ML18348A786

Proposed Change to Technical Specification Based on Eddy-Current Inspection of Steam Generator

ML18348A786
Person / Time
Site:	Palisades
Issue date:	03/10/1975
From:	Sewell R Consumers Power Co
To:	Giambusso A Office of Nuclear Reactor Regulation
References
Download: ML18348A786 (9)

Text

Re: Docket 50-255, License DPR-20 Mr. Angelo Giambusso Palisades Plant Director of Reactor Licensing February 1975 Eddy-Current US Nuclear Regulatory Commission Test Report and Technical Washington, DC 20555 Specification Change Request

Dear Mr. Gia.mbusso:

An eddy-current inspection of the Palisades steam generator has been conducted in accordance with the Commission Order of February 6, 1975 and Palisades Plant Technical Specification 4.14.2. * (The Commission Order added Sections 4.14.4 and 4.14.5 to the Plant Techriical Specifications.)

As a result of this inspection, we are also submitting a Technical Specifications change as an attachment to this letter. This change is sup-plied in three (3) executed and thirty-seven (37) conformed copies and is a Request for Change to the Technical Specifications of Provisional Operating License DPR-20, Docket 50-255, issued to Consumers Power Company for the Palisades Plant.

The following is an item-by-item discussion of the requirements and results of the eddy-current inspection conducted during February 1975.

Requirement 1 Technical Specification 4.14.2 requires that at the end of no more than 90 effective full power days or not more. than six calendar months . ., -

from the date of initial criticality after the August 1973 shutdown which

. was achieved on September 5, 1974, whichever occurs first, an inspection of the steam generator tubes will be conducted in accordance with the re-quirements of Regulatory Guide 1.83, "In-Service Inspection of Pressurized W~;ter Reactor Steam Generator Tubes," (issued June 1974) as it applies to inspections after the baseline inspection.

Disposition This requirement has been completed. The applicable requirements of Regulatory Guide 1.83 are as follows:

• Subrequirement a. No fewer than 3% of the total number of steam generator tubes should undergo eddy current examination during each in-service inspection.

273/"*

Mr. Angelo Giambusso Palisades - Feb 1975 Eddy-Current

• 2 Test Report and Tech Spec Change Request Disposition All tubes on the hot leg side of both steam generators were inspected.

Subrequirement b. Inspection of U-bend design steam generators should routinely concentrate on the hot leg side of the generator a~er the first two in-service inspect ions.

Disposition This was .the third full inspection of these steam generators and it did concentrate on the hot leg side with all hot leg tubes being inspected.

Subrequirement c. *Every inspection subsequent to the baseline inspec-tion should include all tubes which previously had defect indications (not including plugged tubes) and should also consider tubes in those areas (including the cold leg side) where design and experience have indicated potential problems .

• Disposition All tubes which had previous indication (> 20%) in either the hot or cold legs of each steam generator were inspected. In addition this inspection included those areas in the cold leg side where design and experience have indicated potential problems.

Subrequirement d. If the eddy ciirrent inspection pursuant to Regulatory Position C. 4 indicates that more than 10% of the in-spected tubes have detectable wall penetration (> 20%)

or that one or more of the inspected tubes have an indication of an unacceptable defect (see Regulatory Position C.7.a):* (1) The steam generator should be considered unacceptable for continued service until additional examinations are conducted and (2) an addi-tional 3% of the tubes should be inspected, concentrating on tubes in those areas of the tube sheet array where tubes with defects were found.

• Regulatory Guide 1.83 (June 1974) defines an unacceptable defect as one which would result in not satisfying the calculated acceptable minimum tube wall thickness that can sustain a LOCA in combination with a safe .

shutdown earthquake. This definition results in an unacceptable defect being one with more than 73% through wall penetration. The Commission Order of February 6, 1975, however, has effectively redefined this to be any defect with 50% or more wall thinning. For the purpose of this inspec-tion, the Commission's recent requirement has been used to define an unac-ceptable defect.

Mr. Angelo Giambusso Palisades - Feb 1975 Eddy-Current

• 3 Test Report and Tech Spec,Change Request If, in the inspection made in Regulatory Positfon C. 5. a( 2) above, more than 10% of. the inspected tubes have detectable wall penetration ( > 20%) or one or more of the inspected tubes has an indication of an unacceptable defect, additional tubes (no less than 3% of the total tubes in the steam generator) in the area of the defect shoUld be inspected.

