ML20126B412
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UNITED STATES
, NUCLEAR REGULATORY COMMisslON 3 ,g RE3!ON 1 B E -
631 PAME AVENUE 0, ,, KING OF PRUSS6A, PENNSYLVANIA 19406 k*****g April 8,1982 R. R. Keimig, Chief, Projects Branch No. 2 MEMORANDUM FOR:
Division of Project and sident Programs THRU: A. N. Fasano, Chief @
Three Mile Island Section[ -
D. R. Haverkamp, Senior Resident Inspector (TMg- M Three Mlle Island Section FROM:' F.'I. Young, Resident Inspector (TMI-1)
Three Mile Island Section
SUBJECT:
ONCE THROUGH STEAM GENERATOR (OTSG) EDDY CURRENT INSERVICE INSPECTION At present, the THI-1 Technical Specifications require that Eddy Current Testing (ECT) inservice inspection (ISI) be performed on the portion.of the tube that forms the. boundary between the primary and sec6ndary coolant systems. In the case at Till-1 OTSG's, a severe corrosion ' attack, affecting 'between 8,000 to 10,000 tubes out of 31.000, has occurred in the upper tube sheet. This is an area not requiring ECT inservice inspection.
Periodic ISI of OTSG tubes are essential to monitor their integrity for safe operation. The primary safety censideration for degraded tubes at any location is that they retain adequate structural integrity without excessive leakage for the full range of normal and postulated accidents.
ECT is the primary means for performing tube inspections.
I ' '
In light of the severity of the problem at THI-I (a case where approximately one third of all OTSG tubes are in a degradated mode), the required ISI l program for TMI-l is unacceptable (see enclosure 1 with 6 attachments) sinca ECT in the tube sheet area is not required. Licensee has been l looking at the tube sheet area despite ECT requirements.
Enclosed are the details for the technical concern addressed above.
!. Your review of the recommendations in Enclosure 1 is requested for Further, this information should be forwarded to IE '
forwarding to NRR.
Headquarters for dissemination to all licensees with similar TS in the form.of an "Information Notice".
l F.I. hung l . ResidNt Inspector (THI-1) i Three Mile Island Section l
Enclosure r As Stated
, g5061 g 6 850125 DETJEN84-997 PDR
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- Facility Three Mile Island Unit 1 ' Docket No . 50-289
. Dete of Event November 25, 1981 Inspection (or oth'er Report 289/81-32/82-01
- 1. Brief Description of Issue (Not required if included in supporting data)
(See Attached Sheet)
- 2. How Found (If appropriate)
See Attachment 6 GPU Licensee Event Report
- 3. Why Considered Potentially Generic (i.e. - reference applicable criteria or give reason) .
Area of OTSG tube degradation is not addresse,d in the THI Unit 1 Technical Specifications .
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- 4. I ' F. Young A. Fasano Region Originator Section Chief / Branch Chief ,
,. 5. ,J0ther Re.ston Reportino That The Problem Has Also Been Identified By Them Region ' . Chief Reporting _, Docket No. ..
p 5 Evaluation by Headquarters C
Bulletin / / Circular / / Information Notice /___/
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Other / / ,
No further action required / / .
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- 1._ (1) TMI Unit 1 Technical Specifications requires that only the area .
.between the lower face of the upper tube sheet and upper face of l the lower tube sheet be inspected using standard eddy current .
testing. Ninety percent of the tube problems found in Unit 1
. OTSG's are.in the area known as the roll transition in the upper r tube sheet (see' Attachment 1 and 2).- Due to the definition eddy current testing requirement which is standard throughout the
- industry,'the area in question is not addressed in the Technical 6 Specifications (see Attachment 3). In the: inspector's judgement this concern should be evaluated to determine if OTSG eddy current
- ' program should be redefined and amendment made to Technical-Specifications, i
(2) With the use of a standard differential addy current probe
-(industry standard), a signal defection is normally generated.in !
the roll transition zone. This signal from roll transition zone ' -
is normally ignored due to the inability of.:the standard probe ,
to distinguish between roll-and/or a fault. In the case of TMI-1, !
' the licensee did take the time to look at this area. GPU with ;
the aid of Conam (Eddy Current Contractor) and Zetec'(Eddy Current i
. Vendor) developed a new probe comonly known as 4 by 1 absolute ;
t pancake probe. This probe has been very suc:essful in determining l -faults in the transition zone as compared t) metallurgical data obtained. In the inspector's judgement, th roll transition zone- !
is normally overlooked by the standard probe and due to the severity of the problem'at TMI-1, this item should be evaluated for its !
