ML16342B658
| ML16342B658 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 03/20/1990 |
| From: | Rood H Office of Nuclear Reactor Regulation |
| To: | Shiffer J PACIFIC GAS & ELECTRIC CO. |
| References | |
| TAC-74142, TAC-74143, NUDOCS 9003270396 | |
| Download: ML16342B658 (12) | |
Text
March 20, 1990 Docket Nos. 50-275 and 50-323 Hr. J.
D. Shiffer, Vice President Nuclear Power Generation c/o Nuclear Power Generation, Licensing Pacific Gas and Electric Company 77 Beale Street, Room 1451 San Francisco, California 94106
Dear Hr. Shiffer:
DISTRIBUTION c~g NRC 5 LPDR PD5 Reading JZwolinski CTrammell HRood OGC E. Jordan D. Jeng J.
Ma N. Chokshi G. Bagchi R.
Rothman ACRS(10)
H. Hendonca (RV)
P. Narbut (RV)
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION RELATING TO NRC STAFF REVIEW OF MASONRY'WALL ISSUES AT DIABLO CANYON (TAC NOS.
74142 AND 74143)
As you know, the NRC staff is evaluating certain issues related to the seismic qualification of masonry walls at Diablo Canyon.
Enclosed are the issues the staff has defined in this area.
In order to achieve timely closure of these
- issues, we request that you address each issue identified in
,,the enclosure by Hay 20, 1990.
If you have any questions regarding this request, please contact me.
Sincerely,
Enclosures:
as stated cc w/encl:
See next pa DRSP/PD5:PH ET/ SGB'BC HRood GBagchi 03/P)/90 03/q G'/90 original signed by Harry Rood Harry Rood, Senior Project Manager Project Directorate V
Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation R
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Docket Nos.
50-275 and 50-323 UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20555 March 20, 1990 Mr. J.
D. Shiffer, Vice President IIuclear Power Generation c/o Nuclear Power Generation, Licensing Pacific Gas and Electric Company 77 Beale Street, Room 1451 San Francisco, California 94106
Dear Mr. Shiffer:
SUBJECT:
RE(UEST FOR ADDITIONAL INFORMATION RELATING TO NRC STAFF REVIEW OF MASONRY WALL ISSUES AT DIABLO CANYON (TAC NOS.
74142 AND 74143)
As you know, the NRC staff is evaluating certain issues related to the seismic qualification of masonry walls at Diablo Canyon.
Enclosed are the issues the staff has defined in this area.
In order to achieve timely closure of these
- issues, we request that you address each issue identified in the enclosure by May 20, 1990.
If you have any questions regarding this request, please contact me.
Sincerely,
Enclosures:
as stated cc w/encl:
See next page Harry Rood, Senior Project Manager Project Directorate V
Division of Reactor Projects - III, IV, V and Special Projects Office of Nuclear Reactor Regulation
Mr. J.
D. Shiffer Pacific Gas and Electric Company Diablo Canyon CC:
Richard F. Locke, Esq.
Pacific Gas 5 Electric Company Post Office Box 7442 San Francisco, California 94120 Ms. Sandra A. Silver 660 Granite Creek Road Santa Cruz, California 95065 Mr. Peter H. Kaufman Deputy Attorney General State of California 110 West A Street, Suite 700 San Diego, California 92101 Managing Editor The Count Tele ram Tribune 1321 o nson venue P. 0.
Box 112 San Luis Obispo, California 93406 Ms. Nancy Culver 192 Luneta Street San Luis Obispo, California 93401 Regional Administrator, Region V
U.S. Nuclear Regulatory Commission 1450 Maria Lane, Suite 210 Walnut Creek, California 94596 Mr. John Hickman Senior Health Physicist Environmental Radioactive Mgmt. Unit Environmental Management Branch State Department of Health Services 714 P Street, Room 616 Sacramento, California 95814 NRC Resident Inspector Diablo Canyon Nuclear Power Plant c/o U.S. Nuclear Regulatory Commission P. 0.
Box 369 Avila Beach, California 93424 Bruce Norton, Esq.
c/o Richard F. Locke, Esq.
Pacific Gas and Electric Company Post Office Box 7442 San Francisco, California 94120 Dr.
R.
B. Ferguson Sierra Club - Santa Lucia Chapter Rocky Canyon Star Route Creston, California 93432 Chairman San Luis Obispo County Board of Supervisors Room 270 County Government Center San Luis Obispo, California 93408 Michael M. Strumwasser, Esq.
Special Assistant Attorney General State of California Department of Justi ce 3580 Wilshire Boulevard, Room 800 Los Angeles, California 90010
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ENCLOSURE I REQUEST FOR ADDITIONAL INFORMATION RELATING TO DCPP MASONRY WALLS The NRC staff has completed its review of the information contained in PGSE's letter of November 10, 1989, as well as the other information on the Diablo Canyon docket relating to masonry walls.
PG&E's November 10, 1989 letter provided, at the NRC staff's request, information relating to the use of the Energy Balance Technioue (EBT) for qualification of masonry walls at Diablo
- Canyon, and other related information and calculations.
The use of the EBT at Diablo Canyon is based on proprietary tests on masonry walls.
The EBT is a method which is based on the hypothesis that the elastic energy in an elastic system generated by external loads can be absorbed or balanced by an equivalent elasto-plastic energy if the structure or system can deform plastically after the elastic limit has been reached.
