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SUMMARY
ANALYSIS l BY THE I
..i DIVISION OF REACTOR LICENSING q i
a IN THE MATTER OF l'
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PACIFIC GAS & ELECTRIC COMPANY BODEGA HEAD NUCLEAR POWER PLANT DOCKET NO. 50-205 1
October 26, 1964 i
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SUMMARY
ANALYSIS BODEGA HEAD NUCLEAR POWER PLANT Summary In our review of the application from Pacific Gas and Electric Company, we have taken into account the reports of the Commission's Advisory Committee on Reactor Safeguards, and information supplied by our consultants in geology, seismology and structural engineering. .We also have had numerous discussions with representatives of the Company and with PG&E's consultants.
We believe that in all respects except ohe the proposed design of the Bodega Nuclear Power Plant provides reasonable assurance that the plant can r
be built and operattid without undue risk to the health and safety of the.
public. The one exception is the uncertainty associated with the proposed design concept to safeguard the reactor against the effects of a major earth-quake involving substantial shear movement of the foundation rock.
The proposed reactor site is approximately 1000 feet west of the western edge of the San Andreas fault zone. The location has necessitated prolonged and intensive study of factors affecting the safety of the in-sta11ation in the event of the occurrence of a severe earthquake a,t or near the location of the plant.
The fact that' the proposed site is adjacent to the San Andreas fault b zone makes it almost certain that it will be subjected to one or more severe d
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seismic disturbances during the 1ifetime of the' plant.. While there is a 1 1
high probability that.the plant under the proposed design could survive the vibrational stresses of even a very large earthquake without damage, I
it must be recognized that if such an earthquake should also involve several feet of shear ground movement as well'as ground. accelerations as high as
'i 2/3g to 1.0g there is presently no sound experimental or experience basis l t
]j for predicting.the extent of damage that might be-incurred by the reactor-containment. structure and emergency equipment designed'to assure the safety )
1 of the reactor.
. I A novel method is proposed for safeguarding the Bodega Head reactor against differential ground movement of its foundation rock.- This is not in itself a cause for concern. What is of concern is the lack of any experi-mental or experience proof-test of the proposed novel method' that could form an acceptable basis for the required safety evaluation.
Because of the magnitude of possible consequences of a major rupture in the reactor containment accompanied by a failure of emergency equipment, we do not believe that a large nuclear power reactor should be the subject of a pioneering construction effort based on unverified engineering principles, i however sound they may appear to be.
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. For these reasons, it is our conclusion that Bodega Head is not a suitable location f,or the proposed nuclear power plant at the.present state of our knowledge.
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History -
The Pacific Gas and Electric Company of San Francisco on December 28, 1962, submitted an application to the Atomic Energy' Commission (AEC) for a permit to construct and operate a nuclear power plant at Bodega Bay, California, pursuant to the provisions of Title 10, Chapter 1, Code of Federal Regulations, Part 50
, (10 CFR 50). The application, which includes a " Preliminary Hazards' Summary Report," dated December 28, 1962, and Amendments 1 through 9, received during the period March 4,1963, through September 16, 1964, has been reviewed by the AEC's' Division of Reactor Licensing and other members of the Regulatory Staff.
Technical consultants assisted the staff in specialized areas. The application l 1
was also considered by the AEC's Advisory Committee on Reactor Safeguards (ACRS).
The recommendations of the ACRS were expressed in letters to th.e Chairman of the AEC dated April 18, 1963, and October 20, 1964.
Site -
The nuclear power plant is proposed for construction on Bodega Head, a small peninsula in Sonoma County on the Coast of California about 50 miles northwest of San Francisco.' The property owned by Pacific Gas and Electric Company at the site consists of approximately 225 acres and includes the entire southern en'd of the peninsula. The proposed reactor site is approximately 1000 feet vest of the Western edge of the San Andreas fault zone.
The nearest residence to the site is approximately 1-1/2 miles awsy.
Bodega Bay (population 350) is the nearest village and is located approxi-mately 2 miles north-northeast of the reactor site. The total population within 5 miles is about 500 and within 25 miies is abou't 114,000.
