ML19209C992
| ML19209C992 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 10/02/1979 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19209C991 | List: |
| References | |
| NUDOCS 7910180557 | |
| Download: ML19209C992 (4) | |
Text
-[dpaacog%'i UNITED STATES i),c3 NUCLEAR REGULATORY COMMISSION
' "'. I WASHINGTON, D. C. 20555 y
SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SUPPORTING AMENDMENT NO. 21 TO FACILITY OPERATING LICENSE N0. NPF-3 THE TCLED0 EDISON COMPANY AND THE CLEVELAND ELECTRIC ILLUMIPATING COMPANY DAVIS-8 ESSE NUCLEAR POWER STATION, UNIT NO. 1 DOCKET N0. 50-346 Introduction By letter dated July 27, 1979, supplemented by letter dated August 17, 1979, the Toledo Edison Company (TEC0 or the licensee) requested an amendment to Facility Operating License No. NPF-3 for the Davis-Besse Nuclear Power Station, Unit No. 1 (Davis-Besse 11 The amendment would change the Technical Specifications (TSs) by (1) extension of the calendar time to perform the first inservice inspections (ISI) of steam generator (SG) tubes after initial criticality, (2) special provisions for certain categorization of degraded and/or defective SG tubes in various defined groups, and (3) inspection interval requirements based.on the categorization of the results of inspections of SG tubes.
Discussion With regard to item (1) above, Section 4.4.5.3.a of the TSs requires that the first ISI of the SG tubes be performed after six effective full power months, but within 24 calendar months of initial criticality.
Because Davis-Besse 1 has incurred a number of plant outages (seven months, 22 days - or approximately 232 effective full power days) since initial criticality en August 12, 1977, the first scheduled refueling outage has slioped to March 1980.
Therefore, the licensee nas requested relief from the TS provisic.1s to permit the first ISI to be coin-cident with the first scheduled refueling outage.
With respect to item (2) above, operating experience to date with Babcock and Wilcox (B&W) designed SGs indicates that tube degradation is most likely to occur in locali:ed areas adjacent to the tube inspection lane and in the vicinity of the 15th tube support plate where tubes pass througn drilled, as opposed to broached, holes *.
It is believed that degradation preferentially occurs in these areas because of the local combination of flow conditions and fluid propertie's.
The cu'rrent TS for SG tubes requires, and the proposed TS change would require, 1177 J65 A broacned nole is typically a fluted circle rather than a plain circle.
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that 50% of the first sample of tubes selected for insectica (3% of the total number of tubes in all SGs) be from this area (where experience indicates critical areas to be inspected). As an alternative to this requiretrent, the licensee proposed to define one or more areas in the SGs where experience has indicated that degradation is most likely, and to cptionally perform an inspection of all of the tubes in these areas in both SGs.
In addition, the licensee would inspect the tubes not so inspected in accordance with the general provisions of the proposed TS. The criteria for the second and third sample inspections for the general SG group would be based on the results of the general SG tube group inspection, independent of the defined group inspection results when the defined group would be 100% inspected. According to the licensee's proposal, the number of tubes inspected in the defined potential problem area (s) would not reduce the number of tubes examined in the associated general inspection; but at the same time, degraded or defective tubes identified in defined potential problem areas would not be used in detemining the results cr.tegory for the general inspection and vice versa.
With regard to itin (3) above,lhe current TS requires the inspection results to be classified into one of three categories (Specification 4.4.5.2) depending upon the number of defective or degraded tubes discovered. This results category determines the repairs that must be performed; the additional inspection required at that outage, if any; whether prompt raporting of the results to the NRC is required; and the maximum permissible interval until the next inspection is conducted. The licensee is proposing that the maximum inspection interval to the next ISI be determined separately for each:SG tube group based upon the results category for that group. This will provide for an increased frequency of inscection for a problem area, without reducing the frequency of general SG tube inspections.
Evaluation As for item (1), the licensee is requesting relief from Specification 4.4.5.3.a to permit the first ISI to coincide with the first refueling cutage now scheduled for March.1980. This represents approximately a seven-month extension and is justified by the licensee on the basis of the total accumulated outage time of seven months 22 days since initial criticality.