Disposition Tliis requirement was completed. All of the tubes on the hot leg

.side of both steam generators were inspected. The cold leg inspection in-cluded ,a 10% sample (836 tubes) in Steam Generator A and a 4% sample (352 tubes) in Steam Generator B.

Requirement 2 Technical Specification 4.14:4 provides Alt~rnat~ves A and B.

Alternative A was followed and reads as follows:

The Licensee shall conduct, prior to further reactor operation, the following steam generator in-service inspection program:

• Inspect all steam generator tubes in both steam generators which previously had defect indications (not including plugged- *tubes) of greater than 20% wall penetration in the manner prescribed by Regulatory Guide 1.83 (issued June 1914) as that guide applies to inspections after the bas.eline inspection . . All tubes with indications of 50% or more wall thin-ning shall be plugged.

Disposition Item l.d discusses this requirement. In addition, all tubes with indicat.ion of 50% or more .(as defined in Item 3) will be plugged.

Requirement 3 Technical Specification 4*.14. 5 required that any steam generator tubes with eddy-current indications of 50% or more wall thinning shall be removed from service by plugging. Such indications may be confirmed by averaging during a given inspection, but such average shall be based on not less than three readings, in which case an average indication of 50%

or more wall thinning shall result in tube plugging.

Disposition All tubes observed with indications ~ 50%, as defined by Technical Specification 4.14.5, will be plugged. Table 1 below is a tabulation of the tubes which are scheduled for plugging .

Mr. Angelo Giambusso 4 Palisades - Feb 1975 Eddy-Current Test Report and Tech Spec Change Request

\

/ Number of Tubes Scheduled for Steam Generator Plugging in Accordance With TS4.14.5 A Hot 77 B Hot 202**

A Cold 2 B Cold 0 Requirement 4 Technical Specification 4.14.4, Part C, required that the results of the above-described inspection and tube plugging program; and a proposal for the conduct of future operations, including a recommended schedule for the next steam generator tube *inspection, shall be submitted to the NRC Staff for review and approval by letter prior to further operation.

Disposition

. Results of inspection and tube plugging program:

All of the tubes in the hot leg of both steam generators were tested. This test resulted in detection of **approximately 328 tubes with

> 50% wall thinning. A majority of these tubes (> 50%) were retested (a

• mtnimum of two additional times) and the results averaged to determine acceptability. The total tubes remaining in the ~ 50% wall thinning clas-sification following retesting were 281 tubes.

A 3% sample of tubes (272 tubes) was examined in the cold leg of the A stea.ni generator. Two tubes were observed with an indication of > 50%

as *defined in Item 3 and an additional 7% of the tubes (564 tubes) was-inspected, more than meeting the requirements of Item l.d. No additional tubes were observed with indications of > 50%. This inspection showed that 43 tubes had new ( > 20%) or incr'eased wall thinning ( > 5%) above previous test results. This, we believe, meets the intent of Regulatory Guide l.83.C.5(d) including Footnote 5.

A 3% sample of tubes was examined in the cold leg of the B steam generator; No tubes were observed with indications of > 50% and nine (9) tubes had new ( > 20%) or. increased wall thinning ( > 5% Labove previous test results. This, we believe, meets the intent of Regulatory Guide l.83.C.5(d) including Footnote 5.

Some multiple indi.cations were observed during this inspection.

Twenty-eight of these indications showed ~ 50% through wall penetration and will be plugged. A study of this type of indication was made by com-paring a sample of five indications (three in December 1974 and two in February 1975) with the data taken in the summer of 1974. For all of the.

tubes studied, the indications were found to be present in 1974 and had not incurred a significant change .

Mr. Angelo Giambusso 5 Palisades - Feb 1975 Eddy-Current Test Report and Tech Spec Change Request General discussion of tube inspection program:

In December of 1974, a sample of over 500 tubes was measured in the A steam generator and it was concluded that significant further wastage had not taken place since September 1973. This data appears to be in rea-sonably good agreement with the data t8.k.en in the A .steam generator in February 1975. The February data taken in the B steam generator, however, disclosed a larger than expected number of tubes with indications > 50%

tube wall thinning.

