ML18142A450
| ML18142A450 | |
| Person / Time | |
|---|---|
| Site: | Surry, North Anna, 05000000 |
| Issue date: | 06/17/1985 |
| From: | Stewart W VIRGINIA POWER (VIRGINIA ELECTRIC & POWER CO.) |
| To: | Thompson H Office of Nuclear Reactor Regulation |
| References | |
| 85-300, GL-85-02, GL-85-2, NUDOCS 8506240531 | |
| Download: ML18142A450 (17) | |
Text
WULIAML STEWART' Vice President Nuclear Operations June 17, 1985 Mr. Hugh L. Thompson, Jr., Director Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Gentlemen:
VIRGINIA POWER e
Nuclear Operations Department Post Office Box 26666 One James River Plaza Richmorut, Virginia 23261 VIRGINIA POWER Serial No.85-300 NO/ETS:acm.
Docket Nos. 50-280 50-281 50-338 50-339 License Nos. DPR-32 DPR-37 NPF-4 NPF-7 SURRY AND NORTH ANNA POWER STATIONS RESPONSE TO GENERIC LETTER 85-02 We have reviewed Generic Letter
- 85-02, "Staff Recommended Actions Stemming From NRC Intergrated Program for the Resolution of Unresolved Safety Issue Regarding Steam Generator Tube Integrity," dated April 17, 1985. is the description of our overall program for assuring steam generator tube integrity and tube rupture mitigation. Attachment 2 describes our steam generator inspection sampling program and our recommendations pertaining to Category C-2 inspection re.sults obtained during initial sampling.
Should you have any questions concerning this matter we would be happy to discuss them with you.
Very truly yours,
. 1-?j +}a,,/=~ j f-W. L. Stewart Attachments cc:
Dr. J. Nelson Grace Regional Administrator Region II 8506240531 850617 PDR ADOCK 05000280 P
e e
ATTACHMENT 1.
VIRGINIA POWER RESPONSES TO NRC STAFF RECOMMENDED ACTIONS REGARDING STEAM GENERATOR TUBE INTEGRITY I.a.PREVENTION AND DETECTION OF LOOSE PARTS (INSPECTIONS)
Staff Recommended Action Visual-inspections should be perform~d on the steam generator secondary side in the vicinity of the tube sheet, both along the entire periphery of the tube bundle and along the tube lane, for purposes of identifying loose parts or foreign objects on the tubesheet, and external damage to peripheral tubes just *above the tubesheet.
An appropriate.optical device
. should be used (e.g., mini-TV camera, fiber optics).
Loose parts or foreign objects which are found.should be removed from: the steam generators.
Tubes observed to have visual damage should be eddy current inspected and plugged if foundto be defective.
These visual inspections_ should be performed: * (1) for all steam*
' generators at each plant at. the next planned' outage for eddy current':
testing, (2) after any secondary side modifications, or repairs, to steam
- generator internals, and (3) - when eddy current indications aie found* iti the free.span portion of peripheral tubes, unless it has been established that the indication did not result from damage by a loose part or foreign object.
For PWR OL applicants, such inspection should be part of the preservice inspection.
For steam generator models where certain segments or the peripheral region can be shown not to be accessible to, an appropriate optical device, licensees and applicants should implement alternative actions to address these inaccessible areas, as appropriate.
Licensees should take appropriate precautions to m1.n1.m1.ze the potential for corrosion while the tube bundle is exposed to *air.
The presence of chemical species such as sulfur may aggravate this potential, anci may make exposure to the atmosphere inadvisable until appropriate remedial measures are taken.
Reference Section 2.1 of NUREG-0844.
Response
Virginia Power performs steam generator secondary side visual inspections of the steam generators in accordance with approved
- procedures each refueling outage following completion of sludge lancing operations.
This inspection uses appropriate optical devices, typically mini-TV cameras with recorders, and covers the vicinity of the tube sheet, both along the entire periphery of the tube bundle and along the tube lane.
JWO/jlm/8/0GREN
Loose par,ts'.,;or foreign objects which are found are removed from the steam
- .geµ_e_r:~~:ors_i~l:::Jf:* possible.
Foreign objects which cannot be removed are.
. evaluated***to. insure they present no potential for loss of steam generator tube :i:nte'g);J.ifj,rior to placing the steam generator in operation.
The Steam Generator Vendor is _inte:rgrally involved in the evaluat.ion process.