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The nuclear power reactor proposed for construction on Bodega Head is a
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direct. cycle, forced circulation, boiling water type. Reactors of the boiling water type have been operated successfully at Dresden, Illinois, Big Rock, 1 Michigan, and Humboldt Bay, California. Design power at Bodega is 1008 thermal megawatts (Mwt), compared with 700 Mwt for Dresden, 240 Mwt for Big Rock Point
, i and 165 Mwt for Humboldt Bay. l i
The reactor core will have an active fuel length of 125 inches and a diameter of 137 inches. It will contain 592 fuel assemblies and 145 movable I
control rods (cruciform blades). The control rod drives will be similar to '
the rod drives which have been used at Dresden, Big Rock Point, and Humboldt Bay. l l
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ForcontainmentattheBodegaBayplantthecompan[proposestoutilize .
the pressure suppression concept similar to that already in use at its Humboldt Bay plant. The reactor vessel and the coolant recirculation system j are to be enclosed in a dry well vessel, whose volume is about 115,000 cu. ft. J The' dry well is connected through eight vent pipes, each eight feet in diameter, to a suppression chamber with a volume of approximately 142,000 !
cu. ft., o'f which about 62,000 cu f t. is filled with water. In the unlikely ]
event of a complete severance of a reactor coolant recirculation line, the pressure build-up in the dry well would be reduced both in magnitude and l
duration as a result of steam flow to the suppression pool where the steam
% would be condensed'. (Any fission products released either concurrently or subsequently would be trapped either in the dry well or suppression chamber.)
l Test's have been conducted that demonstrate the effectiveness of this concept.
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i The fuel-handling facilities at this plant provide for underwater transfer
'of spent fuel from the reactor vessel to the fuel storage pool through an interconnecting pool of water. These operations are to be conducted inside a refueling building which will be maintained at a slight negative pressure by fans which discharge air through particulate and halogen removal filters to1
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a stack, thereby minimizing the possibility of direct out-leakage from the buil' ding .
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$ Radioactive liquid wastes from the Bodega plant are to be mixed with condenser effluent (about 250,000 gpm) prior to discharge to the Pacific Ocean. All solid wastes with radioactive contamination are to be transferred to licensed waste disposal agents for of f-site disposal. Radioactive gases 4
are to be vented to a special stack the height of which is to be specified ,
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on the basis of results of a meteorological ~ survey now in progress. The dis-pos,a1 of both liquid and gaseous radioactive wastes resulting from plant operations will be monitored and controlledf eo..that at any off-site location the concentration of radioactive contaminants will not exceed the, limits set forth in Title 10, Code of Federal Regulations, Part.20t. ,
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Important Safety Considerations ;
i In our evaluation of this application, we have-given;special consideration to a number of site and design features which .have .important safety implica-tions. The more imp,ortant..of these. safety considerations.are discussed in .
'the following paragraphs.
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- 1. Suitability of the Prdposed Site !
Based on considerations of-potentialnhazards to3p9blic health. pad ,
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safety, this reactor site is an excellent one in all respects except one - the possibility of a severe earthquake ' involving substantial shear
. earth movement at the site. Earthquake problems posed by this l'ocation are considered in a later section of thic report.
By virtue of property ownership by PG&E, as enhanced by the water areas on three sides of the peninsula, the applicant can exert positive control over an area having a minimum radius of about 450 feet from 1 the reactor, and can exert substantial control over an crea extending out to a radius of about 1300 feet, the nearest point on Doran Beach across the harbor entrance channel.
The population in the vicinity of the site is low and the iso- I lation distances are well within acceptable ranges. The meteorology l
is as good as or better than that in California generally. The site is not upstream from any drinking water intakes.
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Suitability of the Nuclear Reactor Design l
The boiling water nuclear reactor proposed for the Bodega plant is of a type that has be en operated safely at a number of other locations including Dresden, Big Rock Point and Humboldt Bay.It is expected to exh'ibit negative temperature and void coefficients of reactivity at ope, rating conditions. Further, the reactor will be a m .