It is our evaluation that any tube degradation which may have occurred during the periods of wet layup has not added significantly to the tube degradation that would normally be incurred in a two-year interval. The most significant form of tube degradation observed in S&W units to date is circumferential cracks induced by fatigue.
These fatigue cracks are due to mechanical sources such as flow induced vibration wnicn does not exist during periods of wet layup.
Experience has shown that tube degradation due to corrosion mechanisms such as wastage and denting is not a prcblem for B&W units.
Indeed, the denting pnenomena has yet to be observed in any B&W unit. Therefore, we find it acceptable to extend the specified 24-alendar month interval before the first inservice inspection by the seven month 22 day outage time accumulated to date.
To ensure that any subsequent outages which may occur prior to March 1980 will not result in further slippage of the first IS*, the licensee nas agreed to a provision in the TSs which states that the first ISI shall be performed by Acril 30, 1980.
As for item (2), the licensee is proposing that the tubes in the SGs be classified into two groups:
(1) a group of tubes in well-defined areas where ex:erience has indicated that tube degradatien is most likely (the defined grouo) f177 J66
and (2) the balance of the tubes in the SGs. The licensee is also proposing that, at their option, these groups may be subject to different inspection requirements. bcifically, the licensee may or may not elect to perform an inspection of cvery tube in the defined group in both SGs.
If they elect to perform such an inspection, the balance of the SG tubes will be subject to the normal inscection requirements with no reduction of sample size. At the sama time, degraded er defective tubes identified within the defined group will only be used to establish the results category for that group and not for the overall population of tubes.
On the other hand, if the licensee elects to not inspect every tube in the defined group in both SGsuthe scecifications.would require that the nomal inspection be performed.
In this case, the specifications vould require that at least 50% of the tubes inspected be in areas where ex:ecience has indicated potential prcblems.
Accordingly, with either option, inspection of tubes in potential problem areas is emchasized.
Under the provisions of the licensee's proposed revision, however, all of the tubes in these areas may be inscected Therefore, we conclude that with the proposed revision the extent of the inscection of tubes in potential problem areas is not diminished and may be increased.
In addition, we conclude that the extent of the inspection of tne balance of the SG tubes is not reduced.
As for item (3), we find the proposed requirements governing inscection intervals of the inscection of a cefined group of tubes would increase the number of inspec-tions of a problem area, yet not reduce the general SG tube inspections.
3ased upon the foregoing, we conclude that extending the 24 calendar month interval before the first inservice inspection by the outage time accumulated to date does not significantly ino ease the probability of a tube failure prior to the first inspection more than what currently exists for the specified 2?
calendar month interval assuming no outages. Thus, this enange to the TSs is acceptable. We further conclude that t:.e inclusion in the TSs of. provisions for (1) electively inspecting all tubes in defined areas and (2) cetermining the inspection intervals for the defined areas from the inspection results of the respective defined arw does not recuce the effectiveness of the overall SG tube inspection program and is therefore acceptable.
Environ ental Consideration We have deternined that the amendmen't does not authorize a chance in ef#luent ty:es or total amounts nor an increase in cwer level anc aill not result in any significant envir:nmantal i=:act.
Havinc mace this determinatien, we nave further concluced that tne amen: ment involves an action anich is insignificant from the stanc:cint of environmental i-:ac: and, cursuant to 10 C.:R IU.5(d)(1), that an env9:nmentai im:act statement, or necetive declaration and envir:n-mental im act 3:Oraisal need ne'; be :re:ared in connect on with the i
iss;ance of this amencment.
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Cenclusion
'n'e have concluded, based on the censiderations discussed above, that:
(1) be ause the amendment does not involve a significant increase in the probability or consequences of accidents previously considered anc does not involve a sicnificant decrease in a safety margin, the ar.endment does not involve a sienificant hazards consideration, (2) there is reasonable assurance teat the health and safety of the public will not be endangered by Operation in the pre:csed manrrer, and (3) such activities will be conducted in comoliance with the Ccmmission's reculatiens and the issuance of this amendment will not be inimica.1
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to ne c mmen defense and security or Oc the health and sa'faty of be public.
Cated: 0ctober 2,1979 I177 J6f3 O