Early in the February 1975 eddy-current testing program, it became apparent that "new" indications were being observed. A review of the summer 1974 data showed that some of the indications had been missed by the eddy-current readers. In an effort to be responsive to this problem and to be able to provide reasonable assurance that all .indications of ~ 50%*. tube wall thinning were detected, the eddy-current testing'progra.m was reviewed. In response to this review, a data verifi~ation process was begun using qualified (ASNT-level II) eddy-current interpreters. This review was separate from the initial inter-pretation. of data and constituted a 100% overcheck 9f the data taken during the February 1975 testing program. We b.elieve that this program along with an intensified quality assurance effort has served to increase the awareness of testing personnel and resulted in increased accuracy of the testing effort. The overcheck effort has resulted in the additional identifica-tion of nine tubes with indications of~ 50% tube wall thinning .

Recommended schedule for next inspection:

The observation of a larger than expected number of additional

' indications makes it impossible to positively conclude that additional tube wall thinning has not taken place. We, therefore, find it prudent to limit the number of effective full power days until the next eddy-current test is performed o~ until an exhaustive review of the eddy-current data (comparing current indication with data taken .pr~viously) can be com-pleted. If, after the review of data has been complet~d, we find that we can conclude that additional tube wall thinning has not taken place, we will review this data with your staff and make an appropriate request for an ex-tensibn of the effective full .power day operating time permitted prior to-the next inspection.

Based on the results of this eddy-current testing program and the assumptions which were used to establish the present licensing requirements, we have concluded that an additional eddy-current testing program should be conducted following an additional (90) Effective Full Power Days of opera-tion. In addition, we have. concluded, as did our January 1975 request for a Technical Specifications *change, that the requirement for conducting a Regulatory Guide 1.83 eddy~current inspection within six calendar months is not required or desirable.

The appropriate request for a change to the Technical Specifi-cations is attached.

Mr. Angelo Giamqusso 6 Palisades - Feb 1975 Eddy-Current Test R.eport and Teen Spec Change Request Additional information concerning Primary System Flow Considerations:

A. Primary System Flow Rate Primary system flow was most .recently measured in August 1974.

A preliminary ~nalysis of that data indicated that the vessel flow rate was 132.2 x iob lbm/h at 532°F. Subsequent refinements in the analytical techniques used to reduce the flow data have led to a downward revision in the vessel flow to 131. 3. x 10~ lbm/h. This vess.el flow is substantially below the 136. 7 x 106 lbm/h pre.df,cted by Combustion Engineering.

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As a result of the February 1975 steam generator inspection, 281 additional tubes are being plugged. Combustion Engineering estimates that this tube plugging will cause an additional loss of 1.1 x 106 lbm/h. This additional loss has been confirmed by our own analysis. Based upon the most recent flow measurements, ther~fore, the vessel flow rate after tube plugging is expected to be i30.2 x 106 lbm/h.

B. Overpower Margin

• On July 22, 1974, Consumers Power submitted a report entitled, "Steam Generator Tube Plugging Criterion, Palisades Plant." Figure 1 in

• Section 5 of this report provides a curve of overpower margin as a function of core flow rate. The minimum core flow rate required to preserve an overpower margin of 122% from 2200 MWt is 123.6 x 106 lbm/h. This cor-responds to a vessel flow. rate of 127.3 x 106 lbm/h. Assuming that the allowance for measurement error is 3%, the required measured vessel flow for 122% overpower margin is 131.2 x 106 lbm/h.

The overpower margin of 122% can be preserved for a vessel flow of 130.2 x 106 lbm/h by restricting thermal power level to 2183 MWt or

99. 2% of full power. It is expected, however, that a refined analysis which takes credit for the improved augmentation model (submitted on November 4, 1974) will justif'y operation at full power. Until that analysis has been submitted, reactor power will be limited to 2100 MWt.

This limitation provides ample margin for uncertainties in the effect of tube plugging on flow reduction.

The Palisades FSAR shows acceptable results for all anticipated transients when they are initiated from conditions which are characterized by an overpower margin of 122% of 2200 MWt* The analysis performed under assumptions of fuel densification shows that the course of each anticipated

-transient is not significantly changed by the effects of fuel densification and none of these transients violate thermal limits.

In addition to the anticipated transients presented in the Pali-sades FSAR, the postulated accidents, with the exception of the LOCA (ie, Steam Line Break, Control Rod Ejection, Steam Generator Tube Rupture, and Locked Rotor) have been reviewed to determine the effects of this lower primary cool.ant flow. The Steam Line Break and Steam Generator Tube Rup-ture Accidents are both relatively insensitive to initial flow rate. The

Mr. AngeloGiambusso 7 Palisades - Feb 1975 Eddy~Current Test-Report and Tech Spec Change Request Locked Rotor Incident is sensitive to initial Iilargin to DNBR, but this maI_'giri is being preserved. The results of this incident, therefore, are no worse than those presented in the FSAR. The Control Rod Ejection Accident is sensiti~e to flux peaking, but not to the flow rate.