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brought to. full. power through a step-wise approach so that any unforeseen instability would be detected before a damaging nuclear excursion could result.
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. The Bodega Bay reactor is to be designed so that at any time
- during core life with all control rods inserted the k-effective of the core will.not exceed 0.97. With the most reactive rod fully
- withdrawn and the other rods fully inserted, the k-effective of the ;
core will be 0.99 or less. Thus, the reactor will remain sub-critical if one rod is inadvertently withdrawn, or it can be shut down even if one rod should become stuck in the fully withdrawn position. In addition, a soluble poison control material can be injected into the reactor vessel if needed to hold the reactor sub-critical.
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The control rod drives proposed for this reactor are similar to, j l
but include certain improvements over, the locking-piston type rod i drives that have been used at other plants. The applicant has stated that prototype and production drives will be subjected to functional and endurance tests before reactor startup.
- 3. Suitability of Fuel Handling Facilities The fuel-handling concept for this facility has favorable sr.fety characteristics. During refueling operations th'e fuel storage pool is connected by a water channel to the reactor vessel, thus providing for visual observation and underwater cooling of all operations, and .,
- l eliminating the potential hazards associated with fuel handling casks.
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- 4. Adequacyoh.thedadioactiveWasteDisposalPlansandDesigns Radioactive liquid wastes from this plant are to be mixed with condenser effluent prior to discharge to the Pacific Ocean. No problem l
is anticipated in maintaining the concentration of radionuclides in the inixture.below the maximum permissible concentrations specified in 10 CFR 20. In addition, the applicant has stated that a radiological
, monitoring survey of this site and its environs will be initiated two years before operation of the reactor and will continue after operation !
l commences. Details of the sampling program have not been completed, I but it is expected that quarterly samples would be taken of marine waters, plankton, bottom sediments, invertebrates, shellfish, resident )
fishes and of the intertidal algae and eel grass. Thus, the applicant would be able to determine any reconcentration of radionuclides that might occur before it became a potential safety problem.
All solid wastes from this plant'are to be transferred to licensed waste disposal agents for off-site disposal.
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The applicant has stated that gaseous wastes disposal will be l
monitored and controlled so that a maximum annual exposure at any l off-site location will not exceed permissible limits. There appears to be no reason to believe that this objective cannot be met. The l
diffusion climatology is expected to be satisfactory and a meteorological facility is being installed at the site to develop.a betterunderst$ndingofthelocalmeteorology,sothatanappropriate radioactive gaseous vaste stack height may be selected. A radiological r- ~~~1
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4 c c-survey. program at the site is planned for initiation two years in advance of reactor operation. Quarterly sampling of Noll, vegetation, local agricultural products, well water, stream water and stream mud, and weekly sampling of air particulate and air background are also planned.
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- 5. Adequacy of Emergency Systems i
The applicant proposes to equip the plant with a substantial number of facilities for the safe handling of emergencies. An emergency feedwater pump is provided to assure that the reactor core is always kept submerged in water so long as the reactor vessel and piping beneath it remain intact. Core sp, ray systems are provided to cool the core if, for some reason, such as pipe failure, the core cannot be kept submerged. An emergency condenser with a large water storage capacity and provisions for make-up from the fire system is provided to serve as a heat sink in case the main condenser is damaged. A bleed-and-feed system is available as a backup to the emergency
- condenser. This system provides for bleeding steam from the main l steam line to the suppression pool, and making up water thus lost l
through action of the auxiliary feed water pump or its backup. A liquid poison injection system is available to keep the reactor sub-critical if such action becomes necessary for any reason. .
