ML20137G225
| ML20137G225 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/22/1985 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML20137G219 | List: |
| References | |
| NUDOCS 8508270243 | |
| Download: ML20137G225 (9) | |
Text
o ENCLOSURE 1 SAFETY EVALUATION ON REQUESTS FOR RELIEF FROM SECTION XI CODE REQUIREMENTS NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE NUCLEAR POWER STATION, UNIT 1 DOCKET N0. 50-245 I.
BACKGROUND INFORMATION 10 CFR 50.55a requires that inservice examinations and tests of Class 1, 2, and 3 systems and components of a boiling or pressurized water-cooled nuclear power facility be performed in accordance with the requirements of the applicable edition and addenda of Section XI of the ASME Co'de unless it is determined by the licensee that con-formance with the requirements is impractical for the facility and
.~s supporting information is submitted to the Commission for evaluation.
If the necessary findings are made, the Commission may grant relief from the requirements and/or may impose alternative requirements giving due consideration to the burden placed upon the licensee by imposition of the requirements.
By letter dated February 26, 1985, Northeast Nuclear Energy Company (NNECO) requested relief from the surface examination requirement for Class 1 and 2 piping welds and the volumetric examination requirement for the Isolation Condenser nozzle-to-vessel welds at Millstone Nuclear Power Station, Unit 1.
These examinations,are required Fy the 1980 Edition, Winter 1980 Addenda of Section XI, the applicable Code Edition and Addenda for the Inservice Inspection Program at Millstone Unit 1.
8508270243 850822 PDN ADOCK 05000245 P
Pursuant to 10 CFR 50.55a(g)(6)(i), the requests and supporting informa-tion have been reviewed and evaluated.
The necessary findings could not be made to grant relief from the examination requirements as requested.
The staff's evaluations and conclusions are given in this report.
II.
REQUESTS FOR RELIEF FROM SECTION XI REQUIREMENTS A.
Relief Request #1 - Relief is requested from performing surface examination on circumferential and longitudinal austenitic pressure retaining piping welds, nominal pipe size > 4 inches, when they are volumetrically examined in accordance with the
- Northeast Utilities Ultrasonic Examination Procedure for Intergranular Stress Corrosion Cracking (IGSCC) NU-UT-6.
CODE REQUIREMENT (ITEMS B9.11 and 89.12, EXAMINATION CATEGORY B-J)
Surface and volumetric examinations shall be performed on circum-ferential and longitudinal welds in piping with nominal pipe size > 4 inches.
The welds examined shall include the following:
1 (a) All terminal ends in each pipe or branch run connected to vessels; (b) All terminal ends and joints in each pipe or branch run connected to other components where the stress levels exceed the following limits under loads associated with specific seismic events and operational conditions:
(1) primary plus secondary stress intensity range of 2.4S, for ferritic steel and austenitic steel; (2) cumulative usage factor U of 0.4.
- (c) All dissimilar metal welds between combinations of:
(1) carbon or low alloy steels to high alloy steels; (2) carbon or low alloy steels to high nickel alloys; (3) high alloy steels to high nickel alloys.
(d) Additional piping welds so that the total number of cir-cumferential butt welds (or branch connection or socket
, welds) selected for examination equals 25% of the cir-cumferential butt welds (or branch connection or socket welds) in the reactor coolant piping system.
This total does not include welds excluded by IWB-1220.
These additional welds may be located in one loop (one loop is currently defined for both PWR and BWR plants in the 1980 Edition).
2 The initially selected welds shall be reexamined during each inspection interval.
3 Includes essentially 100% of weld length.
4 The examination includes at least a pipe-diameter length but not more than 12 in. of each longitudinal weld intersecting the circumferential welds required to be examined by Examination Categories B-F and B-J.
5 For welds in carbon er low alloy steels, only those welds showing reportable preservice transverse indications need be examined for transverse reflectors.
LICENSEE'S BASIS FOR REQUESTING RELIEF Figure IWB-2500-8 of Section XI requires volumetric examination of the bottom one-third of the weld and a surface examination of the weld plus 1/2 inch of base material on each side of the weld.
The " Northeast Utilities Ultrasonic Examination Procedure for Intergranular Stress Corrosion Cracking (IGSCC) NU-UT-6" requires volumetric examination of the full weld volume and a minimum of 1 inch of base material on each side of the weld when practical and with stringent recording criteria beyond Section XI requirements.
For example, NU-UT-6 requires recording all indications determined not to be screen noise and not to be 0.D.
geometry.
NU-UT-6 meets the requirements of I&E bulletins 82-03 and 83-02.
NU-UT-6 full weld volume examination will ensure weld surface integrity without an additional surface examination. ManRem reduction (ALARA) has been considered for this relief request. Weld preparations and actual surface examination time required in a radiation area by personnel can be reduced by an approximate 50% factor with the elimina-tion of this surface examination.