Tubes observed to have.visual damage are eddy current inspected and will,.
by procedure*, be plugged if found to be defective, or meet the plugging criteria.
The steam generators at the four Virginia Power nuclear units underwent steam generator secondary side visual inspections_ during their most recent refueling outages.
Our existing inspection program and procedures require that visual inspections be. performed following secondary side modifications or repairs to steam generator internals.
Under our existing program, eddy current indications found in the free.,span portion of peripheral tubes are evaluated and, if damage from* loose parts or
. foreign objects. could not be eliminated, *a visual inspect"fon of the secondary side _ is performed.
}:
As part of the Virginia Power steam. generator operating - philds,op,ljy~.. -
sp_ecial effort is made to limit the exposure of* the tube_ bundle to.* a;lt.*~c.._
During outage conditions, when activities requiring-the steam generators:_
to be drained are not being performed, the steam generators are placed-;in wet layup.
- Our secondary water chemistry program contains* specified.
limits on impurity levels du.ring wet layup for species such as chloride, sulfate, and sodium.
JWO/jlm/8/0GREN
e e
l.b PREVENTION AND,DETECTION OF LOOSE PARTS (QUALITY ASSURANCE)
Staff:Recominencied Action Quality assurance/quality control procedures for steam generators shouid be reviewed and revised as necessary to ensure that an effective system exists to precl~de introduction* of foreign objects into either the primary or secondary side of. the steam generator whenever it is opened (e.g., for maintenance, sludge lancing, repairs, inspection operations, modifications).
As a minimum, such procedures should include:
(1) detailed accountability procedures for all tools and equipment used during an* operation, (2) appropriate controls on foreign objects such as eye glasses and film badges, (3) cleanliness requirements, and (4) accountability procedures for components and parts removed from the internals of major components (e.g., reassembly of cut and. removed components).
Reference*
Section 2.1 of NUREG-0844.
Response
Station procedures are in place that address cleanliness control of plant systems and components.
The procedures include:
(1)
Detailed accountability procedures for tools and equipment used during an operation.
(2)
Appropriate controls on foreign objects suchas eye glasses and film badges.
-(3)
Cleanliness requirements.
These procedures also require the Quality Control Group to verify independently the cleanliness prior to final closeout.
In addition, controlling procedures (e.g., maintenance procedures, design change packages, modification procedures) provide specific detailed instructions for components and parts removed from the intern.als of major components. _ The controlling procedures
- also alert the worker to the necessity of maintaining cleanliness and provide specific Quality Control Hold Points.
JWO/jlm/8/0GREN
I Condenser preventive maintenance is not presently included in. the Virginia Power preventative maintenance programs.
- However, certain prevent:ive*, maintenance type activities, such as visual inspections. of
- *condenser. i11.ternals during refueling outages and replacement of condenser
- boots when they near the end of their service life, are routinely performed on the condensers.
jwr /LM6':"'"ds069
e 2.a INSERVICE INSPECTION PROGRAM (FULL LENGTH TUBE INSPECTION)
Staff-Recommended Action The Standard Technical Specifications (STS). and. Regulatory Guide 1. 83, Part C.2.f, currently*define a U-tube inspection as meaning an inspection of the steam generator tube from the point of entry on the hot-leg side completely around the U-bend to the top support of. the cold-leg side.
The staff recommends that tube inspections should include an inspection of the entire length of the tube (tube end to tube end) including the hot leg side, U-bend, and cold leg side.
This recommended action does not mean that the hot leg inspection* sample and the cold leg inspection sample should necessarily. involve the same tubes.
That is, it does not preclude making separate entries from the hot and cold leg sides and selecting different tubes on the hot and cold leg sides to meet the minimum sampling requirements for inspect-ion.
Consistent with the current.* STS requirement, supplemental sample
- . ins,pections (after the initial 3% sample) under this stafE recommended.
action may be limite*d to a partial length
- inspection provided_. the inspection* includes those portions of the tube length where *degraciatton..
was found during initial sampling.
Reference Section 2.2.2 of NUREG~0844.
Response
The current
- practice at Virginia Power ~s to* schedule approximately 714 (21%) tubes per. steam generator in two.of the three steam generators to be inspected* each refueling outage.
These. tubes, except those in the small radius U-bend area, are inspected full length (tube end to tube end).
The small radius U-bend area tubes are inspected over the U-bend to the top support on the cold-leg side.
Therefore, approximately 550 tubes (16%) in each steam generator inspected are inspected full length.