. safety significance (see Attachment 4 and 5). .
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TMI-1 Tube Sheet ',
Detail (Typ.)
.051" MIN.M 4 i' .6 3 5" P.EF.
.051" MIN. ,137 _ '
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.875" + .0 03" l' o ., 6 A e.q <- > -
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, + w. TYP. TUBE P ATTERN [
.625" TUBE 0.0. X .034" ,
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< r , MIN.003 of projected. tube defects.
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.435" DIA. HOLE
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- sum?.Y OF FUMECTED DEFECTI'tE TUBES - 3/2/82
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Loca- .
tion Length Metallurgical Summary ECT Summary .
A ** . 312" N3 information - this section No information due to ECT drilled out during sample signal distortion at tube removal. exit.
3 '".125" ' 9 of 9 tube samples have cir- Limited information due to cumferential cracks 95I to ECT signal. distortion at tube ~
100% thru wall and lof 9 also -
exit, had several longitudinal cracks. -
C ca 1" Circumferentici cracks on 3 Limited information due to
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(Rolled tube samples. ECT signal distortion by roll
- ransition. Some indications Section) oa sample of tubes done with -
- ab.tolute pancake probe.
3 # .250" Circumfeccatial cracks on 5 12,770 tubes have distor'ted (Roll *
. tube samples. ECT s.'nnals in this area --
Transition) We project about 7,000 tubes will have circumferential cracks. Additional ECT in March / April to define status.
E <- 7 " Circumferential cracks -- 2,227 defcetive tubes.
confirmed. ,
F e- 5" Circumferential cracks --123 defective tubes.
confirmed. -
C e- 10* Circumferential cracks e-67 defective tubes.
confirmed.
M All tubes Circumferential cracks e-68 defective tubes.
below UTS confirmed. . .
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~TMI OTSG TUBES WITH DEFECT DISTRIBUTION 3 2,000_y . ..: - 2 i I .-I , I ,I , , I , i I , 1
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Uj ] 3 67 ! / [ [ 12,770 [/[/[/ 111,137 k
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/ - US+20 657
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US+15 166 ..
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US- 6 US- 7 .
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_ TUPES WITH MULTIPLE INDICATIONS ARE CATEGORIZED.INTO THE ZONE FURTHEST l
FROM THE TUBE SHEET FACE. 3/5/82 l
Attachment 3 -
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4.19 OTSG TUBE INSERVICE INSFECTION ,
Applicability This Technical Sppcification applies to the inservice inspection of the OTSG tube portion of the reacter coolant pressure boundary. .
Objective The objective of this inservice inspection program is to provide assurance of continued integrity of thg tube cortion of the Once-Through Steam Gen _e_ratorA..while at the same time minimizing radiation Eptnrife to personnel in the performance of the inspection.
Specification .
Each steam generator shall be demonstrated OPERABLE by performanc'e 2-of the following augmented inservice inspection program and the -
requirements of Specification 3.1.6.3. -
4.19.1 Steam Generator Sample Selection and Inspection Methods
- a. Each steam generator shall be determined OPERABLE during [
shutdown by selecting and inspecting at least the minimum -4 number of steam generators specified in Table 4.19.1 at the ].
frequency specified in 4.19.3. ,
- b. Inservice inspection of steam generator tubing shall include =
nondestructive examination by eddy-current testing or other 4 equivalent techniques. The inspection equipment shall be calibrated to provide a sensitivity that will detect defects _
with a penetration of 20 percent or more of the minimum __
allowable as-manufactured tube wall thickness. 3 4.19.2 Steam Generator Tube Sample Selectior and Insoection The steam generator tube minimum sample size, inspection result ;
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classification, and the corresponding action required shall be as specified in Table 4.19.2. The inservice inspection g
of steam generator tubes shall be performed at the frequencies e specified in Specification 4.19.3 and the inspected tubes _
shall be verified acceptable per the acceptance criteria of Specification 4.19.4. The tubes selected for E a
^
4-77 k-Amendment'No.k7 k
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. a.
Each inservice inspection shall include et least 3% of the total nu=ber -
of tubes in all steam generators; the tubes selected for these inspections shall be selected on a random basis except:
- a. The first sample of tubes selected for each inservice inspection (cubsequent to the preservice inspection) of each steam generator shall include:
- 1. All nonplugged tubes that previously had detectable vall penetrations (>20%).