C. Loss of Coolant Accident Analysis

• The most recently. submitted Loss* of Coolant Accident analysis (submitted October 21, 1974 _and amended on No6ember 4, 1974). was performed using an initial vessel flow rate of 130 x 10 lbm/b. A sensitivity analy-sis of peak clad temperature as a function of initial vessel flow rate has not been performed. In the narrow band of vessel flows under considera-tion, however, the variation in peak clad temperature with flow rate is not expected to be significant.

Conclusion The SARB has concluded, based.on the foregoing, that the eddy-current testing has been performed in a manner that complies with the  ;

Technical Specifications Section 4.14 and .the "Or.der for Modification of License" dated Februaey 6, 1975.

In addition, SARB has concluded that the safety analysis of the Palisades Plant incorporating the effects of plUgging an additional 281 tubes in the steam generators is satisfactory forreactor power levels

_up to and including 2100 MWt*

Following authority for operation, we plan to continue the flush-ing program and will consider it completed upon s~tisfactory operation at 2100 MWt*

We expect the plant to be ready for start*up early in the week of March 23, 1975. Timely approval of the prop(>sed Technieal Specifications change and authority to allow continued operation of the plant is requested.

Yours very truly, RBS/map Ralph B. Sewell Nuclear Licensing Administrator

' i ...

-* CONSUMERS POWER COMPANY Docket No 50-255 Request for Change to the Technical Specifications License No DPR-20 For the reasons hereinaf'ter set forth, it is requested that the Technical Specifications contained in Provisional Operating License No DPR-20, Docket No 50-255, issued to Con,sumers Power Company on October 16, 1972, be changed as described in Section I, "Changes."

I. *Change A. Change Section 4.14 .. 2 to read as follows:

. I "At the end of no more .:t!han 90. effective full power days of operation from the initial criticality after February 1975, an inspection of the steam generator tubes will be conducted

• in accordance with the requirements of Regulatory Guide 1.83,

'Inservice Inspection of Pressurized Water Reactor Steam Generator Tubes' (issued June 1974) as it applies to inspec-tions after the baseline inspection."

II. Discussion The purpose of this proposed change is to allow the Palisades Plant to achieve an adequate period of operation following the last full eddy-current inspection of the steam generators. This will allow meaning-ful conclusions to be drawn with respect to corrosion rates that might be experienced in the Palisades Plant steam generators.

Previous Technical Specifications require that eddy-current testing be performed in accordance with Regulatory Guide 1.83 at the end of no more than 90 effective full power days or six calendar months. Our previous concern (and, therefore, the reason for the six months) was the possibility of prolonged operation at low power levels with significant phosphate concentrations due to the conversion from a phosphate to an all-volatile secondary side water treatment program. Procedures had been

• established for the conversion of the secondary water treatment (refer to

J " ** ..

2 \.

• our August 20, 1974 proposed Technical Specifications Change) and these procedures required that phosphates be removed to the extent practicable at low power levels prior to proceeding to higher power levels. It was estimated during the summer of 1974 that this conversion could take three or four months or more. Further, corrosion rates for *operation during the transition period from phosphate to an all-volatile treatment had not been established. Thus, a limit was proposed which was intended to provide an upper time restriction in terms of months of power operation during the transition phase of the converi:;ion of the secondary water treatment. Since the original surveillance program was proposed, the plant has operated within the all-volatile specifiCations (at power levels up to 60%) for secondary water chemistry. This conversion was achieved in approximately one day of power operatic;>n*and approximately 30.days' operation at hot standby condi-tions. Details have been reported in flushing reports submitted in accord-ance with our operating license and were summarized in a flushing report submitted November 6, 1974. We conclude that there is no need for additional restriction other than the 90 effective full power days of operation.

III.

• Conclusions Based on the foregoing, both the Palisades Plant Review Committee and the Safety and Audit Review Board have concluded that this proposed Technical Specifications Change does not involve an unreviewed safety

• question.

CONSUMERS POWER COMPANY By t{?,4*~

R. A. Lamley, ~ident Sworn and subscribed to before me this 10th day of March 1975.

SyfYi'B. Ball, Notary Public Jackson County, Michigan

• • My commission expires May 18, 1976