIV (i.e., slow closure) when it is already ope The two 4-Way valves are shown on Attachments 5 and 6 as Valve #1 and Valve # Valve #1 is controlled by SOV #1 or #2 (only one SOV is required to open the MSIV) and Valve #2 is controlled by SOV # Since, as discussed earlier, SOV #3 is only used for exercising the MSIV, Valve #2 normally does not change position from that show _Attachment 5 shows the configuration of the MSIV pneumatic manifold to close the MSI Pi-lot air cannot pass through the 3-Way SOVs since they are de-energize Without pilot air, the two pistons in Valve #1 are located to their normal positions by their respective spring The left piston is forced up to seal exhaust port #1 and allows air to pass from the inlet to the over piston area of the actuato The right piston is forced down, thus blocking the inlet air and allowing exhaust port #2 to be open to Valve # Valve #2 does not have pilot air directed to it so it's internal spring forces the piston up, sealing exhaust port #3 and allowing the under piston area to be vented through Valve #1 and exhaust port # With the MSIV actuator over piston area pressurized, the under piston area vented to atmosphere, and the MSIV springs pushing down, the MSIV is forced close Attachment 6 shows the configu~ation of the MSIV pneumatic manifold to open the MSI SOVs #1 and #2 are shown energized, thus allowing the passage of pilot air to Valve # The pilot air forces the left piston down against spring pressure, allowing the MSIV actuator over piston area to be vented to atmosphere and blocking the inlet ai This also allows the over piston area of the right piston of Valve

1. 1 to be vented to atmospher With the above piston area of Valve

1. 1 vented, ihlet air can force the right piston up against spring

..

<

• _pressure and thus allow the inlet air to then pass through Valve #2 to the under piston area of the MSIV actuato With the MSIV actuator under piston area pressurized and the over piston area vented to atmosphere sufficient force is provided to open the MSIV against the spring force that is tending :to hQl.9_ it_ close Drywell Pneumatic System The drywell pneumatic (DP) system supplies "instrument air" to components in the drywel However, unlike the instrument air system described below, the DP system takes its suttion from the drywell rather than outside air. Since during normal operation, the drywell is inerted with nitrogen, the DP S}'Stem supplies nitrogen, rather than oxygenated air, to the drywell component This reduces the need for venting of the drywell due to continuous bleeding of air from pneumatic components, which would otherwise lead to an internal pressure rise in the containment and excessive oxygen concentration in the inerted atmospher The motive force for the DP system normally comes from the pump back system (Attachment 7).

The pump back system includes two air compressors, after coolers, and an air receiver tan Other than supplying DP, the purpose of the pump back system is to maintain the drywell to torus differential pressure. This is done in order to decrease the amount of hydro shocking of the torus support structure during drywell pressurizatio As a backup to the pump back system, nitrogen can also be supplied to the drywell components from the nitrogen makeup syste Instrument Air System The purpose of the instrument air (IA) system is to supply clean, dry, compressed air for air-operated control devices and instrument This includes the outboard MSIV The system (Attachment 8)

consists of compressors, after coolers, air receiver tanks, dryers, oil fi 1 ters, and the necessary contra 1 and support equipmen The pressure control valve provides backup instrument air supplied from the Unit 1 instrument air syste This supply is normally valved ou The IA also has a service air crosstie. This crosstie provides IA backup from the service air heade The crosstie valve will automatically operate if the IA header pressure falls below 85 psig: Integrated Operation of Pneumatic and Instrument Air Systems Pneumatic Pumpback System The pumpback compressors, which supply nitrogen to the drywell pneumatic system, are backed up by the nitrogen makeup syste A "pneumatic supply trouble" alarms in the control room when system pressure decreases below 70 psig and a "drywell pneumatic supply low pressure" also annunciates when system pressure decreases below 60 psi An emergency nitrogen makeup supply valve automatically opens at 60 psig to provide backup

• supply from the nitrogen makeup syste Since several of the air operated valves for the pumpback system are located outside of the drywell and are actuated by instrument air, the AIT reviewed the actuator supply to the emetgency nitrogen ~akeup supply val~~, the associated valves in the.makeup system and the integrated valves between the makeup.and pumpback system The review revealed that upon a loss or degradation of the instrument air system, the inboard MSIVs would be sufficiently supplied nitrogen for actuation from the makeup system through the emergency nitrogen makeup supply valye prior to the system pressure decreasing to the pneumatic phenomenon setpoint of 48 psig (as noted in Paragraph IV.B.).

Instrument Air System As stated above, the instrument air system receives backup supply from the service air system at 85 psig through a automatically operating valv In addition, the Unit 2 instrument ~ir system receives backup from the Unit 1 instrument air system (Unit l's instrument air system is maintained per Technical Specifications). Several annunciators alarm in the control room to alert the operator of degrading instrument air system pressur "Low Pressure in Instrument Air Receiver" alarms for both units at 85 psig. Additionally;-the instrument air dryers are automatically bypassed at 60 psig to maintain downstream air pressure and the Service Air to Instrument Air cross-connects also automatically open at 85 psig. Additional redundancy is provided by three available Unit 1 instrument air compressors, two Unit 2 instrument air compressors and three Unit 3 instrument air compressor Based upon these reviews, the AIT concluded that the nitrogen pneumatic and instrument air systems are adequately separated and supported by backup system I Investigative Efforts Synopsis of AIT Activities The AIT initially reviewed the special test procedure (SP 88-3-15)

and results of the May 16 and 17 testin From this review the team determined that five possible root causes existed in two general area The May 16 test results indicated that a possible physical restriction may have prevented the MSIVs from closing on springs onl The team identified MSIV spring tension degradation and excessive valve packing friction as possible cause The review of the May 17 testing revealed that three additional causes associated with the motive force (instrument air for the outboards and pneumatic air for the inboards) may have prevented* the MSIVs from fully closing; excessive leakage of stored accumulator air (check valve failure),

failure of the MSIV solenoid manifold pilot valves, or air purit On May 19, the licensee began a series of troubleshooting tests to determine the root caus Listed below is a summary of these areas of possible root cause and reasons why they were chose.