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- 2. At least 50% of the tubes inspected shall be-in those areas where experience has indicated potential .proble=s.- :
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5 3. 'A tube inspection (pursuant to Specification 4.19.4.a.8)
. shall be performed on each selected tube. If any selected tube doe.s not permit the passage of the eddy
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- current probe for a tube inspection, this shall be recorded and an adjacent tube shall be selected and subjected to a tube inspection.
- 4. Tubes in the following groups may be excluded from the first random sample if all tubes in a group in both steam generators J are inspected. No credit will be taken for these tubes in l
. meeting minimum sa=ple size requirements. .
(1) Group A-1: Tubes within one, two or three revs of the ,
E open inspection lane.
(2) Group A-2: Tubes having a drilled opening in the 15th @
support plate. -(
- b. The tubes selected as the second and third samples (if required by Table 4.19.2) during each inservice inspection may be subjected to a partial tube inspectier provided: :
- 1. The tubes selected for these second and third samples include the tubes from those areas of the tube sheet array where tubes with imperfections were previously found. *
- 2. The inspection includes those portions of the tuies where
- imperfections were previously found. , ;
e The results of.each sample inspection shall be classified into one of the '
following three categories:
Catecorv Inspection Results -
. i C-1 Less than 5% of the total tubes inspected in a steam -
generator are degraded tubes and none of the inspected :
tubes.are defective. a
- C-2 One or more tubes, but not more than 1*' of the total L tubes' inspected in a steam generator are defective, b or between 5% and 10*: of the total tubes inspected ;
are degraded tubes. y Amendment No. 47I ;-78 s--
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~C-3' horo then 10% of tha totc1 tubts.inspectcd in a t,.- .
a stsam gsnsrctor.oro degredsd tubse or core then
. 1% of tha inspscted tubss aro defective.
NOTES: '(1) In all inspections, previously degraded tubes must-exhibit significant (>10%) further wall penetrations
, to be' included in the above percentage calculations.
(2) Where special inspections are performed pursuant to 4.19.2.a.4, defective or degraded tubes found as a result of the inspection shall be included in determining the Inspection Results Ch egory for that special inspection but need not be included in determining the Inspection Results-Category for the general steam generator inspection.
4.19.3 Inspection Frequencies The required' inservice inspections of steam generator tubes shall be performed at the following frequencies:
- a. The first (baseline') inspection was performed af ter 6 effective .
full power months but within 24 calendar months of. initial criticality. The subsequent inservice inspections shall be performed not more than 24 calendar months after the previous
' inspection. If the results of .two consecutive inspections for a given group of tubes
- encompassing not less than 18 calendar months all fall,into the C-1 category or demonstrate that' previously observed degradation has not continusd and no additional degradation has occurred, the inspection interval .
for that group may be extenced to a maximum of once per 40 months.
- b. .If the results of'the inservice inspection of a steam generator conducted in accordance with Table 4.19-2 at 40 month intervals for a given group of tubes
- fall into Category C-3, the inspection frequency for that group shall be increased to at least once per 20 months. The. increase in inspection frequency shall apply until the subsequent inspections satisfy the criteria of ,
Specification 4.19.3.a; the interval may then be extended to a maximum of once per 40 months.
- c. Additional, unscheduled inservice inspections shall be performed l on each steam generator'in accordance with the first sample, ,
i inspection specified in Table 4.19-2 during the shutdown
- j. subsequent to any of ,the following conditions:
- 1. Primary-to-secondary tubes leaks (not including leaks originating from tube-to-tube sheet welds) in excess of the limits of Specification 3.1.6.3.
l p = *A group of tubes means: (a) All tubes inspected pursuant to 4.19.2.a.4, or l
= (b) All tubes in a steam generator less those
! inspected pursuant to 4.19.2.a.4.
f'- '
. 4-79 Amendment No. 47'
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. 2. A seismic occurrence greater than the Operating Basis
. Earthquake.
A loss of, coolant accident requiring actuation of the 3.
engineering safeguards, or
- 4. A major main steam line or feedwater line break.
- - 4.19.4 -Acceptance Criteria a.. As used'in this Specification:
- 1. Imperfection means an exception to the dimensions,'
finish or contour of a tube from that required by fabrication drawing' or specifications. Eddy current l
. testing indications below 20% of the nominal ~ tube wall. thickness, if detectable, may.be considered as imperfections.
