秋の大会 原子力安全部会セッション
SMR等革新炉の安全と安全規制についてー今後の取組ー
Safety of Advanced and Innovative Nuclear Reactors and the Preparationof Regulatory Infrastructure– future Initiatives –（２）海外で検討が進んでいる革新炉の安全設計の特徴等について（事例紹介：NuScale）(2) Safety design features of innovative reactors- Case study: NuScale

吉田 英爾（日揮）
Sep. 2020© 2020 JGC Corporation

NuScale power plant current status
 NuScale Power plant is:

based on PWR technology
an evolutionary simple and innovativeadvancement.

incorporates unique features that
reduce complexity, improve safety andresilience, enhance operability, andreduce costs.

progressed to completion of Phase 4of NRC review in Dec. 2019.



in January 2021.
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on track to meet the significant
milestone of NRC design certification

NuScale power plant NuScale general description

60MWe/NuScale Power Module (NPM) x 12 NPMs
=720 MWe

Primary system components in an integral reactor
pressure vessel (RPV) surrounded by a steel
containment vessel

NPM immersed in a large pool of water (UltimateHeat Sink)© 2020 JGC Corporation

Copyright © 2017 JGC Corporation All Rights ReservedSafety features(1)Maximizing Simplicity
 All major reactor coolant systems inside the reactor pressure vessel.
 By simplifying the NuScale design, the plant's response to design basis andbeyond design basis accidents (BDBA) is also simpler.

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Copyright © 2017 JGC Corporation All Rights ReservedSafety features(2)Design basis accident
 Risk information is used in early design stages and simultaneously improvessafety and reduces cost.
 Enhancing plant safety through its deliberate design choices that eliminate or
reduce the likelihood of potential accident initiators.
 Six of eight traditional design basis accidents applicable to existing PWRs areeliminated or have reduced risks for NuScale NPMs.
NuScale Response
Reduced consequences from lower fuel failure fraction
No change
Eliminated with natural circulation of primary coolant
No change
Reduced likelihood from tubes in compression (shell-side primary flow)
Eliminated by use of integral primary system configuration
Reduced consequences from no fuel heatup
Reduced source term from half-height fuel assemblies and 15.2 m of© 2017 JGC Corporation All Rights Reserved
water above spent Copyrightfuel assemblies© 2020 JGC Corporation

Design Basis Accident
Steam system pipe break
Feedwater system pipe break
Reactor coolant pump shaft failure
Spectrum of control rod ejections
Steam generator tube rupture
Large break LOCA
Small break LOCA
Design basis fuel handling accidentsSafety features(3)DHRS and ECCS
 The NPMs are submerged in the reactor pool, which is part of the UHS.
 Passive heat removal to the UHS using Decay Heat Removal System (DHRS)
and Emergency Core Cooling System (ECCS) maintains core cooling without
pool inventory makeup or operator action.

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Copyright © 2017 JGC Corporation All Rights ReservedSafety features(4)EPZ reduction
 Reducing the size of theNuScale plant emergency
planning zone (EPZ) fromthe current 10-mile radiusof most U.S. nuclear
plants to the siteboundary.
 Reducing the EPZ sizedue to the incredible
NuScale safety© 2020 JGC Corporation

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Regulatory Perspective

NuScale requests in design certification application:
Exemptionsare necessary to address the passive safety approach inherent in NuScale design
are an alternative to existing requirements
are not requesting NRC to relax safety requirement, this exemption process ensures thatalternatives to existing requirements protect public health and safety.

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Summary New requirements and safety standards
 New safety requirements and safety standards different from existing lightwater reactors should be considered and established for innovative reactors
such as SMR.
 When considering safety requirements and safety standards suitable for an
innovative reactor, it is necessary to aim for the establishment of safety
requirements and safety standards that higher safety can be achieved.

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 Approach to develop the requirements and the standards
 A serious discussion on “What should be the safety requirements and safety
standards for innovative reactors such as SMR?” should be started.
 A new regulatory framework be applied to innovative reactors such as SMR
are created based on the results of such discussions.