MSIV Actuator Springs:

The springs were chosen because of the generic f~ilure of all eight MSIVs during the Spring Only Closure Test on May 1.

MSIV Stem Packing:

The packing was chosen by the AIT because of prior experience of some of the Team's members with steam valves and packin The team determined that, for packing to be the generic cause of all eight failures, the maintenance practices and procedures would also be investigate.

Automatic Valve Co.. (AVCo) Air/Pneumatic Manifold:

The manifold, including solenoids, pilots and 4-Way valves, was selected based upon similar failures documented in NUREG 1275, Volume.

Loss of Accumulator Volume:

During the May 17, 1988 testing, the accumulator volume bled down to 0 psig without positioning the MSIVs fully close Based upon the understanding of the function of accumulator, the team selected the accumulator check valves and the integrity of the air system as likely suspect.

Air Supply Purity:

The team selected the quality of the air motive system because of similar problems noted in NUREG 127 The team also established a quarantine of the MSIVs and their associated systems to assure that the initial "as found" conditions would be maintaine The licensee conducted an extensive "as found" documentation to assist in the root cause determinatio Based upon th~se efforts and the May 16 test results the following

"as failed" conditions were determined for the inboard and outboard MSIVs:

(inboards)

(outboards)

Valve N lA 203-lB 203-lC 203-10 203-2A 203-2B 203-2C 203-20 Position 2 1/4

1/8" 2 5/8"

'8 1/4" 3/4

8 1 5/8" 5 5/8" 2 1/2" from full open II

. I'

It should be noted that valves 203-18 and 203-2A traveled less than 10% from the full open position while all others traveled beyond the 90% of full open scram setpoin On May 18, the licensee conducted an initial troubleshooting test on the inboard 203-lA valv The objective of the test was to determine the effect that valve packing had on preventing the MSIV from closing on spring force onl The licensee loosened the valve packing and conducted the May 16 testing using the exercise control solenoid (venting the above and.below MSIV actuator piston cavities)

and allowing closure on spring force only. Additionally, the Technical Specification surveillance test DOS 250-2, "Quarterly MSIV Closure Timing, 11 was conducte DOS 250-2 tests the ability of th MSIVs to close between 3 to 5 seconds with instrument/pneumatic air and spring assistanc The results of both tests revealed that the MSIV would fully close on spring force only within 30 seconds and within 3 to 5 seconds (as required by Technical Specifications) on pneumatic air with spring assistanc The licensee additionally applied lubricant to the valve stem and the valve guide The lubrication improved the valve's response to spring only closure to less than 20 seconds but did not have any noticeable affect on the pneumatic air with spring assistance closure (DOS 250-2).

The team reviewed these results and determined that further testing would still be required to identify the root caus On May 19, the licensee commenced a formal troubleshooting progra.

Licensee Actions On May 17, 1988, the licensee formed a task force to investigate the event and determine the root caus The root cause analysis determined possible causes in agreement with the AIT determination as listed previousl The following is a summary of troubleshooting tests conducted by the licensee with brief descriptions of test objectives, results and methods: Spe.cial Test SP 88-5-56, "Leak Rate Test of the MSIV Accumulator Check Valves"

Test Objectives:

To verify that the accumulator check valves will maintain the stored volume during a slow loss of ai Results:

inboards lA 2.86 SCFH, lC 2.32 SCFH, 18 4.42 SCFH, lD 8.55 SCFH outboards 2A 12.13 SCFH, 2C 33.19 SCFH, 28 8.29 SCFH, 2D 7.02 SCFH

,*

Conclusion:

Although the leakage from 2C was excessive and ID, 2A, 2B and 2D were high, th~ team concluded that check valve leakage was not the root cause of the 8 MSIV failures or the associated losses of accumulator volume because several of the valves did not exhibit leakag.

Special Test SP 88-5-57, "MSIV Manifold Assembly Testing"

Test Objective:

Simulate Rapid and Slow Loss of Air (SLOA) to determine response of AVCo 4-Way valve and Pilot valv *

Test Method:

The manifold was removed from the IC inboard MSIV.and tested with a bench assembly that included a 90 psi air supply, simulated above and below MSIV piston cavities, and an installed accumulato *

Results:

During Rapid Loss of Air, the pilot and 4-Way valve responded as required and per desig However, during the SLOA test, the pilot intermediately positioned allowing the accumulator and below (opening) piston to vent to the atmospher This phenomenon started at a reduced system pressure of 48 psi and maintained the 4-Way*in an intermediate position until system pressure reduced to 6 psi. At 6 psi, the pilot would position (due to internal spring tension) to allow pressurizing the above (closing) and complete venting of the below (opening) piston and close the valv *

Conclusions:

The team could not determine that the failure of the 4-Way to position was the root caus.

Special Test SP 88-5-57 (Second Test), "MSIV Manifold Assembly Testing."

(a)

Test Objective:

Simulate the phenomenon on a newly rebuilt AVCo 4-Way valv (b) Test Method was the same as SP 88-5-57 on the IC manifol (c)

Results:

The same as the IC test f:

• Special Test SP 88-5-60, "Determination of Force to Compress MSIV Springs"

Test Objective:

Demonstrate that MSIV closure springs have not degraded from original tension value *

Test Method:

• The lC MSIV springs were compressed on a bench test assembl *

Results:

1968 Data 1988 Test Data a. Total Spring Constant 650 lbs/in 643 lbs/in Closed Preload 4300 lbs 4335 lbs Open Force 10280 lbs 10121 1 bs

Conclusion:

No significant degradation of the spring.