- 2. Degradation means a service-induced cracking, vastage, wear or general corrosion occurring on either inside ,
or outside of a tube.. ,
L
- 3. Degraded Tube means a tube containing imperfections
,20%
> of'the nominal wall thickness caused by degradation.
)'
- 4. % Degradation means the percentage of the tube wall .
thickness affected or removed by degradation.
- 5. ' Defect means an imperfection of such severity that it-
-exceeds the plugging limit. A tube containing a defect is defective.
- 6. Plugging Limit means the imperfection depth at or '
beyond.which the tube shall be. removed from service because it may become unserviceable prior to the next inspection and is equal to 40% of the nominal' tube wall thickness, unless higher limits are shown to be acceptable by analysis andcapproved by the NRC.
- 7. Unserviceable describes the condition of a tube if,it-leaks or contains a defect large enough to affect.its structural integrity in the event of.an Operating Basis Earthquake, a loss of coolant accident, or a steam line or feedwater line break as specified in 4.19.3.c, above.
- 8. Tube Inspection means an inspection of the steam 47 generator tube from the bottom of the upper tubesheet completely to the top of the lower tubesheet, except as permitteo by 4.ly.2.b.z, above. .
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4-80
.AmendmentNo.$7
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- b. 'The steam generator shall be determined OPERABLE after completing the corresponding actions (plugging including all tubes exceeding the plugging limit and all tubes l containing throughwall' cracks) required by Table 4.19.2.
4.19.5 Reports
- a. Following the completion of. each inservice inspection of steam generator tubes, the number of tubes plugged in each
, steam generator shall be reported to the NRC within 15 days.
- b. The complete results of the steam generator tube inservice inspection shall be reported to the NRC within 3 months following completion of the inspection. This report shall include:
- 1. Number and extent of tubes inspected.
- 2. Location and percent of vall-thickness penetration for -
each indication of an imperfection.
3.- Identification of tubes plugged. ,
- c. Results of steam generator tube inspections which fall into Category C-3 and require prompt notification of the NRC shall be reported pursuant to Specification 6.9.2 prior to resumption of plant operation. The written followup of this report shall provide a description of investigations conducted to determine cause of the tube degradation and corrective measures taken to prevent recu'rrence.
Bases The Surveillance Require =ents for inspection of the steam generator tubes ensure that the structural integrity of this portion of the RCS will be maintained. . .
4-81 .
Amendment No. -
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. . Attachment 4 -
p@Kt s, January 27, 1982 f SECY-82-35
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POLICY ISSUE- :-
(Information)
FOR: The Commission FROM: -
William J. Dircks Exe'cutive Director for Operatio'ns
SUBJECT:
TMI-l STEAM GENERATOR' PROBLEM-PURPOSE: To provide the Commissioners wit,h infonnation concerning
' the status of the tube leak problems on the TMI-l steam generators. -
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DISCUSSION: . At the Commission briefing on.TMI-l status held on .
December 21,1981, the nature and extent of the leaking
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steam generator tubes at TMI-l was discussed. At that time, it was stated that at least two months were needed foi the utility to identify the causes and correct the problem. -
On January 25, 1982, at the staff's rec.uest, General -
Public Utilities (GPU) presented an upcate on this pr'oblem.- The licensee has nearly completed ' eddy current testing (ECT) of all tubes in both steam generators. To date, appitximately 2250 tubes have been identified to
! have defects. There are also indications on many other
' tubes, which will require additional testing using a more sensitive probe to verify the presence of defects. At the present time, it is estimated that several thousand additional tubes may have' defects needing repair.
l .
L The licensee has stated that virtually all defects are l located in the upper tube sheet area of the tube. Based l
'on extensive metallography tests on two tubes, there is now evidence that the mechanism appears to be intergranular l attack from the primary side, instead of the secondary L -
side, resulting in the development of very tight circum-ferential cracks. There is evidence of sulphur and chlorine impurities in every defect on the'two removed tubes examined..
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Contact:
R. Jacobs, DL/NRR 49-27471 ~-..
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The Commission .
DISCUSSION: -The, licensee is conducting a broad based program in the (continued) areas of eddy current testing, tube failure analysis, -
accident analysis and tube repair techniques. The licensee preseritly estimates that it will take at least six months to resolve the problem.
The staff has some additional areas of concerns related' to the steam generator degradation problem at TMI-1.
.. A corrosive agent may exist, or have existed, in the reactor system at TMI-l which could have corroded other: primary pressure boundary materials.