Several sources, of emergency electric power;are available. A
,startup-standby transformer is provided to supply station service power during plant startup, or in emergencies, from the 220 KV trans-mission system. An auxiliary standby transformer can supply sufficient l
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. . i power for orderly shu'tdown from.a 12 KV distribution line from a, nearby substation. If both'these sources fail, an engine driven )
I generator can supply power for safe shutdown and decayfheat removal. I
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In addition to these sources a substantial station battery will supply power for control instruments and, through an inverter,
.1 essential AC loads. ]
.. .J l 6. Adequacy of the Containment Concept :
1 l l This plant'is to utilize the pressure suppression concept in its containment design. Mockup tests have been conducted by the appli- ]
cant to determine the maximum pressure the containment would experience as a result of the complete severance of one of the ,
i 28-inch recirculation loop lines under a variety of reactor coolant pressures and temperatures, and dry well temperatures. These tests have provided a suitable basis for designing the system and have also I l
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shown that the steam exhausted to the suppression pool is completely. !
condensed beneath the pool surface. ]
The applicant has proposed a number of'special provisions to assure reliable containment performance in the event of an accident.
. Redundant isolation valves are to be placed in the main steam lines.
Containment leak rate tests are to be conducted after installation of all penetrations by applying dry well design pressure to the-
, completed dry well and suppression chamber design pressure to.the
, completed suppression chamber. The containment leaktightness will be l i
tested at periodic intervels throughout the life.of the' plant.
l Specifications for containment design pressure pnd leak rate will limit potential accident consequences to acceptable levels.
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- 7. ' Acceptability of Potential Exposure to the Maximum Credible Accident
- The applicant has evaluated the consequences of a number of credible _l accidents, based on the assumption that the'containme'nt and other safe ' )
guards function as designed. In most cases they would create no significant hazard to'the health and safety of the public. Of those credible accidents which were considered by the applicant to have a e
d - potential for significant releases of radioactivity to the environment, the accident categorized as the refueling accident result'ed in the highest L potential off-site doses. It was assumed in the refueling accident 1 analysis that a fuel bundle was dropped into a near-critical reactor, causing a nuclear excursion which releases fission products into the re-l
. fueling building. Using standard calculation procedures and realistic !
i numbers, the applicant calculated that the maximum off-site potential
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- whole body dose for the duration of this accident'would be 1ess than 1.0 l
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rem. Noble gases are the major contributor to the potential whole body doses from such an accident. Potential thyroid doses from this assumed- l accident would not result in potential whole body or thyroid exposures in excess.of Part 100 guidelines for reactor site criteria.
Research and Development Programs Pacific Gas and Electric Company and its contractors are planning a number of research and development programs, the results of which will be
' utilized in final design of the plant. They include the following: ;
- 1. Radiological Survey l
A preoperational monitoring survey of the site and its environs to be initiated two years before commencement of operation-of the reactor. Although the details of this program have not been completed, 1
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it is anticip&ted that it will be similar to that conducted for the l f
company's llumboldt Bay nuclear unit.
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- 2. Meteorology i A meteorological facility is being installed at the site to pro-vide necessary data for atmospheric diffusion studies. Instruments )
- will be mounted at three levels on a 250 ft. tower and will measure All readings will-be temperature..and' wind speed and direction.
The results of this program digitized and recorded on paper tape.
will be used in calculating the potential dilution of radioactive j
J gases, and.in selecting a suitable stack height.
- 3. Oceanography The capacity of the ocean to diffuse the condenser cooling water and minimize the effects of temperature and radioactivity on
' the marine biota is being' investigated in a series of experiments at the site. These tests include yse of drift poles and uranine dye l
as well as measurements of temperature and salinity. They will continue through at least one annual cycle of oceanographic and meteorological conditions.
- 4. Marine Biology Survey An ecological survey is being conducted to prepare lists of ;
the marine fauna and flora of Bodega Head and Harbor.
- 5. Pressure Suppression Tests Extensive tests of the pressure suppression concept have been conducted at the Company's test facility at its. Moss Landing Power J
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Plant, Additi[onal. t'ests wi11 be conducted at the company's plant to determine whether or not baffles between vent pipes are required in the Bodega suppression pool.
- 6. Fuel Development i
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Results from fuel element development tests and experience with f fuel' designs now employed in existing reactors will form the basis for the selection of the Bodega ~ fuel cladding and its thickness.
- 7. Instrumentation Development In-core startup range neutron detectors are being developed as a possible substitute for the presently planned'out-of-core detectors.
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- 8. Control System Development A prototype Bodega control rod drive will be subjected to extensive
' developmental testing before the final drive design is released for
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- manufacture. Several devices which would reduce the liklihood or ~
magnitude of a control rod dropout accident.are being developed for possible use in the Bodega control system.
I Seismic Considerations !
Ihe. proposed location of the Bodega Nuclear Power Reactor is approxi-mately 1000 feet west of the Western edge of the San Andreas fault zone, a ;
along prominent band of seismic activity running generally north and southL most of the State of California. The choice of this location by the applicant has n, necessitated prolonged and intensive study of factors affecting-the safety of the installation in the event of the occurrence of a severe earthquake at or near the location of the plant.
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Since the field's of. f,eology, seismology and earthquake structural design
- I are highly specialized, it has been necessary to call upon he services of expert consultants for help in analyzing the various pr lems involved in arriving at a decision on the technical feasibility of building the Bodega ]
plant at the proposed location with reasonable assurance that'it will safely withstand the maximum earthquake that might credibly. occur during the life of the plant.
1 The consultants employed by the applicant (PG&E) include Dr. George W. I I
Housner, Professor of Civil Engineering and Applied Mechanics at the California Institute of Technology, Dr. Hugo Benioff, prominent West Coast l Engineering Seismologist, and Mr. E. C. Mar 11 ave,. Consulting Geologist.
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The AEC Regulatory Staff has retained the services of Dr. N. M. Newmark, Professor of Civil Engineering at the University of Illinois and Mr. Robert j
A. Williamson of Holmes & Narver. The staff has been assisted by the U. S.
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I Coast and Geodetic Survey (USC&GS) and the U. S. Geological Survey (USGS) on seismicity and geology.
There is a substantial difference between the viewpoint of the applicant l and that of the USC&GS and USGS with respect to the maximum credible earth-I quake that should be taken as the design basis for the Bodega Head plant.
The PG&E earthquake consultants feel strongly that the maximum ground acceleration to be expected during any credible earthquake at or near the plant site is 0.3,3g, and they consider it incredible that there should ever
' be more than a few inches of differential ground motion under the site. The USC&CS, on the'other hand, has recommended that the reactor and its
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containment structure be, designed to withstand a ground response spectrum of 2/3g, with peak accelerations up to 1.0g, together with possible differential shear ground motion of up to 2-1/2 feet. The USGS, pointing out that the geologic setting of Bodega Head is similar to that of Point Reyes Peninsula where bedrock ruptures did occur in the 1906 California earthquake, feels that there is a possibility of a comparable rupture of up to 3 feet at the proposed reactor site in the event of a severe earthquake in that area.
There is also a wide difference of opinion respecting the size of the l l
tsunamis (seismic induced ocean waves) that may be expected to result from l off-shore earthquakes. Consultants to the applicant are firm in their l' l
opinion, based on all available records along the West Coast, that no 1
j tsunami will ever push water more than 15 feet above mean water level at the plant site. However, the USC&GS has recommended that protection against j 50-foot tsunamis be provided in the design of the plant. I The applicant was made aware of the recommendations of the USC&GS and USGS, and was asked a number of questions designed to determine whether the !
- j. company considered it feasible to design the Bodega plant so as to provide reasonable assurance that the integrity of the reactor containment would be I preserved and that the reactor would be shut down and maintained in a safe condition in the event of the occurrence of an earthquake of the severity postulated by the USC&GS and USGS. The technical basis for their conclusion was also requested.
While continuing to. disagree strongly with the credibility of such an i extreme earthquake, the applicant has nevertheless proposed a design which i
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quake should occur,' the containment might be tipped or rotated slightly,' but .i l
there would be no breach in its. leak-tightness and no release of. fission- l products, in the opinion of the applicant.