Special Test, "Unit 2 Outboard MSIV Air Isolation Testing Following Packing Adjustment"

Test Objective:

To demonstrate the effect that packing adjustments have on the MSIV ability to go full closed during SLOA or spring-onl *

Test Method:

a. SP 88-3-15 testing for spring force only by isolating instrument air from the MSIV with the exercise control solenoi b. DOS 250-2, "Quarterly MSIV Closure Timing,"

using air with spring to assist in closure of the valve c. DOS 250-3, "Loss of Air, 11 using the SLOA testing (accumulator plus spring as motive force) to achieve the phenomeno d. The packing in valves 203-2A and 2C was adjusted per the results of the May 18 testing of valve 203-lA to allow operation with spring force only while valves 203-28 and 2D remained in the May 16 and 17 as failed packing conditio * *

Results:

Valves 203-2A and 2C passed all testing; fully closing on spring force only per SP 88-3-15 and closing within 3 to 5 seconds per DOS 250-2 with instrument air and spring forc Valves 203-2A and 2C achieved full-closed on spring force only even during the SLOA test designed to achieve the phenomeno Valves 203-2B and 2D did not go full closed during either SP 88-3-15 (Spring-Only) or DOS 250-3, SLOA Phenomeno However, both 2B and 2D did go full closed within 3 to 5 seconds durin~ the air plus spring to close (DOS 250-2)

tes *

Conclusion:

The Phenomenon is only effective on preventing the valve from going full closed if the resistance due to tight packing is excessiv Valves 2A and 2C achieved full closure with springs-only and correctly adjusted packing with the accumulator clearly venting to the atmospher Also, the excessively tight packing did not prevent any of the MSIVs from going closed within the Technical Specification requirement of 3 to 5 seconds with normal system air availabl *

Special Test, 11 Packing Variable with MSIV Air Isolation Testing

• Test Objective:

To determine if valve stem lubrication or valve stroking per the May 18 testing would free up valves 203-2B and 2D without loosening valve packin *

Test Method:

The 2B valve's stem and guide posts were lubricated and stroked per DOS 250- Valve 2D was not lubricated but stroked per DOS 250-2 as initial conditions to performing the special air isolation testin *

Results:

Both valves failed to go fully closed on spring only.

' ' Details of Testing and Inspection Activities Pneumatic Manifold-Inspection and Testing Results of bench testing the IC-Inboard MSIV solenoid manifold assembly (valve pack 3-Way and 4-Way pilot valves) revealed that the Automatic Valve Company (AVCo) 4-Way pilot valve functioned as designed during a rapid loss of air. However, under a slow loss of supply air condition, the AVCo pilot valve positioned in a manner which enabled the stored air in the accumulator to bleed off at the same rate as the supply air heade The phenomenon, locking the 4-Way pilot valve in a mid-position, allowed both the below piston capacity and the stored accumulator capacity to vent off through the same manifold exhaust port. The phenomenon began, as repeated through subsequent testing, at about 48 psig supply air header pressure and persisted until both the accumulator and below piston pressure had reduced to about 7 psi At about 7 psig, the 4-Way pilot valve's internal springs would overcome the phenomenon condition and complete the positioning of the pilot valve, allowing the remaining 7 psig stored air to be directed to the above piston cavity for assisting in MSIV closur Thus, for the MSIVs to go full closed under this slow loss of air condition, little stored air would be available to assist in valve closure, requiring the springs to close the MSIVs unassiste On May 21, 1988, members of the AIT witnessed disassembly of the lC MSIV 4-Way AVCo pilot valve. All of the viton o-rings were intact with no visible degradatio Patches of Dow-Corning Selecone lubricant were observed on several of the o-rings. Small black particles were observed adhering to the plunger It could not be determined if the p~rticles were from plant instrument air, or from bench testing, which had been conducted with service air in the hot shop subsequent to the May 17th even Nonetheless, the internal parts of the AVCo pilot valve are so large it appeared unlikely that the small particles could have been a factor in the 4-Way pilot valve's performanc Additionally, the AIT reviewed the maintenance procedure used in disassembly and assembly of the manifold solenoid valves and found the procedure adequate in instruction. The procedure also contained good clear diagrams that were of assistance to maintenance technicians during the disassembly and assembly evolution.

Drywell Pneumatic System and Instrument Air System Inspection/

Testing The AIT witnessed and reviewed the results of the licensee's inspection and leak testing of the pneumatic and instrument

• air system The results revealed that most of the p1p1ng connections associated with the pneumatic/air systems had leak However, ~one of the leaks were significant individually or cumulatively to explain the loss of accumulator stored air during the slow loss of air conditio Additionally, the licensee conducted leak rate testing of the eight accumulator check valve Several of the check valves had high leakage rates and one had significant leakage (accumulator check valve associated with outboard MSIV 203~2C)

requiring corrective maintenance, however; the leakage rate of all eight*check valves was not at a sufficient*rate to explain the loss of accumulator stored air during the duration of the slow loss of air tes.

MSIV Closure Spring Inspection/Testing The eight closure springs from the lC inboard MSIV were tested to determine the force required to compress the MSIV spring All springs performed as anticipate.

MSIV Stem Packing Assessment The Team reviewed maintenance procedures, vendor manual and maintenance history to assess the type of packing installed in the Unit 2 MSIV The initial type of packing that was installed prior to 1986 was Q-P Self-setting packing (Q-P).

