Provisional Translation(Feb.19,2013 Rev.0）

February 6, 2013

Outline of New Safety Standard(Earthquake and Tsunami)(DRAFT)For Public Comment0February 6, 2013
Outline of New Safety Standard (Earthquake and Tsunami) (DRAFT)

Table of Contents

1. Basic Policies for Earthquake and Tsunami Design ..................................................... 2
2. Importance Level Classification of Facilities ............................................................... 5
3. Formulation of Design Basis Groud Motion ................................................................ 8
4. Seismic Design Policies .............................................................................................. 14
5. Consideration of Ground Stability .............................................................................. 21
6. Formulation of Design Basis Tsunami ........................................................................ 22
7. Tsunami Design Policies ............................................................................................. 25
8. Design Considerations related to the Stability of Surrounding Slopes ....................... 31(Caution)
This document is an outline of the new safety standard concerning earthquake andtsunami currently compiled based on discussions during investigation team meetings.
The “Basic Requirements” and “Requirement Details” in this document are mentioned
assuming compatibility with Nuclear Regulation Authority’s regulations and Nuclear
Regulation Authority’s regulation by laws, respectively.
Furthermore, during the codifying the process, definitions of terms, framework
structure and content shall be determined in accordance with examples of laws andregulations.

11. Basic Policies for Earthquake and Tsunami Design[Basic Requirements]
1. Since the entire reactor facility (hereinafter referred to as, “facility”) is required tohave the highest levels of safety the following basic design policies shall be satisfied.

a. Facilities with important safety functions shall be installed on the ground forwhich it has been confirmed that there is no outcrop of a fault that may become
active in future.
b. Facilities with important safety functions shall be designed so as not to lose such
safety function due to seismic forces resulting from seismic ground motions thathave the potential to dramatically impact the facility (hereinafter referred to as,“design basis ground motion”) and that may occur during facility operation, albeit
extremely rare. Furthermore, the facility shall be designed to sufficiently withstandsuitable levels of seismic force in accordance with its level of significance from theperspectives of the possible loss of safety function due to an earthquake and theensuing impact of radiation on the environment.
c. Facilities shall be constructed on ground that has sufficient bearing capacities tosupport the facilities against the seismic force described in the above item.
d. Facilities with important safety functions shall be designed so as not to lose such
safety functions due to a tsunami that has the potential to dramatically impact thefacility (hereinafter referred to as, “design basis tsunami”) and that may occur
during facility operation, albeit extremely rare.

2. When performing surveys in order to determine the design basis ground motion anddesign basis tsunami a survey method that meets the objective shall be selected andreliable and accurate survey results shall be guaranteed by considering survey
method application conditions and accuracy, etc.

2

[Requirement Details](1) “Faults that may become active in the future” include active faults considered to beearthquake sources and faults that cause permanent displacement in conjunction
with the activity of the aforementioned faults in addition to landslide facets thatintersect supporting ground.
(2) “Faults that may become active in the future” refer to the faults for which thepossibility that the faulting occurred in late Pleistocene (approximately 120,000 to
130,000 years ago) and later cannot be ruled out. If it is difficult to definitelydetermine the activity in late Pleistocene, for example, no existence of more than
one geomorphic surfaces or continuous strata layers formed in late Pleistocene andlater, a survey should be performed tracking back to middle Pleistocene(approximately 400,000 years ago) and later by comprehensively studying thegeomorphology, geology, subsurface structure and stress fields to determine theactivity of a fault. Furthermore, when assessing activity, if it is difficult to confirm
the fault at the location of the facility a conservative determination of activity shallbe made in accordance with the characteristics of the fault confirmed at extensionsof the aforementioned fault.
(3) The above paragraph 1.a. is specified to avoid a risk that if any facility with safetyfunctions is located in places where there are rocky outcrops of a fault that may
become active in the future; the activity of the fault may cause significant
influence on the safety function.
(4) There is “residual risk” to be considered in the determination of design basis
ground motion and design basis tsunami.
From a seismological perspective, the possibility of an earthquake having aground motion that exceeds the design basis ground motion cannot be ruled out.
Similarly, the possibility of a tsunami exceeding the design basis tsunami cannot
be denied. This means that there will always be some risk associated with impacts
on the facility resulting from exceeding the design basis ground motion and designbasis tsunami. These risks include an event that causes large-scale damage to thefacility, an event that results in the dispersion of a large amount of radioactive
material from the facility, or a disaster that results in radiation exposure to thesurrounding public. Therefore, when designing the facility, appropriate
consideration should be given to the possibility of the occurrence of an event thatexceeds the specified design basis ground motion and design basis tsunami.
3Precaution should be taken at every stage of design. The existence of this “residualrisk” should be sufficiently recognized and efforts should be made to minimize thisrisk as less as possible in a reasonable manner.

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2. Importance Level Classification of Facilities[Basic Requirements]
1. Since the entire facility is required to have a high level of safety as a whole, allfacilities that have important safety functions shall be graded as S class from theperspective of preventing the loss of safety function due to an earthquake andconsequential influence of the resulting discharge of radiation into the environment.
Furthermore, facilities with less influence than S class facilities shall be graded as B
class facilities, and other general industrial facilities for which the safety level
equivalent to that of public facilities is required shall be categorized as C classfacilities.

2. Facilities that have tsunami protection functions as stipulated in Clause e. of 7.
Tsunami Design Policies shall be graded as S class facility from the perspective of
the impact on safety function due to the possible loss of the aforementioned tsunami
protection function caused by an earthquake.