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. The plugging of. large groups of tubes as an interim solution may not be a viable solution without signi-
- ficant derating to avoid the erosion-corrosion effects of moisture droplets that can impinge on
. the.superheated portion of the tubes. The licensee is having thermal hydraulic studies performed to evaluate this concern. .
' The staff and its ' consultants will independently review eddy current data, operational chemistry data, suscepti-bility. of other primary system materials and results
.,' of thermal hydraulic analyses. Additionally, staff .
consultants will be visiting. Battelle and B&W.(labs used by GPU) to review methods and results of tube
. examinations..
i A copy of a news release from GPU Nuclear Corporation l- dated January 25, 1982 regarding the THI-l steam generator reports is enclosed for your information.
? /
l William . Dircks Executive Director for Operations
Enclosure:
As Stated
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Post O! fica Brx 480 - 2
- Middletcwn. PA 17057 .
'17 946 8197 , . Public Inforrnation Services x Further information .
Centact: John Fidier - -
For Release: Imediately Date: January 25. 1982 Ird
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- SE' STEAM'. GENERATOR REPAIRS 'FOR THI! UNIT 1 SR 3 F ,
Middletown, PA - Officials of GPU Nuclear Corporation said today that repairs to steam generator tubes at Three Mile Island Nuclear Station's Unit 14eactor prob '
ably will result in at least a six month delay in the readiness of the reactor for restart. .
Recent testing of steam lienerator tubes indicates the repa, irs,will be sub-t ,
stantially more extensive than initially anticipated, Company officials explained.
The Company had expected:the unit to be ready for restart b'y the end of Febru,ary, subject to permission from the U.S. Nuclear Regulat'ory Comission. - -
Additional testing and evaluation will be required before the full ext 2at of the steam generator problem is known. Company officials met with members of the NRC staff .to, day to brief them on the inforrration developed to date.
Company officials said it was encertain whe'ther the timing for restart of Unit 1 would be controlled by the steam generatdr problem or by a recent order of the .U.S. Court of Appeals, if allowed to stand. The Court has directed the NRC to make an envirorimental assessment! of psycholpgical stress that might result from return of Unit 1 to operation. -
The Unit I reactor was shut down for refueling at the time of the March 28, 1979accidentthatdamagedTMIdnit2. T111 Unit 1 remained closed for modificatfor3s, i
and for restart hearings before the NRC's Atomic safety Licensing Board..
Inspections and tests during the 21-years after the accident did not reveal
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any abnormal conditicas, compiny officials said. In(eed, the hot f6nctional tests
-t . ore- .
L -2 .* January 25,1982 q 3.
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, condu~cted in late sunrner.showed no evidence of the problem. It was not until a l
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'rcpressurization of the system in November that small leaks were discovered in the tubes in both Unit 1 s.team g~enerators. . J:
.T,he tubes normally carry ho,t, pressurized radioactive water from the reactor.
This water causes non-radioactive water outside the tubes to turn'to steam. This
, steam' turns the turb~ine, which .in turn spins the generator to make electricity. ,-, . ('
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,. . The tube leaks Sa~v' e resu'lted in minor additions to the routine levels of
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. radioactive releases fiom the plant. All releases ha,ve been.well within federal env.ironmental technical specifications. .
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,( The two steam generators are about 70 feet Mgh, and each contains approxi- -
'.r.dtely ...~.
15,500 tube,s. which a.re 52 feet long and five-eights of an inch in diameter.
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. The tubes are made of .inconel, an alley of iron, chromium and nickel. Their walls - -
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. are . . .three . . h.undredths of a'n. inch thick. .
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<. "ina. pre.ssurizedt:ater actor, such as Unit 1, the steam generators are'
., 'r,.y.- ,
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. .where the. plant's radioactive "primry system" and its non-radioactive " secondary
. . . . -r . . ..
si' stem" pass each other to exchange heat. The steam generators adjoin the reactor ' '
.w .. . . .. . . .-
-in the Unit 1 containment building. Norcaliy, there is no' radioactivity in the
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". secondary system.". .. ,. >~
' [, The *Atomic Safety ,and L.icensing Board has concluded extensive hearings into i
the restart of 1141-1, and has advised the NRC that the. management of GPU Nuclear .' ,
Corp: ration, technical modifications to the plant, and plans for emergency prepared-ness are sufficient to assure that Unit 1 can be restarted without endangering the
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health and safety of the public. .
A special inquiry into cheacing on NRC operator examinations has also been concluded, and a final report from the special hearing master is expected shortly.
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