ML16342B162
| ML16342B162 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/25/1985 |
| From: | Martin J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION V) |
| To: | Dircks W NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| References | |
| NUDOCS 8512020012 | |
| Download: ML16342B162 (8) | |
Text
NOV 25 1S86 MEMORANDUM FOR:
M. J. Dircks Executive Director for Operations FROM:
bcc w/enclosure:
Mr. Faulkenberry Mr. Cook Resident Inspector Project Inspector RSB/Document Control Desk (RIDS)
J.
B. Martin, Regional Administrator 1
SUBJECT:
Response
to Congressman Icon E.'anetta Letter Dated October 24, 1985 f
The enclosed letter is a draft response to Congressman Panetta's letter concerning the automatic shutdown of Diablo Canyon Unit'3, on~ May 18, 1985.
3 Original Signed bg John 8 h1attN 1
J. B."'Martin
,Regional Administrator REGION V/dot BURD ot 11
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DRAFT The Honorable Leon E. Panetta Congressman 18th District California House of Representatives Washington, 3.C.
20515 Dear Congressman Panetta:
In response to your letter of October 24, 1985, I have described the event and corrective measures taken to prevent a similar occurrence which was the concern of Mrs. Marie Cattoir.
At approximately 0714 PDT, May 18, 1985, while in Mode 1 (Power Operation),
Unit 1 had a reactor trip followed by a safety injection.
All automatic equipment, including the turbine-driven auxiliary feedwater pump (TDAFWP),
responded as designed except for diesel generator 1-3, which failed to maintain speed.
The plant was stabilized in Mode 3 (Hot Standby) in accordance with procedures.
All systems and equipment affected by this event were returned to normal operation.
This event was promptly reported to the NRC as required by regulation.
The issuance of IER 85-14 satisfied the requirements for written reportability.
On June 6,
1985, the licensee identified a damaged hydraulic snubber on the steam supply pipe to the turbine-driven auxiliary feedwater pump.
The licensee's walkdown of the associated piping found another four damaged mechanical snubbers and one mechanical snubber that, was found to be binding.
All of these damaged snubbers were on the two 'steam supply lines to the turbine driven auxiliary feedwater pump.
The licensee declared the turbine driven auxiliary feedwater pump inoperable.
All six damaged snubbers were replaced.
To provide additional conservatism in the system, one of the snubbers was replaced with a larger capacity snubber.
In addition, another snubber will>e modified to reduce. its stanchion length.
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A preliminary assessment of operability was conducted after; the snubbers were replaced.
The associated steam lines were declared operable and a performance test on the turbine-driven auxiliary feedwater pump was undertaken on June 8, 1985 with the results showing no adverse effects.
The auxiliary feedwater system was declared operable on June 8, 1985.
No damage was expected, since the turbine is similar to a Pelton wheel and is resistant to damage from entrained water.
An evaluation of representative anchor bolts on all applicable anchors and snubber supports and on 25/ of the applicable rigid supports was performed.
The results indicated that all concrete expansion anchors tested remain functional.
Investigation into the snubber damage found that",two steam traps on the auxiliary feedwater pump steam supply 'line, had "been inadvertently'eft isolated after the completion of the one-time,vendor, turbine 'generator warranty test and the plant performance benchmark test.,
Test valve check I
lists indicated that the steam traps had been unisolated, twice, but apparently
.f were left isolated due to multiple operations, during the repeated testing.
The isolated traps caused condensation to collect. It is believed that the initial pressure increase caused by the main steam isolation valve closure on May 18, 1985 displaced the condensate from its resting position.
'When the flow control valve opened a few seconds later, condensate began flashing as the dropping pressure created a water hammer environment in the steam line.
Slugs of water and steam caused thermal-hydraulic loads in excess of the design basis loads to be applied to the piping and supports.
A program is being initiated to walk down and verify on a weekly basis that all steam traps are correctly valved to assure that the steam lines are properly drained.
A piping analysis has been performed to assess the effect of the inoperable snubbers on the qualification of the affected steam supply line.
This evaluation indicated that the steam lines were operable and undamaged and that the piping system satisfies the design criteria and would remain functional for both seismic and thermal loadings.
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The piping analysis will continue until the exact limits of potential dynamic effects have been defined.
Walkdowns will be conducted of the snubbers after starts of the steam driven auxiliary feedwater pump and the lines will be monitored with accel'erometers.
The licensee plans to complete their analysis of the dynamic effects on the steam line by mid-December and plans to report their evaluations and findings to the NRC.
In summary, the licensee satisfied the regulations in reporting the event.
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'G&E's immediate analysis of the causes of the event and early corrective measures taken to preclude the reoccurrence of a similar event demonstrated good operating practices, and the continued monitoring 'and evaluation of the piping system exemplifies conservative/safe engineering practices.
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ii It is concluded that this issue h'as been properly'handled and dispositioned by I
the licensee and poses no threat to'he,, health and 'safety" of the, public.
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Since'rely, 1
W. J. Dircks Executive Director for Operations Nuclear Regulatory Commission
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