[Requirement Details]
The concept of categorizing facilities according to the safety function and thefacilities in each class are shown below:(1) Class requirements put forth in paragraph 1 are as follows:① S Class
All facilities that have important safety functions shall be graded as S classfacility. The facilities that have important safety functions include; those having
functions required to shut down the reactor and cool the core in case of an eventthat may be caused by an earthquake; those containing radioactive materials:
those directly related to the facility containing radioactive material and have thepossibility of dispersing radioactive materials off-site in case of the loss of thefunction of the concerned facility; those having functions required to mitigate the5effects of an accident that is caused by the loss of the function of the facility
containing radioactive materials and consequential radioactive release to theenvironment; and those necessary to support these safety functions and having
significant influence. The S class facilities include, but are not limited to, thefollowing:

Equipment and piping systems that comprise reactor coolant pressure
boundaries



Facilities for storing spent fuel

Facilities that insert sudden negative reactivity for emergency shutdownof the reactor, and facilities used to maintain reactor shutdown status

Facilities for removing decay heat from the core after reactor shutdownFacilities for removing decay heat from the core after a reactor coolant
pressure boundary damage accident

Facilities that act as pressure boundaries and directly prevent thedispersion of radioactive material in the event of a reactor coolant
pressure boundary damage accident

Any other facilities not mentioned that suppress the off-site dispersion ofradioactive material in the event of an accident that leads to a discharge ofradioactive material.

② B ClassAmong the facilities with safety functions, those having less influence when its
safety function is lost compared with the influence caused by the S class facility
can be classified as B Class. The following facilities are examples of B Classfacilities:

Facilities that are directly connected to reactor coolant pressure
boundaries and contain, or may contain, primary coolant.



Facilities that contain radioactive waste. This excludes facilities that store
small amounts of radioactive waste and facilities where the storage
method lessens the impact of radiation on the public in the event of an
accident and the impact is small in comparison to the annual dose limits
specified for areas outside the environment surveillance area.
6Facilities related to radioactive materials other than radioactive waste that
may cause excessive radiation exposure of the general public or workers
when it is damaged.



Facilities for cooling spent fuel

Facilities that suppress the off-site dispersion of radioactive material in
the event of an accident that leads to a discharge of radioactive material
and are not considered S Class facilities.

(2) Class requirements put forth in paragraph 2 are as follows. When these facilities
lose their functions due to an earthquake and a tsunami arrives while such situation
continues, there is the possibility of a tsunami impacting the safety function. The
significance of such facilities in terms of seismic design is determined as S class.
① Facilities that have tsunami protection functions and facilities that have flooding
prevention functions.
② Facilities that have onsite tsunami monitoring functions (facilities that detect anoncoming tsunami and are needed to guarantee the function of the facilities
mentioned in ① above)7

3. Formulation of Design Basis Earthquake Ground Motion[Basic Requirements]
The design basis earthquake ground motion used for the seismic design of reactor
facilities shall be formulated by following policies, as an appropriate one supposing
from the seismological and earthquake engineering points of view such as geologicalfeature and structure, geotechnical structure and seismic activity on and around thesite based on the latest scientific and technical knowledge.
a. Design basis earthquake ground motion shall be formulated as the earthquake
ground motions in the horizontal and vertical directions on the free surface of thebase stratum, respectively regarding the “Earthquake ground motions formulatedwith specifying the seismic source for each site” as mentioned in the next
paragraph, and “Earthquake ground motions formulated without specific seismic
source” as mentioned in the paragraph c.
b. In order to formulate “Earthquake ground motions formulated with specifying theseismic source for each site” more than one earthquakes having risks to give
serious damages to the site (hereinafter referred to as “Earthquakes forinvestigation”) shall be selected with respect to inland crustal earthquakes,
inter-plate earthquakes and oceanic intraplate earthquakes. And earthquake
ground motions shall be evaluated both with response spectra and with the method
using a fault model for each “Earthquake for investigation” considering theuncertainty and propagating path effect for seismic waves up to the free surface ofthe base stratumc. “Earthquake ground motions formulated without specific seismic source” shall be
formulated by collecting the observation records close to the seismic source of thepast inland crustal earthquake for which it is difficult to associate with the active
fault, and setting the response spectra in consideration of the various uncertainty
and ground condition of the site.

8[Requirement Details](1) The characteristics of the design basis earthquake ground motion
The design basis earthquake ground motion is the premise ground motion for theseismic design to ensure seismic safety of the facilities. Its formulation requires
sufficient checks of its adequacy, with reference to the latest scientific and technicalknowledge in specific review cases.
(2) The definitions and interpretations of the terminology used in formulating thedesign basis earthquake ground motions are described below.
① “Free surface of the base stratum” for formulating the design basis earthquake
ground motion is a hypothetically assumed free surface with no surface layers or
structures thereon the base stratum, which is almost flat with no significant
unevenness and with a considerable expanse. The “Base stratum” here is defined asa solid foundation, not significantly weathered, the shear velocity Vs of which
exceeds 700 m/s.
② “Inland crustal earthquake” is an earthquake which occurs in the upper crust
seismogenic layers, including those in the near offshore coasts.
③ “Inter-plate earthquake” is an earthquake which occurs in the interfacial plane oftwo plates.
④ “Oceanic intraplate earthquake” is an earthquake which occurs inside a subducting(or having subducted oceanic plate, and is classified into the following two types: an“earthquake in the subducting oceanic plates” which occurs near the axis of a sea
trench or in its near offshore areas; or an “earthquake in the subducted oceanic
plates (intra-slab earthquakes)” which occurs in the land side of the axis of a sea
trench.
(3) “Earthquake ground motions formulated with specifying the seismic source foreach site” shall be formulated according to the following policies.
①

More than one “Earthquakes for investigation” shall be selected through detailed
examination of the active fault characteristics and seismicity, comprehensively
considering the distribution of middle, small and micro earthquakes, stress field
and occurrence patterns of earthquakes (including the plate geometries,
movements and mutual interactions) with respect to the inland crustal
earthquakes, inter-plate earthquakes and oceanic intraplate earthquakes.

