ML13317B229

Review & Reassessment of SONGS 1 Lower Reactor Internals & Vessel Insp

ML13317B229
Person / Time
Site:	San Onofre
Issue date:	11/29/1990
From:	Christopher Boyd WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:
Shared Package
ML13317B228	List: ML13317B227 ML13317B229
References
SCE-90-695, NUDOCS 9012030096
Download: ML13317B229 (23)

Text

WESTINGHOUSE CLASS 3 Attachment to SCE-90-695 MED-RPV-3056 REVIEW AND ASSESSMENT OF SONGS 1 LOWER REACTOR INTERNALS AND VESSEL INSPECTION (SUMMER 1990)

L. J. BALOG Approved by:

C. H. Boyd, Manager Reactor Pressure Vessel System Analysis WESTINGHOUSE ELECTRIC CORPORATION Nuclear and Advanced Technology Division P.O. Box 2728 Pittsburgh, Pennsylvania 15230-2728 o 1990 Westinghouse Electric Corp.

9012030096 901129 PDR ADOCK 05000,:206 P

PDC 4774s/110190:10

WESTINGHOUSE CLASS 3 TABLE OF CONTENTS Section Title Page A

Flexures 1

B Limiter Keys 2

C Irradiation Specimen Guides 3

D Lower Support Blocks and Fasteners 3

E Lower Core Barrel 5

F Lower Raidal Support Keys 5

G Outlet Nozzles 5

H Lower Vessel Plenum Scan 6

I Thermal Shield Motion 6

J Thermal Shield Displacement 8

K Conclusions 9

4774s/1 10190:10

WESTINGHOUSE CLASS 3 REVIEW AND ASSESSMENT OF SONGS I LOWER REACTOR INTERNALS AND VESSEL INSPECTION (SUMMER - 1990)

The photographic evidence, (5 video tapes), of the SONGS 1 Lower Reactor Internals and Pressure Vessel inspection was reviewed and evaluated on August 24-28, 1990. These tapes, 2 recorded from the mini-sub, (color film), on 7/30/90, and 3 others in black and white recorded 8/8/90 and 8/9/90 represent good efforts by the operators whereby water clarity, good lighting and sound technique resulted in execellent picture definition and detail.

Of particular interest was the condition of the Internals Thermal Shield and its various attachments and contacts with the Lower Core Barrel; namely the Flexures, Limiter Keys, and Irradiation Specimen Guides near the top of the Shield, and the Support Blocks and Fasteners near the bottom. (See Figures 1

& 2 for the disposition of these components.)

A summary of the visual examination is as follows:

A. Flexures (See Figures 3 & 4)

1. 5 of 6 cracked and fully severed across entire 8.0 inch width.

2. Locations - 21*, 850, 2050, 2440, and 325*.

These same 5 flexures were seen to be broken in 1988 when the Lower Internals were partially inspected.

3. The 124* flexure remains undamaged.

4. All cracks appear to have emanated from the Heat Affected Zone (HAZ) of each flexure blade, (thermal shield side exclusively), and then randomly progressed across the 8 inch width until the blades were completely separated.

4774s/1 10190:10

1 WESTINGHOUSE CLASS 3

5. The "widest" gap in the cracked flexure blades appears to be the 325 flexure, where the gap width is estimated to be 3/16 inch at its widest.

6. The welds attaching the flexures to the thermal shield have no anomalies and the flexure block and the screws which attach them to the core barrel are as they should be.

B. Limiter Keys (See Figure 5)

1. The four limiter keys (00, 900, 1800, 270*) each initially had a "cold" radial clearance or "gap" of.024 inches between the "nose" of the key and the opposing point on the core barrel.

2. The "gaps" measured during this repair outage were:

(This is the first measurement taken since plant operation began) 00

.100 -

.170 inches (range) 900

.024 inches 1800 -

.028 inches 2700

.213 -

.233 inches (range)

4. The tangential gaps between the Limiter Pin noses and the side of the keyway type configurations in the core barrel component were nominally 3/8 inches as installed. Recent measurements disclose:

(looking down, standing outside the thermal shield)

Left Side Key Right Side

.446 in. -

00 -

.241 in.

.398 in. -

900 -

.378 in.

.472 in. - 1800 -

.350 in.

.405 in. - 270* -

.371 in.

