ML20085K317
| ML20085K317 | |
| Person / Time | |
|---|---|
| Site: | Cooper  |
| Issue date: | 10/25/1991 |
| From: | Horn G NEBRASKA PUBLIC POWER DISTRICT |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| CNSS910350, NUDOCS 9110300302 | |
| Download: ML20085K317 (2) | |
Text
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w Cf.'S S 910 3 50 October 25, 1991 U.S, Nuclear Regulat or y Commi: tion Attentlon:
Docume nt Cont rol lho. ):
Vashington, DC 205 %
Subject.
Plan for Pimetor Pr e< cure Versel lleod Stud Rejtetable Imlication Cooper Nuclear Station NRC Docket No.
50-7/B, License No. 1;PR - 4 6 Gentlemen:
On October 21, 1991, a conference rall was held with membert of yom staff to discurs a rej e c t abl e Imlicat ion in a reactor pressure versel (RPV) nead stud discovered during planned i tu.pec t i on ac t i vi t i er buring t his conf erence call, t he Di st rict: wan request ed t o submi t let ter det ril.ing our plans regardity; t his a
discovery.
The requested information it cont alned he rein.
General Ei
-ic Company Rapid I n f orma t i on Comno.ni ca t l om. Se rvi ce.
Inf or mat ion Letter (RICasL) Number 55 wan inut d on lehruary 1, 1991, to notify affected utilJtles of the RPV bead
.tud cracking phenomenon.
The RICSIL ascrlhed the phenomenon to ntuds memuf ac t ured fiom material with high hardnese enlues l'u r t he r, it re c omn+ nde d that utilitier evaluate the head stud material for installed studn and u l L. a t o n i c. i l 1 *, e:: amine the fivt studn with che h i r,h e n t hardnenn values at the next available oppo rt uni ty.
Tne Cooper Nuclear St at ion (CNS) RPV hr: a t ot al of 5? RPV head et uds lh ad stud numbers 1 t hrough 2i and M we rt f abricated f rom the same heat lot of SAS40 grade l
B24 alloy steel having relatively high hardner-and low charpy V notch impact s trengt h.
Thene head <tuds were scheduled to le ultrasonically examined per h1CS1L Number 55 during t.be IWl Refueling Outage Although HICSl!. Number %
recommended ul t rasonic examitotion of only f ive RPV head st uds wi t h t he highest i
hardners value:
the Dist rict t ook t he more conservat ive appr( ach of planning t o examine all ntuds from the heat lot in question in order to eliminat e any varichler associat ed wi t h t he hardoo< testing of these studs in additlon, a review of CNS inservice Inspection records and AS til: Section *: 1 r"quirements indicat ed that examina t ion of s t ud n.uabers 18 through 35 shoulo also be scheduled for the 1991 Refueling Outar,e CNS shut down for the 1991 Refueling Outage on October 4,
- 1991, On October 7,
t he ult rasonic (:. amination of RPV head stud numbers 1 through n was performed.
The examination wm coeducted using a
O' L vave tecnnique in accordance with Section XI of the ASME Code RP" head st od nun.he r 26 w a r.
tound to have a rejectahle ul t reu.onic indication 1ocat ed 15 incher below the top of the u t tut.
This indicat ion ext ends f or.pproximat ely 18tv of t he t ud c i rc umf e t ( nce, and bre.
an apparent depth of 1.5 i nc her
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A U.S. Nuclear Regulatory Commission October 25, 1991 Page ?
As a result of this discovery, the District plans to pe r t: oi m the following additional.ond(strut tive examinationn on CNS RPV bead st uds prior t o commencing startup from the refueling outage 1.
RPV head st ud numbers 36 through 57 will be subjected to a 0*
h wave ultrn onic examination in accordance witn the requirena nt s of Section XI of the ASME Code.
Stud numbers 36 and 41 through 52 will be examined while installed in the RPV flenge.
St ud nwnbet s 37 through 40 have been removed f rom the RPV flange to f acilitet e ref ueling ac tivit ies and will be examined prior to reinrta11ation.
?.
RPV head stud number 26 will be subjected to a shear wave ultrasonic examination f ro.n the t v.t e ns i ome t e r (eenterline) bore in accordance with Af,ME Section XI Code C,se N-301-1 prior to retroval. Thi s e:.aminat ion has been endorsed by the NRC Regulatory Guide 1 = M7 and will provide adnit lonal indication nizing informent lon.
3.
Threc additional RPV head studs selected from t h( nuspect lot will be subjected to a shear wave ult rasonic exauination in accordance with Code Case N-307-1.
This examination will be petformed while these studn are installed in the RPV flange.
As a final item, the Dist rict intends to either replace st ud number 26 or just i f y another cycle of operation af ter the aforementioned addit ional indicat. ion sizing information is obtained.
Should you have any questions or require any additional information regarding thin submittal, please contact me.
Sincfrely, nu Y U~
G. (st Horn Nuc ear Power Group Manager GPJl/JMM/ya ec:
NRC Regional Office Region IV Arlington, TX NRG Resident Inspector Coopet Nuclear Station
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