Q-P packing is made from heavy woven asbestos in a general chevron shap Asbestos packing has a natural moisture content and when used to seal steam, has a tendency to dry ou Because of the packing drying out, shrinkage of the packing will exist resulting in the need to insert additional packing to maintain adequate sealing and contact against the glan The instructions contained within the Q-P manufacturer's manual listed several important notes for installation and use of Q-P Self-setting packin The manual noted that additional packing rings may be added to maintain the necessary contact with the gland and that the number of additional rings should be equal to approximately 10% of the number of rings required to initially fill the stuffing bo Based upon this instruc-tion, one or two additional rings would be sufficient to maintain gland contact and adequate steam sealing. Addition-ally, the manual cautioned that Q-P packing must not be jammed o~ forced into the stuffing box (as is the practice with square and other types of packing) because the packing friction would clamp the stem and prevent free movemen The review of maintenance history revealed that in 1986, the Unit 2 MSIV Q-P packing was replaced with John Crane Model 287 chevron packin Model 287-I is a non-asbestos replacement packing for John Crane Model 187-I packing (equivalent packing to Q-P Self-setting).

The review also revealed that Unit 3 still has Q-P installe.'

The AIT determined that additional packing rings were installed or adjusted at an infrequent basis over three years (noted in Paragra~h V) with no occurrences o~ adjustment on the Unit 2 MSIVs since 198 Subsequent to the review and testing, the licensee replaced the John Crane 287-I packing on the four inboard MSIVs (203-IA, 18, IC and ID) with Chesterton Live Loaded packin During the replacement, extreme difficulty was experienced in removing the installed John Crane 287-I packin One noticeable advantage with the Chesterton packing is vendor supplied torque values for the gland to prevent over tightening that could result in stem binding. Additionally, the new packing is squared graphoil type GIP! 5300 with an upper and lower carbon wiper to prevent excessive packing wear and provide consistent stem frictio Additional review of the packing installation instructions and maintenance procedures revealed that the John Crane 287-I did not have specific instructions or cautions, applicable to chevron type packing, supplied by the vendor or addressed in the maintenance procedur The AIT was not able to determine if the lack of specific instructions was the root cause of the stem binding, but did determine that because of the lack of instructions there was nothing to prevent recurrence of stem packing binding with future installation of John Crane 287-I chevron packin.

Unit 2 Outboard MSIV Air Isolation Testing Following Packing Adjustments This test was the integrated Slow Loss of Air Test (SLOA)

following the cycling of MSIVs 2A and 2 Dresden Operating Surveillance DOS-250-3 was performed on May 21, 1988, to determine conclusively that valve packing was the major contributor preventing the MSIVs from fully closin This was accomplished by simulating the same test conditions that existed during the original failure, the only difference being that the packing was adjusted on only 2 MSIVs (2A and 2C).

The 28 and 2D MSIVs were maintained in their as-found condition with no packing adjustments, lubrication or any other maintenanc Packing on the 2A and 2C outboard MSIVs was adjusted as identified in the previous test. This adjustment actually

"loosened up 11 the packing, that is, the force applied to the valve stem by the packing was decrease The integrated test was performed by isolating the air supply to the outboard MSIVs, starting the valve timing at that time and observing the control room MSIV position indicating light As pressure in the air supply to the MSIVs was decreasing, operations personnel were observing the pressure at the MSIV. *.

'"

At about 48 psig air header pressure, the pneumatic phenomenon initiated as expected from the manifold testing results. After approximately 5 minutes, MSIV 2C began to drift closed as indicated by lights in the control room and by confirmation of actual valve moveme~t, when the MSIV air pressure reached 30 psi. Subsequently, MSIV 2A began to drift closed when the air pressure reached approximately 25 psi, which was also verified by both control room and local indication The 2A and 2C MSIVs reached the full closed position in 9 minutes 44 seconds and 9 minutes 15 seconds from the start of the test and about 15 seconds from start of stem movement, respectivel The 2B and 20 MSIVs did not reach the full closed position and only moved 3.75 and 4.75 inches out of approximately 17 inches total trave The test demonstrated that with properly adjusted packing (MSIVs 2A and 2C), the MSIVs would achieve full fail safe closure on spring force onl Additionally, the test demonstrated that the pneumatic phenomenon, as experienced during the bench testing, would not prevent closure of the MSIVs unless aided by excessive packing frictio.

Testing/Cycling of MSIVs 2A and 2C On May 21, 1988, members of the AIT witnessed closure tests of the 2A and 2C MSIV The tests were run to determine the effects that packing tightness and lubrication have upon MSIV closure timin The procedure was to loosen the valve packing and then observe the time for closure in the spring only

"fail-safe" mode as well as with an "air assist" (instrument accumulator air).

In order to obtain motion of MSIV 2C with only spring forces it was necessary to loosen up the packing nuts four flat Full closure in the fail-safe/spring-only mode was achieved in 29.7 second Next the packing nuts were tightened to the original positio Closure of the MSIV was then obtained with only spring forces in about 35 second Following this the stem was greased with Felpro N5000 lubrican The MSIV was then tested two times with instrument air. The valve closed during the air test in 5.2 and 4.7 seconds respectivel Subsequently, another fail-safe/spring-only test was performe The closure time for this fail-safe/spring-only test was 1 second Next the valve guide posts were lubricated and two more air assist tests were performe Closure times for these two air assist tests were 4.8 and 4.5 seconds respectivel Another fail-safe/spring-only test was then ru Closure was achieved in 16.5 seconds.

..

