ML20062C756
| ML20062C756 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 10/16/1978 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20062C749 | List: |
| References | |
| NUDOCS 7811140036 | |
| Download: ML20062C756 (5) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION g, %. ,
) ,j WASHINGTON, D. C. 20556
%Yy z SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMEND!!ENT NO. 39 TO LICENSE NO. DPR-31 .
FLORIDA POWER AND LIGHT COMPANY ,
TURKEY POINT NUCLEAR GENERATING UNIT NO. 3 DOCKET NO. 50-250 ,
g Introduction /Backcround ,
By letter (L-73-312) dated September 26, 1978,. as supplemented by letter (L-73-323) dated October 2,1978, Florida Power & Light Company (FPL) submitted information to justify continued operation of Turkey Point :
Unit No. 3 for an additional four (4) equivalent months beyond the eight (0) months, beginning February 1,1978, currently authorized by License Amendments Nos. 32 and 36, dated January 31, 1978, and June 2,.1978, respectively.
License Amendment No. 32 authorized six equivalent months of operation. ;
The basis for establishing a six month period.of operation was the pre-ventive tube plugging performed by FPL under accepted plugging criteria ,
implemented following the last inspection of the steam generators completed in Decemoer 1977, along with an analysis of the information developed as a result of the steam generator tube inspections conducted in Turkey Point Unit No. 3, in November and December 1977. The criteria for preventive
{J tube plugging were determined from the predicted growth of regions in the ;
tube support plate in which the severity of tube denting would make tubes in these regions susceptible to stress corrosion cracking. Speci fically, >
the rate of growth of these regions was one-third distance between tube rows per month of equivalent power operation for tubes in columns 14 thru.
80 and two-thirds distance between tube rows per month in columns 1 thru 13 and 81 thru 94 License Amendment No. 36 authorized two additional equivalent months of !
operation. The basis for allowing two more months of operation was that the consequences of the maximum primary to secondary leakage rate, estimated i by the staff, that would be expected during a postulated main steam line break (MSLB) were acceptable. In order to bound the number of tubes that could possibly develop thru-wall cracks, we conservatively assumed that all tubes predicted to De within the 17.55 hoop strain contour are in a state -
of incipient cracking and would crack through when subjected to the expected pressure differentials during a postulated MSL3 accident. This assumption is conservative in that successive inspection results indicated that not all tubes within the predicted boundary (17.5% strain) actually restrict the 0.540 inch probe.
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Discussion The licensee has used steam generator inspection results from Turkey Point 4 to predict the conditio'ns that will exist in thE Turkey Point 3 steam generators. The progression of flow slot closure in the worst steam generator of Turkey Point 3, generator B, is approximately six ,
months behind that observed in the worst steam generator of Turkey j Point 4, also generator B. The two inspections of Turkey Point 4 steam l generators at points. beyond full closure of flow slots were examined and. l based on these data, FPL estimates that at 12 EFPM beyond closure the
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i maximum predicte'd' number 'of restricted unplsiged tubes' within the 17.5% !
tube hoop strain contour for Turkey Point 3 is 184. Restricted tubes are f defined as those which restrict either the 0.650, 0.610, or 0.540 inch O probes.- Turkey Point 3 will be at approximately 12 EFPM beyond full flow slot closure at the end of an additional 4 months of operation. Assuming i
i all 184 restficted tubes developed thru-wall cracks during a postulated l MSLB, the licensee has estimated a maximum primary to secondary leakage . !
rate of approximately 9.90 gpm. i FPL has evaluated the effects of the calculated leakage rate. Analyses !
i have shown that such ' low leakage rates during a MSLB would have a negligible effect on primary system thermal hydraulic parameters, the !
DNBR, the percent of coolant volume lost by leakage, or the time to !
terminate the core transient. Also, the effect of secondary to primary leakage during a LOCA would be negligible relativa to primary system :
thermal hydraulic-parameters when compared to the effects of the LOCA on !'
these parameters.
n Based on the information discussed above, FPL roncludes that Turkey Point 3 l V _can be safely operated for an additional four (4) equivalent months beyond t
.the . currently authorized eight (8). l The licensee assumes in their leakage rate calculations that only one crack !
per tube could develop during a postulated MSLB. To justify this assump- i tion, they reference Figure 1-3 in their June 9,1977, (L-77-173), Turkey ;
Point 4 submittal. This figure indicates that one tube / support plate !
intersection leads the others in the magnitude of denting to the extent l that leakage would occur at this intersection during normal operation prior !
.to any other dented intersection along a . tube degrading to such a- poin .
that it vauld . develop a leak during a postulated MSLB accident. ;
In conjunction with their request for an extension of four (4) months, the !
licensee has proposed additional operating restrictions to the Turkey l Point 3 operating license. They include requiring a gauging inspection [
of a steam generator if the 0.3 gpm primary to sec'ondary leakage rate l limit is exceeded or a shutdown to repair any leak due to the .dentino :
. phencmenon occurs, and requiring an inspection of all three steam gener- !
ators if leakage attributable to the denting phenomenon occurs in two or !
more tubes in any 20 day period.
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. 1 Evaluation The licensee submitted leakage rate calculations for conditions that would be expected during a postulated MSLB accident. These calculations are based on the assumption that only tubes predicted to be restricted within the projected 17.5% tube hoop strain contour could develop a crack and leak during a postulated MSLB. In our previous safety evaluation reports on this subject, e.g., as in our safety evaluation report attached to l
-Amsmdment No. 36 to Facility Operating License No. DPR-31 for Turkey l Point 3 dated June 2,1978, we assumed that all tubes predicted to be !
within the 17.5% strain contour could crack under postulated MSLB con-ditions. However, this is the first time a licensee has estimated the total number of tubes expected to restrict all three probe sizes. Since O' 1) preventive plugging in the tubelane regions is based on the number and location of tubes found to restrict either the 0.540 or 0.610 inch probes, 2) inspection results indicate that not all tubes within the 17.5% hoop strain boundary-restrict even the 0.650 inch probe, and 3) it is not likely that any tubes besides those dented to such a point that they do not allow passage of a 0.540 inch probe will develop cracks and leak, we believe that the licensee's assumptions are conservative for estimating the maximum expected leakage during a postulated MSLB accident.
Therefore,_ the conclusions reached by the licensee are valid and the NRC
- staff has concluded the following
- 1. The primary degradation mechanism in Turkey Point 3 steam generators is associated with the denting phenomenon and the tube cracking is expected to occur at tube / support plate intersections (since all row 1 tubes have been previously plugged). The type of cracks associated with tube denting are constrained by the support plate, O -and will not burst oPea durin9 a nsta accident.
- 2. The leak rate associated with-these cracks is very smalT. The estimated leakage rate of 0.05 gpm per tube under accident loads o
is reasonably conservative. This leakaga -rate has been determined
-experimentally by Westinghouse.
- 3. The data discussed above, i.e., Figure 1-3 of the June 9,1977, Turkey Point 4 submittal, will most likely also be valid for the Turkey Point .3 steam generators and, therefore, only one crack per tube need be postulated for the leakage rate calculations.
- 4. It is a reasonably conservative assumption that only restricted tubes within the 17.5% strain contour could crack and leak during a postu-lated MSLB accident and the actual leakage rate should be bounded by the calculated rr.ce.
. 5. Therefore, the total leakage rate in the affected steam -generator would j most likely not exceed 10 gpm.
- 6. A primary to secondary leak rate of 10 gpm will have a negligible effect on primary system thermal hydraulic parameters, the CNB ratio, the percentage of reactor coolant volume lost by leakage, and the ,
time to terminate the core transient during a postulatac MSL3 accident.
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! 7. The effect of secondary to primary leakage during a LOCA would be l negligible relative to primary system themal hydraulic parameters when compared to the effects of the LOCA itself on these parameters. :
- 8. Although tubes that, according to the current plugging criteria should ,
be plugged, are remaining in service, the currently imposed operating restrictions adequately address the possibility of cracks and sub- I sequent leakage developing during normal operation.
- 9. The additionally imposed operating restrictions will assure that ;
unexpected acceleration of tube denting is re:ognized and dealt with l in a timely, orderly fashion.
O 10. An additional four (4) equivalent
- months of operation of Turkey point 3 is therefore acceptable. ,
l For the foregoing reasons -we conclude that an additional four months of j operation, under the constraints imposed by the existing facility operating ;
license and new constraints agreed to by the licensee, will not significantly ,
change the basic conclusions stated in the previous safety evaluation report ;
attached to License Amendment No. 32, dated January 31, 1978. j Environmental Consideration i We have tietermined that the amendment does not authorize a change in i effluent types or total amounts nor an increase in power level and will ;
not result in any significant envirtnmental impact. Having made this :
detemination, we have further concluded that the amendment involves an 0 action which is insignificant from the standpoint of environmental impact and pursuant to 10 CFR 5 Sl.5(d)(4), that an environmental impact statement or negative declaration and environmental impact appraisal need i not be prepared in connection with the issuance of this amendment. l Conclusion ;
We have concluded, based on the considerations discussed above, that: !
(1) because the amendments do not involve a significant increase in the i probability or consequences of accidents previously considered and do not !
involve a significant decrease in a safety margin, the amendments do not l I
involve a significant hazards consideration, (2) there is reasonable assurance that the health and safety of the public will not be endangered i' by operation in the proposed manner, and (3) such activities will be con-ducted in compliance with the Comission's regulations and the issuance :
of these amend: rents will not be inimical to tne common defense and security !'
l or to the health and safety of the oublic.
- For purposes of this SER, equivalent aperation is defined as operation with a primary coolant temcerature greater than 350*F. >
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-5 References
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- 1. Letter from R. E. Uhrig to NRC dated March 1,1978.
! 2. Letter from C. M. Stalling VEPC0 to B. C. 'Rusche NRC dated j- March 25,1977 (Cocket No. 50-280). -
1 j 3. Letter to FPL granting Amendment No. 32 to DPR-31 dated
- January 31, 1978.
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