ML042080139

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E-mail from M. Hamer of Vermont Yankee to Various, Regarding Pro for MSIV V2-80B LLRT Failure
ML042080139
Person / Time
Site: Vermont Yankee Entergy icon.png
Issue date: 05/17/2004
From: Hamer M
Vermont Yankee
To: Bronson K, Desilets M, Devincentis J, Dreyfuss J, Finn B, David Pelton, Pelzer B, Rusin R, Beth Sienel, Thayer J, Wanczyk R, Wierzbowski G
NRC Region 1, Vermont Yankee
References
FOIA/PA-2004-0267
Download: ML042080139 (10)
v • d • e


Text

Sienel, Beth From: Hamer, Mike Sent: Monday, May 17, 2004 9:48 AM To: Rusin, Richard; Pelzer, Bill; Dreyfuss, John; Wierzbowski, George; Bronson, Kevin; Devincentis, Jim; Pelton, David; Sienel, Beth; Wanczyk, Robert; Thayer, Jay; Desilets, Mike; Finn, Brian

Subject:

PRO for MSIV V2-80B LLRT failure Please see the attached PRO. This event is reportable to the NRC Operations Center as a Condition Prohibited by Technical Specifications pursuant to §50.73(a)(2)(i)(B). There is no associated §50.72.

PRO-0400841.pdf (491 KB)

Mike Hamer Technical Specialist, Licensing X4226

INTEROFFICE MEMORANDUM LICENSING POTENTIALLY REPORTABLE OCCURRENCE REPORT TO: MIKE DESILETS, TECHNICAL SERVICES MANAGER FROM: MIKE HAMER, TECHNICAL SPECIALIST III

SUBJECT:

CR-VTY-2004-00836, 00839, 00841, 00955; V2-80B, V2-86A AND V2-86C LOCAL LEAK RATE TEST RESULTS EXCEED THE TECHNICAL SPECIFICATION ACCCEPTANCE CRITERIA DATE: MAY 4, 2004 PRO NUMBER: PRO-0400841 EVENT DESCRIPTION:

On 04/05/04, with the plant shutdown for refueling, three Main Steam Isolation Valves (MSIVs) on separate main steam lines exceeded the Technical Specification (TS) allowable leak rate limit during as-found local leak rate testing.

The following regulations were considered when determining reportability for this event.

Operation or Condition Prohibited by Technical Specifications

§50.73(a)(2)(i)(B) "[The licensee shall report:] Any operation or condition which was prohibited by the plant's Technical Specifications except when:" (exceptions do not apply).

Degraded or Unanalyzed Condition

§50.73(a)(2)(ii) "[The licensee shall report] Any event or condition that resulted in:

(A) The condition of the nuclear power plant, including its principal safety barriers, being seriously degraded; or (B) The nuclear power plant being in an unanalyzed condition that significantly degraded plant safety."

Event or Condition That Could Have Prevented the Fulfillment of a Safety Function

§50.73(a)(2)(v) "[The licensee shall report:] Any event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to:

(C) Control the release of radioactive material."

DISCUSSION/BASES:

TS 4.7.A.4 requires that the leakage rate through each MSIV be verified to be less than or equal to 23 standard cubic feet per hour (SCFH) when tested at greater than or equal to 24 psig (Pt).

I

TS 3.7.A.4 states that whenever primary containment is required, the leakage from any one main steam line isolation valve shall not exceed 31 scfh/hr at 44psig (Pa), and the combined leakage from all four main steam lines shall not exceed 62 scfh/hr at 44 psig (Pa).