• MSIV 2A was tested in a manner similar to that which had been performed on 2 The packing nuts were loosened 3 flats but the valve would not close in the spring-only ~ode. The packing nuts were *then tightened flat and the valve was cycled and **

closed using air assists in 4.2 and 3.8 seconds, respectivel The valve was then tested in the spring-only mode in 3 second The valve stem was then greased and 2 more air assist tests were ru The valve closed in 4.0 and 3.6 seconds respectivel Next, a spring-only test was run and the valve closed in 23.1 second The guide posts were then greased with-Felpro N-500 Two air assist tests were run, resulting in closure times of 3.9 and 3.5 seconds respectivel One spring-only test was then run resulting in a closure time of 21.1 second Lessons Learned and Corrective Actions Based upon the testing results and reviews of procedures, maintenance history and information associated with the failure of the.MSIV to achieve full closure, several corrective actions and lessons learned were implemented by the licensee both prior

.to and subsequent to the May 24, 1988, AIT exi Provided below are summaries of some of the lessons learned and corrective actions: The reviews revealed that, although several alarms would annunciate during degrading conditions of the pneumatic and instrument air systems, the operator actions required per the various Dresden Operating and Abnormal procedures were directed at finding the problem with the air system and correcting the condition instead of addressing the affected equipmen Based upon this lesson learned, the licensee revised the following annunciator procedures on May 24, 1988, to address operator actions required to mitigate adverse affects upon equipmen Abnormal operations procedure DOA 4700-1, "Instrument Air System Failure, 11 was revised to require a manual scram at 55 psig instrument air header pressure and to manually close the affected outboard MSIV Annunciator Procedures DOA 923-1 {F6), "Instrument Air Dryer Trouble, 11 and DOA 923-1 ( F4), "Low Pressure in Instrument Air Receiver, 11 were also revised to require a ma~ual scram and closure of the affected MSIVs upon a decrease in instrument air system pressure below 55 psi.

The testing and vendor manual reviews revealed that inadvertent over tightness of chevron type packing could result in MSIV stem bindin Based upon this lesson learned, the licensee replaced the inboard MSIV chevron packing with Chesterton Live Load

square type packin The square type packing was recommended as a replacement because of its relatively good steam sealing properties without exerting additional stem friction and because it allows control of stem friction by use of glan_d torque value The chevron type packing was not supplied with applicable torque values by the manufacture The Chesterton packing was installed in the Unit 2 inboards subsequent to the May 24, 1988 AIT exi Additionally, the licensee initiated an evaluation of the maintenance procedure to ensure that adequate instructions and cautions are included for the applicable type of packin.

The testing revealed that the pneumatic phenomenon associated with the AVCo solenoid valves would render the MSIV accumulators inoperable during a gra~ual loss of pneumatic/air condition.* The licensee committed to evaluate the possibility of eliminating the phenomenon as a requirement for satisfying the CA This evaluation is expected to be completed within six months after the May 24, 1988 AIT exi.

The FSAR description and the licensee's determination of fail safe closure of the MSIVs does not appear to be in agreement with the demonstrated spring only closure testing. The FSAR is not clear on the fail-safe closure~

whether the closure is to be achieved by the MSIV external springs only or by the stored accumulator air with spring assistanc The licensee, GE and the Office of Nuclea Reactor Regulation (NRR) were continuing to evaluate the design basis of the MSIVs subsequent to the May 24, 1988 AIT exi Historical Reviews MSIV Maintenance Inservice Testing of MSIVs The development of the current fail-safe test (FST) procedures by the licensee was a result of IE Information Notice No. 85-84:

"Inadequate Inservice Testing of Main Steam Isolation Valves,"

and a previous failure identified in DVR No. 12-2-87-16 The FST was developed to verify MSIV closure upon a loss of actuator power, in this case, ai ASME Code Section XI Paragraph IWV-34/5 states, in part "Valves with fail-safe actuators shall be tested by observing the operation of the valves upon loss of actuator power."

• Upon review of the licensee's past and current !ST programs, it was found that the FST was neither required nor performed prior to May 17, 1988, which appears to be contrary to the ASME Section XI Cod However, it is not certain that MSIV closure on spring force only is within the design basis, and therefore, may not be required by the ASME Code Section X In the interim, the licensee has committed to testing the MSIVs to verify closure on spring force alone on a cold-shutdown frequency by performing the SLOA tes Again, the design basis of the MSIVs needs review in order to determine what would be the correct fail-safe mechanism of the valve and that the !ST program adequately addresses fail-safe testing for the MSIV.

Valve Maintenance History The team reviewed the maintenance history listing for the Unit 2 inboard and outboard MSIV The review revealed that the Unit 2 MSIV packing (Q-P self-setting asbestos packing)

was replaced with John Crane Model 287 in December 198 The review also revealed that on only two occasions since 1984 was packing added during non-overhaul maintenance activities (valves 203-2A on January 14, 1985, and 203-28 on June 28, 1984), and that packing was adjusted on only three occasions (valves 203-lA and 203-lD on October 26, 1985, and valve 203-28 on April 6, 1986).

A similar review of Unit 3 maintenance history also indicated that packing was added on only two occasions (valves 203-lC and 203-lD on July 12, 1986) and no adjustments during other than overhaul activitie In general, the team found that both types of packing, QP and John Crane, has required little maintenance during operating cycles (seven occasions within three years for 16 valves with Q-P self setting and no occasions between December 20, 1986, and May 16, 1988, for 8 valves with John Crane #287 installed.) Industry Events A review of NUREG-1275, Volume 2, "Operating Experience Feedback Report - Air System Problems" and related NRC and industry informa-tion pertaining to MSIV failure to close was conducte Listed below are the various documents reviewed: NRC IEC 81-14, "Main Steam Isolation Valve Failure to Close" IEN 81-28, "Failure of Rockwell-Edwards MSIVs"