4774s/1 10190:10 2

WESTINGHOUSE CLASS 3 C. Irradiation Specimen Guides (See Figures 1 and 6)

1. Four of the eight Irradiation Specimen Guide Tubes, (rectangular tubing), showed fairly significant damage, (11*, 280, 251*, 2580).

The 2510 tube was most severely damaged. A 5 inch long section was torn away from three sides of the rectangular tube directly below the point where it engages the round section of Guide Tubing (Extension Coupling), at about 10 inches above the top of the Thermal Shield. The 280 Tube has a crack across it's front face which begins at the right side at the beginning of the weld bead and extends about 3/4 the way across the tube's face. The 110 and 2580 rectangular Guide Tubes have cracks on at least one corner beginning at their entrance into the round section of Guide Tube and extending downward for a distance of 1 inch or slightly more.

2. The 32*, 131*, 138*, and 1510 rectangular Guide Tubes, (which incidentally, are consecutively located around the arc of the Thermal Shield), show little or no damage with the exception of some "fretting" where they enter the round section of Guide Tubes.

3. Four of the rectangular Irradiation Guide Tubes are shifted as much as 3/16 inch to their right, (viewed looking radially inward), as evidenced by their skewed position in the round sections of their respective Guide Tubes. These are the 110, 280, 320 and 1310 Tubes.

On the other hand, the 2580 Tube appears shifted approximately 1/8 inch to the left of its center.

D. Lower Support Blocks and Fasteners (See Figures 1, 7 & 8)

1. Six support blocks, 00, 600, 1200, 240* and 300*, support the lower end of the Thermal Shield. Seating of all six blocks in the base of the circumferential groove cut into the lower core barrel appears to be normal.

4774s/110190 10 3

WESTINGHOUSE CLASS 3

2. All lower dowels and bolts which attach the lower portions of the support blocks to the core barrel show no anomalies as viewed from the outside of the thermal shield.

3. 00 Block - both dowels have cracked lock welds.

There appears to be a vertical gap where the Thermal Shield rests on the Support Block.

This is a comparative judgement based on the appearance of this seat on the other five support blocks. The gap appears to be of uniform thickness across the full width of the block. A bolt protruding inside the core barrel was observed during the 1988 inspection.

(Broken, exiting the back of the tapped hole.)

4. 600, 1200, and 1800 Blocks outwardly appear normal.

(No protruding dowels or cracked lock bar welds on the bolts.)

5. 2400 Block - The left dowel protrudes 3/4 inch from the face of the Thermal Shield. Lock Bar tack welds are cracked on both bolts. A bolt protruding inside the core barrel was observed during the 1988 inspection.

(Bolt broken and "backing out".)

6. 3000 Block -

the right dowel protrudes approximately 3/4 inch from the face of the Thermal Shield. Lock bar tack welds are cracked on the left bolt.

7. See Figures 10 & 11 for a summary of support block fastener damage as discovered upon block removal in Sept. 1990. Note that the 0*

and 2400 locations exhibit the most extensive damage, (as discerned at the 1988 inspection), and the 300* location is next, as was predicted analytically in the Westinghouse topical report WCAP 12148.

4774s/110190:10 4

WESTINGHOUSE CLASS 3 E. Lower Core Barrel Groove (Vicinity of Support Block Positions) (See Fig. 8)

On Sept. 10, and 11, 1990, a U.T. inspection was performed in regions of the Reactor Internals Lower Core Barrel where the Thermal Shield Support Blocks are attached. With the blocks removed, all six locations were scanned looking for cracks or defects in the core barrel.

None were found. Although 2 indications were recorded at the 3000 block location, closer evaluation (including a review of the video tapes), identified them as remmants of the broken bolts which remained in the tapped holes of the core barrel.

F. Lower Radial Support Keys and Vessel Keyways (See Figure 1)

1. An examination of the 6 Lower Radial Support keys showed no anomalies.

The keys, situated near the lower end of the separate Reactor Internals, engage 6 keyways in the Pressure Vessel, (tight fit), to position the Internals and limit the amplitude of any flow induced vibration. The vessel keyways looked equally good, with all their attachment bolts and locking bars appearing unimpaired. Bearing surfaces appeared clean and burnished with no obvious signs of severe wear or impact damage. (The clearance in this fit is.010 inches per surface, tangentially.)

G. Reactor Internals and Vessel Outlet Nozzles (See Figure 1)

1. A scan of the three outlet nozzle faces on both the Pressure Vessel and Lower Reactor Internals disclosed nothing unusual.