Regarding Technical Specification requirements, the MSIV Local Leak Rate Test results listed in Table 1 determined the following:

  • The TS 4.7.A.4 surveillance limit of < 46 scfh @ > 24 PSIG (Pt) for the combined maximum pathway leakage rate for all four main steam lines was exceeded with a value of 272.645 scfh.
  • The TS 3.7.A.4 LCO limit of 31 scfh @ 44 psig (Pa) for any one MSIV was exceeded by V2-80B, V2-86A and V2-86C.
  • The combined leakage from all four mnain steam lines of 23.585 scfh did not exceed the TS 3.7.A.4 LCO limit of 62 scfh @ 44 psig (Pa).
  • The total combined primary containment leak rate (Type 'B" and "C" test), calculated on a minimum pathway basis at Pa=44 psig of 76.118 scfh did not exceed the TS limit of 192.126 scfh (L0.6La).
  • The total combined Primary Containment leak rate (Type UBr and 'C" Test), calculated on a minimum pathway basis at Pa=44 psig, with a single failure of one MSIV to shut in the MS line with the highest MSIV leakage (maximum pathway) was 295.302 scfh.

§50.73(a)(2)(i)(B) Any Operation or Condition Prohibited by Technical Specifications TS 4.7.A.4 states:

uVerify Leakage rate through each main steam isolation valve is < 23 scfh and that the combined maximum pathway leakage rate for all four main steam lines is < 46 scfh when tested at > 24 psig (Pt)."

TS surveillance test failures performed at the required interval are assumed to occur at the time of the test unless there is firm evidence that indicates the discrepancy existed previously.

NUREG 1022, Rev. 2 states:

"For testing that is conducted within the required time (i.e., the surveillance interval plus any allowed extension), it should be assumed that the discrepancy occurred at the time of discovery unless there is firm evidence, based on a review of relevant information such as the equipment history and the cause of failure, to indicate that the discrepancy existed previously."

(Emphasis from MJH)

A Root Cause Analysis team was assembled to investigate the MSIV LLRT failures.

V2-86A and V2-86C both passed as-found LLRT on 10/07/02. There has been no evidence during the current operating cycle that these valves were incapable of performing their specified safety function.

The stems for these valves were not scored or galled as detailed below with V2-80B. Therefore, there is no "firm evidence" to indicate that this condition existed with these particular valves prior to the "time of discovery".

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During the investigation of V2-801, the valve stem was found galled and bound into the packing follower. Stem material was raised up due to scoring at the packing spacer and took up clearances between the stem and the packing follower that resulted in binding.

The following is a summary of conditions noted by the RCA Team during the event time line preceding the V2-80B stem galling condition.

  • V2-80B failed as-found LLRT on 10/07/02 [CR-VTY-2002-0221 1]. The valve was repaired under WO 01-004406-000. During repair, the stem was reported in good condition with no scoring and a new packing spacer was installed.
  • On 10/14/02 the valve failed as-left LLRT [CR-VTY-2002-02503]. The valve was disassembled and repaired, which included replacing the stem.
  • On 10/01/03 scoring was identified on the'stem [CR-VTY-2003-02165].
  • On 04/05/04 the V2-80B failed as-found LLRT [CR-VTY-2004-00841].
  • On 04/08/04 the stem was discovered to be bound in the packing follower (CR-VTY-2004-0955].

During the investigation of the condition recorded on 04/08/04, the valve seating surfaces were inspected and considered to be in good as-found condition. It also became apparent that the leak rate failure was the result of a reduced seating force that was caused by a stem galling condition. CR-VTY-2004-00955 was written to address the discovery of the galled stem on V2-80B and a Root Cause Team was formed that led to the following analysis and significant discovery.

Prior to 1999, the V2-80B stuffing box was 'cleaned up", "machined" or uhoned" without adequate control of the work activity. The significance of the tolerance in this area was not recognized, therefore, the packing/stuffing box clearance was riot verified to be within design allowable clearances. With excessive clearance between the packing spacer and the stuffing box ID, the clearance between the stem and packing spacer ID is compromised. The oversized condition of the stuffing box allowed the packing spacer to contact the stem, leading to stem scoring and galling that ultimately resulted in stem/packing follower binding to a point where the valve failed the post-shutdown LLRT. Additionally, the design change process utilized in 1989 when the packing configuration was changed, failed to incorporate guidance from the vendor that the stuffing box dimensional clearances should be verified.