9② The followings shall be considered in regard to inland crustal earthquakesi) When evaluating active faults to be considered as the seismic source, the location,geometry and activity of active faults shall be clarified through the comprehensive
evaluation obtained from the appropriately combined investigations of the review
of previous research documents with tectonic geomorphic, geological andgeophysical surveys in accordance with the geomorphic and geological conditionsof the survey area.
ii) In evaluating the geometry of the fault plane model and the source parameters,
multiple faulting shall be considered with carefully handling an isolated shortactive fault.
③ The fault plane model shall be designated for inter-plate earthquakes and oceanic
intraplate earthquakes in consideration of similarities in the earthquake
occurrence mechanisms and tectonic background of past large earthquakes
occurring not just in Japan but also all over the world.
④ Design basis earthquake ground motions shall be formulated for each
“Earthquakes for investigation” selected in ① above by performing the groundmotion evaluation with response spectra i) and the method with fault models ii). In
evaluating the earthquake ground motions, sufficient consideration shall be madeto the various characteristics due to the occurrence patterns of the earthquakes
and seismic propagation path effects, etc. including the regional peculiarities).
i)Evaluation of earthquake ground motions with response spectra
For respective “Earthquakes for investigation” response spectra shall be evaluatedby appropriate methods and the design response spectra shall be defined based onthese spectra. Earthquake ground motions shall be evaluated appropriately inconsidering their characteristics such as duration times, time dependent change ofenvelope functions suitably.
ii) Evaluation of earthquake ground motions by the method with fault models
For respective “Earthquake for investigation” earthquake ground motions shall be
evaluated by setting the source parameters with appropriate methods.
⑤ Various uncertainties associated with the formulation process of the design basis
earthquake ground motions in ④ above (uncertainties of fault length, upper andlower limits of the seismogenic zone, dip angle of the fault, location and size ofasperities, stress drop and rupture starting point as well as uncertainties causedby differences in of concepts and interpretations) shall be considered by using
appropriate methods that combine different kind of uncertainties as necessary with10

analysis of dominant parameters that are expected to greatly impact the groundmotion evaluation for the site.
⑥ If the source of an inland crustal earthquake selected as an “Earthquake forinvestigation” is extremely close to the site, the adequacy of the geometry and thelocation of the fault plane model, positional relationship with the site and thefacilities on the site, as well as the adequacy of the assumed source parameters
shall be investigated in detail while considering the entire fault associated with thesurface displacement. And the design basis earthquake ground motions shall be
formulated through the careful examination of the effects of various uncertainties
in ⑤ above to the evaluated ground motions noting the applicability of theevaluation method based on these obtained investigation results, with sufficiently
safety margins taking into account the latest scientific and technical knowledge
related to the characteristics of the ground motions extremely close to the seismic
source.
⑦ Surveys and evaluations conducting for the selection of the “Earthquakes forinvestigation” and the formulation of the design basis earthquake ground motions
shall be based on the latest scientific and technical knowledge. The sufficiency andaccuracies of existing materials and documents shall be duly considered andreferred to. If the different opinion from the existing documents is adopted or theevaluation results are different from the existing ones, their grounds should be
accountable.
⑧ When employing facilities that have relatively long predominant periods forseismic response, such as facilities with seismically isolated structures, the groundmotion evaluation that focuses on its frequency characteristics shall be performed
and a separate design basis earthquake ground motions shall be formulated asneeded.
(4) “Earthquake ground motions formulated without specific seismic source” shall be
formulated according to the following policies.
① In formulating the “Earthquake ground motions formulated without specificseismic source” the propagating path effects for the seismic waves up to the freesurface of the base stratum shall be reflected to the assumed response spectra asnecessary and the ground motion characteristics such as duration times and timedependent change of envelope functions, etc. shall be appropriately considered forthe assumed response spectra.

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② The adequacy of the design basis earthquake ground motions formulated as the“Earthquake ground motions formulated without specific seismic source” shall be
confirmed for each application, referring to the latest scientific and technicalknowledge at the time of the safety review. In this occasion reference should bemade to the probabilistic evaluation as needed regarding the ground motions near
the source region, caused by the earthquake faults with no clear traces on the
ground surface.
(5) In the evaluation of the ground motions for the “Earthquake ground motions
formulated with specifying the seismic source for each site” and “Earthquake
ground motions formulated without specific seismic source”, the following items
associated with the propagating path effects for the seismic waves shall beconsidered while taking into account the specific data required for the applied
evaluation method.
① In order to examine the effect of both deep and shallow subsurface structure in andaround the site on the propagating characteristics of the seismic waves, thegeological structure such as tilted strata, faults and folds beneath the site andsurrounding areas shall be evaluated along with the location and shape of seismic
bedrock, heterogeneity of lithofacies and lithology, and subsurface velocity
structure and attenuation characteristics. On the process of the evaluation
three-dimensional subsurface structure should be considered except in cases where
the subsurface structure is deemed to be horizontally stratified and laterally
homogeneous.
② Surveys of the site and surrounding areas needed to the evaluation of ① shall be
conducted with appropriate procedures and combinations for the regional
characteristics, review of the previous research documents, collection and analysisof existing data, analysis of ground-motion observation records, geological survey,
boring survey, two- or three-dimensional geophysical exploration, etc.
(6) The exceedance probability of “Earthquake ground motions formulated withspecifying the seismic source for each site” and “Earthquake ground motions
formulated without specific seismic source” shall be referenced to evaluate a
relationship between the response spectrum for each formulated ground motion
and its exceedance probability.