The hypothesis upon which the EBT is based is believed to be logical; however its use must be verified with ample data.
Pecent NRC staff review of the benchmarking and criteria of the EBT used at the DCPP walls has raised five concerns which need to be addressed.
These issues are described below.
Issue No.
1 Justification For Using Displacement Ductility Ratio (U)
= 5 Our review of the masonry wall test data used indicates that the maximum displacement ductility ratios developed in the three applicable test walls was in the range of 2.3 to 3.3.
Based on the this, we request that you provide justification that a value of U =
5 can be used for the SSE (Hosgri) condition since the tests do not appear to have substantiated a value this large.
Issue No.
2 Consideration of Wall Stability In the Vertical Direction A plastic hinge at the wall-footing connection and another plastic hinge near the wall mid-height formed during the tests.
Even with these two plastic
- hinges, no wall stability problems in the vertical direction were observed.
The stability problem would not occur for the test set up because there was a
positive connection at the top of test walls.
However, the situati'on may be different in the DCPP walls.
The DCPP walls are connected to the top beams by two clip angles bearing against drypack (unreinforced concrete),
which was poured on the top of the masonry walls.
This is not a positive connection.
It appears that a coefficient of friction of 0.4 was used between the drypack and clip angle to establish stability. If this use of frictional force between the drypack and the clip angles is meant to eliminate the wall stability problem in the vertical direction by pulling the wall upwards, we request that you provide evidence as to the magnitude and reliability of such forces.
In addition, we note that the test walls were loaded only by horizontal actuators placed perpendicular to the walls at the top and bottom of the walls.
Therefore, the tests do not include any vertical seismic motions, which would occur in real earthquakes.
Consequently, we request that you address the wall stability problem in the vertical direction considering three-directional seismic motions.
Issue No.
3 Use of an Unreinforced Concrete Connection In Safety-Related Walls Since the DCPP walls were not designed as cantilevers, they wi 11 rotate against the wall-footing connection and become unstable and fail during an earthquake if the top connection fails.
Since the top connection is brittle and its failure will lead to the failure of the entire wall, the capability of the connection to transfer wall loads to the top beam must be assured with a high degree of confidence.
Stresses around a connection are local stresses and their nature and magnitude are difficult to assess and calculate.
Therefore, physical tests are usually performed for new types of connections to gain understanding of their behavior and strength.
PG5f has not provided'ny test data for these connections and appears to justify the connection capability only by calculating its shear transfer capability on uncracked concrete sections with shear acting alone.
This justification is not adequate.
It appears that the end restraint from the clip angles to the drypack will produce a bending moment, which will generate tension on one side of the wall, due to horizontal seismic motions, and a direct tension over the whole cross-section due to vertical seismic motions.
The shear, bending
- moment, and direct tension act simultaneously on the top connection during seismic
- motions, and they all produce tension because even the shear is actually creating a diagonal tension in this case.
Furthermore, shrinkage cracks, if present, will reduce the concrete tensile strength, and the quality of construction workmanship influences the tensi le strength of the drypack and the bond strength between the drypack and masonry.
It is an almost universal
- practice, and a building code requirement, in situations such as this one, which involve a high degree of uncertainty and structures located in high-seismic
- zones, to use positive ductile connections to transfer tensile fo>ce instead of relying on the tensile strength of unreinforced concrete.
In light of the above, we request that you provide justification for the use of drypack top connections in safety-related masonry walls at Diablo Canyon.
Issue No.
4 Discrepancy Between Measured and Calculated Values of Rebar Strains The rebar strains measured in the three test walls differ by a factor of about 2 from those calculated using the EBT.
Rebar strain is the basic element in establishing the moment-curvature relationship of a cross-section that is needed for calculating wall deflection.
Therefore, the above discrepancy in calculated and measured rebar strains is an indication of problems with the EBT hypothesis.
This'ndicates the need for benchmarking of nearly identical end conditions.
Nearly perfect matches have been obtained and reported in deflections of reinforced concrete beams loaded in the inelastic range and up to collapse between test measurements and calculations usino the moment-area method.*
Therefore, we request that you re-examine the adequacy of the application of the EBT to the DCPP situation.
You appear to have used rebar strain variations over the height of the wall to calculate wall deflections.
If that was the case, it would have been incorrect, because curvature variations should be used rather than of rebar strain variations.
Please discuss this item in your re-examination.
Issue No.
5 Lack of Engineering Similitude Analyses PG&E benchmarked the EBT against three of the test walls (other walls were reported as not applicable because no rebar yielded near the mid-height of walls),
and applied it without modifications to the DCPP walls.
Although the rebar and concrete properties and the height of walls are different between the test walls and the DCPP walls, PGLE has not addressed whether or not these differences would lead to different criteria for the EBT.
For example, an x value of U for the height test walls may be equivalent to a y value of U
for a wall at DCPP of about half the height of the test wall, through engineering similitude analyses.
Without such a proper transformation or modification, applying the criteria b'enchmarked from the test walls with certain kind of material properties to walls of substantially different heights with different material properties may be in error.
He request that you address this issue.
- Several Master theses and Ph.D dissertations published by the University of Texas at Austin have used this method for reinforced concrete beams and prestressed concrete beams with both bonded and unbonded tendons
7