NUREG 1022, Rev.2 provides the following examples for determining reportability; (1) LCO Exceeded "In conducting a timely 30 day-surveillance test a licensee found a standby component with a 7-day LCO allowed outage time and associated 8-hour shutdown action statement to be inoperable. Subsequent review indicated that the component was reassembled improperly during maintenance conducted 30 days earlier and the post maintenance test was not adequate to identify the error. Thus, there was firm evidence that the standby component had been inoperable for the entire 30 days." (Emphasis from MJH)

TS 3.7.A..4 for Limiting Conditions of Operation states;

'Whenever Primary containment is required, the leakage from any one main steam line isolation valve shall not exceed 31 scfh at 44 psig (Pa), and the combined leakage from all four main steam lines shall not exceed 62 scfh at 44 psig."

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The excessive removal of valve material from the stuffing box, and subsequent failure to determine clearances or to provide instructions within the work package to perform this function, as recommended by the vendor when assembling V2-80B, constitutes reasonable assurance that the "component was reassembled improperly".

TS 3.7.A..8 states; "if Specifications 3.7.A.1 through 3.7.A.7 cannot be met, and orderly shutdown shall be initiated immediately and the reactor shall be in a cold shutdown condition within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />."

For this condition to be reportable under this criterion for TS 3.7.A.8, the condition must have existed for a time period longer than the allowable LCO time period, which in this case is 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

The stem scoring and eventual galling began and continued, as noted by the time line above at some point after assembly in RFO-23. Although it is impossible to determine precisely when the MSIV would have failed LLRT (since this surveillance is only required to be performed following a reactor shutdown), the progressive nature of the scoring identified on 10/01/2003 from cycling the valves quarterly led to the stem binding and an LLRT failure of approximately 4 times the leak rate limit for a single MSIV. It is therefore reasonable to assume that V2-80B would not have passed an LLRT had it been performed greater than 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> before shutdown.

Additional evidence that this condition existed outside of the 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> LCO period, as would be required to substantiate a claim for reporting, may be demonstrated in the following example detailed below.

(3) Multiple Test Failures "An example of multiple test failures involves the sequential testing of safety valves.

Sometimes multiple valves are found to lift with set points outside of technical specification limits.

As discussed above, discrepancies found in technical specifications surveillance tests should be assumed to occur at the time of the test unless there is firm evidence, based on a review of relevant information (e.g., the equipment history and the cause of failure) to indicate that the discrepancy occurred earlier. However, the existence of similar discrepancies in multiple valves is an indication that the discrepancies may well have arisen over a period of time and the failure mode should be evaluated to make this determination. If so, the condition existed during plant operation and the event is reportable under §50.73(a)(2)(i)(B) "Any operation or condition prohibited by the plant's Technical Specifications." (Emphasis from MJH)

If the discrepancies are large enough that multiple valves are inoperable the event may also be reportable under § 50.73(a)(2)(vii) 'Any event where a single cause or condition caused at least one independent train or channel to become inoperable in multiple systems or two independent trains or channels to become inoperable in a single system ....

In order to determine the extent of the condition, and to effect repair on the valves that failed the LLRT, additional valves previously identified during RFO-23 with stem scoring were disassembled. Table 2 displays the results of the LLRT failures versus the inspection of stems for scoring due to the condition detailed in CR-VTY-2004-00955.

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Two of the MSIVs that failed LLRT did not have stem scoring and two of the MSIVs that passed LLRT exhibited indication of stem scoring through the process explained previously. Uncorrected, the scoring of these MSIV stems could have eventually resulted in binding of the stem and packing follower, thereby causing additional increased leakage through the main steam process lines.

Based upon the evaluation listed above, this condition is reportable In accordance with

§50.73(a)(2)(i)(B) as an Operation or Condition Prohibited by Technical Specifications.

450.73(a)(2)(ii) Degraded or Unanalyzed Condition NUREG 1022, Rev. 2 provides guidance for the evaluation of leak rate test data when considering a loss of containment function or integrity under the §50.72(b)(3)(ii)(A) reporting criteria that states:

'Examples of Reportable Conditions:

(5) Loss of containment function or integrity, including containment leak rate tests where the total containment as-found, minimum-pathway leak rate exceeds the limiting condition for operation (LCO) in the facility's TS.4 "

"Minimum-pathway leak rate means the minimum leak rate that can be attributed to a penetration leakage path; for example, the smaller of either the inboard or outboard valve's individual leak rates."

