ML19246A591
| ML19246A591 | |
| Person / Time | |
|---|---|
| Site: | Maine Yankee |
| Issue date: | 05/24/1979 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Groce R YANKEE ATOMIC ELECTRIC CO. |
| Shared Package | |
| ML19246A593 | List: |
| References | |
| NUDOCS 7907060155 | |
| Download: ML19246A591 (9) | |
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UNITED STATES NUCLEAR REGULATORY COMMISSION y
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May 24, 1979 S
Docket No.: 30'309 Mr. Robert H. Groce Licensing Engineer Yankee Atomic Electric Company 20 Turnpike Road Westboro, Massachusetts 01581
Dear Mr. Groce:
The Commission has issued a Termination of Order to Show Cause for the Maine Yankee Atomic Power Station. A copy is attached as Enclosure 1.
This Order terminates the Order to Show Cause issued March 13, 1979, thereby allowing the facility to be restarted. The bases for this action are set forth in the staff's Safety Evaluation attached as.
Also attached (as Enclosure 3) is a staff document titled " Discussion of Conservatisms in Maine Yankee's Seismic Design."
A copy of this Order is being filed with the Office of the Federal Register for publication.
Sincerely, f
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Operating Reactors Branch #4 Division of Operating Reactors Er. closures:
1.
Termination of Order to Shcw Cause 2.
Safety Evaluation 3.
Discussion of Conservatisms in Maine Yankee's Seismic Design cc w/ enclosure : See next page 907 c
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Yankee Atomic Electric Company
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cc w/ enclosure (s):
Mrs. L. Patricia Doyle, President E. W. Thurl ow, Presi dent SAFE POWER FOR MAINE Maine Yankee Atomic Power Company Post Of fice Box 774 9 Green Street Camden, Maine 04843 Augusta, Maine 0433u First Selectnan of Wiscasset Mr. Donald E. Vandenburgh Municipal Building Vice Presicent - Engineering U. S. Route 1 Yankee Atonic Electric Conpany Wiscasset, Maine 04578 20 Turnpike Road Westocro, Massachuset+.s 01581 Director, Technical Assessment Division John A. Ritsher, Esquire Office of Radiation Programs Ropes & Gray (AW-459) 225 Franklin Street U. S. Environmental Protection Agency Boston, Massachusetts 02110 Crystal Mall #2 Ailington, Virginia 20460 Mr. John M. R. Paterson Assistant Attorney General U. S. Environmental Protection Agency State of Maine Region I Of fice Augusta, Maine 04330 ATTN:
EIS COORDINATOR JFK Federal Building Mr. Nicholas Barth Boston, Massachusetts 02203 Executive Director Sheepscot Valley Conservation Association, Inc.
P. O. Box 125 State Plannina Of ficer Al an, Maine 04535 Executive Department State of Maine Wiscassett Public Library Association 169 State Street High Street Augusta, Maine 04330 Wiscasset, Maine 04578 Mr. Robert R. Radcliffe Of fice of Energy Resources 55 Capitol street Augusta, Maine 04330 Mr. Harold T. Judd Deputy Consumer Advocate State of New Hampshire Legisittive Utility Consumer's Council 109 North Ma n Street i
Concord, New Hampshire 03301 r,
DISCUSSION OF CONSERVATISMS IN MAINE YANKEE'S SEISMIC DESIGN While increasing the SSE seismic input from 0.1g with a Housner spectrum to between 0.13 to 0.2g with a Regulatory Guide 1.60 see:Lrum may seem to be a large percentage increase in seismi.c input, the inherent resistance of a facility properly designed to 0.19 should, in general, provide adequate resistance to the relatively low seismic input of between 0.13 to 0.2g.
For example, the impact of increasing from 0.19 to 0.2g is much less severe than going from 0.25g to 0.59 Tnis is because nuclear plant designs are based on various combinations of loads with seismic loads as only one part. As an example, of the 85 piping runs analyzed at Maine Yankee, all of the peak stress points would be less than 50" of ultimate strength even if the seismic stresses are doubled from the 0.1g level. Only six of the runs would have peak stresses greater than current allowable stress limits, even though eleven runs would have peak stresses exceeding the more conservative criteri3 in the FSAR. Of the six runs with peak stresses over current allowable stress limits, it is likely that these stresses would be less than the actual material yield stress.
Seismic design of nuclear power requires interaction between these principal endeavors: (1) definition of the seismic hazard, in terms of intensity and characteristics of shaking, and (2) design of structures, systems and components to resist the defined seismic shaking.
The definition of seismic hazard invloves consideration of the geology and seis-mology of the region, observed ground motion, and observed effects of earthquakes.
The information available for historic records, measurements recorded in more recent years, and insights that can be gained from analyses and damage assessment I
following earthquakes have been synthesized to arrive at the engineering methods we use to define the seismic hazards for nuclear power plants, dams and other public structures.
The seismic input, once defined, is used in a mathematical process to determine how the structure would vibrate in response to the seismic shaking. Throughout this process very complex natural phenomena and the response of complex structures and equipment are idealized so that the principles of applied mechanics and mathematics can be employed to determine the response of each of the major portions of the structures and equipment. To compensate for these idealizations the engineering practices involved in the seismic design for nuclear power plants establish a conservative design quantity at each stage in the analytical process (see the attached 'ist of conservatisms). The 'inal design, resulting from compounding of the conservatisms in each step, is therefore also conservative.
For plants of the Maine Yankee vintage, conservatisms in the seismic analysis and design for structures, systems and components are generally found in the following areas:
(1) Elastic' dynamic analyses are performed using conservatively low damping values.
