ML20024H621

Discusses 910424 & 25 Visits to Plant to Review Design & Scanning Capabilities of ABB Tekniska Rontgencentralen Manipulator for Ultrasonic Exam of BWR Vessel Sheld Welds

ML20024H621
Person / Time
Site:	Monticello
Issue date:	04/26/1991
From:	Gieske J SANDIA NATIONAL LABORATORIES
To:	Hum M NRC
References
TAC-80168, NUDOCS 9106070100
Download: ML20024H621 (4)

Text

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Sandia National Laboratories Abuquef Qae, he W Mo s tC O I4 71fda April 26, 1991 pyc. go /48

.50-263 Mr. Martin Hum MS 7-D-4 U. S. Nuclear Regulatory Commission Materials Engineering Branch Washington, DC 20555

Subject:

TRC Tool Performance for UT Scanning of Beltline Vessel Wolds at Monticello Nuclear Power Plant

Dear Mr. Hum:

JNTRODUCTION A visit was made at Monticello Nucicar Power Plant on April 24 and 25, 1991 to review the design and scanning capabilities of the ABB Tekniska Rontgencnntralen (TRC) manipulator for ultra-sonic examination of BWR vessel shell welds.

Of particular, interest was the ability of the manipulator to scan the vessel shell wolds in the restricted area of the jet pumps and the core shroud.

The clearances in this area for the transducer scanning head may only be several inches.

Design of the transducer head must allow the transducer face to stay in contact with the ID vessel surface as the transducer head is moved over the rough clad surface of the vessel during normal scanning speeds for data acquisition.

TRC. TOOL DESIGE on April 24, the manipulator was inspected at close range as it laid on the refueling floor of the reactor building while it was being prepared to be inserted into the vessel.

The manipulator consists of a large mast which is mounted on the flange of the vessel and extends down adjacent to the vessel inner wall to the core shroud.

A motorized extension arm is attached to the mast between it and the vessel wall.

A motorized slide and transducer l

holder is attached to the end of the extension arm.

A TV camera i

is also mounted on the end of the extension arm which allows some visual inspection of the clad surface and the movement of the transducer holder over the clad surface.

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o The donign of the transducer holder, slido, and extennion arm woro examined closely.

The transducer holder contained four indopondent transducora for a atraight boam, a 45 degree phear beam, a 60 degroo shear boam, and a dual 70 degroo beam inspec-tion.

Each of thoso tranoducers was in a spring loaded gimbal device which allowed independent movement of the trannducer in all directions perpendicular to the plano of the transducer holdor faco.

Thorofore, ao the transducer holder pasnos over a rough clad area of varioun heights, each tranuducer is able to rotate trooly and stay in contact with the clad ourface.

The donign of the extension arm is auch that the tranoducer plato is also spring loaded against the vossol wall.

Only the presence of a very charp atop in the clad nurface of grontor than 1/8 inch in height may cause a transducer to hang up on the stop.

The transducer holder is connected to a shaft that can be rotated through 360 degreen no that opposing transverno and longitudinal scans of the wold can be mado connocutively.

The rotation shaft is mounted on a rigid compound transverno slide which in attached perpendicular to the extension arm of the mant.

The slido han a curvaturo equal to the vensal wall curvaturo.

As the slido extendo the transducer holder circum-forentially by approximately 2 foot, it maintainn an equal distance of the trannducer holdor from the vessel wall and a constant force against the wall.

The compound slido and trann-ducer holder with transducers attached in approximately 3 to 4 inches in thickness.

Thoroforo, when the transducern are scanning behind the rostricted area of the jot pumps, a constant clearanco distance of about 2 inchos is maintained betwoon the jot pumps and the transducer holder.

The main mast can be moved a cortain distance in the circum-forential direction of tho vessel.

On the end of the main mast is an electromagnetic sonsor which is used to locate the exact position of a lug in the shroud flango.

At this position the extension arm can bo loworod past the shroud and betwoon the longitudinal clearanco passage way of the jet pumpa.

The extension arm can be loworod to the level just above the core shroud support uhelf.

A scan of the circumferential weld in thin area can then be made in a rastor scan by moving the extension arm up and down and incromanting the compound slido in tho

-circumferential direction after each vertical scan.

In this position of the mast the circumferential and longitudinal bolt-line welds can be examined for a distance of approximately 2 feet on either side of the mast; i.e.,

plus and minus 16 degrees of the vescol wall from the shroud support shelf to the nhroud flange. -After examination of the wolds in this area is complete, the extoncion arm.is extracted and the tool is moved to the next

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lug position in the shroud flango where another longitudinal clearance passago way of the jet pumpa is present.

The passage ways are separated by 30 degroos so completo coverage of the welds behind the jet pumps in possible.

To examine the welds above the core shroud, the main mast is replaced with another one of similar design, which allows transducer scanning to tako place on the welds betwoon the core shroud flange and the upper flango of the vessel.

To0L EVALUAT1QH A video tape of the operation of the manipulator in the area of the core shroud as soon on a mock up of the vossel was also viewed on April 14.

The tape demonstrated that manipulation of the transducers passed the restricted area of the core shroud and jet pumps was easily accomplished.

The tapo also showed how the extension arm worked and how the transducer holder was moved laterally with the compound slido mechanism.

All positions of the tool motion are encoded.

Transduenr motion is encoded to givo a 0.2 mm resolution in the scanning directions.

At approximately 2:00 AM on April 25, the tool was lowered and mounted in the vossol.

At approximately 9:00 AM a scan of 15 degrees of the circumferential wold nunber 2 which is just above the core shroud support shelf was scannid using the Dynacon acquisition system.

Approximately 100 scans were taken across the weld crown with an increment of 7 mm betwoon each vertical scan.

The scanning and data acquicition time for this pre-liminary test took approximately 1.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br />.

The transducer head was then moved to scan the same area of the circumferential vold number 3 which is at the core shroud flange.

At the beginning of this scan, I was present in the data acquisition tent to witness the exam.

Unfortunately, a problem developed with the interface of the encoder pulsos of the transducer positions and the Dynacon data acquisition system.

This problem was not resolved while I was there, but I was able to observe a manual movement of the transducers over the clad surface as seen on the TV monitor.

From what could be seen, the transducer movement over the clad surface worked smoothly and only an occasional drop out of the ultrasonic signals occurred from lift off of the transducer over the clad roughness.

CONCLUSIONS The tool design and transducer holder are well conceived designs.

Manipulation of the transducers in the restricted area of the jet pumps can be effected efficiently with the tool design. One hundred percent coverage of the wold in this area can be accom-I

a.

4 plished.

A raster scan pattern of the full volume of the weld can be accomplished.

After experience with the tool, it is estimated that on the averago a 30 degree section of a given wold can be accomplished within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> for two opposing transvouse and longitudinal scans.

Sincoroly, r tt ohn 11. Gioske HDT Technology Division 7552 JilGtjk Copy tot

" dE William O.

Long

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MS 13-D-18 U.

S.

Nuclear Regulatory Commission Washington, DC 20555 i

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