The design basis loss of coolant accident (LOCA) analyzed at 1.5 %wtJday (600.394 scfh) provides sufficient margin between off-site doses and 10CFR1 00 guidelines. An additional factor of two is added for conservatism by limiting the LOCA test leak rate (La) to a value of 0.80 %wt./day (320.210 scfh).

The Technical Specification limit for the combined local leak rate test (Type B and C test) acceptance criterion is < 0.6 La.(192.126 scfh) when primary containment is required. For NRC notification and reporting purposes, the minimum pathway leak rate test results were considered as noted in the preceding table. The combined local leak rate test (Type B and C tests), calculated on a minimum pathway basis was 76.118 scfh. This value is less than the 0.6 La limit by a fraction of 0.60 (116.008 scfh) and therefore is not reportable in accordance with §50.73(a)(2)(ii).

For single failure analysis when evaluating a Degraded or Unanalyzed Condition, NUREG 1022,'Rev.

2 states;

"... an example of an event reportable as an unanalyzed condition that significantly degraded plant safety would be the discovery that a system required to meet the single failure criterion does not do so."

The total combined Primary Containment leak rate (Type UB" and UC" Test), calculated on a minimum pathway basis at Pa=44 psig, with a single failure of one MSIV to shut in the MS line with the highest MSIV leakage (maximum pathway) was 295.302 scfh. This value is less than the TS 6.7.C.

requirement by a factor of 0.08 (25 scfh) which states that the maximum allowable leak rate shall be no greater than La (320.21. scfh).

This event is not reportable as a Degraded or Unanalyzed Condition that Significantly Degrades Plant Safety.

5

650.73(a)(2)(v) Event or Condition That Could Have Prevented Fulfillment of a Safety Function The intent of the criteria listed under §50.73(a)(2)(v), is to capture those events where there would have been a failure of a safety system to properly complete a safety function, regardless of whether there was an actual demand.

NUREG 1022, Rev. 2 states:

"If the event or condition could have prevented fulfillment of the safety function at the time of discovery an ENS notification is required. If it could have prevented fulfillment of the safety function at any time within three years of the date of discovery an LER is required" The reactor was shutdown with reactor disassembly in progress. At the time of discovery, the safety function of these valves was not required, therefore, a §50.72(b)(3)(v) notification is not required.

For MSIV leakage to cause a safety system functional failure, the leakage would have to be in an amount that would cause the total combined Primary Containment leakage to exceed the design bases for Primary Containment. The Primary Containment analytical accident leak rate of 1.5 wt/O/fday (600.394 scfh) at 44 psig, results in acceptable doses pursuant to the limits provided in 10CFR1 00 for a design basis loss of coolant accident (LOCA). A leak rate test failure of >1.5%wVday, would demonstrate that Primary Containment was unable to properly complete its required safety function.

For additional conservatism, 0.80 wt/O/day (320.210 scfh) at 44 psig is the established limit for the maximum allowable (test) leak rate (La); per the Technical Specification 6.7.C.4. Additional conservatism is added to the MSIV as-found leak rate testing. The TS limit for the combined local leak rate test (type B and C test) acceptance criterion is < 0.6 La (192.126 scfh).

Although the local leak rate test results were above the various Technical Specification limits for MSIV testing, the total primary containment combined leak rate, calculated on a minimum pathway basis was 76.118 scfh. This value is significantly below the most restrictive limit of 0.6 La (192.126 scfh) as required by TS Section 6.7, thereby demonstrating that primary containment integrity was maintained.

The combined minimum pathway leakage of all four main steam lines (23.585 scfh) was below the TS limit of 62 scfh for addressing control room habitability during a LOCA.