12(Reference)“Shall be referenced” as described in Item (6) of the requirement details means torecognize the possibility of an event occurrence that exceeds the formulated groundmotion, give appropriate consideration during facility design, and continually strive to
reduce “residual risk”, including during stages after basic design as mentioned in therequirement details (4) for “1. Basic Policies for Earthquake and Tsunami Design”

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4. Seismic Design Policies[Basic Requirements]
Individual facilities shall satisfy the following basic policies regarding seismic
design according to seismic design class.
a. S Class facilities shall be designed to maintain safety function when subjected toseismic force caused by the design basis ground motion. Furthermore, thesefacilities shall be able to withstand the seismic force caused by seismic motion
for elastic design, or static seismic force, whichever is larger so that it cangenerally remain in a elastic stateb. B Class facilities shall withstand static seismic force so that it can generally
remain in an elastic state. Furthermore, the effect of resonance shall be
investigated for those facilities that are susceptible.
c. C Class facilities shall withstand static seismic force so that it can generally
remain in an elastic state.
d. A facility belonging to a lower class shall not cause any spreading impact on thesafety function of a facility of higher classes[Requirement Details](1) The regulations of the seismic design policies are interpreted as follows.
① Setting seismic motions for elastic design:
S Class facilities shall be able to “withstand seismic force” caused by seismic
motions used for elastic design so that it can generally remain in an elastic state,
and this elastic design seismic motion shall be determined based on engineering
judgment. Elastic state is a state under which the impact that seismic motions on afacility and the state of the facility can be clearly assessed. By ascertaining whether
or not a facility will remain in an elastic state when subjected to seismic force
caused by elastic design seismic motions, it becomes possible to ascertain with14

100% certainty that the safety function of the facility will be maintained whensubjected to seismic force caused by the design basis ground motion.
The specific setpoints and bases for elastic design seismic motions shall be
sufficiently clarified for each application and the ratio between elastic design
seismic force and design basis ground motion response spectrum (elastic design
seismic motion/design basis ground motion) shall be above a certain level in order
to meet the requirements for elastic design seismic motions and should not, as arule, be below 0.5.
② As specified that “the effect of resonance shall be investigated for those facilities
that are susceptible” for B Class facilities, the seismic motion multiplied by a half
the elastic design seismic motion shall be used in this investigation.
③In item d above, it is specified that “a facility belonging to a lower class shall notcause any spreading impact on the safety function of a facility of higher classes”.
However, it shall be confirmed at least for the following items that safety functionof a facility belonging to upper classes shall not be impaired." During this impact
assessment, the adequacy of selected evens and impact assessment results,
including the details of surveys and investigations that take the entire site into
consideration, shall be demonstrated. In conducting the impact assessment, seismic
motions or seismic force used for the design of the facility belonging to upperclasses shall be applied.
i) The impact of relative displacement or unequal sinking caused by the difference
in seismic response characteristics and the ground where the facility is located.
ii) The mutual effect of connections between upper class and lower class facilities.
iii) The impact on upper-class facilities of the damage, toppling, or falling of lower
class facilities within the building.
iv) The impact on upper-class facilities of the damage, toppling, or falling of lower
class facilities outside the building.
(2) Seismic force calculation method:
The following methods shall be used to calculate seismic forces used in theseismic design of a facility:① Seismic forces obtained from the seismic response analysis
Seismic force obtained from seismic response analysis must be calculated in15

accordance with the following methods.
i) Seismic forces caused by design basis ground motions
Seismic force caused by design basis ground motions shall be calculated byappropriately combining seismic forces in two horizontal directions with thevertical direction. The mutual action between buildings/structures and theground, embedding effect and the nonlinearity of the surrounding ground shallbe considered as necessary.
ii) Seismic force from elastic design seismic motion
Elastic design seismic motion is determined using engineering standards
based on the design basis ground motion. Seismic force from elastic design
seismic motion must be calculated by appropriately combining two horizontal
directions with the vertical direction. The interaction between
buildings/structures and the ground, embedding effect and the nonlinearity ofthe surrounding ground shall be considered as necessary.
iii) Seismic response analysis
When calculating seismic forces caused by design basis ground motions andelastic design seismic motions an appropriate analysis method shall be selectedconsidering the applicability and limits of application of seismic response
analysis methods. Furthermore, analytical conditions shall be set appropriately
based on sufficient surveys.
During the process of calculating seismic forces, the dynamic deformation
characteristics related to the nonlinear response of the input seismic motions,which are evaluated by the installation location of buildings/structures, shall beconsidered as necessary, and the propagation attributes of the seismic waves
from the free rock surface shall be appropriately considered. Adequacy shallalso be proven based on the latest scientific and technical knowledge andobservation records from the site.
② Static seismic force
Static seismic forces shall be calculated by the following method.
i) Buildings/Structures
Horizontal seismic forces shall be calculated by multiplying the earthquake
layer shear force coefficient Ci by a coefficient that corresponds to thesignificance level classification of the facility shown below, and thenmultiplying it by a weight that exceeds the aforementioned layer.
16