No striations or signs of impact damage or fretting wear is evident. The fact that these close-fitting interfacing surfaces are "clean" denotes a stable Lower Internals Assembly. The condition of the Lower Radial Support Keys and Keyways, (F above), also support this conclusion.

H. Bottom of Pressure Vessel Scan

1. Several pieces of metal were evident that appear to be the debris from the heavily damaged 251* Irradiation Specimen Guide Tube.

4774s/I 10190:10 5

(1)

WESTINGHOUSE CLASS 3

2. Other debris in evidence consisted of a crescent wrench, (the jaw appeared to be missing), and directly under this object; what appears to be two shim plates estimated to be 2.5 in. x 8 in. x 1/8 in. thick in size. Also, several objects which appeared to be pieces of tape were observed.

3. There were some small, light-weight, water borne particles which were disturbed by the mini-sub, but no "sediment" collected in the bottom of the vessel.

THERMAL SHIELD HARDWARE ASSESSMENT AND COMMENTARY I. Motion at the Top of the Thermal Shield The 900 and 1800 Limiter Keys have maintained their close radial gaps to the core barrel within several mils, leading to the conclusion that there was minimal motion or preturbation of the thermal shield in this segment of its arc. Further confirmation of this observation derives from the fact that other support and restraining hardware in this general vicinity appear to be in reasonably good condition:

1. 1240 flexure - unimpaired/no apparent damage.

2. Irradiation Specimen Guide Tubes - 1310, 138* and 1510 locations have no obvious damage such as corner or face cracking or pieces torn away.

3. Lower Support Blocks and Fasteners - 600, 1200, and 1800 blocks and fasteners appear normal, as viewed from the outside.

Conversely, the 0* and 2700 Limiter Keys reveal that radial gapping to the core barrel has increased from.024 inch to as much as.170 inch and

.233 inch respectively. The condition of nearby support and restraint hardware is consistent with the conclusion that significant thermal shield motion has occured in this area.

o4774s o

10190:10 6

WESTINGHOUSE CLASS 3

4. 210, 3250, and 2440 Flexures are fractured with the 3250 flexure exhibiting the largest "gap" between the separated sections of the flexure blade, 3/16 inch.

5. Irradiation Specimen Guide Tubes 280,

110, 258* and 251* show signs of cracking and even worse in the case of the 251* Tube where a large section has been physically torn away.

6. Lower Support Blocks and Fasteners - 00, 300*, and 240* Support Block Fasteners have degraded to various degrees. The 0 and 2400 blocks had bolts, which tie them to the Thermal Shield and Lower Core Barrel, partially protruding out of their tapped holes on the inside of the Core Barrel, as observed during a 1988 inspection.

7. Viewing the blocks now from the outside of the Thermal Shield, the 240* location has one of its two dowels protruding, and cracked welds on the bolt lock bars. The 00 location shows both dowel pin lock welds cracked which is likely the precursor to their subsequent "backing out".

The 3000 block has one dowel pin emerging from the face of the Thermal Shield and a cracked weld on a bolt lock bar.

In a similar thermal shield damage episode at another plant, flexures were removed early on when it was discovered that they had fractured.

SCE's choice to leave failed flexures in place, (4 had failed by 1976), very likely was helpful in restraining motion at the top of the shield. Although cracked, the partially separated blades could act as "buffers" to deter or limit radial displacement of the shield with respect to the core barrel.

In some cases, even some part of the shield's tangential motion could be limited based on the direction in which the crack propagated across the flexure blade and the resulting configuration. The 2050 and 3250 flexures would provide some tangential restraint based on the nature and shape of the "fracture line" in the blades.

4774s/11 0190:10 7

WESTINGHOUSE CLASS 3 J. Thermal Shield Displacement (Top) (See Figure 2)

A review of the video tapes and the written comments on the inspection sheets suggest that the top of the shield has moved to the right or counter-clockwise in the arc extending from 85* to 3250. A move to the left or a clockwise "set" seems apparent in the arc from 1800 thru 270*.

The arc between 900 and 1800 seems stable in the terms of left or right movement with the undegraded 1240 flexure residing in that zone.

These observations are as viewed looking down onto the Thermal Shield as regards clockwise or counter-clockwise and outside looking in as regards left or right.

(See Figure 9)

1. 850 to 3250 arc - features showing displacement, in sequence, are:

(Counter clockwise rotation or left to right as viewed "looking in".)

(a) 850 Flexure 1/16 inch (b) 32* Specimen Tube 1/8 inch (c) 210 Flexure 3/16 inch (d) 11* Specimen Tube 5/32 inch (e) 3250 Flexure 3/16 inch NOTE:

The 00 Limiter Key is displaced 0.102 inch to the right of the center (see Para. B4 above), and this observation would support the "shift to the right" scenario. However, it was reported from plant site on 8/25/90 that shims were found in the Limiter Key to Thermal Shield fit at 0* and 180* during the operation which removed the existing Limiter Keys. These shims were ostensibly used when the Limiter Keys were removed, repaired, and then replaced following the plant's first hot functional test in 1966. Note from the measurements presented in para. B4 that the 0* and 180* Limiter Keys have the most disparate "left" and "right" values.

4774s/1 10190:10 8

WESTINGHOUSE CLASS 3

2. 1800 to 2700 arc - features indicating displacement, in sequence, are:

(Clockwise rotation or right to left as viewed "looking in".)

(a) 1/16 inch 2050 Flexure (b) 1/16 - 1/8 inch 2240 Flexure (c) 3/32 - 1/8 inch 2580 Specimen Tube

3. 900 to 1800 arc - no left or right displacement; features supporting this are:

(a) 90' Limiter Key - change in radial.gap less than.010 inch.

(b) 1240 Flexure undamaged (c) 1310, 1380 and 1510 Specimen Tubes -

little or no damage and little or no apparent displacement.

If there is any kind of a pattern to be seen in these data, one might say, "anchor" the top of the Shield at the 1240 undamaged Flexure and draw a diametral line thru 3040 and say that the Shield has taken a "set" in that direction, and that might come close to explaining the direction and magnitude of the displacements seen in the various Specimen Guide Tubes and Flexures described above. (See Figure 9.)

Also, the widest gap in a cracked Flexure is the 3/16 inch gap at 325* (closest Flexure to the 124*

- 304 0 vector).

The next largest Flexure blade gaps are judged to be the 2440 and 210 locations which "straddle" the proposed 1240 - 304* line of Thermal Shield motion.

Further inspection results which became available on 9/2/90 lend further support to the perceived position of the thermal shield. After the bolts and dowels connecting the lower end of the Shield to the Core Barrel were removed, height dimensions were taken from the bottom surface of the Shield down to the Core Barrel groove in which the Support Blocks reside.

(See figure 8 Sect. B-B) Dimension "B" at original assembly was nominally 3.190 inches as measured in the vicinity of each of the 6 Blocks. These measurements now show the Shield to be slightly "tipped" along the 120*

300* axis, with the Shield lifted.020 inches at 1200, and sitting low at 4774s/1 10190:10 9

WESTINGHOUSE CLASS 3 3000 to the extent of.150 inches. Also note on Figure 11, that the only unbroken hidden bolt is at the 1200 Block. (Almost directly below the undamaged 1240 Flexure above.)

K. Conclusions The decision by Southern California Edison and Westinghouse in the summer of 1988 to run the plant for another cycle in order to provide time for evaluation, analysis, and a repair design has obviously been justified.

Although the Thermal Shield and its associated hardware may have suffered some degree of further degradation in the interval, it is safe to say that the amount of additional degradation represents no safety issue, nor would it have been considered to pose any undue risk during the last 18 months of operation.

The conditions of the Thermal Shield, and its supporting hardware, described in this report, closely resemble those predicted in Westinghouse WCAP 12148, "Engineering Evaluation of the SONGS I Thermal Shield Supports," dated February 1989.

4774s/I 10190:10 10

WESTINGHOUSE PROPRIETARY CLASS 3 SONGS 1 THERMAL SHIELD SUPPORT SYSTEM FIGUE 1 0TATED INTO vI

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WESTINGHOUSE PROPRIETARY cLAss 3 SONGS 1 THERMAL SHIELD SUPPORT SYSTEM EXISTING SUPPORT BLOCK FIGURE 7 A

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WaINGHOUSE PROPRIETARY CLAS&

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THERMAL SHIELD DIRECTIONAL "SET" (TOP)

FIGURE 9 2580 Spec Tube 1/ 8 2,700 2440 Flexure 304 3/32 3/ 6 3250 Flexure 1/16 2050 Flexr 1800 0

5/32 110 Spec Tube

/16 210 Flexure 1/8 320 Spec Tube Thermal Shield 124e Flexure 1/16

85.

Flexure 900

WINGHOUSE CLASS 3 Fizue 10 4

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