ML20076N264
| ML20076N264 | |
| Person / Time | |
|---|---|
| Site: | Midland |
| Issue date: | 07/15/1983 |
| From: | Shunmugavel P BECHTEL GROUP, INC., CONSUMERS ENERGY CO. (FORMERLY CONSUMERS POWER CO.) |
| To: | |
| Shared Package | |
| ML20076N260 | List: |
| References | |
| ISSUANCES-OL, ISSUANCES-OM, NUDOCS 8307210261 | |
| Download: ML20076N264 (15) | |
Text
e A
July 15, 1983 State of Illinois SS.
County of Cook UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING BOARD In the Matter of
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Docket Nos. 50-329-OM CONSUMERS POWER COMPANY
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50-330-OM
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50-329-OL (Midland Plant, Units 1
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50-330-OL and 2)
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Affidavit of Dr. Palanichamy Shunmugavel My name is Dr. Palanichamy Shunmugavel.
I have previously been a witness in this proceeding and my pro-fessional qualifications are in the record.
I swear that the statements made in the attached Affidavit are true and correct.
&n c-Palanichamy Shunmugavel Signed and sworn y before me this /5 day of July, 1983.
%wv-Notary Public My' Commission Expires January 14. M 9307210261 830718 PDR ADOCK 05000329 PDR
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7 AFFIDAVIT OF DR. PALANICHAMY SHUNMUGAVEL ON BEHALF OF THE APPLICANT REGARDING THE SIGNIFICANCE OF OBSERVED CRACKS IN CONTAINMENTS My name is Palanichamy Shunmugavel, and I am an engineering specialist in the civil / structural department of Bechtel Power Corporation in Ann Arbor, Michigan.
My resume has been introduced earlier in this hearing.
In connection F
with my role'as engineering specialist, in January 1983 I participated in the preparation of Bechtel project engineering comments in response to NRC Staff questions concerning cracks observed in Midland's Unit 1 containment.
Information we supplied to the NRC Staff at that time is repeated and expanded upon below.
Containment There are two structurally independent but identical prestressed concrete containments at the Midland jobsite.
Containments house the nuclear steam supply systems, and their primary function is to. control the release of radioactivity.
The containments are pressure vessels that are designed for an internal pressure of 70 psig.
As shown in Figure 1, each containment has a 3'-6"-
thick prestressed concrete vertical cylindrical wall, a 3'-0"-thick prestressed concrete dome at the top of the cylinder,
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ind a reinforced concrete circular base slab.
The base slab is
[
l 128 feet in diameter and 13 feet thick in the central portion.
The thickness of the outer portion varies from 13 feet to 9 feet.
The inner diameter of the containment is 116 feet, and the overall height is 209 feet.
The primary shield wall and secondary shield walls are internal structures supported by the base slab.
Each containment is lined with a 1/4-inch-thick steel plate at the inner surface to ensure leaktightness.
The cylindrical wall and dome of each containment are prestressed to induce biaxial compression using 110 vertical tendons, 162 hoop tendons, and 87 dome tendons.
Each tendon is made of 170 1/4-inch-diameter wires, placed in a semi-rigid duct buried in the concrete, posttensioned, and anchored at its two ends.
The duct is then filled with a corrosion-inhibiting material (grease).
The vertical tendons are anchored at the underside of the base slab and at the ring girder, which is at the junction of the dome with the cylindri-cal wall.
A peripheral tendon gallery at the bottom of the base slab provides access to the vertical tendon anchorages.
Three 12-foot-wide vertical buttresses equally spaced around j
the outside of each containment are used to anchor hoop tendons (see Figure 2).
The successive hoop tendons are anchored at alternate buttresses so that three consecutive tendons provide l
l two complete hoops.
Three sets of dome tendons inclined at 60 degrees to each other are anchored at the ring girder.
The effective prestress level is about 1.2 times the internal design pressure.
r Bonded reinforcing steel bars are provided through-out the structure to control the width and distribution of cracks which are expected to occur as a result of anticipated shrinkage and temperature effects.
In addition, the bonded reinforcing steel bars in the base slab and in the areas of structural discontinuities provide required strength.
The discontinuities include the junction between the base slab and the cylindrical wall, vertical buttresses, ring girder, and penetrations.
The containments are designed for various loads and load combinations as explained in FSAR Section 3.8.
The major One of loads are dead load, prestress, and internal pressure.
the load combinations requires that the dead and prestress loads be combined with 1.5 times the internal-design pressure load.
The base slab has predominately flexural behavior (bending moment and shear force).
It has convex curvature in the central portion under dead load and-concave curvature under internal pressure load.
The cylindrical wall and dome are shells with predominantly membrance (axial forces) behavior.
