ML20235D506
| ML20235D506 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 09/21/1987 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20235D493 | List: |
| References | |
| TAC-65287, TAC-67463, NUDOCS 8709250248 | |
| Download: ML20235D506 (3) | |
Text
_
[(pa nac(%,
a UNITED STATES g
NUCLEAR REGULATORY COMMISSION -
f 5
- j WASHINGTON, D C. 20555
\\...../
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
)
SUPPORTING AMENDMENT N0. 64 TO OPERATING LICENSE NO. NPF-8 ALABAMA POWER COMPANY JOSEPH M. FARLEY NUCLEAR PLANT, UNIT 2 i
DOCKET NO. 50-364 j
1.0 INTRODUCTION
By letter dated May 4, 1987, Alabama Power Company submitted a request for changes to the Joseph M. Farley Nuclear Plant, Unit 2, (Farley 2) Technical Specification (TS) 3/4.4.6, Steam Generators, surveillance and reporting j
requirements for testing tubes in the tubesheet region, j
The amendment would allow operation with tube degradation in excess of the plugging or repair limits when the degradation is located below the F*
distance from the top of the tubesheet or the bottom of the roll expansion, whichever is lower. The F* distance is defined as the length of continuous undergraded tube expansion in the tubesheet such that tube pullout would not occur during nomal or postulated accident loading conditions. The bases for this change is described in Westinghouse Electric Corporation Report WCAP 11306, Revision 2. "Tubesheet Region Plugging Criterion for i
the Alabama Power Company Farley Nuclear Station Unit 2 Steam Generators,"
~
revised April 1987. The Westinghouse report was provided as Enclosure 1,
in the May 4, 1987 letter.
]
The criteria for determining whether steam generator tube plugging and j
repair are required is described in Regulatory Guide (RG) 1.121, " Bases for Plugging Degraded PWR Steam Generator Tubes." This regulatory guide 1
indicates three factors should be considered when establishing tube degradation limits. They are (1) the minimum tube wall thickness needed in order for tubes with defects to sustain the imposed loadings under nonnal operating conditions and postulated accident conditions, (2) an operational allowance for degradation between inspections, and (3) the crack size required to ensure the leakage per steam generator does not.
exceed the technical specifications limit. To determine the minimum wall l
thickness, the RG requires a margin of safety of not less than three l
against tube rupture under normal operating conditions and, the margin of safety required against tube failure under postulated accident conditions should be consistent with the margin of safety determined by the stress limits specified in NB-3225 of Section III of the ASME Code.
The Farley 2 steam generator tubes were fabricated with a full depth hardroll of the tubes within the tubesheet.
When tubes are fabricated with a full depth hardroll, a transition region exists between the unrolled and fully expanded tube.
In the definition of F*, the bottom of the hardroll means the location where the tube has been fully expanded below 8709250248 870921 PDR ADOCK 05000364 P
._.. _ =
4 l,
the transition region.
In lieu of meeting wall thickness limitations, the F* criterion establishes the length of fully expanded hardroll tube-l I
required to meet the wall thickness margins of safety required by RG 1.121.
2.0 DISCUSSION AND EVALUATION 4
Westinghouse Report WCAP-11306 indicates that the presence of the tubesheet
)
will enhance the tube integrity in the region of the hardroll by precluding tube deformation beyond the initial expanded outside diameter. The resis-tance to both tubesheet rupture and tube collapse is strengthened by the i
presence of the tubesheet in that region. The result of the hardroll of 1
the tube into the tubesheet is an interference fit between the tube and the j
tubesheet. This interference fit produces an elastic preload between the j
tube and the tubesheet. Tube rupture can not occur because the contact l
between the tube and tubesheet does not permit sufficient movement'of the tube material.
In a similar manner, the tubesheet does not permit suffi-cient movement of tube material to permit buckling collapse of the tube during postulated LOCA loadings. Thus, the only method of significantly j
damaging the pressure boundary provided by the tube is pullout of the tube j
from the tubesheet.