IEN 82-25, "Failure of Hiller Actuators Upon Gradual Loss of Air Pressure" IN 85-17, "Possible Sticking of ASCo Solenoid Valves" IN 85-35, "Failure of Air Check Valves to Seat" IN 86-51, "Excessive Pneumatic Leakage in ADS" IN 86-57, "Operating Problems with Solenoid Valves" IN 86-81, "Broken Closure Springs on A&M MSIVs" IN 87-28, "Air System Problems at Light Water Reactors" INPO O&MR-35, "MSIV Solenoid Actuator Lubricant Degradation" O&MR-36,

"MSIV Pilot Valve Adjustment/Testing" SER 26-84, "Failure of MSIV to Fully Close During Surveillance" SER 8-82, "MSIV Closure and Inadvertent Primary Safety Valve Actuation" OPEX 4563518503800, "Failure of MSIVs to Close" General Electric (GE)

SIL 309, "Lubrication of MSIV Guide Rod.s" SIL 442, "Inspection of Atwood & Morrill MSIV External Springs" Dresden Deviation (DVRs) and Event Reports (LERs)

DVR 12-2-73, "Reactor Scram, Drywell Pneumatic Isolated, MSIV Drift Close" DVR 12-2-87-166, "MSIV Drifts Partially Closed" DVR 12-3-81-16, "MSIV Closure During Scram Without Group I Signal" DVR 12-3-81-56, "MSIV Closure During Testing" DNR 12-2-87-166, "MSIV Partial Closure Due to Loose Air Line" LER 86-017, "MSIV Full Closure During Surveillance" The review of NRC Circular IEC 81-14, revealed that, in 1980, six failures of MSIVs to close were due to stem binding related to over 20.

tightening of packing glands or inappropriate lubricants on the guide post The majority of the above NRC and industry information pertains to air syste~ related problems with a few addressing broken closure sp~ings (IN 86~81 a~d GE SIL 442} or lubrication of guide posts (GESIL 309 and INPO O&MR-35).

Circular IEC 81-14 also recommended that maintenance procedures should be reviewed to ensure that they include precautions against detrimental affects such as over tightening of packing glands and that testing should demonstrate that the valves wi 11 perform under operating conditi ans before being placed in service. However, the IEC 81-14 was vague on what type of testing or operating conditions would be required to demonstrate operability of the MSIV It has been demonstrated that the Technical Specification required surveillance testing does not demonstrate the fail safe condition of the MSIVs with a loss of pneumatic/air suppl The licensee's response to !EC 81-14, dated January 8, 1982, also did not address the potential failure of the MSIVs to close upon a loss of pneumatic/ai The response addressed the Dresden specific problems of MSIV closure times being outside the Technical Specification required 3 to 5 seconds due to hydraulic dash pot adjustment The review of licensee's DVRs and LERs revealed that on July 12, 1986, MSIV 203-lC (Unit 2) went full closed d~ring the surveillance test DOS 500-8, "MSIV Not Full Open Scram."

The test normally allows the MSIV to go only 10% closed to test the MSIV-not-full-open-scram-setpoint by venting the above and below piston capacity and slowly closing on springs onl However, because of a limit switch failure, the MSIV went fully closed on spring onl This event, LER 86-017, demonstrated the ability of the MSIV to close on spring onl Procedure Reviews The AIT reviewed the Dresden Operating Annunciator (DOA) procedures to determine the required operator actions during a loss of pneumatic or instrument air header pressur The review revealed that the majority of operator actions were focused upon finding the cause of the loss of air pressure rather than alerting the operator to significant actions to be taken with regard to specific equipmen The exception was DOA 902(3)-5 A-1, "Scram Valve Air Supply Low Pressure." The procedure stated that, "if the air header pressure is decreasing rapidly, or if the cause of the low air pressure cannot be determined in a timely manner, then immediately scram the reactor."

The setpoint for the annunciator is 55 psig (decreasing), which would be also an indicator of instrument air supply header decreasin The AIT also rev~ewed various maintenance procedures, including those pertaining to overhauling and testing of the MSIV pneumatic manifold and installation of MSIV stem packin *

V Safety Significance Immediate This event had no immediate_~afety significance since the special loss of air test to Unit 2 MSIVs was conducted while Unit 2 was in cold shutdown and Unit 3 was in a refueling outag Under Operational Conditions If this event were to occur while operating, it would be of minimal safety significance since the MSIVs would start to drift closed \\'Jith either a loss of instrument air to the outboard MSIVs or a loss of the drywell pneumatic supply to the inboard MSIVs resulting in an automatic reactor scram due to an MSIV not full open (§90% open)

scram setpoint. Also, the inboard and outboard MSIVs have two separate and independent air supply system The outboards MSIVs are supplied by the Instrument Air System. and the inboard MSIVs are supplied with nitrogen from the Pump Back Syste Thus, there is little safety significance if this slow loss of air condition developed while operatin If either the inboard or outboard MSIVs failed to go full closed due to a slow loss of supply air, the capability to isolate the main steam lines by closing the other MSIV, since it's air supply is independent of the first one, would still assure isolatio VII. AIT Conclusion Based upon the testing results, the AIT concluded that the root cause of all eight Unit 2 MSIVs failure to close was due to the restriction force supplied by the John Crane manufactured 287-I chevron packin The integrated slow loss of air test demonstrated that with properly adjusted packing, the stored tension of the MSIV springs would close the MSIVs independent of air motive force, even during the pneumatic phenomeno Additionally, the integrated test demonstrated that the MSIVs would close during the routine Technical Specification surveillance for MSIV timing using the normal pneumatic/air supplie The AIT found that the routine surveillance would not reveal that packing restriction or the pneumatic/air phenomenon existed because of the ~ignificant force supplied by the normal pneumatic/air suppl The ratio of normal closing forces verses resistance forces is about 8 to 1 with actuator (air supply) force availabl Normal closing forces include the mass of moving parts (2%), inertia force of the valve mass (1%), spring force (27%) and the actuator force associated with the pneumatic or air supply (70%).