(2) Multiple-directional seismic input, with each horizontal component having equal intensity, is considered in design of plants. Actual earthquakes are typically stronger in one direction.
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3-(3) The OBE is selected at one-half of the SSE and controls the design in many cases, rather than the SSE, dae to the substantially lower allowable stretses for the OSE.
(4) Loading combinations consider other loadings (dead weight, live loads, pressure loads, etc.) in addition to the seismic loadings.
Seismic loading is therefore only a part of the total loading and in fact, loadings other than seismic may govern designs. A sizable increase in seismic stresses may be only a small addition to the total stresses.
(5)
In the design of structures and equipment, all elements of the structure or eq ipment are designed to stress levels well below the actual strength of the materials so that any permanent deformation is very small. This approach obviates the need for complex and costly inelastic analyses.
Inelastic behavior would significantly reduce structural response prior to failure.
(6) Stress limits, whethea elastic ar inelastic, are based upon material behavior under static loading conditions. Since dynamic loads contain a limited amount of energy, the margin (between the stress limits and failure) under dynamic loads is greater than under static loads if elastically calculated peak response is compared to the stress limits with strain ' rate effects neglected.
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. (7) The design of the structural elements is such that their capacity usually exceeds the seismic requirements called for by the analyses.* In Maine Yankee, orthogonally spaced reinforcing steel was used in the containment wall with additional diagonal reinforcement at large penetrations. Much of the actual structural design is controlled by the availability of standard structural members, such as beams and piping sections, so that larger sizes than are needed are often used.
(8) Engineering codes specify " code minimum stiength" for materials.
In-situ strengths are usually higher.
Additional conservatisms for major mechanical components and piping can be tcund in:
(1 ) When the floor response spectra are developed for the design of components located at different locatior.s in the structure, the peaks in the individual floor response spectra are broadened in order to reflect conservative responses.
(2) Where the system has multiple supports, maximum response spectra is usually applied to all support points.
(3) When calculating the seismic loads for components, conservatively estab',ished values are applied several times (first, to major structures, then to the intermediate structures and finally the equipment themselves).
- The staff has also considered that this containment design does not have diagonal reinforcing in certain areas of the containment (as discussed in the Septemter 26, 1969 letter to Dr. Peter A. Morris, Director, Division of Reactor Licensing, USAEC, frcm Bruce B. Seckley, Maire Yankee At;mic Pcwer Station) in reaching its conclusions regarding the conservatisms in the Maine Yankee seismic design. The containment design, using orthcgonal reinforcement, nas been re-examined by the staff in conjunction with the licensee and has been shown to have the required seismic resistance. The re-examination was based upon consideration of the inherent strength of the concrete shell which incluced aggregate interlock considerations that had not been considered in previous analyses.
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. (4) Even identically designed redundant systems may not always experience similar seismic excitation due to different mounting locations-with different structural filtering effects. Thus, a loss of a redundant c-1ent may not mean a loss of function for the system.
The end result of the conservatisms employed in the analyses, followed by the conservatisms resulting ffom standard design practices, is structures and components with seismic capability well in excess of the established design goal.
This is the reason that the record is replete with cases where weli engineered structures, even those for which no specific seismic design sti. idard was invoked, have withstood major earthquakes while reiaaining fully fun'.. anal. A number of plants of various kinds have been subjected to large earthauakes.
The Esso re-finery in Managua, Nicaragua is a good example. Another example is the pump stations in the Exxon pipeline in Italy, subjected to the Friuli earthquakes.
These are structures that were designed by ordinary codes, wina perhaps the seismic design coefficient of the order of.05 to.08g.
The earthquakes that occurred had accelerations that were measured of the order of.35g in Managua and perhaps more than that in Friuli. The Esso refinery was able to continue operating with no damage to any of the equipment while the pump stations on the Exxon pipeline were able to continue operating without damage to the equipme.it.
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. For these reasons the staff judgment is that the major structural components of the Maine Yankee facility will likely remain functional even for an increased range of seismic ir,.t of frcm 0.13 to 0.29 Even at the 0.29 level, it is unlikely that the seismic event would initiate a serious accident. For minor mechanical and electrical equipment, wnere the fragility is likely-lower, loss of function is not expected to be sufficient to prevent plant shutdcwn when all plant systems and available corrective actions are considered.
The likelihood of the SSE is presently judged to be on the order of 10-3 or 10-4 per year for the 0.13 to 0.29 range, decreasing with the higher values.
The confidence in the judgment that major structural components will likely remain functional increases at the lower SSE range.
The NRC will be further considering the issue of seismic design capability of all operating reactors within the next few months. That effort will further examine the seismic design capability of Maine Yankee. That effort
.will also assist the staff in detennining whether additional seismic re-evaluation is needed at any operating' facility.
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CONSERVATISMS IN SEISMIC DESIGN I.
Seismic Design for Ground Motion Enveloping response spectra and time histories Conservative OBE (usually controls design)
II. Seismic Analysis and Design Method Structures, systems and components a.
Elastic dynamic analysis (inelastic behavior can significantly reduce response spectra)
Da-;ing values Multi-directional earthquakes Loading combinations (seismic only a fraction of total loads) b.
Additional conservatisms for piping and major components Peak widening of floor response spectra System Redundancy Generic Qualification for Many Plants Use of maximum and widened response spectra for multiple supported systems Multiple applications of damping values III. Structural and mechanical resistance factors Allowable stress from Code Dynamic resistance of materials 25 cay concrete strength Ductility to failure Minor attachments absorb energy Redundancy in structural elements Use of standard size pipe and equipment Quality Assurance IV. Seismic Experience to Date Inherent resistance shown for large industrial facilities Nuclear plant resistance shown in Japan Other loads (wind and pressure) influence design I