In hardrolled tubes, pullout is resisted by frictional force resulting from I
(1) the elastic preload between the tube and tube sheet, (2) thennal expan-sion, and (3) internal pressure.
Frictional forces are reduced by tube sheet bowing. Westinghouse has laboratory tested steam generator tubing to deter-mine the elastic preload caused by hardrolling.
Forces resulting from thermalexpansion,internalpressureandtubesheetbowingweredeterminep f
analytically. Using a conservative coefficient of friction between the tube 1
and tube sheet, Westinghouse has determined the net axial resistance to tube pullout for normal and faulted conditions. These net axial resistance forces were used to detemine the hardrolled tube length required to meet the RG 1.121 safety margins against tube rupture during nomal operation conditions and tube failure under postulated accident conditions. The F*
length includes (1) the distances re against tube rupture and failures, (quired to meet RG 1.121 safety margins
- 2) a distance to account for eddy current measurementuncertaintyand(3)adistancetoaccountforreducedpreload from material discontinuity at the hardroll transition and the postulated circumferential through-wall flaw. The Westinghouse analysis demonstrates that the F* distance produces sufficient frictional forces to meet the margins of safety required by RG 1.121 and uncertainties in eddy current testing and material discontinuities.
In lieu of determining an operational allowance for degradation between inspections, the analysis postulated circumferential flaws propagated to a t1 rough-wall depth for 360 degrees around the tube. This results in a conservative estimation of flaw growth and precludes the need to determine operational allowances for degradation between inspections.
The F* distance of roll expansion, which contains undegraded tubing, will prevent significant primary to secondary leakage from through-wall flaws
-8.
located below the F* distance. The existing Technical. Specification :
leakage rate requirements and accident analysis assumptions remain.
unchanged in the unlikely event that significant leakage from this i
region does occur. As noted above, the tube rupture and subsequent tube pullout is not expected for a'. tube ~using the:F* criteria. Any leakage out of the tube from within the tubesheet at any elevation in-the tubesheet'is fully bounded by the existing steam generator tube rupture analysis included in the Updated Final Safety Analysis Report.
The proposed F* criteris do not adversely impact any.other previously evaluated design basis accident.
Based on the above, we conclude'that the proposed changes-to the steam generator tube plugging surveillance limits meet-the safety margins and intent of RG 1.121. Also, the'.other related Technical-Specification' changes proposed by the licensee are acceptable.
3.0 ENVIRONMENTAL CONSIDERATION
.I This amendment changes a requirement with respect to installation or'use of a facility component located within the restricted area as defined-in 10 CFR Part'20 and changes to the surveillance requirements. The' staff has determined that the~ amendment involves no significant. increase in the amounts, of any effluents.that may be released and no significant change in the types,4 off site, and that there is no significant increase in individual or cumulative
. The Comission has previously issued.a occupational radiation exposure.
proposed finding that this amendment involves no significant hazards consid-eration, and there has been no-public coment on such finding. Accordingly, this amendment meets the eligibility criteria'for categorical exclusion set-forth in 10 CFR 51.22(c)(9). Pursuant to 10 CFR 51.22(b), no environmental impact-statement or environmental assessment need be prepared in connection with the issuance of this amendment.
4.0 CONCLUSION
The Comission made a proposed determination that this amendment involves no significant hazards consideration which was published in the Federal Register on June 17,'1987 at 52 FR 23093 on'and consulted with the State of Alabama. No public ctaments were received, and the State of Alabama did not have any coments.
The staff has concluded, based on the considerations discussed above that:
(1) there is reasonable assurance that the. health and safety of the public will not be endangered by operation in the proposed manner, and (2) such activities will be conducted in compliance with the Comission's regulations and the issuance of this amendment will not be inimical to the comon defense and security or to the health and safety of the public.
Principal Contributor:
B. Elliot Dated: