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IAEAInternational Atomic Energy Agency
International Conference on Topical Issues in Nuclear Installation Safety,
Safety Demonstration of Advanced Water Cooled Nuclear Power Plants
6 – 9 June 2017
Design Safety Considerations for Water-cooled
Small Modular Reactors As reported in IAEA-TECDOC-1785, published in March 2016
Hadid Subki (IAEA/NENP/NPTDS), Manwoong Kim (IAEA/NSNI/SAS),
K.B. Park (KAERI, Republic of Korea), Susyadi (BATAN, Indonesia),
M.E. Ricotti (Politecnico di Milano, Italy) and C. Zeliang (UOIT, Canada)
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SMR: definition & development objectives
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Advanced Reactors to produce up to 300 MW(e), built in factories and
transported as modules to sites for installation as demand arises
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SMRs for immediate & near term deploymentSamples for land-based SMRs
Water cooled SMRs Gas cooled SMRs Liquid metal cooled SMRs
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Marine-based SMRs (Examples)
KLT-40S FLEXBLUE
FPU and Fixed Platform
Compact-loop PWR
• 60 MW(e) / 200 MW(th)• Core Outlet Temp.: 322oC• Fuel Enrichment: < 5%• FPU for cogeneration• Once through SG, passive
safety features• Fuel cycle: 30 months• To be moored to coastal or
offshore facilities• Completion of conceptual
design programme
Transportable, immersed nuclear power plant
PWR for Naval application
• 160 MW(e) / 530 MW(th)• Core Outlet Temp.: 318oC• Fuel Enrichment 4.95%• Fuel Cycle: 38 months• passive safety features• Transportable NPP,
submerged operation• Up to 6 module per on shore
main control room
Floating Power Units (FPU)
Compact-loop PWR
• 35 MW(e) / 150 MW(th)• Core Outlet Temp.: 316oC• Fuel Enrichment: 18.6%• FPU for cogeneration• Without Onsite Refuelling• Fuel cycle: 36 months• Spent fuel take back• Advanced stage of
construction, planned commercial start:2019 – 2020
ACPR50S
Transportable, immersed NPP
Integral-PWR• 6.4 MW(e) / 28 MW(th)• 40,000 hours continuous
operation period• Fuel Enrichment: < 30%• Combined active and passive
safety features• Power source for users in remote
and hard-to-reach locations;• Can be used for both floating and
submerged NPPs
SHELF
Images reproduced courtesy of OKBM Afrikantov, CGNPC, DCNS, and NIKIET
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Adopted Safety Features of
Advanced Passive Water-Cooled ReactorsIndependent of AC Power
• Require no AC power to actuate
/operate Engineered Safety
Features;
• Only gravity flow, condensation
natural circulation forces needed
to safely cool the reactor core
• Passively safe shutdown the
reactor, cools the core, and
removes decay heat out of
containment
1 Less reliance on operator action
Provides 3 to more than 7 days of reactor cooling
without AC power or operator action
2
Incorporating lessons-learned from the
Fukushima Dai-ichi nuclear accident
• Enhanced robustness to extreme external events
by addressing potential vulnerabilities
• Alternate AC independent water additions in
Accident Management – SBO mitigation
• Ambient air as alternate Ultimate Heat Sink
• Filtered containment venting
• Diversity in Emergency Core Cooling SystemDesign simplification
• Fewer number of plant systems
and components
• Reducing plant construction and
O&M costs
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Images Courtesy of Westinghouse and GE Nuclear Energy
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❖ Hydrogen control for DBA & severe accidents
• Filtered venting system
❖ Enhanced instrumentation and monitoring system
for DBA & severe accidents
❖ Diversity in spent fuel cooling (reliability)
❖ Effective use of PSA
❖ Emergency preparedness and response
❖ Assure safety on multiple reactors or modules plant
❖ Diversity in emergency core cooling systems
following loss of all AC power onsite
❖ Ensure diversity in depressurization means for high
pressure transient
❖ Confirm independence in reactor trip and ECCS for
sensors, power supplies and actuation systems.
Incorporating Lessons Learned from Major
Accidents to Advanced Reactor Developments
Resilience towards Extreme external events (regions and sites specific)
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Benefits of integral vessel configuration:
• eliminates loop piping and external components, thus enabling compact containment and plant size reduced cost
• Eliminates large break loss of coolant accident (improved safety)
Integral Primary System Configuration
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Courtesy: Westinghouse Electric Company LLC, All Rights Reserved
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Safety Expectations from
iPWR SMR Design Features (1) Design
FeaturesFunctional Details Safety Benefits
Low Core Power
• Reduces fission product source term
• Low level of decay heat and, therefore,
would require less cooling after reactor trip
• Enhances in-vessel corium retention
• Reduces accident consequences
• Simplifies emergency planning
RCS integrated to the RPV
• No large external primary coolant piping
• Longer RPV lifetime due to reduced fast
neutron fluence
• Increased coolant inventory/increased
thermal inertia results in fewer severe
transients and reduced necessity for
operator intervention
• Eliminate or reduce susceptibility to
events, such as LBLOCA
• Long response time in the case of
transient or accident
Integrated steam
generator (Once-
through helical coil)
• Steam generator is designed to
withstand the primary pressure without
pressure in the secondary side
• Steam system is designed to withstand
primary pressure up to isolation valves.
• Steam generator tubes are in
compression.