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The postulated earthquakeLinvolves'a. pattern of ground motion generally
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similar to that recorded by the Coast and Geodetic Survey in the El Centro Earthquake of May 18, 1940,- but with approximately twice the intensity, corresponding to a maximum acceleration of two-thirds gravity, a maximum velocity of 2.5 ft/sec, and a maximum ground displacement of 3 feet, and -
with occasional intermittent pulses of acceleration up t'0 1.0g. The structures are considered to be subjected to simultaneous shear displace-ments ranging up to 3 feet, aloag lines ex' tending under' the containment structure or other parts of the plant, with motions in either horizontal or.
i vertical directions along the fault. It is also assumed that aftershocks of intensity equal to the El Centro quake might be suffered before remedial l
action could be taken.
There are two major problems posed by the postulated earthquake. The most unusual one is that of providing for shea,r ground displacement of as
, much as three feet underneath the reactor building. The other is that of vibrational stresstIs.
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Although there:,'is a substantial dedign.effortLinvolved in computing the vibrational stresses, and ' judgment has oto be' exercised as to. the proper
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. vibrational spectrum and structural damping factors.co use in assuring
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that the reactor-containment structure and all the' vital equipment inside it will safely withstand the vibrational aspects-of the earthquake, the technology.is well understood. 'The critical area here is the~ ability of vital structural components to withstand the stresses put on them by the simultaneous occurrence of the maximum postulated accident' (rupture l of reactor coolant system) and maximum postulated earthquake. Under l
these extreme conditions the question focuses on the maximum allowable stresses that should be used in the design computation relative to.
the yield stress of the various materials undpr consideration. While many of these details have not yet been resolved for the Bodega reactor, par-ticularlywithregardtothevibrationalstress. criteria [thereappearsto' be no reason to believe that anything of a fundamental nature with respect to vibrational problems will arise that cannot be'successfully handled.
Building the reactor structure and its foundation in such a'way'that it will safely survive a shear ground movement underneath it of as much as 3 feet poses a more troublesome problem. The applicant proposes to accomplish this by a design which provides for a 3 foot unobstructed radial clearance between the outside of the reinforced concrete contain -
ment structure and the inside of a containment pit, completely around:the circumference, from elevation -73 feet to yard elevation at +25 feet. The walls of. the ,reacto'r containment . pit will be ' lined with reinforced concrete e.
to prevent possible spalling of material into the pit. The annular space
- will be permitted to fill with water. The reactor containment structure will be founded on a layer of carefully selected sand of characteristics which the
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- applicant believes will permit horizontal movements up to 13 feet without L
impairing the function of the containment structure, although the structure might be shifted or rotated. Differential vertical motions up to 3 feet may cause the containment structure to tilt or shift, but, in the opinion of the applicant, in no case will the containment function be impaired .
It is proposed that the plant be designed with no rigid structural interconnection between any major components. The reactor containment structure will be structurally independent of the turbine generator founda-tion, the plant control building, the radwaste facility, the stack, and the plant service buildings. Piping and wiring interconnections important to safety between the reactor containment structure, the control building and the turbine generator will have sufficient flexibility to accommodate 3 feet of relative movement. In order to prevent overstress at point of penetration l
. for piping connecting the dry well with the turbine, the company proposes to l provide adequate anchors and bracing adjacent to the containment shell and ;
beyond the double isolation valves. These anchors will be adequate to ;
withstand all piping loads due to differential motion in any direction up to 3 feet b'etween the reactor containment structure and the turbine generator foundation.
The foregoing proposal for safeguarding the Bodega Reactor and its containment structure against the postulated shear differential ground motion embodies concepts which are in many respects novel and fcr which little or no preced'ent exists. The Regulatory Staff Consultants, Dr. N. M.
Newmark and Mr. Robert Williamson have come to the conclusion after carefully
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4 studying the basis of the proposal, that the structural integrity and leak-tightness of the containment building can be maintained under the i
earthquake conditions postulated.
They-point out, hewever, that certain precautions must be considered especially in the design of umbilicals and of penetrations to the ,
I containment building. All attachments and primary system piping must be arranged to prevent failure by shearing or crushing due to contact with valls, rock, earth, etc. , in the event of major earthquake motions. The I
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relative movement of 3 feet without failure, and at the same time be damped to reduce its dynamic response to earthquake oscillati.ons.