S Class 3.0
B Class 1.5
C Class 1.0
Earthquake layer shear force coefficient Ci is obtained by considering thevibration attributes of the building/structure and the type of ground, etc., whilesetting the reference shear force coefficient C0 at over 0.2.
It is also necessary to confirm that the horizontal load bearing capacity of thebuilding/structure exceeds required horizontal load bearing capacity. Whencalculating required horizontal load bearing capacity, the coefficients inaccordance with the significance level classification of facilities that shall be
multiplied to the earthquake layer shear force coefficient shall be 1.0 for S
Class, B Class and C Class, and the reference shear force coefficient C0 used inthis case shall be over 1.0. In this instance it shall be confirmed that thestructures have adequate safety margins in accordance with the significancelevel of the facility.
For S Class facilities, it shall be assumed that horizontal seismic force andvertical seismic force act simultaneously on the structure in a disadvantageous
directional combination. The reference vertical seismic force shall be calculated
by using a seismic intensity of over 0.3 and a vertical seismic intensity obtainedby considering the vibration attributes of the building/structure and the type ofground. However, the vertical seismic intensity shall be assumed to be identicalin the height direction.
ii) Equipment/piping systems
Seismic force for each seismic class shall be obtained by using the productobtained by multiplying earthquake layer shear force coefficient Ci by acoefficient that corresponds to the significance level of the facility as illustrated
in i) above as the horizontal seismic intensity, and increasing both theaforementioned horizontal seismic intensity and the vertical seismic intensity
mentioned above in i) by 20%.
Horizontal seismic force and vertical seismic force shall act simultaneouslyon the structure in a disadvantageous directional combination. However, thevertical seismic intensity shall be assumed to be identical in the height
direction.
17iii) The objective of using a reference shear force coefficient C0 of over 0.2 in i)
and ii) is to encourage the nuclear reactor licensees to construct the reactor
facilities with high earthquake resistance by appropriately assessing theimportance level of individual buildings/structures and equipment/piping
systems during the design phase and using appropriate shear force values foreach of these components. From the perspective of improving earthquake
resistance, when deciding to what extent coefficients should be increased for
different types of facilities it is important that parties involved in design andconstruction set the shear force coefficient considering the relevance to seismic
standards for industrial and public facilities.
(3) Load combinations and allowable limits
The fundamental concept in regard to load combinations and acceptable limits thatshould be considered when evaluating the adequacy of design policies related toseismic safety is as follows.
① Building/structuresi) S Class buildings/structures:(a) Combination with design basis ground motions and acceptable limits:
The deformation capability (deformation under ultimate proof strength)of the building/structures when taken as a whole structure shall havesufficient safety margins against a combination of seismic forces causedby the design basis ground motion and normal loads as well as loads
under operation, and the ultimate strength of the building/structure shallhave adequate safety margins against the aforementioned combinations.
(b) Combinations with elastic design seismic motions and acceptable limits:
Acceptable limits for stress generated as a result of combinations ofnormal loads and loads under operation, and seismic forces and static
seismic forces caused by elastic design seismic motions, shall be theallowable stress levels specified in the codes and standards deemed to beappropriate from a safety standpoint.
ii) B Class, C Class buildings/structures:
Acceptable limits for stress generated as a result of combinations of normalloads and loads under operation with static seismic forces shall be theallowable stress levels mentioned above in ① i) (b).

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② Equipment/piping systemsi) S Class equipment/piping systems(a) Combination with design basis ground motions and acceptable limits
The facility shall maintain its required function under load conditions thatcombine loads generated during normal operation, loads during abnormaltransient during operation, and loads during accidents, and seismic forces
caused by design basis ground motions. Furthermore, functions required forthe facility shall not be impaired even in the event that an extremely small
plastic strain is generated by the aforementioned loads. Active components
shall maintain its intended functions even when subjected to the response of
the design basis ground motion. Specifically, acceleration levels at whichfunction is maintained that have been confirmed through demonstrated
experiments shall be used as acceptable limits.
(b) Combinations with elastic design seismic motion and acceptable limits
Response as a whole shall remains elastic when subjected to loadconditions that combine loads generated under normal operation, loads
during abnormal transient during operation and loads during an accident
with seismic forces and static forces caused by elastic design seismic
motions.
ii) B Class, C Class equipment/piping systems
Response as a whole shall remains elastic when subjected to the load
generated as a result of combinations between loads generated during normal
operation and loads during abnormal transient during operation with static
seismic forces.
③ The regulations concerning load combinations and acceptable limits shall beinterpreted as follows:i) In regard to “loads generated during normal operation, loads during
abnormal transient during operation, and loads during accidents”, loads
generated by a possible event caused by an earthquake, and loads generated
by a event that continues over a long period of time in the event of an
accident even if the event cannot be caused by an earthquake must be
considered in combination with appropriate seismic force based on therelationship among the occurrence probability of an accident/event and its
duration, and the exceedance probability of seismic motion.
19ii) It is mentioned that acceptable limits for combinations of loads withbuilding/structure elastic design seismic motions shall be the “allowablestress levels specified in the codes and standards deemed to be appropriate
from a safety standpoint” which specifically corresponds to the BuildingStandards Act.
iii) “Ultimate proof strengths” mentioned in the paragraph regarding the
combinations of loads with the design basis ground motion forbuildings/structures refers to the ultimate maximum load that a structure canwithstand before it suffers a remarkable increase in structural deformation or
strain, which is considered to be the structure’s “ultimate state”, in the eventthat load on the structure gradually increases.
iv) In regard to the acceptable limits for equipment/piping systems in
combination of loads with elastic design seismic motions, the basic concept
is that “response as a whole shall remain elastic”, which corresponds
specifically to the “Technical Standards for Power Generating Reactor
Facilities” (*) as specified in the Electric Business Act.

