ML20114C296
| ML20114C296 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/07/1992 |
| From: | Plumstead W FLUOR DANIEL, INC. |
| To: | Hosey C NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| Shared Package | |
| ML20114C257 | List: |
| References | |
| NUDOCS 9209020107 | |
| Download: ML20114C296 (6) | |
Text
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A FLUOR DANIEL r w can,ei. %
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Green o fie SC ?WO7-2W (6031 281 4 0 0 July 7,1992 (REVISED) j 3
Charles M. Hosey, Chief Nuclear Materials Safety Section Nuclear Materials Safety and l
Safeguards Branch Division of Radiation Safety and Safeguards USNRC 101 Marietta St.N.W.
Suite 2900 Atlanta, GA 30323
Reference:
South Carolina Radioactive Material License No. 043 Gentlemen:
SUllJECT:
REQUEST FOR MODIFICATION OF GUIDE tulle FOR RADIOGRAPIIY 4
Fluor Danielis providing radiographic examination senices for the Millstone Unit 2 Steam Generator Replacement Program. We are working at the Connecticut location in accordance with our South Carolina License No. 043 and the " RECOGNITION OF RECIPROCITY" letter dated March 13, 1992 from your office.
l This is to request a, one-time only, modification of source guide tubes for Amersham (Techops) cobalt 60 source device model numbers TO680 (Registry NR 0628-D-134-U) and TO676 (Registry l
NRC28-D-135-U) per 10 CFR 34.20 " Performance requirements for radiography equipment" l
paragraph (b)(3). Radiographic activity invohing this modification is scheduled beginning July 30, 1992 through early September,1992.
l RATIONALE The source guide tube modification is needed to efficiently perform radiographic examination and reduce personnel staytimes inside the steam generators during the steam generator replacement I
program (SGRP) far Millstone Unit 2 in Waterford, Connecticut. Personnel access to the girth weld inside the steam generator is slow and difficult due to space restrictions. Personnel staytimes should be reduced or climinated due to anticipated high tempereture associated with the minimum weld i
preheat of 250 degrees F during welding and postweld heat treat (PWHT) temperature of 1100-1200 degrees F.
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NDE PLAN A nondestructive exammation plan has been developed to minimize personnel exposure to the harsh temperature environment and reduce the critical path time during radiography of the steam generator i
girth weld. Three (3) 100 curie cobalt 60 sources will be exposed concurrently to reduce total exposure time required for radiographic examination of the steam generator girth weld.
The number of times that radiography personnel will have to enter the steam generator will be minimized by prepositioning twenty-seven (27) stainless steel rigid source guide tubes inside cach i
steam generator (SG). Rigid guide tube connections will be located below the SG access hole line-of-j sight and attached to the generator shroud with tube blocks. Eighteen (18) guide tubes will be-i located at one SG access opening for exposures using two source devices. Nine (9) guik tubes will l
be located at the SG access located 180 degrees from the other SG access opening. The rigid guide tube ends at the weld will be attached to positioning clamps for the focal locations required to j
complete the girth weld radiography (Attachment A). The rigid guide tubes should remain in position until radiography of two intermediate weld thicknesses, a completed weld prior to PWHT, and the:
final weld after PWHT is compkte.
Each source device (camera) will be connecte<1 to the appropriate rigid guide tube by a flexible guide-tube. The connections will be identified sequentially in three sets of nine'(9) guide tubes that j
correlate with the specific exposures at three selected locations approximately 120 degree positions around the girth weld circumference. Nine (9) such exposure setups sequenced around the j
circumference will complete the weld (Attachment B).
i Personnel assigned to perform radiographic examination of the SG girth weld will receive approximately four (4) hours of specialized training on the SG mockup. Training will include full l
radiographic exposure simulation using a training camera and dummy source. Each radiographer will i
perform a practical examination to demonstrate an understand:ng of the radiographic requirements and demonstrate the capability to work within the access restrictions.
ADVANTAGES i
An alternative radiographic technique was considered where radioactive sources would be outside the L
steam generator for exposures; however, the current plan eliminates the disadvantage of the-
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considerable staytime accumulation for personnel involved in placing film cassettes inside the steam generator in the high temperature environment. The plan to expose sources on the inside of the
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steam generators provide additional shielding for radiography personnel consistent with ALARA l-policies. Thice (3) sources used simultaneously reduces the overall exposure time by approximately two-thirds (2/3).