1 The sand layer under the containment building is intended to act in !
i two ways:
(1) to isolate in part the containment structure from the high peaks of acceleration that might be transmitted to it from the ground
, beneath it; and (2) to permit either horizontal.or vertical faulting to take pla.ce.in the rock beneath the containment structure without damaging the structure. Dr. Newmark feels that the effectiveness of the sand layer in reducing the peak accelerations may be questionable, but that its effectiveness in reducing the consequences of faulting will be substantial.
Protection of the plant against the possible occurrence of la'rge tsunamis has not, pet been completely resolved but does not appear to offer any unsurmountable design barriers.
It is difficult to evaluate the public safety risks involved in a new type of construction for which there is little or no experience background.
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Other reactor installations have presented seismic design problems, but not ;
I in the extreme form presented by Bodega Head under the e,arthquake postulated 4
by the Coast and Geodetic Survey and the Geological Survey. One problem which the Bodega plant has in common with all other nuclear power plants subject to.special seismic design considerations is the inability to conduct any sort of performance test on the finished structure that will demonstrate that the design objectives have been achieved. The uncertainty presented by this situation has been accepted as a reasonable risk in the seismic design at other locations where the only problem involved is the ability to withstand vibrational stresses, since this aspect of earthquake design is well under- i stood and has a considerable amount of experience background. There is difficulty in applying the same philosophy'at Bodega Head, however, because of the necessity of considering the additional problem of designing the reactor structure to safely. withstand differential ground motion as well as high vibrational stresses, and because there is no realistic way of evaluating the proposed solution to the problem. '
i The fact that the proposed site is adjacent to the San Andreas fault zone makes it almost certain that it will be subjected to one or more severe i seismic disturbances during the lifetime of the plant. While there is a high probability tha.t,the plant under the proposed design could survive the vibrations from even a very large earthquake without damage, it must be recognized that if such an earthquake should also involve several feet of
- bear ground movement as well as ground accelerations as high as 2/3g to 1.0g there is pr'es'ently no sound experimental or experience basis for predicting the extent of damage that might be incurred by the reactor con-tainment structure and emergency equipment designed to assure the safety of e
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The fact that a novel method is proposed for safeguarding the Bodega
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/ b Head' reactor ag'ainst. differential ground movement of its: foundation rock is j l
not in itself a cause for concern. The nuclear power industry is, rehlete 1 with new methods of coping with a large variety' of problems never previously 1
encountered until the arrival of the' atomic age. 'What is of concern is the j lack of any experimental!or experience' proof-test of therproposed novel method that could form an acceptable basis. for the required safety evaluation. a h- 3 . '
i The pressure-suppression concept of reactdr (containment was completely I novel when it was first proposed for use at the Humboldt' Bay Nuclear Power 4 Plant. In many respects it was much simpler than the pedestal concept for.
safeguarding against shear movement of foundation rock proposed for the Bodega Head reactor. But it was not approved for use as reactor containment until after the successful conclusion of a long series of engineering tests em at the PG&E's Moss Landing power generation plant which proved beyond reasonable doubt that the concept could be utilized safely for boiling water reactors. Similar proof-test standards have consistently been applied to ,
i other new and previously untried featu'res incorporated from time to time in l nuclear power plants.
1 1
The fact that meaningful proof tests are difficult to achieve in the
- )a case of seismic, safeguards does not, in our' opinion, constitute a valid j I .
( reason for accepting these safeguards in critical areas on the basis of )
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l s I theoretical reasons alone. Nor does it justify relying on opinions as to cp!
l the feasibility of the'~ proposed seismic' safeguards unless these are supported
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by somewhere.near the same kind of experimental evidence required of all other safeguards. We do not see such evidence in support of the pedestal concept for safeguarding the Bodega Reactor against differentini ground motion.