The resistance force includes the packing friction (39%) and the stem unbalanced force (61%).

During spring only closure, the ratio is normally only about 2 to 1 which is more than sufficient to fully close the MSIV However, if the packing resistance is increased to reduce the rati-0 to nearly 1 to 1, the MSIVs would not travel to full closure on spring only force Since the surveillance procedure uses normal actuator forces (pneumatic/air) to stroke the

MSIVs, an increase of packing resistance to twice its normal force would still produce a closing force ratio of about 6 to 1, sufficient to achieve full closur VII I. Concerns Based upon the AIT reviews, the following concerns address the various maintenance, inspection and testing programs at Dresde The AIT reviewed the Inservice Testing (!ST) Plan and determined that prior to the May 16 and 17 MSIV failure, fail safe testing with MSIV closure on spring only or slow loss of air testing, Instrument Air/

Pneumatic system leak tightness testing or MSIV accumulator check valve leak rate testing had not been periodically performe The accumulator check valve leak rate testing performed as part of the root cause determination associated with the MSIVs failure demonstrated leakage ranging from 2.3 to 8.6 SCFH for the inboard MSIVs and 7.0 to 33.2 SCFH for the outboards. Since the accumulator volumes are less than 24 SCF, the outboard 203-2C leakage of 33.2 SCFH would render the accumulator inoperable in less than one hou Additionally, two others only had the ability of maintaining their stored volume for under three hour Section XI of the ASME code requires testing of accumulator check valve The licensee has committed to performing periodic leak rate testing of MSIV accumulator check valve Subsequent to the May 24, 1988, exit, the iicensee tested the Unit 3 accumulator check valves and replaced one outboard check valve because of excessive leakage. Additionally, the Unit 2 outboard MSIV (203-2C) accumulator check valve was replaced prior to returning the unit to servic The slow loss of air testing is a method recommended by both the industry and the NRC based upon the failures experienced with the Automatic Switch Company (ASCo) solenoid valves. Dresden has Automatic Valve Company (AVCo) solenoid valves installed, as noted in NRC Information Notice IN 85-17 and IN 86-5 The slow loss of air testing will detect solenoid valve pilots sticking or locking in intermediate positions, where as testing the solenoids by only de-energizing the electrical solenoids and repositioning the solenoid valve pilots with motive air (pilot or system air), will not usually detect the pneumatic phenomeno The licensee agreed that slow loss of air testing would be performed and conducted the Unit 2 integrated slow loss of air test on Unit 3 MSIVs subsequent

. to the May 24, 1988, AIT exi Pneumatic/air system leakage has been discussed in NRC Information Notice IN 86-51, "Excessive Pneumatic Leakage in the Automatic Depressurization System."

The licensee is re-evaluating the type of testing and frequency

• for system testing. Currently, the Maintenance Work Analyst instructions verify the quality of pneumatic and instrument air but do not appear to contain periodic system leak tightness inspections..

The licensee's MSIV closure testing does not appear to meet ASME Code XI Paragraph IWV-3415, which requires that valves with fail-safe actuators

• I *

be tested by observing the operation of the valves upon loss of actuator powe Since the MSIVs are actuated by air (pneumatic for inboards and instrument air for the outboards) with spring assist for closure, and maintained open by compressed air below the actuator piston, the AIT ascertained that fail-safe operation would be without air and with spring only for closur The licensee responded to NRC Information Notice IN 87-28 and Supplement 1, "Air Systems Problems at U.S. Light Water Reactors," on May 9, 198 The response addressed the NRC Recommendation

1. 5, "all operating plants should be required to perform gradual loss of instrument air system pressure tests," by providing a description of the current testing procedure In addition, a new surveillance procedure, DOS 250-3, "Main Steam Isolation Valve Fail-Safe Test During Cold Shutdown, 11 (dated July 1987) was developed; DOS 250-3 was the basis for the special test performed on May 16 and 17, 1988, that discovered the failure of MSIVs to close on loss of air. Because the MSIVs would not close on spring only, the licensee declared the MSIVs inoperabl However, a review of DOS 250-3 revealed that the intended fail-safe operation is springs assisting stored accumulator air to actuate the MSIV closur The test method contained within DOS 250-3 isolated the main pneumatic/air supplies from the accumulators and allowed gradual decrease of pneumatic/air system pressure until the pressure stored under the MSIV actuator piston had vented, when the stored air within the accumu-lators would be directed through the pneumatic manifold solenoid valves (repositioned by internal springs to closing ports because of.loss of pilot air) to the actuator above piston cavit Because of the pneumatic phenomenon (demonstrated during bench testing of the manifold valves) the accumulators would not be available during a gradual loss of air and, as a result, the true fail-safe operation is the MSIV external springs onl Once the pneumatic phenomenon was understood, DOS 250-3 became the basis of the special integrated slow loss of air test. This test clearly demonstrated that fail-safe operation (per DOS 250-3) can be achieved if packing friction does not exceed the spring tension forc The AIT also reviewed the slow loss of air test performed at Dresden's sister facility, Quad Citie The Quad Cities test clearly demonstrated that fail-safe operation was achieved on MSIV external springs only but did not verify whether the pneumatic phenomenon did or did not exis The difference between the Dresden and Quad Cities tests was Quad Cities ability to isolate and vent the MSIV accumulators prior to isolating the pneumatic/instrument air syste The licensee has agreed to perform the integrated slow loss of air test periodically and after significant maintenance involving MSIV stem packin The licensee is evaluating a criteria in determining when testing will be required for less significant maintenance, such as adjusting the packing on one or two MSIVs onl AIT Recommendations The AIT recommends that MSIV fail safe testing should be conducted with spring only forces to close and that this testing should also be conducted prior to unit startup after significant maintenance activities involving stem packing; such as, replacement of packing, modification of packing type, addition to and adjustment of installed packing, to ensure that closing resistance has not increased to prevent fail safe closure of MSIVs during a loss of actuatGr pneumatic/air suppl *

Additionally, the AIT reconunend~ the following testing, inspection and evaluation activitie IST Activities Criteria and testing should be established for MSIV pneumatic/

air accumulators, accumulator check valve and system piping for air leakage to ensure that system and component degradation does not result in loss of air condition The leak rate testing performed as part of the root cause determination revealed that the capacity of the accumulators was only 24 SCF and that measured check valve leakage ranged from 2.3 to 8.6 SCFH for the inboards (the licensee*repaired the 203-2C accumulator check valve because of leakage greater than 24 SCFH).

