05000344/LER-1985-013, Forwards Comments on 860627 Draft Info Notice Re Steam Generator Hydraulic Snubber Failures,Based Primarily on LER 85-13 & Suppl 1 to LER

Forwards Comments on 860627 Draft Info Notice Re Steam Generator Hydraulic Snubber Failures,Based Primarily on LER 85-13 & Suppl 1 to LER

ML20207J633
Person / Time
Site:	Trojan File:Portland General Electric icon.png
Issue date:	07/24/1986
From:	Withers B PORTLAND GENERAL ELECTRIC CO.
To:	Baer R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE)
References
NUDOCS 8607290198
Download: ML20207J633 (4)

LER-2085-013, Forwards Comments on 860627 Draft Info Notice Re Steam Generator Hydraulic Snubber Failures,Based Primarily on LER 85-13 & Suppl 1 to LER

Event date:
Report date:
3442085013R00 - NRC Website

text

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mE Bart D. Wahers Vce President July 24, 1986 Trojan Nuclear Plant Docket 50-344 License NPF-1 Mr. Robert L. Baer, Chief Engineering and Ceneric Communications Branch Division of Emergency Preparedness and Engineering Response Office of Inspection and Enforcement U.S. Nuclear Regulatory Commission Washington DC 20555

Dear Sir:

Comments on Draft IE Information Notice On June 27, 1986, a draft Information Notice concerning steam generator hydraulic snubber failures was forwarded to us for review and comment.

The draf t Information Notice is based primarily upon Licensee Event Report (LER) 85-13 and Supplement 1 to that LER. Additional information has been obtained through recent inspections and monitoring which is provided in the attachment to this letter for inclusion in the Information Notice, l

If you have any questions concerning these comments, please do not hesitate to contact me.

Sincerely, v

- 'f A Bart D. Withers Vice President Nuclear Attachment l

l 8607290198 860724 PDR ADOCK 05000344 G PDR 4

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121 S W Simon Street. Pomyn Oregon 972CM

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Trojan Nuclear Plant Mr. Robert L. Baer Docket 50-344 July 24, 1986 License NPF-1 Attachment Page 1 of 3 COMMENTS ON DRAFT INFORMATION NOTICE

GENERAL COMMENT

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1. Based on results of the thermal expansion monitoring program during startup from the 1986 refueling outage, it has been determined that most, if not all, of the observed movement of the pressurizer surge line is expected due to normal thermal transients experienced by this line during heatups and cooldowns. Much of the movement which has been observed since 1982 and classified as " unusual" is now classified as " expected" novement.

2. It has not been confirmed that the snubbers were in fact ever locked up. Paul-Munroe, Inc. concluded in 1985, as a result of evidence found during refurbishment of the snubbers, that the snubbers would not have restrained RCS thermal growth. Testing of the control valves performed by Wyle Laboratories in May 1986 demonstrated that the snubbers on a particular steam generator would not restrict growth of that loop unless all four were locked up because the snubber hydraulic lines are connected in parallel. Based on these findings, we have concluded the most likely cause of RCS thermal restraint was due solely to the inadequate size of the gaps between l RCS components and associated seismic or pipe whip restraints.

Therefore, it is recommended that the title of the Information Notice be changed to " Repeated Multiple Failures of Steam Generator i

Hydraulic Snutbers Due to Control Valve Sensitivity" and that i references to the snubber failures causing the unusual pressurizer surge line movements be deleted.

SPECIFIC COMMENTS

1. The applicability of this Notice probably should not be limited to PWRs. The issue is large-bore snubbers with control valves. This may apply to BWRs also.

2. Under Purpose, first sentence:

! Change the first sentence to end after the word " outages", so it reads as follows: ". . .were found at two consecutive refueling outages." Based upon General Comment Number 2, the movement of the pressurizer surge line has been determined to have not have been

" erratic", and not caused by the hydraulic snubber failures.

e t.

Trojan Nuclear Plant Mr. Robert L. Baer Docket 50-344 July 24, 1986 License NPF-1 Attachment Page 2 of 3

3. Description of Circumstances

a. Page 2, first paragraph, fourth line:

The decision to not perform "an engineering evaluation of the effect of the failed snubbers on the steam generators" was based upon the information provided by the company retained to perform snubber testing. It is recommended that this line be revised to read: ". . . decision was based on the snubber-testing Company's judgment that the foreign material. . .".

b. Page 2, first paragraph, last two sentences:

It has been determined that all four snubbers would have to have failed simultaneously to have prevented movement of a steam generator. It is recommended that the last sentence be revised to read: "Should this have occurred to all four snubbers on one steam generator simultaneously, the snubbers would have become locked until a load reversal possibly cleared the bleed orifice in at least one control valve."

c. Page 2, fourth paragraph, last sentence:

Although the difference in viscosity of the two fluids was insignificant, modifications were made to the control valves. It is recommended that this sentence be revised to read: ". . .The viscosity difference between the two fluids was analyzed and, as a result, stiffer springs were installed in the snubber ball check valves."

d. Page 2, fifth paragraph:

It is recommended that the following be added: " Subsequently, it was determined that movement of the pressurizer surge line was not unusual or erratic and had not been caused by the snubber failures." Refer to General Comment 2.

e. Pages 2 (and 3), sixth paragraph:

There were a total of 12 steam generator hydraulic snubbers which failed functional testing ir. 1986. Six of these could not achieve minimum velocity for thermal expansion (excessive drag).

One of the six also had high bleed rate at faulted load and a second one of the six had no bleed rate at faulted load. Three snubbers failed solely due to high bleed rate at faulted load and the remaining three failures were solely due to no bleed at I faulted load.

t, Trojan Nuclear Plant Mr. Robert L. Baer Docket 50-344 July 24, 1986 License NPF-1 Attachment Page 3 of 3

4. Discussion

a. Page 3, first paragraph, second sentence:

Please revise to read: . . . caused them to activate at very low fluid velocity through the main flow port." It is important to differentiate here between "very low fluid velocity" and

" slightest movement of fluid".

, b. Page 3, first paragraph, third sentence:

It is felt that the viscosity difference of the new fluid had an insignificant effect on snubber operability. However, the slight viscosity change was accounted for by using stiffer springs in .

the snubber ball check valves when the control valves were refurbished.

c. Page 3, second paragraph:

The decision to change out the control valves was made shortly

after the testing of the snubbers in 1985. The decision was based on the difficulty encountered in testing the snubbers after they had been refurbished. The decision was further supported by the root cause analysis performed in 1986.

The new control valve activation velocity is 6-9 in./ min.

Additionally, the new control valve bleed ports are self-cleaning j whenever there is flow past the poppet valve, not just during flow reversals.

5. In the attachment to the Information Notice, it indicates that two of the four main steam line hydraulic snubbers failed functional test-ing. All four of these snubbers were declared inoperable along with the 14 remaining steam generator snubbers when the first two steam generator snubbers failed the bench test in 1985.

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