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Whether the public benefits to be . gained from opet.ation of the Bodega Nuclear Power Plant are high enough to justify acceptance of the added uncertaintiesinvolved'intheseisnicdesignofthepifbitowithstand several feet of shear ground movt)aent is, of course, a matter of judgment.
s The regulatory requirement that there be " reasonable aanurance" that any licensed nucicar reactor can be built and operated without undue risk to the health and safety of the public recognizes that there is no way of elim'.nating all of the uncertainties; experienced judgment is therefore s
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required. The standata bf !'reas~ohablemassuririch!! 'isrmorhtdifficult to meet when it becomes necessary to take into consideration external forces having the potential of invalidating some of the safeguards built into the reactor installation. The difficulty is enfarged when there are uncertaintiesfin the design measures intended to counteract the external forces. Somewhere along the line enough uncertainties will create a situation in which the
" assurance" can no longer be said to be " reasonable." We believe that this situation would exist if the proposed pedestal concept of seismic design were to be approved without more convincing evidence of its validity than is afforded by presently available information.
Conclusions .'
The containment and all of the emergency equipment for shutting down the Bodega reactor and maintaining it indefinitely in a safe condition in i
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the absence of seismic disturbances are designed on the basis of well-i established engineering principles. They can also be. tested to ascertain that the design objectives'have been achieved. Consequently, there is a.
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highdegreeof.assurancethatthereactorcanbIbuilt.andoperatedwithout T,
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L :s "toseismicdesignofthereactorstructuretowithstaNdperely 1 ; }
vibrational elfects .is also based on well-establishdiengineering principles
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which in sorrpcases at least have been verified in the presence of earthquakes, y
Thus, whileiir is not possible to carry out any measurements on the finished structure to assure that the seisW . design objectives' have been accomplished, f i triere is sufficient 2xperience background to justify a c mclusion that the specified seismic. vibrational crit'eria can be achieved and that the plant can
- 7 therefore.be. safeguarded against any credible earthquake that dpes not rupture the foundation rock. j 5
We believe there is room for reasonable doubt, however, that a comparable y
situation exists with respect to that particular aspect of the proposed seismic Neign of the Bodega reactor structure intended to assure that the containment i
and reactor shutdown functions will remain intact in the event of a shiar I T
displacement of its foundation bedrock as great as three feet in any didection.
WhiletheproposedengineeringprinciplesappearreasondNe, experimental 4
,z verification and experience background on the proposed novel construction
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method are lacking. If , approved, this would, to the iyst of our knowledge,
'1 1 I be the first attempt on record to design a buildirt, structure and its j
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f associated vital equipment to withstand the effects of substantial movement in its foundation simultaneously with the vibration accompanying a severe earthquake. Because of the magnitude of the possible consequences of a major rupture in the reactor containment accompanied by a failure of ]
emergency equipment, we do not believe~that a lar 1 nuclear power reactor ;
s should be the subject of a pioneering construction effort based on unverified
- engineering principles, however sound they may appear to be. {
The Advisory Committee on Reactor Safeguards has reached the conclusion .l that the reactor can be constructed and operated at the proposed location i
without undue risk to the health and safety of the public. We have carefully ,
1 considered the views of the ACRS. We have the highest respect for those views and we do not lightly reach an opposite conclusion. This is a kind ]
1 of case, however, on which reasonable men may differ. In our view, the 1 .
l proposal to rely on unproven and perhaps unprovable design measures to cope with forces as great as would be produced by several feet of shear ground
..y movement under a large reactor building in a severe earthquake raises a substantial safety questions.
In all respects except one the proposed design of the Bodega Nuclear Power Plant provides reasonable assurance that the plant can be built and operated without undue risk to the health and safety of the public. However,
- the single exception is quite important if one accepts the credibility of an earthquake of sufficient magnitude to cause a major displacement of
' 1
- foundation roc'k undernea th the plant. Although there is a wide difference of
. expert opinion on the credibility of such an earthquake, prudent judgment
, ! favors accepting the conservative recommendations of the USC6GS and the USGS.
On this basis and for reasons given above, it is our conclusion that Bodega Head is not a suitable location for the proposed nuclear power plant at the present stage of our knowledge.
w es,
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