(*) The details mentioned here are the same as the requirements mentioned in
the Regulatory Guide for Seismic Design Review, but in the future clausesthat correspond to “’Technical Standards for Power Generating Reactor
Facilities’(*) as stipulated in the Electric Business Act” shall be quoted in
Nuclear Regulation Authority regulation by laws.

20

5. Consideration of Ground Stability[Basic Requirements]
1. The ground upon which facilities are to be constructed shall have sufficient bearing
capacities to support the facility when subjected to the seismic force specified in
Section 4 “Seismic Design Policies”.
2. The facilities with important safety functions shall not be greatly impacted by thetilting or bending of the supporting ground caused by crustal deformation in
conjunction with an earthquake.
3. The safety functions of the facility shall not be greatly impacted by deformation of
the surrounding ground, such as uneven settlement of buildings/structures,liquefaction, or liquefaction-induced settlement in conjunction with an earthquake.

[Requirement Details]
Regarding the ground for which it has been confirmed that there is no outcrop of
faults that may become active in future according to Section 1, “Basic Policies for
Earthquake and Tsunami Design”, the bearing capacity of the ground underneathbuildings/structures that support S Class equipment/systems against the designbasis ground motion shall be confirmed including that there is no slip on weakplanes in response to a seismic motion.

The “tilting or bending of the supporting ground caused by crustal deformation in
conjunction with an earthquake” mentioned in paragraph 2 includes local grounddeformation in addition to ground deformation caused by uplift or subsidence ofthe ground over a wide area. Of these events, local ground deformation shall begiven particular attention due to the great impact on tilting or bending of the
supporting ground.

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6. Formulation of Design Basis Tsunami[Basic Requirements]
The design basis tsunami for the safety design of nuclear facilities shall be
formulated appropriately in consideration of bathymetry feature, tectonic map, andseismic activity at the periphery of tsunami source, and geomorphic between tsunami
source and the site.
Furthermore, the design basis tsunami shall be formulated by selecting plural
tsunamis caused by not only earthquakes but also other factors, such as submarine andonshore landslides, etc., and then taking into account uncertainties in conducting
numerical analysis.

[Requirement Details](1) Characteristics of design basis tsunami:
The design basis tsunami is a tsunami used to draw up tsunami countermeasures inorder to acquire facility safety. It is determined through numerical analysis of thetsunami sources as described in paragraph (2). It is the tsunami that would have themost significant impact on the facility among all those anticipated. When expressing
the time history of water level change due to the design basis tsunami, the tsunami that
occurs in offshore regions with little seabed undulation in a water depth of 50m to
100m shall be used.
The adequacy of design basis tsunamis shall be sufficiently confirmed considering
the latest knowledge available at the time of individual safety reviews.
(2) Policies on the formulation of design basis tsunamis:①The following factors shall be considered as possible tsunami sources and severalof sources causing a significant damage on the site shall be selected.
Furthermore，based on the geosciences background of the site, relevant activitiesof plural tsunami sources shall be considered under combinations of, such as:inter-plate earthquakes and other types of earthquakes，or combinations of22

earthquakes and landslides or slope failures, etc..
Inter-plate earthquakeOcean inter-plate earthquakes



Crustal earthquakes caused by active faults in ocean areasSubmarine and onshore landslideVolcanic phenomena (eruptions, massif collapse, caldera subsidence, etc.)② A scale of Tsunami sources deemed appropriately on the basis of plate geometry，back slip distribution, fault shape, geography/geology and volcano location shallbe considered. In this instance, investigations shall be based on large-scaletsunamis that have occurred not just in Japan but in the entire world, based upon
the similarity between tsunami generation mechanisms and tectonic background.
Furthermore，distant tsunamis shall be considered based on a actual tsunamis thathave occurred not just in Japan but in the entire world.
③ Source region of Inter-plate earthquakes shall be extended from the bottom of
seimogenic zone to the sea trench axis on the plate boundary.
④ If changes in water level have been observed off the coast of regions in which alarge-scale tsunami has occurred, these water level changes shall be consideredafter comparing the tsunami generation mechanism, similarity of tectonic
background，and topographical characteristics of the ocean where the records
were observed⑤ Wave run-up caused by a design basis tsunami shall exceed the height of thetsunami estimated from geological evidence，such as tsunami deposit in the areasurrounding the site，and historical record for large inundated regions. Tsunami
heights by a design basis tsunami shall exceed the height and inundation area ofthe tsunami which have occurred at the site and surrounding areas had have been
evaluated by public organizations⑥ In order to ensure sufficient margins in tsunami design, appropriate methods shallbe employed when considering uncertainties that accompany the process ofdetermining design basis tsunamis. Uncertainty factors (fault location, length,
width, strike angle, slope angle, slip amount, slip angle, slip distribution, rupture
starting points, destruction propagation speed, etc.) affecting tsunami source
23attributes and assumed to have a large impact on the formulation of design basis
tsunamis need to be sufficiently considered. Also, the degree of impact of thesefactors, as well as uncertainties caused by the difference in concepts andinterpretations related to these factors shall be considered.
⑦ When surveying tsunamis, the required survey area shall be expanded beyond thatfor seismic motion surveys and the attributes of review of the previous
researches, tectonic geomorphic surveys, geological surveys, and geophysicalsurveys shall be leveraged in accordance with the geomorphic and geologicalconditions of the survey area to assure a survey that appropriately combines allof these survey findings. Furthermore, surveys related to tsunami generation
factors, surveys needed to formulate tsunami source models, surveys related totsunami that may affect areas surrounding the site, and surveys related to tsunami
propagation channels and tsunami required for evaluating sediment transport,
shall all be conducted.
⑧ Surveys and assessments conducted for the formulation of design basis tsunamis
shall be based on the latest scientific and technical knowledge. Furthermore, pastrecords shall be referenced with sufficient consideration given to thecompleteness and accuracy of the record based on the scale of the survey region.
Furthermore, if views different from existing literature are employed, the basis
for the views shall be clearly stated.
⑨ Exceedance probabilities that correspond to the formulated design basis tsunami
shall be referenced to ascertain to what degree of exceedance probability
corresponds to the formulated design tsunami.

