ML17037B591
| ML17037B591 | |
| Person / Time | |
|---|---|
| Site: | Nine Mile Point  |
| Issue date: | 04/26/1978 |
| From: | Rhode G Niagara Mohawk Power Corp |
| To: | Lear G Office of Nuclear Reactor Regulation |
| References | |
| Download: ML17037B591 (14) | |
Text
REGULATORY INFORMATION DISTRIBUTION SYSTEM
< RIDS)
DISTRIBUTION FOR INCOMING MATERIAL 50-220 REC:
LEAR G ORG:
RHODE G
K NRC NIAGARA MOHAWK PWR DOCDATE: 04/26/78 DATE RCVD: 05/Oi/78 DOCTYPE:
LETTER NOTARIZED:
NO COPIES RECEIVED
SUBJECT:
LTR i ENCL i FORWARDING DESCRIPTION OF APPLICANT"S PROPOSED INSPEC PROGRAM FOR FEEDWATER AND CONTROL ROD DRIVE NOZZLES FOR THE i979 SPRING REFUELING OUTAGE.
PLANT NAME: NINE MII E PT UNIT i REVIEWER INITIAL:
XJM DISTRIBUTOR INITIAL:~
++++++++~l~~H~++~~+ DISTRIBUTION OF THIS MATERIAL IS AS FOLLOWS BWR FEEDWATER NOZZLES/SPARGERS OR CONTROL ROD DRIVE RETURN LINE NOZZLE (DISTRIBUTION CODE A024)
FOR ACTION:
INTERNAL:
EXTERNAL:
BR CHIE~EAR++W/4 ENCL EG FILE+4W/ENCL NRC P
CHECK4%W/ENCL R MATTU++W/ENCL M HUM~4W/ENCL D EISENHUT>~W/ENCL L SHAO++W/ENCL R BAER>+W/ENCL D DAVIS44W/ENCL LPDR S
OSWEGO NY++W/ENCL ACRS CAT B44W/i6 ENCL K SEYFRIT-IE4+W/2 ENCL OELD~~W/ENCL V STELLO+4W/ENCL C
D SELLERS++W/ENCL J KNIGHT4+W/ENCL K GOLLER4+W/ENCL W BUTLER44W/ENCL EEB+4W/ENCL R SNAIDER+%W/ENCL DISTRIBUTION:
LTR 40 ENCL 40 SIZE: iP+5P
%%%%% 4%%%%% 4% 01.%%4%4 4 %%4 %4%%% NF%%%%%%
THE END CONTROL NBR:
78i22008i 7
~
I,
~
I t
II II
, II
NIAGARAMOHAWKPOWER CORPORATION NIAGARA ~
MOHAWK 300 ERIE BOULEVARD. WEST SYRACUSE. N. Y. I3202 April 26, 1978 Director of Nuclear Reactor Regulation Attn:
Mr. George Lear, Chief Operating Reactors
'ranch g3 U.
S. Nuclear Regulatory Commission Washington, D.
C.
20555 Gentlemen:
V S IIII~EISUIATDyg DO~SSIOII MSCuCI gP Re:
Nine Mile Point Unit 1 Docket No. 50-220 DPR-63 Pursuant to your letter of August ll, 1977, provided herewith i's a description of our proposed inspection program for feedwater and control rod drive nozzles.
The inspection program will consist of ultrasonic examinations on the feedwater nozzles with the sensi-tivity to detect cracks as small as 5/64 inches in depth.
In addition, an underwater visual examination of accessible areas of the spargers, flow baffles and supports will be performed.
The only examination to be done on the control rod drive hydraulic return nozzle will be an underwater visual of accessible areas.
A final report will be submitted following completion of the refueling outage.
Very truly yours,
~)g>>g t,
I' NIAGARA MOHAWK POWER CORPORATION
~ggIa~
9~4KLI I ~
Gerald K. Rhod Vice President System Project Management MGM/szd Attachment 7SS220Oa>
gozg s<
I/g
I' k
NINE MILE POINT UNIT 1 FEEDWATER AND CONTROL, ROD DRIVE NOZZLE INSPECTION PLAN FOR SPRING 1979 REFUELING OUTAGE
~ t ~
I
% 1,
Back round A.
Feedwater Nozzles During the Spring 1977 refueling, the feedwater,spargers were removed and the Sour nozzles were inspected.
The cladding and a thin layer -of base.'metal were removed using a specially developed, remote-controlled single point boring machine.
Cracks of up to approximately 1.5 inches total depth (including clad) were identified and removed from one nozzle and up to 1.3 inches in another nozzle.
The resulting nozzle configurations were analyzed. and were found to be satisfactory under Section XI of the ASME Code.
.Replacement spargers were installed and the Station was subsequently returned. to service.