STEAM GENERATOR / RIGID GUIDE TUBE MOCKUP l
A full scale mockup of a section of the Millstone Unit 2 steam generator (SG) was used to demonstrate the feasibility of using stainless steel rigid guide tubest i
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l Amersham engineering provided 'he technical requirements to design the rigid guide tubes. Guide tubes were fabricated using 304 stainless steel (SS) tubing one half (1/2) in outside diameter (OD) j with a 0.065 inch wall, an Amersham guide tube fitting, and Swageloc daans and end cap. A crushing test (ANSI N432,8.o)is not considered appropriate for this application for two reasons; first,-
j the position of the rigid guide tubing in the steam generator is not accessible to personnel traffic and second, the 304 SS material has a minimum Brinell hardness of 192 per ASTM A 269. Hardness of metal is commonly defined as resistance of the material to plastic deformation. In a sense; this j
nroperty is closely related to strength since both involve the ability of the metal to resist permanent i
deformation beyond the clastic range, i
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An Amersham male fitting part no. 40210-1 was TIG welded to one end of a section of tubing that -
l was positioned at the access hole of the SG mockup and routed vertically downward to the top of the feedwater pipe (approximately 10-12 feet). The Amersham male fitting provides the connection l
necessary for the standard flexible Amersham guide tube that will conneet the camera to the rigid j
guide tube, i-Two (2) sections of SS tubing (approximately 3-4 feet) were formed around a two feet diameter wood pattern. Rese two (2) tube sections were joined to the positioned (longer) tubing using Swageloc j
unions part no. SS-810-6. He Swageloc unions were positioned on straight portions of the tubing j
to eliminate restrictions or wear that could be associated with the additional pressure at the bend l
locations during manipulation of the source. Additionally, tubing ends were flared to provide smooth entry and travel at the Swagek)c union connections.
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A Swageloc end cap part no. SS-810-C was attached to the end of the SS tubing at the focal position j
to provide a positive, physical stop. A tensile test (ANSI N432,r.7) is not considered appropriate i
because the working design tensile strength is significantly greater than required. Swagek>e tables l
provide a working pressure factor of 0.0290 x 75,000 psi tensile strength for a working pressure of j.
21,750 psi. This working pressure is significantly greater than the pressure that can be developed by j
a radiographer using the drive control assembly.
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RIGID GUIDE TUBE DEMONSTRATION ei-A physical demonstration of functionality was performed using two (2) rigid guide assemblies designed as " worst case" to simulate any resistance caused by Swageloc connections or bending radii. An L_
Amersham TO-660 training camera was used with a dummy source pigtail assembly to test for i
smoothness and ease of travel through the rigid guide tubes and detect any abnormal or undesirable -
p functioning.
The training camera was positioned on a platform at the access opening of the steam generator girth weld mockup. The drive cable assembly was connected to. the training camera and a seven (7) feet -
flexible guide tube was used to connect each of the rigid guide tube assemblics to the camera for testing. The drive cable was manipulated several times, at various speeds of travel, to the end of each rigid guide tube and returned to the stored position in the camera.
This test should satisfy the kinking test (ANSI N432,8.5) in that it demonstrates that the control (drive) cable will withstand conditions it is likely to experience during use.
NRC Page 4 CONCLUSION The steam generator / rigid guide tube mockup provides adequate simulation to-demonstrate functionality of the rigid guide tube design. Both rigid guide tube assemblics provided smooth, unrestricted travel of the drive cable and source pigtail No malfunctioning, binding, snagging or catching were apparent. A positive stop is provided by the end cap when manipulating the drive cable.
A training camera with a dummy source pigtail will be marupulated through each rigid guide tube in each steam generator after final assembly and before any radiography is performed using any rigid guide tube to assure proper operation of actual insitu guide tubes.
Potential premature wear concerns were addressed with Amersham engineering. Premature wear is not considered a concern because of the inherent lubrication characteristic associated with stainless steels and the limited exposure cycles involved; anticipated use of each cobalt 60 pigtail assembly is less than 100 exposure cycles in the rigid guide tubes for completion of both of the steam generator girth welds.
REOUEST We would appreciate your expedient approval of thi.e design change for the rigid source guide tubes to be used with the Amersham TO.680 and TO 676 cobalt 60 source devices for radiographic examination of the steam generator girth welds during the Millstone Unit 2 SGRP.
Early approval is needed permit ordering of materials and fabricating rigid guide tube assemblies to --
meet current steam generator replacement program scheduling for radiography.
Thank you for consideretion of this request. Please contact me or leave messages at (803) 281-5337, 1
for any needed clarification or questions.
Very truly yours
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oow & k 1 M' William C. Plumstead -
Radiation Safety Officer WCP92142:cm cy:
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LOCATION MARKER & SOURCE GUIDE TUBE LAYOUT SKETCH