(Reference)“Shall be referenced” in the requirement details (2) ⑨ means referencing to theextent required to identify the possibility of occurrence of an event that exceeds
formulated design basis ground motions, given appropriate consideration during
facility design, and continually striving to reduce “residual risk”, in every stage evenafter the stage of basic design, as mentioned in the requirement details (4) for “1. Basic
Policies for Earthquake and Tsunami Design”

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7. Tsunami Design Policies[Basic Requirements]
Since the reactor facilities are required to have a high level of safety against
tsunamis the following basic design requirements shall be fulfilled so that the facilities
will not lose their functions even if they are struck by a design basis tsunami.
a. The site on which facilities that have important safety function are located shallnot be susceptible to the direct arrival of, or inundation by, run-up of a designbasis tsunami. Furthermore, the site shall not be susceptible to direct inflow fromflow paths such as water intake and drainage channels.
b. The impact on the safety functions of facilities shall be prevented by limiting theinundation area by leaking water in consideration of the possibility of waterleaking into intake/discharge facilities and underground areas from any kind ofchannel.
c. In addition to the stipulations of b. above, facilities that have important safetyfunctions shall be isolated from the impact of tsunami by preventing tsunami
inflow.
d. The impact of degraded water intake performance associated with a decline inwater level on the safety function of facilities shall be prevented.
e. The measures designed to prevent impact of tsunami on facilities that haveimportant safety functions (hereinafter referred to as, “tsunami protection
facilities/equipment”) shall be able to maintain tsunami protection function andflood/inflow prevention function when subjected to design tsunamis.
f. Uplift/subsidence of the site due to an earthquake, main shocks and aftershocksof an earthquake, influence of repeated tsunamis, and the secondary effect oftsunamis (scours, sediment transport, debris, etc.,) shall be considered.

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[Requirement Details](1) Regarding the basic requirements of paragraph a. above, the following policies
shall be fulfilled. Furthermore, with regard to preventing the site from being
subjected to the direct arrival of, or inflow of, a tsunami shall be minimized. Thisis specified as a design requirement in order to ensure safety because if inundation
area in the site is extensive the possibility of the following events can increasecausing a significant impact on the safety function of a facility. It should be notedthat as the area of outer boundaries becomes larger, the number of inflow paths andintakes will increase, resulting in a relatively high possibility that the safetyfunction of a facility will be impacted by flooding. : The generation of debris caused by inflow and outflow of seawater at the site andthe extended impact that such debris would have on tsunami protection
equipment and outdoor equipment (equipment/piping), and degraded access tothe site caused by seawater inflow and generation of debris.
 Changes in the condition of the ground, such as scours around buildings,liquefaction during aftershocks, reduced accessibility to the site due to changes in
the condition and resultant impact on tsunami protection facilities and subsurface
structures.
① Buildings that contain equipment having important safety functions and outdoor
equipment that has important safety functions shall be situated on ground that ishigh enough not to be impacted by the arrival of wave run-up caused by a designbasis tsunami. Furthermore, if such equipment is located at a height that can bereached by the arrival of wave run-up caused by a design basis tsunami, tsunami
protection facilities, such as a seawall, shall be erected.
② In preventing the arrival of tsunami run-up as mentioned in ① above, thepossibility of tsunami run-up hitting the site shall be determined considering thegeomorphic and elevation of the site and surrounding area, existence of rivers,and extensive uplift/subsidence. Furthermore, the impact on upstream channels
to the site shall be determined in the event that changes in ground conditions due
to an earthquake or changes in geomorphic and river streams could occur due topossible erosions and depositions resulting from repeated tsunamis.

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(2) Regarding the basic requirements of paragraph b. above, the following policies
shall be fulfilled.
① Upon considering all the possibilities of water leaking into intake/water discharge
facilities and underground areas from various channels, predicted inundation
area due to continuous leaking water (hereinafter referred to as, “predicted
inundation area”) shall be determined, and inflow prevention measures
implemented for those channels and opening (doors, open holes, penetration
seals, etc.) at the boundary of this range that have been identified as being
susceptible to tsunami inflow.
② If there are systems or equipment that have important safety functions around thepredicted inundation area, these areas will be made waterproof throughdemarcation and an evaluation of the possible inflow volume will be conducted
as necessary in order to confirm that there will not be an impact on safetyfunction.
③ If it is anticipated that the predicted inundation area may be submerged for a long
period of time water drainage equipment shall be installed.
(3) Regarding the basic requirements of paragraph c. above, the following policies
shall be fulfilled. Furthermore, in addition to tsunami inflow prevention
implemented for design basis tsunamis in accordance with the requirements of a.
and b. (“external protection”), focus must also be put on protecting buildings andcompartments that contain equipment and systems having safety functions(“internal protection”). The requirements of a. through c. aim to make design basis
tsunami protection redundant and can ensure that the impact of tsunami on safetyfunction is prevented as much as possible through isolation. Furthermore,achieving internal protection will make it easier to protect equipment and systems
that have safety functions from the combined impact of earthquakes and tsunami
such as inundation due to damage to circulation system piping and tanks onsite andin buildings caused by an earthquake, and the inflow of ground water due to
shutdown of drain system pumps in lower class buildings due to an earthquake.
① The buildings and compartments that contain equipment and systems havingsafety functions shall be clearly defined as focused inundation prevention area
and inflow prevention measures implemented for those channels and opening(doors, open holes, penetration seals, etc.) at the boundary of this range that havebeen identified as being susceptible to tsunami inflow if it is anticipated that27

