ML20077E748
| ML20077E748 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 07/25/1983 |
| From: | Lundvall A BALTIMORE GAS & ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8307280430 | |
| Download: ML20077E748 (4) | |
Text
.
L BALTI M ORE GAS AND ELECTRIC CHARLES CENTER P.O. BOX 1475 BALTIMORE, MARYLAND 21203 ARTHUR E. LUNDVALL. JR.
VICE PRESIDENT SUPPLY Director of Nuclear Reactor Regulation Attention: Mr. R. A. Clark, Chief Operating Reactors Branch #3 Division of Licensing U.S.. Nuclear Regulatory Commission Washington, D.C. 20555
Subject:
Calvert Cliffs Nuclear Power Plant Units Nos.1 & 2; Dockets Nos. 50-317 and 50-318 Main Steam Line Break Inside Containment
Reference:
- 1. BG&E letter from Mr. A. E. Lundvall, Jr.
to Mr. R. A. Clark, dated June 8,1983
- 2. BG&E letter from Mr. B. S. Montgomery to s
a -
Mr. R. A. Clark, dated July 1,1983.
Gentlemen:
Reference 1 forwarded the results of our statistical evaluation of the actual material strengths (concrete and reinforcing steel) used in the Calvert Cliffs containments.
You had requested this information to support your evaluation of continued oeprations at Calvert Cliffs until such time as corrective modifications to the main feedwater system had been completed.
On June 23, 1983 you requested (via telephone) that a similar~ evaluation of
. material strengths be performed for the containment tendons. In response to that
'. request, we stated in Reference 2 that the maximum stress levels in the containment post-tensioning system would be well within allowable limits for the postulated main steam line break (MSLB) accident, and that as a consequence, an evaluation of actual material strengths for tendons was unnecessary.
During a second telephone conversation on July 7,1983, you acknowledged our-response and requested that we specifically quantify the stress levels that will
...present in the containment post-tensioning system following the postulated MSLB. The requested information, along with a narrative of stress distributions in containment
- cemponents versus time, is attached for your review.
,c The Baltimore Gas and Electric Company reaffirms its assessment that continued operation of the Calvert Cliffs Nuclear Power Plant, until such time as horrective actions are completed (November 17,1983), does not represent an undue risk to the health and safety of the public. As indicated in our letter of May 17,1983 we are proceeding with the installation of an automatic trip of main feedwater system pumps I
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- Mr. R. A. Clark l
1 upon containment high pressure.
This design feature will provide a backup to the automatic action of the main feed regulating valve as a means for terminating runout feedwater flow to the affected steam generator after a MLSB.
If there are an questions, please do n'ot hesitate to contact us.
Sincerely,
[,.
, &<redi ' A.-
AEL/BSM/vf Enclosure cc: 3. A. Biddison, Jr., Esq.
G. F. Trowbridge, Esq.
Mr. D. H. Jaf fe, NRC
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Mr. R. E. Architzel, NRC m
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a What is the state of stress in the Calvert Cliffs prestressed Question concrete containment for a postulated internal differential Pressure of 80 psi? In particular, why was the rebar considered as the critical structural elment rather than the prestressing system?
Under normal operating conditions the contaiment is subjected to
Response
stress due to daadweight and the prestressing forces. 'Ihe prestressing places the tendons in tension and the other structural elerrents, the liner plate, the reinforcing steel, and the concrete in cortpression. '1he basic function of the reinforcing steel is to resist stresses due to tertperature, and concrete shrinkage as well as local secondary forces (see FSAR Sect. 5.1.2.1).
As the postulated accident pressure increases, the initial effect on the containment state of stress is a reduction of the initial corpressive stress field without a significant change in the tendon tension. For exattple, at a pressure of 1.2P (60 psi), these catpressive stresses reduce to zero in the hoop direction and would be equivalent to the stress resulting frcra deadweight alone in the meridonal direction. As the pressure further increases, the concrete is assumed to crack. Although any additional tensile forces due to the increased pressure 5xuld mainly be resisted by the tendons, the contribution of the liner plate and reinforcing steel can be included. As these tensile elements are stressed above their yield, further pressure increases are resisted entirely by the prestressing tendons. 'Ihe pressure which can be resisted by the l
tendons at their yield point is in excess of 100 psi. A detailed l
discussion and quantification of the design basis of the Calvert Cliffs containment is provided in Section 5.1.2.1 of the FSAR.
'IM re-evaluation of the stresses in the containment at a postulated internal pressure of 80 psi indicates the tendon stress levels range between 58% to 73% of the ultimate capacity.
'ihese levels of stress are within the allowable design limits of the prestressing system. Table 1 prM% a sumary of the I
tendon and reinforcing steel stress A -
st three critical sections in the meridonal direction ano et a typical midheight section in the hoop direction. 'Ihe basis of these tabulated stresses are the previously evaluated load cmbinations which include D+F, D&F+1.5P, and D+F+1.5P+Ta.
In calculating the increase in cxxtponent stress due to the higher pressure, strain ocarpatibility of the section (reinforement, liner plate and I
prestressing) is utilized. 'Ihe 1.5P term in the above load l
ocarbinations has therefore been increased to 1.6P or 80 psi.
Based on the Table 1 results it is concluded that at the postulated pressure of 80 psi, the reinforcing steel yield stress r
is reached while the stresses in the prestressing tendons remain i
within allowable design limits.
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t Table 1: Critical Section Tendon and kbar Stress for Postulated 80 psi Internal Pressure Critical Direction load
'hmdon fst Reinforcing Steel Section Cortb.
Stress fpu Inside Outside Iocation (hsi)
(%)
face face (ksi)
(ksi)
Spring line Meridonal D+F+1.6P+Ta 164 68%
16.
50.
Cylinder Meridonal D+F+1.6P+Ta 157 66%
14.
37.
Midheight Cylinder Hoop D+F+1.6P+Ta 175 73%
13.
60.
Midheight Base haunch Meridonal D+F+1.6P+Ta 147 61%
7.
21.
- Base haunch Meridonal D+F+1.6P 140 58%
60.
-11.
- Critical load cabination for reinforcement in the base haunch area N0tENCIA'IURE D - Dead weight F - Prestressing force P - Design pressure (50 psi) l fst - Stresses in tendon fpu - Ultimate tendon strength t
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