If previous inspections have shown evidence of potential tube degradation, this minimum inspection program will be expanded to schedule the inspection of mo~e tubes per steam generator, inspection*of the third steam.generator, or inspection of both additional tubes and the third steam generator.
If additional tubes per steam generator are added to the inspection plan, they will typically* be examined over the ar*ea of interest based on prior examination results.
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2.b INSERVICE INSPECTION PROGRAM (INSPECTION INTERVAL)
Staff-Recommended Action The0 maximum allowable time between eddy current inspection of an individual steam generator*should be limited in a manner consistent with Section 4.4.5.3 of. the Standard Technical Specifications, and in addition should not extend beyorid 72 months.
Reference Section 2.2.4 of NUREG-0844.
Response
The Virginia Power steam generator inservice inspection program insures
. that the* maximum allowable time between eddy current inspections of an individual steam generator does not exceed the* inteival
- specified in Section 4.4.5.3 of the Standard Technical Specifications and does not exceed 72 months.
Virginia Power has four operating units
- with three steam
- generators:;-pi~:-:.-~--
unit.
The Virginia Power steam generator inservice inspection program,.. ::
specifies. that at least two steam generators per unit be inspectedja"f.~.
each refueling outage, with the steam generators selected for inspect+/-tfo*_
each outage being alternated such that over a two refueling_outage cycle all three steam generators will normally be inspected at least one time.
Therefo~e, each steam generator will normally undergo eddy current inspection at least once every 18 to 36 months.
Recent history indicates that the interval between eddy current inspections for each of our steam generators has not exceeded 30 months.
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__ _J
e 3~a SECONDARY WATER CHEMISTRY PROGRAM Li~:en~~e:S~--a~il~f~;~-licants should have a secondary water chemistry program (SWCP) to*'*minimize steam generator t~be degradation.
_ The;,,i._specific*. plant - program.should* incorporate the secondary wate_r
- _chemistry-*gt1;delines in SGOG Special Report EPRI-NP-2704, l'PWR Secondary_
Water Chemistry-Guidelines," October. 1982, and should address measures taken. to minimize steam generator
- corrosion, including materials
- . selection,. chemistry limits, and control methods.
In_ addition, the specific plant procedures, should include* _progressively. *more-stringent.*
corrective actions for out-of-specification water chemistry conditions.
These* corrective actions should include power reductions and shutdowns,*
as appropriate, when excessively corro_sive conditions exist.. Specific functional individuals
- should be identified; as~.,. J1a,Ving.
the
- responsibility/authority to interpret plant.. water chemistryi 0iilformation and initiate appropriate plant actions to adjust: chemistry*, ':cf~'"jiecessary-*.
- _~,. :~--*: '_.~::;=,~--...
The referenced SGOG guidelines above were prepared by* the: _St~1fui *Gen;:ra,t.pr *.*
Owners Group Water. Chemistry Guidelines Committee. ancf rep:resen.ti;{iai,.d{;J;-_f consensus opfnion of a
significant portion* of the. indust,ry,~-:.;fqr *>.
state-of-the-art secondary water chemistry cotifi*or.*
/~;.{/'.~
Reference Section 2.5 of NUREG-0844.
Response
In order to provide maximum chemical_protection.to the secondary system components and to minimize steam generator *tube degradation,. a Virginia Power Nuclear Operations Department Policy has been established that incorporates the "PWR Secondary Water Chemistry Guidelines" into the appropriate station procedures at the operating plants.
Specifications have been adopted from the Steam Generator Owners Group Guidelines (SGOG) that address four unit conditions:
- 1.
Wet Layup:
The steam generators will be placed in wet chemical layup* when maintenance schedules allow.
The chemistry specifica-tions are list.ed in Table I. -
- 2.
Unit Startup:
Prior to heatup, the steam generator should meet the
_values listed in Table II.
A chemistry hold will be implemented at S5% reactor power and again at S30% reactor power.to ensure that the specifications are met prior to p_ower escalation. _
- 3.
Unit Operations:
Table III lists the
- control parameters for power operation with associated Action Levels.
- 4.
Unit Shutdown:
A chemistry hold at 350°F will be implemented at each planned unit shutdown. when the plant_. is being brought to cold shutdown condition to enhance impurity hideout return/steam generator cleapup~
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e For each of the above unit conditions, the SGOG Guidelines have been implemented.* -*** To*. ensure system integrity, Action Levels have been establishea*~':for) at power out-of-specification conditions.
