05000280/LER-1979-012-03, During Shutdown Functional Test of 74 Snubbers Revealed 21 Not Meeting Design Criteria.Caused by Snubbers Not Being Readjusted to Design Conditions.Units Reset

During Shutdown Functional Test of 74 Snubbers Revealed 21 Not Meeting Design Criteria.Caused by Snubbers Not Being Readjusted to Design Conditions.Units Reset

ML18139A782
Person / Time
Site:	Surry
Issue date:	10/27/1980
From:	Joshua Wilson VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.)
To:	NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II)
Shared Package
ML18139A781	List: 05000280/LER-1979-012, Forwards Updated LER 79-012/03X-1 05000280/LER-1979-012-03, During Shutdown Functional Test of 74 Snubbers Revealed 21 Not Meeting Design Criteria.Caused by Snubbers Not Being Readjusted to Design Conditions.Units Reset
References
LER-79-012-03X, LER-79-12-3X, NUDOCS 8011030433
Download: ML18139A782 (3)

LER-1979-012, During Shutdown Functional Test of 74 Snubbers Revealed 21 Not Meeting Design Criteria.Caused by Snubbers Not Being Readjusted to Design Conditions.Units Reset

Event date:
Report date:
2801979012R03 - NRC Website

text

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1 NRC FORM 366

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U.S. NUCLEAR REGULATORY COMMISSION (7-77)

LICENSEE EVENT REPORT UPDATED* REPORT CONTROL BLOCK:.._I _......... ___._....__...___.._I 8 1

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EVENT DATE 74 75 REPORT DATE 80 EVENT DESCRIPTION AND PROBABLE CONSEQUENCES@

J With the unit shut down a special functional test of 74 snubbers in Unit 1 resu1 ted

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j in 21 not meeting the acceptance criteria stipulated in the governing procedure.

-~ j These tests were performed as a result of the high failure rate experienced in Unit

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I 2 during the performance of PT-39.2.

This event is reportable in accordance with [QJ]J 1T.S.6.6.2.b(2).

The health and safety of the general public were not affected.

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I I I 2 IO l 7 I CAUSE DESCRIPTION AND CORRECTIVE ACTIONS @

42 43 44 47 [II£] I During all previous functional tests, the snubbers were not readjusted to optimum design conditions.

This, in combination with test machine instrumentation inaccuracies l [III]

caused the snubber setpoints to fall outside the acceptable ranges.

The failed units [J]1J were reset to optimum design conditions prior to reinstallation.

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ATTACHMENT (page 1 of 2)

SURRY POWER STATION, UNIT 1 DOCKET NO:

50-280 REPORT NO:

79-012/03X-1 EVENT DATE:

04-02-79 TITLE OF REPORT:

1.

Description of Event

UPDATED REPORT INOPERABLE SNUBBERS With the unit shut down, a special functional test of 74 snubbers in Unit 1 resulted in 21 not meeting the acceptance criteria stipulated in the governing Mechanical Maintenance procedures.

These tests were performed as a result of the high failure rate experienced in Unit 2 during the performance of PT-39.2 (Snubber Functional Test).

This event is reportable in accordance with Tech.

Spec.6.6.2.b(2).

2.

Probable Consequences of Event:

As with Unit 2, the failures were the result of lockup and bleed rates falling below minimum acceptable levels.

However, since the majority of the failing snubbers exhibited lockup *and bleed rates greater than zero in. /min., the units would still allow pipe movement during the normal operating conditions.

Two snubbers exhibited zero lockup.

Each was in a separate system, therefore, the affected systems would not have experienced excessive stresses under normal conditions and would still perform as rigid constraints during seismic disturbances.

Finally, since unit operation was normal, the health and safety of the general public were not affected.

3.

Cause of Event

During all previous functional tests, the snubbers were not readjusted to optimum design conditions prior to reinstallation.

This, in combination with test machine instrumentation inaccuracies caused the snubber settings to fall outside the acceptance ranges.

A follow up test of the additional 46 snubbers in Unit No. 1 revealed 14 of these failed; totaling 35 failures of the 120 tested.

4.

Immediate Corrective Action

The snubbers were reset to the optimum design setpoints.

Those that could not be reset were repaired or replaced.

5.

Future Corrective Action:

When any snubber is functionally tested, the lockup and bleed rates will be reset to optimum design conditions prior to reinstallation.

6.

Action Taken to Prevent Recurrence:

A test program was run to find the reason for snubber drift.

Two rebuilt snubbers and two new snubbers (one 1~ inch and one 4 inch rebuilt and one 1~

inch and one 4 inch new) were tested ten times each at the station and at an independent laboratory.

The results from the laboratory were more consistant than ours (i.e., within a tighter band).

The conclusion is that the instrument-tation on our snubber test machine must be refined.

This should allow more

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ATTACHMENT (page 2 of 2)

SURRY POWER STATION, UNIT 1 DOCKET NO:

50-280 REPORT NO~

79-012/03X-1 EVENT DATE:

04-02-79 TITLE OF REPORT:

INOPERABLE SNUBBERS

6.

Actions taken to prevent Recurrence (Continue) consistant test results which will result in a higher pass/fail ratio.

The improvements needed in the instrumentation are expected to be identified and corrected prior to the next testing of snubbers.

7.

Generic Implications:

Based upon tests conducted on Unit No 2 snubbers it is believe.d that the generic problems have been addressed.