In addition to membrane forces, the areas of structural discontinuities in the shells entail bending moments and shear forces.
Prior to operation, for each containment a structural integrity test (SIT) will be performed, during which each containment will be pressurized to 1.15 times the design pressure, i
r and the containment responses will be measured and compared with those predicted by the analyses.
As explained in FSAR Subsection 3.8.1.7.1 and Regulatory Guide 1.18, structural deformations will be measured and concrete cracks monitored at various representative areas of the containments.
In addition, the general condition of the posttension-ing system will be checked periodically during plant operation in accordance with a surveillance program explained in FSAR Subsection 3.8.1.7.3 and Regulatory Guide 1.35.
According to this surveillance program, a set of representative tendons will be randomly selected, and their anchorages, surrounding concrete surfaces, existing tendon forces, wire corrosion level, duct filler material, etc. will be checked and evaluated.
Observed Cracks In December 1982 some cracks were observed at the junction between the cylindrical wall and the base slab near the buttress at the southeast corner of Unit 1 containment.
These cracks were observed from Room 110 of the Auxiliary Building and are shown in Figure 3.
(Figure 3 was copied from Field Engineer's Report CC-183 dated December 17, 1982, attached to Dr. Corley's affidavit).
The cracks were situated on the outer surface of the cylindrical wall within approximately 5 feet from the top of the base slab and within approximately l
The maximum width of
'12 feet on either side of the buttress.
4.
the cracks on the coating surface observed was less than 0.005 inch.
When the coating was removed, the width of the crack is only about 0.002 inch.
As stated in Dr.
Corley's affidavit, it was observed that coating had penetrated the cracks.
As shown in Figure 3, the cracks had no definite orientation; there were vertical, horizontal, and inclined cracks.
Dr. Corley's affidavit also indicates that he observed a similar crack near a buttress in the Unit 2 con-tainment from Room 116 of the Auxiliary Building.
In July 1983 after I was asked to respond to Ms.
Stamiris' Motion to Reopen the Record, I asked site personnel to map the cracks in all six areas where buttresses meet the base slabs of the containments.
On July 13 I visited the site and observed four of the buttresses.
I found that the cracks in Room 110 have not changed since they were described in the Field Engineer's Report Form CC-183 dated December 17, 1982.
After trying for 20 minutes I could nyt i
find the " extremely narrow" crack in the Unit 2 containment Dr. Corley saw in Room 116.
My own observations as well as the crack mapping indicate that there are other cracks similar to those in Room 110 at the remaining four buttress-basemat junctions.
The largest crack observed was recorded by the crack mappers (Wiss, Janney, Elstner and Assor lates) as.015 inch.
I measured it and found it to be.010 inch.
While I have not seen any other crabks in either containment, I would not be surprised or disturbed to learn that there might be some minor shrinkage cracks in other locations, for the reasons described below.
Significance of Cracks The base slabs were built in 1974, the cylindrical walls and domes were completed in 1977, the outer surfaces inside the auxiliary building were coated in 1977, and the containments were prestressed between 1979 and 1981.
Thus far, the containments have been subjected to primary loads of dead and prestressing loads.
Internal forces have to be developed to equilibrate the primary loads.
The internal forces in the crack locations are compressive membrane (axial) forces, bending moments, and shear forces.
The containments have also been subjected to restrained volume change effects from shrinkage, creep, and thermal effects.
The internal strains and forces developed from these effects are secondary and not required to equilibrate externally applied loads.
These secondary internal forces will be partially relieved as the containments deform, and the ultimate capacity of containments will not be affected.
Shrinkage is the greatest contributing f actor to the -
secondary effects compared to creep and normal thermal gradient.
When the wet, newly placed concrete cures, the moisture is lost a't the outer surface-and the concrete shrinks.
The shrinkage
strain, if restrained, can cause cracking of concrete.
The shrinkage strain can vary from 0.0002 to 0.001 in./in., 90%
of which occurs within the first year.
For the Midland con-tainment, the shrinkage strain is estimated to be about 0.0005 in./in. before prestressing.
Therefore, small cracks are commonly visible on the outer surface of containments, especially near discontinuities where shrinkage is restrained.
This is one of the reasons why the bonded reinforcement is added, to distribute and limit the width of shrinkage cracks.
The prestressing causes a compressive strain of about 0.0003 in./in., which helps to partially close the existing shrinkage cracks.
The observed cracks described above are from volume change effects predominantly contributed by shrinkage strain in the cylindrical wall restrained by the base slab and buttress.
The cracks probably occurred before the coating was applied and continued to increase by a small amount before prestressing.
During the period from 1979 to 1981 the duct-filling operation was carried out.