Action Level responses are'.suminarized as follows:
Action Level 1:
Return parameter to within normal value range within one week or Action Level 2 is initiated.
Action Level 2:
Reduce power to 30% or less within six hours of initiation of Action Level 2.
Return parameter to within normal value range within 100 hours0.00116 days <br />0.0278 hours <br />1.653439e-4 weeks <br />3.805e-5 months <br /> or go to Action Level 3.
Action Level 3:
Shutdown within six hours after entering Action Level 3.
Station procedures that implement this policy, delineate the management responsibilities and the necessary corrective actions for out-of-specification parameters have been developed..
JWO/jlm/8/0GREN
e TABLE I COLD SHUTDOWN/WET.LAYUP LIMITS STEAM GENERATORS Parameter Normal Value Initiate Action
_pH @25°C Hydrazine, ppm Sodium 9 ppm Chloride, ppm Sulfate, ppm 9.8-10.5 75-200 (1.000
<0.500 (1.000
. TABLE II START-UP LIMITS STEAM.GENERATORS Parameter Value Prior to Value Prior Leaving 200°F Power)5%
pH @25°C Cation Con-ductivity, µS
<2.0 Sodium, ppm
. <0.100
<0.100 Chloride, ppm
<0.100.
<0.100 Sulfate, ppm
<0.100<2>
<0.100< 2>
Silica, ppm
<9.8
<75
)1.000
>0.500
)1.000 to Value Prior to Power )30%
- 8. 5-9.o (1)
<0.80
<0.020
<0.020
<0~020<2>
<0.300<2>
(1)
(2) pH value of )7.0 at North Anna Diagnostic values-for North Anna only at this time; the Action Level time clock begins when the unit is escalated above 30% power.
Parameter Normal Value pH @2S°C 8.5-9.0(1)
Cation Con-ductivity~ µS
<0.80 Sodium, ppm
<0.020 Chloride, ppm
<0.020 Sulfate, ppm(2)
<0.020 Silica, ppm
<0.300 (1)
North Anna 7.0-9.2 TABLE III POWER OPERATION STEAM GENERATORS e
Action Level 1
2
<8.S,>9.0(1)
>0.80
>2.0
>0.020
>0.100
>0.020
>0.100
>0.020
>0.100
>0.300 3
>7.0
>0.500 (2)
The Action Level clock for North Anna on sulfates applies only when the unit is >30% reactor power.
lOCHEM
e 3.b CONDENSER INSERVICE INSPECTION PROGRAM
- Staff*-Recomended Action
.. *.. ~..... -*... _... _.
Licensees*should implement a condenser inservice inspection program.* The program should be defined in plant specific safety-related procedures and include:
- 1.
- Procedures to implement. a condenser_ inservice inspection program that will be initiated if condenser leakage is of such a magnitude that a power reduction corrective action. is required more than once
- per_ three month period; and is required more than once _ per three month period; and
- 2.
Identification and location of leakage source (s); either water or air; 3 *-
Methods of repair of leakage;
- 4.
Methodology for determining the cause{s) of leakage;
- 5. -
A-preventive maintenance program.
Reference Section 2.6 of NUREG-0844
_ Response Virginia Power has implemented a secondary_ side inservice inspection program which. includes inspection of the condensers.
This _program includes eddy current examination of a number of condenser tubes each refueling outage, with. the selection of tubes _ to be examined based on historical records of condenser performance.
As part of the Virginia Power secondary* water chemistry program, secondary chemistry is closely monitored and indications of condenser leakage will result in initiating procedures to identify and correct the source of either water or air leakage.
The _ prpcedures used to identify, locate and repair condenser leaks are appr~ved plant specific procedures, however, our condensers are llOt
~lassifijd safety related.
At *present, Virginia Power has no specific procedures detailing the methodology for determining the cause of condenser leakage.
However, as a matter of practice, the occurrence of condenser
- leakage of such a magnitude that power reduction corrective action is required. will initiate an investigation to determine the cause of the leakage.
As an example, Virginia Power has recently completed an investigation of the causes of an increased incidence of condenser tube leaks at the North Anna Power Station during January and February. 1985.
Based on the results of this investigation, actions (e.g., evaluation and initial engineering) are presently in progress to correct the causes of the tube leaks.
jwr/LM6-ds069
- 4.