LICENSEE'S PROPOSED ALTERNATE EXAMINATION Perform a full volumetric examination in accordance with the " Northeast i
Utilities Ultrasonic Examination Procedure for Intergranular Stress Corrosion Cracking (IGSCC) NU-UT-6" on austenitic pressure retaining circumferential and longitundinal piping welds, nominal pipe size > 4 inches.
i
STAFF EVALUATION The impracticality of the surface examination requirement cannot be determined by the supporting information provided by the licensee.
The Northeast Utilities ultrasonic test procedure, NU-UT-6, was used primarily for detection of IGSCC and is proposed as an alternative to the the surface examination requirement. This procedure can be accepted as an alternative only if it is-demonstrated to be equivalent or superior to the surface examination requirement and the full volume of weld and base metal is scanned.
B.
Relief Request # 2 - Relief is requested from performing volumetric examination on the Isolation Condenser nozzle-to-vessel welds.
CODE REQUIREMENTS (Item C2.21, Examination Category C-B)
Surface and volumetric examinations shall be performed on nozzle-to-shell welds at terminal ends each inspection interval.
LICENSEE'S BASIS FOR REQUESTING RELIEF Weld joint configuration does not permit a meaningful ultrasonic examination of the entire length of the nozzle-to vessel weld.
(see.TJ:00 Drawing #25202-20338 sheet 51 attached).
Half vee ultrasonic examination does not inspect the weld volume.
Full vee examination is not possible due to the attenuation caused by the stainless steel cladding on the nozzle and vessel I.D.
Radiography is not practical since the film would have to be located inside the nozzle which is not normally accessible.
I.D. accessibility requires grinding out of the diaphragm seal weld on the access manway and re-welding.
LICENSEE'S PROPOSED ALTERNATE EXAMINATION Perform a surface examination on the nozzle-to-vessel weld 0.D. each inspection interval, and perform a surface examination of the weld I.D. when the I.D. surface is made accessible.
The I.D. surface is not made accessible during normal refueling outages.
STAFF EVALUATION The weld joint configuration makes ultrasonic examination of the entire volume required by Section XI impractical to perform.
- However, a lignificant portion of the weld volume can be examined and should be examined to the extent practical in view of service induced flaws experienced in the other welds and base metal in the Isolation condenser piping.
The staff, therefore, requires that surface examination and volumetric to the extent practical be performed in order that adequate assurance of the structural integrity of the nozzle-to vessel welds is maintained.
C.
Relief Request # 3 - Relief is requested from performing surface examinations on circumferential and longitudinal austenitic pressure retaining piping welds >1/2 inch nominal wall thickness when they are volumetrically examined in accordance with the Northeast Utilities Ultrasonic Examination Procedure for Intergranular Stress Corrosion Cracking (IGSCC) NU-UT-6.
CODE REQUIREMENTS (Items C5.21 & C5.22, Examination Category C-F)
Surface and volumetric examinations shall be performed on pressure retaining welds in piping with nominal wall thickness greater than 1/2 inch.
LICENSEE'S BASIS FOR REQUESTING RELIEF Figure IWC-2500-7 of Section XI requires volumetric examination of the bottom one-third of the weld and a surface examination of the weld plus 1/2 inch of base material on each side of the weld.
The
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" Northeast Utilities Ultrasonic Examination Procedure for Intergranular i
Stress Corrosion Cracking (IGSCC) NU-UT-6" requires volumetric examina-tion of the full weld volume and a minimum of 1 inch of base material on each side of the weld when practical and with stringent recording criteria beyond Section XI requirements.
For example, NU-UT-6 requires recording all indications determined not to be screen noise and not to' be 0.0. geo~etry.
NU-UT-6 meets the requirements of I&E bulletins m
82-03 and 83-02.
NU-UT-6 full weld volume examination will ensure surface integrity without an additional surface examination.
ManRem reduction (ALARA) has been considered for this relief request.
Weld preparations and actual surface examination time required in a radiation area by personnel can be reduced by an approximate 50%
factor'with the elimination of this surface examination.
i 1
i LICENSEE'S PROPOSED ALTERNATE EXAMINATION Perform a full volumetric examination in accordance with the " Northeast Utilities Ultrasonic Examination Procedure for Intergranular Stress Corrosion Cracking (IGSCC) NU-UT-6" on austenitic pressure retaining
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circumferential and longitudinal piping welds >1/2 inch nominal wall thickness.
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STAFF EVALUATION The impracticality of the surface examination requirement cannot be determined by the supporting information provided by the licensee.
The ultrasonic test procedure, NU-UT-6, was used primarily for de-tection of IGSCC and is proposed by Northeast Utilities as an alter-native to the surface examination.
This alternative can be accepted only if it is demonstrated to be equivalent or superior to the surface examination requirement and the full volume of weld and base metal is scanned.
ACKNOWLEDGMENT This Safety Evaluation was prepared by G. Johnson.
Dated: August 22, 1985
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