The replacement sparger design provides assurance of reducing the high frequency'emperature cycling.
Additionally, the effectiveness of the thermal sleeve in insulating the nozzle from normal plant thermal transients is considerably improved.
The main, features which provide these improvements are:
1.
The replacement spargers incorporate interference fit thermal sleeves and piston ring seals to minimize bypass leakage.
2.
The replacement sparger design incorporates double flow baffles which prevent mixing of hot recirculation water with cooler feedwater on. reactor vessel and nozzle surfaces.
These flow baffles seat against machined conical surfaces in the face of each nozzle with a significant preload.
The preload, double baffle, and positive seating arrangement provide assurance of a good seal to the vessel.
In addition, leakoffs are provided. in each baffle to direct any leakage away from the nozzle surfaces.
Either the piston ring seals or the flow baffles are considered sufficient to prevent appreciable thermal cycling in the feedwater nozzles.
These features in conjunction with removal of stainless steel cladding assure that nozzle degradation will not occur.
During the Spring 1977 refueling, ultrasonic examinations~~2 of the nozzles were performed by the reactor manufacturer.
The results were correlated with the actual defects.
As a result of. this and other work, an ultrasonic examination procedure is now available. to detect significant future feedwater nozzle cracks.
A
B.
Control Rod, Drive Nozzle The control rod drive hydraulic system return nozzle was also inspected to determine, whether similar, cracks had developed.'in the nozzle.
The inspection involved destructively removing the nozzle.safe end and =thermal
- sleeve, so that liquid penetrant examination could be performed on the nozzle.
No nozzle cracks were identified.
The nozzle safe end was also PT examined, and three cracks were foundin the inside bore.
These cracks were metallurgically examined and. were found to be stress corrosion cracks, attributable to the safe end's furnace sensitized type'04 stainless steel material.
.Accordingly, solution heat treated'ype 316 stainless steel with low carbon was used. for the replacement safe end and thermal sleeve.
This, material provides substantially increased resistance to stress corrosion cracking.
II.
Ultrasonic Testin Plan A.
Feedwater"Nozzles During the Spring 1979 refueling outage, Niagara Mohawk Power Corporation will perform ultrasonic testing on all feedwater nozzles at Nine Mile Point Unit 1.
Testing will be performed by General Electric in accordance with their ultrasonic test procedure des'cribed in NEDE-21821, "Boiling Water. Reactor Feedwater Nozzle/Sparger. Final Report."
In addition to.the. ultrasonic examination, an underwater visual examination'will be performed on, all accessible areas of the spargers, flow. baffles and.supports.
General,Electric's ultrasonic techniques are capable of detecting, cracks as small as 5/64 inches deep into base metal when. cladding has been removed, from the inner radius. and bore of the feedwater. nozzle.
These ultrasonic techniques and procedures.'for feedwater nozzle inner radius and bore examination were qualified, at the Nine Mile Point reactor.
'General Electric personnel examined the southeast nozzle. before. clad.removal, where multiple cracks were found, by. liquid penetrant techniques.
Ten areas were identified fro'm repair records'as sites where cracks had penetrated" into the.low alloy, steel forging at least 7/32,inches.
The significant cracks (greater than 7/32 inches deep) were detected and evaluated as cracks, by the ultrasonic te'chnique, which has a sensi-tivity of 5/16 inches on. clad nozzles.'nalyses indicate that a future crack of at least 1/2 inch in depth can be tolerated in any location. of a feedwater nozzle.
Repair of such a crack by grinding could be accommodated within the criteria previously established.l Adequate margin between allowable crack depth and ultrasonic sensitivity is thus available to assure ultrasonic detection of any crack before it reaches the maximum allowable depth.
0
'b
II.
A.
Feedwater Nozzles (Continued)
Should indications of, cracks. be: found in, any, nozzles during the Spring 1979 testing sparger removal,and dye penetrant tests will be. performed, on those nozzles.
If cracks are found by penetrant testing in, any nozzle, sparger removal and penetrant testing will be performed on'all nozzles.
B.
Control Rod. Drive Nozzles During, the Spring, 1979. refueling. outage, we will perform an underwater visual examina'tion of all accessible areas of the control rod drive,'hydraulic return nozzle.
This examination
's based. on the results of. the previous;inspection where no nozzle cracks were found.and the furnace sensitized stainless steel. safe end and thermal, sleeve were replaced with material resistant to stress corrosion cracking.
0 C
REFERENCES 1
"Summary Report. - 1977 Feedwater Sparger Replacement Project-Nine Mile Point Nuclear Station Unit 1" dated November 16, 1977.
2 NEDE 24047 "Ultrasonic Examination of Feedwater Nozzle Inner, Radius and"Bore at Nine Mile Point Unit 1."
1 r