PRIMARY TO SECONDARY LEAKAGE LIMIT
~: _;=-~~-.:.. ~:~~~~t~::~~:~~~::~i{;:~~i~;-:.~-:
AlL-:..PWRs:':t,tna-t::-~liave Technical Specifications limits for primary to
. s~cond~ry'~I-;i"~~e rates which are less restrictive than the. Standard Technical Specifications (STS) limits should implement the STS limits.
Reference** *_.
Section 2.8 of NUREG-0844.
Response
The primary to secondary leakage rate limits currently contained in the
- Technical Specifications for all four of the Virginia -Power units are identical to the Standard Technical Specification limits :of ~:c-_gpm through all steam generators not isolated from the reactor coolant _si,~trem and 500*
- gpd through any one steam generator not isolated from the,* reictor cooiant system.
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~'
- 5.
e COOLANT IODINE ACTIVITY LIMIT
- .-:?:'*.:?:.:.-:./
- Staff-Recommended: Action
, pt;Jii.:'th;{. h~v-e\\,Technical Specifications*. limits and surveillance for
- coolant* ;iodine ~-activity that are less restrictive than the Standard
. Technical Specification (STS) should implement the STS limits.
Those plants identified abov*e that also have low head high pressure safety injection pumps should either:
(1) implement iodine.limits which are 20%
of the STS values, or (2) implement _reactor coolant pump trip criteria which wiil ensure that if offsite power is retained, no loss of forced reactor coolant system flow will occur for steam generator tube rupture
- events up to and including the design basis double-.ended break of a single steam generator tube, and implement iodine limits con~istent with the STS.
Reference Section 2.9 of NUREG-0844.
Response
- The coolant iodine activity limits currently contained in the Technical~
Specifications for all four of the Virginia Power units are identical;"t.cJ\\*:-',
or more restrictive than the Standard Technical Specification limits~_,for*'"--
coolant iodine activity.
All four -
Virginia Power - units injection/charging pumps and low head the use of coolant iodine activity Technical Specification values is not have both high-head safety safety injection pumps.* Therefore, limits that are io% of Standard_
applicable to Virginia Power.
JWO/jmj /OM3-18
- 6.
e SAFETY INJECTION SIGNAL RESET 1
- __ Staff~R.ec:oumiended Action
. The coritrol_logic associated with the safety injection pump suction flow path should be reviewed and modified as necessary, by licensees, to minimize the loss of safety function associated with safety injection reset during an SGTR event.
Automatic switchover of* safety* injection pump suction from the boric acid storage tanks (BAST) to the refueling water storage tanks should be evaluated with respect to whether the switchover should be made on the basis of low BAST level alone without consideration of the condition of the SI signal.
Reference Section 2.11 of NUREG-0844.
Response
All four Virginia Power units have high head safety. in:j~ctfon/charging pumps which take a. suction from a Volume Control Tank du.ring normal operation.
The _control logic for the high head safety injection/charging-*'<
- pump automatically transfers suction* from the Volume Control-Tank. to t-n~',-:::;-::'.
- refueling water storage tank on either a low Volume Control Tank level/(.)_r**:
a safety injection signal.
Reset of the safety injection signal wHl not affect the high head safety injection/charging pump suction alignment.
Realignment to the Volume Control Tank can only be restored manually using the motor operated valve controls.
Therefore, the* present control logic associated with high head safety injection/charging pump suction minimizes the loss of safety function associated with safety injection signal reset during.a SGTR event.
JWO/jmj/OM3-18
1' e
e ATTACHMENT 2 VIRGINIA POWER RESPONSE TO NRC STAFF
.REQUEST FOR INFORMATION CONCERNING CATEGORY C-2 STEAM GENERATOR TUBE INSPECTIONS Information Requested The enclosed draft NUREG-0844. Section 2. 2.1. 2 describes certain limitations which the staff believes to be inherent in the present Technical Specification steam generator !SI requirements pertaining to* Category*_ C-2 inspection results.
L_icensees and applicants are requested to provide a description of their current. policy and actions relative to this issue and any r~commendations they have concerning how existing Technical Specification steam generator IS! requirements pertaining to Category C-2 inspection results could be improved to better ensure that. adequate inspections will be performed.
This description should include a response to *the following questions:
- 1.
What factors do, or would, the licensee or -applicant consider;::f.n,*
- determining '(a) whether additional tubes* should be* inspected bey<;>n&:
- what is required by the Technical Specifications, (b) whether :all steam generators should be.included in the inspection program, and (c) when the steam generators.. should be reinspected.