During this operation, hot (140 to 150F) duct filler material (grease) is pumped in at about 40 psi to fill the tendon ducts.
The tendon ducts are not leak-proof.
No grease was observed leaking through the cracks at that time.
Moreover, such grease would have left a very visible stain on the containment surface.
I did not see any such stains when I o,bserved the cracks. at Midland in July 1983.
I am f amiliar with another prestressed concrete structure which did leak during such a duct filling operation.
The f act that such leaking did not occur at Midland is ad-ditional evidence that the observed cracks are narrow and shallow.
As explained earlier, representative areas on the outer surfaces of the contain'ents will be monitored for cracks m
before, during, and after SIT.
The representative areas will include a portion of cylindrical wall near the base slab and another portion of the cylindrical wall near the buttress.
(These representative areas have already been selected and do not include the areas described above in which cracks have been observed.)
During plant operation some portions of the containments' outer surfaces near tendon anchorages will be inspected during the periodic tendon surveillance operations.
Containment Crack Monitoring to be Performed in Addition to the SIT During the SIT, exterior surfaces in accessible areas near each of the six buttresses will be monitored.
The areas to be monitored will. extend from El 591'-6" to El 597'-6" vertically.
Horizontally, monitoring will be done on all unobstructed areas of the buttress and of the containment for a distance of about 10 f t each side of the buttress.
All coatings and other obstructions will remain
'in place and undisturbed.
Crack mapping done in mid-July
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. 1983 can serve as a base line.
Cracks will again be mapped before the SIT begins and after the SIT is finished.
During the SIT the cracks in these areas will be visually monitored.
The crack mapping and monitoring described in the preceding paragraph will be performed in a manner similar to the crack mapping and monitoring done with respect to other structures such as the DGB and SWPS at the Midland Plant.
It will not be as extensive an effort as that required in certain other locations by Regulatory Guide 1.18 for purposes of the Structural Integrity Test.
Therefore, I have been asked by site personnel to emphasize that this containment crack mapping and monitoring commitment is in addition to and not part of the SIT program and is not being performed in accordance with the requirements of Regulatory Guide 1.18.
Foundation Material The containments are founded on a uniform, natural clay material with an ultimate bearing capacity of 45 ksf (see FSAR Table 2.5-14).
The sustained loads of containments The correspond to a uniform soil pressure of about 9.5 ksf.
containment base slab is 9 to 13 feet thick and is stiffened by the cylindrical, primary shield, and secondary shield walls.
The containment structure is very stiff as demonstrated by an Under dead load, the structural deformation elastic analysis.
in the central portion of the base slab over 40 feet of radial
' distance is calculated to be only about 0.012 inch of differential l
vertical deflection.
Thus, the structural behavior of the i
contai*
3nt is relatively insensitive to variations in the properties of the foundation material.
This has been demonstrated by a study conducted in 1978, which showed that the stresses in the containment change less than 0.5 percent for the load combination with 1.5 times the design pressure when the foundation soil stiffness is uniformly changed by 25 percent.
The total estimated settlement for the containments for 40 years is about 2.5 inches (see FSAR Figure 2.5-48, Rev 47).
This includes the estimated settlement of about 0.8 inch from permanent dewatering.
These estimated settlements have not been exceeded.
Measured settlements indicate that the containments have experienced only rigid-body vertical displacement (settlement) and rotation (tilt).
This has caused the containment structures to experience only minor stresses or strains.
Conclusion The Midland plant has two prestressed concrete con-tainments.
Small cracks with random orientation have been observed at the outer surf ace of the Unit 1 and Unit 2 con-tainment walls near the junction base slabs and the buttresses.
These cracks are determined to be from volume change effects, predominantly shrinkage strains, in the containment wall-re-strained by the base slab and the buttress.
This type of 9
Ahrinkage crack is to be expected and is secondary in nature,
-with no effect_on the capability of the containment.
Shrinkage cracks on the outer surfaces of similar prestressed concrete containments situated at different parts of the country have been reported in SIT reports for Arkansas Nuclear One, Unit 2, Palisades, Farley Unit 1 and Calvert Cliffs, Unit 2.
Because the containments are very stiff, their structural behavior is not sensitive to variations in the properties of foundation soil material.
The containments have experienced only rigid-body, vertical displacement-(settlement) and rotation (tilt) from settlement of the foundation material.
Representative portions of the outer surface of the containments will be inspected and monitored for cracks during 1
the SIT and during tendon surveillance.
In addition, Applicant has agreed to carry out the containment crack monitoring described in this affidavit.
Therefore, in my judgment the cracks observed in the Midland containments do not represent a safety problem and do not call into question the integrity of the containment structures or the adequacy of the foundation material.
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