underground areas surrounding this range would all be submerged.
(4) Regarding the basic requirements of paragraph d. above, the following policies
shall be fulfilled:① In regard to emergency seawater cooling systems, seawater pumps shall not bedamaged due to a drop in water level caused by a design basis tsunami andseawater intake shall be ensured. Furthermore, intakes shall not be blocked by
sediment transport/deposition or debris caused by the design basis tsunami, andthat seawater pumps shall not be damaged due to contamination by sand.
(5) Regarding the basic requirements of paragraph e. above, the following policies
shall be fulfilled.
① Tsunami protection facilities refer to tide sea wall and embankment structures.
Furthermore, tsunami protection equipment refers to water tight doors andequipment for countermeasures to prevent tsunami flow through openings andpenetration seals. In addition, there are also tsunami impact mitigation
facilities/equipment, such as breakwaters that are expected to mitigate the impactof the wave force on tsunami protection facilities.
② The “design tsunami” used in tsunami resistance design for tsunami protection
facilities and equipment shall be determined by using tsunami time history
waveforms based on the location of facilities and equipment for design basis
tsunamis to consider site geometries, the geomorphic of the seabed off the coastof the site, the angle of tsunami inflow into the site, the existence of rivers,
effects of inland water run-up and propagation, artificial structures located on thepath of propagation, etc.. The following shall be appropriately assessed andconsidered when determining the design tsunami.
 The excitation of natural frequencies on the local sea surface within the bay due
to a tsunami
 Fluctuations in tide level resulting from tide or other factors③ Tsunami protection facilities shall be designed to sufficiently maintain tsunami
protection functions when subjected to design tsunami by evaluating theresistance against corrosion, and erosion, and stability against sliding/toppling aswell as the resistance against overflow according to the structure.
④ Tsunami protection equipment shall be designed to sufficiently maintain28

inundation prevention functions when subjected to the design tsunami byevaluating resistance against wave pressure during inundation and after being
submerged of the predicted inundation area while considering the resistance ofthe tsunami protection equipment against overflow.
⑤ It shall be confirmed that buildings and structures provided with tsunami
protection facilities as well as tsunami protection facilities maintain inundation
prevention functions and tsunami protection functions against the design basis
tsunami so that these facilities can achieve their functions in the event of anearthquake (main shocks and aftershocks).
⑥ If there is the possibility that buildings/structures or installed structures within ornear the nuclear power plant site but on the outside of the tsunami protection
features may be damaged, toppled, or washed away, measures to prevent an
impact on tsunami protection features shall be taken. This will include measures
to prevent debris from affecting the tsunami protection features, such as tidewalls.
⑦ During the design process of ③, ④ and ⑥ above, in order to include sufficienttsunami design margins, loads corresponding to the function failure modes foreach facility/equipment (inundation height, wave force/wave pressure, scouring
effects, buoyancy, etc.) shall be set through considering sufficient margins interms of the design tsunami. Combinations of loads applied by aftershocks andloads applied by the design tsunami shall be considered as necessary based on anassumption of the occurrence of aftershocks. Furthermore, the time history
waveform for design tsunami shall be used to investigate the impact of
successive tsunami waves on tsunami protection functions and inundation
prevention function.
⑧ When considering the effect of tsunami impact mitigation during the design oftsunami protection features/equipment, such equipment shall be designed so as
to maintain tsunami impact mitigation function when subjected to design basis
tsunamis and the requirements of ⑤ thru ⑦ above.
(6) Other requirements to be fulfilled.
When evaluating tsunami protection facilities/equipment design and emergency
seawater cooling systems, an evaluation on the conservative side shall be performed
considering mean sea levels during new and full moons against water level changes
caused for the design tsunami. If it is anticipated that land areas will protrude or sink29

as a result of an earthquake, an evaluation on the conservative side shall be
performed considering the amount of crustal deformation of the site, which is
calculated by using fault plane models for anticipated earthquakes.

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8. Design Considerations Related to the Stability of Surrounding Slopes[Basic Requirements]
The reactor facilities shall be designed so that anticipated collapse of slopes in thesurrounding areas in the event of an earthquake will not cause significant influence on
the safety function of facilities.

[Requirement Details]
The following shall be considered when assessing the stability of slopes surrounding
the facility:① Slopes that may impact the buildings that contain equipment having importantsafety functions are installed or outdoor equipment that have important safetyfunctions shall be assessed for stability. In addition slopes surrounding severe
accident management equipment and emergency access roads shall also beassessed.
② The slopes shall be assessed using sliding safety factors or other evaluation inconsideration of the impact of geologic/ground structure, rock mass classification,
the possibility of liquefaction and the effect of the groundwater.
③ Ground models, ground parameters and seismic forces used for assessment shallbe set in accordance with the assessment results of the bearing capacity offoundation ground. Particular attention shall be given to the effect ofgroundwater.

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