- 2.
To what extent do. these factors include considerat_ion of the degradation mechanism itself and its potential for causing a tube to be vulnerable to rupture during severe transients or postulated accident before rupture or leakage of that tube occurs during normal operation.
Reference Section 2.2 of NUREG-0844.
Response
As was described
- in Section 2. a of Attachment 1, the* current Virginia Power practice is to schedule approximately 714 tubes (21%) per steam generator in two of the three steam generators for eddy current inspection each refueling outage.
This number is based on performing a thorough inspection in those areas of* the steam generator which have been identified as being of generic
_ concern bas.ed on past industry experience for our model steam generators and, in addition, inspecting a sufficient number of randomly selected tubes to indicate overall steam generator condition.
If the steam generators of a particular unit have shown indications of tube degradation during previous inspections, or there are other reasons to believe that increased inspection is necessary, the initial inspection plan will be expanded to include more tubes per steam generator, the thir~ steam generator, or. both addi_tional tubes per steam generator and the third _steam generator.
JWO/jmj/OM3-18
~ <1l
,.:~
e Virginia Power.* has formed an advisory committee composed of members with expei;ieilce_,,.iri~.:~A~~:l,~_t:ry, metallurgy,
- non-dest_ructive examination techniques, operat+/-ons*;;~:"'*i:na:i.:n~i¥ahce, and includes - a representative from* the steam generatori-Dlarii:ifa'ctur.et'. The Committee IS purpose iS tO monitor Steam generator performance: ~t~:Virgi~ia Power and in the industry, and make recommendations to manageinent-*on steam-*generator operation and maintenance.
This committee, for example, recommends the number. __ of tubes and number of steam generators to be inspected during.. the: 11ext inspection.
In formulating'*these recommendations, the committee considers various factors such as_past inspection results, chemistry history, industry experiences, the results of-- industry research programs, vendor recommendations, and unit operating-history.. -It is the intent of Virginia Power to
- have a steam generator inspec*tion-program_ which, - along with
- other efforts - such as the secondary, chemistry-program, reduces the potential for a tube rupture, and also reduces*the-potential for the leakage during-normal operation. It is our
- ' goal to eli~it_1at~- tube degradation in _our steam generators.
_ Consideration of the degradation mechanism plays an _important part in the
- development of steam generator tube inspection plans.
Our currE!:nt plans are
- to'- pull* a number -of sections of tube from one -of the steam generators -*during~:.,
-tlie-upcoming refueling outage at North Anna Unit 1 to perform analys*~sc~/tci}:': _,-;,--
cha,racterize the degradation mechanism that is present.
- While the degradati9ri:,,_.. : -' _
presently occurring_ in these steam - generators is not severe and, in- - qur* -
- judgement,. poses no threat of -causing a tube to be vulnerable to rupttii:e*
during transients or postulated accidents; it is prudent to identify the degradation me_chanism so that appropriate corrective actions may *be initiated.
Virginia Powe_r believes the present Technical Specification steam generator
'-"IS! requirements pertaining to Category C-2 inspection results are -adequate and that the proposed changes are overly restrictive.
Assume, for ~xample, that -Virginia Power had elected to inspe_ct only one of the three steam
-generators during a refueling outage.
The initial 3% sample would consist of 305 tubes.
Under the proposed rule, the discovery of a single tube with an indication of a 40% through-wall defect, a mere 0.33% of the tubes inspected and 0.03% of the total_ tubes in the steam generator, would require that a 100%
inspection be performed in that steam generator and that the other two steam generators be opened up for an ins_pection of 6% of the tubes.
- This, obviously, involves a considerable increase in radiation exposure.
It is :not_ *unc-onimon-to have only one tube in a steam generator that _shows a plugglibl~- indication.
Therefore, it
- would appear much more reasonable. to expand- -the'.trtspection to inspect an additional 6% Qf the tubes in one steam gene:r:ato_:r:_ to verify that the indication is indeed an. anomaly,. rather than immediately expanding to 100% of the tubes and two additional.steam generators given the additional radiat'ion exposure involved.
It is* our view that these changes are not necessary.
However, -if any change to the existing requirements is* felt to be necessary, it may be more r_easonable to go to Category C-3 requirements if the results of the 3rd *sample inspection are categorized as C-2.
JWO/jmj/OM3-18
-~