Since a leakage rate of 12 SCFH would render an accumulator inoperable with insufficient capacity in less than two hours, it is recommended that the basis for the criteria of less than 24 SCFH be determined and that the criteria address the length of time that the stored air is required to be available to meet the design basis of the MSIV.

Fail-Safe Testing of MSIV as Required by ASME Code Section XI

{The Code) Paragraph IWV-3415 (IWV-3415).

The code requires "valves with fail-safe actuators shall be tested by observing the operation of the valves upon loss of actuator power."

Prior to the test performed on May 17, 1988, no fail-safe te.st (FST) was performed on the MSIV The team observed this situation and contends that the proper FST is conducted with loss of air to the MSIV, requiring closure solely by spring pressur The licensee contends that closure by spring force alone is not within the design basis, and therefore does not fall into the scope of IWV-341 To properly resolve this issue, the team has requested NRR to include fail-safe testing methodology of the MSIVs along with the design basis revie Procedures Procedures pertaining to installation and adjustment of MSIV stem packing should contain adequate instructions and criteria to ensure that packing friction forces do not restrict closure of MSIVs during fail safe condition.

Operating procedures should provide for operator actions prior to pneumatic/air system pressure decreasing to about 48 psi Testing demonstrated that the pneumatic phenomenon exists during slow loss of air conditions at about 48 psig to 7 psi Operator action prior to the phenomenon initiation pressure region would ensure isolation availabilit.

Maintenance procedures should provide adequate instruction for installation of applicable packing types used in the MSIV Since Unit 3 has Q-P Self-setting installed while Unit 2 has Chesterton Live Load type installed in the four inboard valves and John Crane 287-I in the outboards, procedures should address the different practices associated with each type of packin The Review of Vendor instructions demonstrated that chevron type packing cannot be installed in the same method, jamming into the stuffing box, as with square and other types without causing stem bindin Evaluations The licensee should conduct an evaluation to determine the adequacy of the pneumatic/air phenomenon and the possibility of eliminating its existenc Since the AVCo pneumatic phenomenon contributed to the failures experienced on May 16 and 17, it is recommended that in order to assure successful MSIV closure upon gradual loss of air, the licensee should evaluate modifications to eliminate the

. phenomen The licensee has committed to complete an evalua-tion within six months as long term corrective actions to the CA.

An additional evaluation should be conducted to determine the possibility of the phenomenon existing with other pneumatic control valves in systems requiring a fail safe conditio.

An evaluation should be conducted to determine the adequacy of fail safe testing on other systems to ensure that proper testing methodology is being used to verify compliance of system designs~ An evaluation of maintenance procedures should be conducted to ensure that adequate instructions and cautions are included to address the appropriate type of packing being used for different application.

IE Circular IEC 81-14 should be re-evaluated for applicability to stem binding and post maintenance testing associated with packing installation, repacking, addition of rings and adjust-ment The testing should demonstrate operability of the valves during operating and, as reasonable as possible, accident conditions including fail-safe conditions with and without stored accumulator ai.

An evaluation of Quad Cities Units 1 and 2 should be conducted to determine the applicability of MSIV fail-safe testing, MSIV stem packing practices and the existence of the pneumatic phenomeno.. -

'

• Testing The AIT recommends that periodic fail-safe MSIV closure on springs only testing be performe In addition, fail-safe testing should also be performed as post maintenance requirements associated with significant maintenance to MSIV stem packin Information Notice The AIT recommends that the NRC issue an Information Notice~

addressing the Dresden Unit 2 MSIV failure, including the importance of fail-safe testing, post packing maintenance testing and the pneumatic phenomeno.

The AIT recommends that CECo communicate to the industry the lessons learned from the MSIV failure to close event, including the pneumatic phenomenon and post maintenance testing associated with stem packin Inspection The AIT recommends that Hope Creek's MSIV fail-safe testing be evaluated by the NR Hope Creek has a similar air manifold (although different MSIVs) and may experience similar pneumatic phenomen The AIT reviewed, subsequent to the May 24, 1988 exit, the Hope Creek slow loss of air test data (performed in December 1985).

Examination of the test data revealed that the MSIVs closed on s~rings only (between 15 and 30 seconds).

However, it was not apparent from the review of the test procedure that the MSIV closure was expected to be on spring only and not to be assisted by the stored accumulator ai The testing conducted at Dresden demonstrated that during the pneumatic phenomenon condition, MSIV closure will occur within about 20 seconds on spring only instead of between 3 to 5 seconds via stored accumulator ai.

Exit Interview (30703)

The inspectors met with licensee representatives (denoted in Paragraph 1)

on May 24, 1988, and informally throughout the inspection period, and summarized the scope and findings of the inspection activitie The inspectors also discussed the likely informational content of the inspection report with regard to documents or processes reviewed by the inspector during the inspectio The licensee did not identify any such documents/processes as proprietar The licensee acknowledged the findings of the inspection.

27