For single failure analysis when evaluating an event or condition that could have prevented the fulfillment of a safety function, NUREG 1022, Rev. 2 states; "in determining the reportability of an event or condition that affects a system, it is not necessary to assume an additional random single failure in that system; however, it is necessary to consider other existing plant conditions."

Additionally, any radioactive material associated with MSIV leakage would pass through the main steam piping, turbines, moisture separators and condenser where most of the iodine would be removed by deposition, impaction and adsorption. Subsequent leakage from the condenser would be released via the turbine building ventilation system to the primary vent stack. It should be noted that although the Turbine Building Ventilation system is non-safety class, experience has demonstrated that there have been no operational problems with this system. No increase to off-site dose or control room dose as a result of this condition during a design basis loss of coolant accident would have been expected to occur.

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CONCLUSION: This event is reportable as an LER as a Condition Prohibited by Technical Specifications in accordance with §50.73(a)(2)(i)(B).

SUMMARY

Due to the large number of Condition Reports associated with this PRO, the following summary is provided to designate the appropriate CR to which the conclusion pertains.
  • CR-VTY-2004-00836: V2-86A LLRT Failure - Not reportable. v
  • CR-VTY-2004-00839: V2-86C LLRT Failure - Not reportable. -
  • CR-VTY-2004-00841: V2-80B LLRT Failure - Reportable' V
  • CR-VTY-2004-00955: V2-80B3 Galled Stem - Reportable.

This PRO will be attached to all of the Condition Reports listed above.

ATTACHMENTS: Attachment 1- Table 1: MSIV Leak Rate Test Data for Reportability Determination Attachment 2- Table 2: MSIV Testing and Inspection Data Comparison for Reportability Determination RECOMMENDED: , 5/-4-N Michael J. Hamer Date Technical Specialist IlIl APPROVED: / 5l11/04~

Michel P. Desilets Technical Services Manager

REFERENCES:

CR-VTY-2004-00955, "As-found Condition of V2-80B (Inboard MSIV) included a galled stem" [Root Cause Analysis for Stem Binding], 04/08/2004.

Event Report 2002-221 1, "V2-80B Local Leak Rate Test results exceed the acceptance criteria',

10/07/02.

Event Report 2002-2212. V2.-86B Local Leak Rate Test results exceed the acceptance criteria',

10/07/02.

Technical Specifications; 3.7.A.2, 3.7.A.4, 4.7 Bases p. 167, 168, 6.C.

VYOPF 4030.02, Section 2, Rev. 35; "Type C Test", Test Date: 04/05/04.

LER 98-009-00, 'Main Steam Isolation Valve Leakage Exceed Technical Specification Limit which could have Impacted the Ability of a System to Mitigate the Consequences of an Accident" 04/18/98.

LER 98-009-01 "Main Steam Isolation Valve Leakage Exceed Technical Specification Limit which could have Impacted the Ability of a System to Mitigate the Consequences of an Accident', 02/10/99.

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ATTACHMENT 1 Table 1: MSIV Leak Rate Test Data for Reportability Determination This table presents the as-found testing results from 04/05/04. The test pressure (Pt) was approximately 24 psig and calculated to 44 psig.

Valve Number Leak Rate in scfh @ >24 # Leak Rate in scfh @ > 44 #

V2-80A 2.506 3.393 V2-86A 26.313 35.627 V2-80B 162.381 219.864 V2-86B 0.502 0.680 V2-80C 10.024 13.572 V2-86C 75.180 101.55 V2-80D 8.771 11.876 V2-86D 4.387 5.940 MS Une Total Min 17.419 23.585 MS Line Total Max 272.645 369.161 Total Combined Primary Containment Min As-Found NIA 76.118 Leak Rate with As-found MSIV Min Leakage 8

ATTACHMENT 2 Table 2: MSIV Testing and Inspection Data Comparison for Reportability Determination This table displays the relationship between MSIVs that were leak rate tested and had their stems inspected.

Stem Scoring Indication LLRT Result Valve Number (Yes/No) (Pass/Fail)

V2-80A -Yes Pass*

V2-86A No Fail V2-80B Yes Fail V2-86C No Fail V2-86D Yes Pass 9

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