• Reduced tube-side water inventory
• Improved steam generator tube
integrity. Frequency for steam
generator tube rupture reduced
• The addition of reactivity would be
limited and the reactor power
increase may not exceed critical
safety limits from steam line break
due to smaller quantity of heat removal (larger number of SGs)
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Design
FeaturesFunctional Details Safety Benefits
Natural circulation
• Simplified design and reduced
maintenance costs, due to the absence of main coolant pumps
• Eliminate loss of flow accident
(LOFA)
• Eliminates accidents from reactor
coolant pumps (shaft breaks, seal
leakage, pump seizure and pump leaks)
Passive safety
systems
(No active High/ Low‐pressure safety injection system)
• The passive safety systems reduce or
eliminate the need for external power
under accident conditions
• Auxiliary feed-water system may not be
required
• Spray systems are not required to
reduce steam pressure or to remove radioiodine from containment.
• Simpler Solutions to SBO
• Active safety systems are not
required (low core damage
frequency).
• Removal of core heat without an
auxiliary feed-water.
• No safety-related pumps for accident mitigation.
Internal CRDMs
• Elimination of rod ejection
• Elimination/reduction of vessel head penetrations
• The Reactivity Initiated Accident
(RIA) due to rod ejection is eliminated
Safety Expectations from
iPWR SMR Design Features (2)
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Design Features Functional Details Safety Benefit
High design
pressure,
temperature and
vacuum metallic
containments
• Containment pressure and
temperature for worst-case design
basis accident remains below design
• All water lost from RPV stays within
containment and is returned to
reactor vessel by passive means
• More Sub atmospheric pressure
during normal operation
• The engineered safety systems are
simplified
• Improved seismic capability
• No postulated small-break LOCA
(SBLOCA) to uncover nuclear fuel
• Containment integrity assured
(metallic containment, no molten
core concrete interaction)
• The deep vacuum enhance steam
condensation rates for containment
heat removal during a postulated
SBLOCA
• Prevent Hydrogen explosion during a
severe accidents as limited Oxygen will be present.
Soluble boron free
core
• No Boron dilution
• Less corrosion
• Reduces volume of liquid radwaste
• Strong negative moderator
temperature coefficient
• Boron monitor and adjustment systems eliminated
• Reactivity initiated event is precluded
• Reduced occupational radiation dose
• Improved reactor transient
performance as well as operational safety
Safety Expectations from
iPWR SMR Design Features (3)
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LEVEL 5
LEVEL 4
LEVEL 3
LEVEL 2
LEVEL 1
• Mitigation of radiological consequences to protect people & environment against significant releases of radioactive mats.
• Control of abnormal operation and detection of failures
• Prevention of abnormal operation and system failures
• Control of accident within
the design basis
• Control of severe plant conditions
incl. prevention & mitigation of
severe accidents progression
INSAG-10: DiD Levels in Nuclear Safety
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LEVEL 1 of Defense-in-Depth
Design features Design objectives SMR designs Relevant safety
Requirements
Elimination of
liquid boron
reactivity control
system
Exclusion of
inadvertent
reactivity insertion
as a result of boron
dilution
KLT-40S, IRIS
CAREM25,IMR,
ABV-6M, mPower
RITM-200, SMR-
160, Flexblue
IAEA Safety
Standards Series
Specific Safety
Requirements
No. SSR–2/1
(Rev. 1), Safety of
Nuclear Power
Plants: Design
Requirement 20,
Paragraph 4.11
[(a) and (b)] and
relevant
Paragraphs
Integral design of
primary circuit
with in-vessel
location of steam
generators
Exclusion of large-
break, loss of
coolant accidents
(LOCA)
CAREM25, IRIS,
ACP100, DMS,
IMR, SMART,
ABV-6M,
NuScale, mPower
1
2
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LEVEL 1 of Defense-in-Depth
Primary pressure
boundary
enclosed in a
pressurized, low
enthalpy
containment
Elimination of
LOCA resulting
from failure of the
primary coolant
pressure boundary
NuScaleIAEA Safety
Standards Series
Specific Safety
Requirements
No. SSR–2/1
(Rev. 1), Safety of
Nuclear Power
Plants: Design
Requirement 20,
Paragraph 4.11
[(a) and (b)] and
relevant
Paragraphs
Natural circulation
in normal
operation
Elimination of loss
of flow accidents
CAREM25, DMS,
IMR, ABV-6M,
NuScale, AHWR
SMR-160
3
4
CRDM in side
Reactor pressure
vessel
Eliminate control
rod ejection
accidents
CAREM25, IRIS
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Design features Design objectives SMR designs Relevant safety
Requirements
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LEVEL 2 of Defense-in-Depth
SI.
No.
Design features Design objectives SMR designs Relevant
safety
requirements
1. A relatively large
coolant inventory
in the primary
circuit, resulting in
large thermal
inertia
Slow progression of
transients due to
abnormal operation
and failures
CAREM25,
IRIS
Requirement
20, Paragraph
4.11 [(a) and
(c)] and
relevant
Paragraphs
2. Implementation of
the leak before
break concept
Facilitate
implementation of
leak before break
concept
KLT-40S
3. Redundant and
diverse passive or
active shutdown
systems
Reactor shutdown All designs
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LEVEL 2 of Defense-in-Depth
SI.
No.
Design features Design objectives SMR designs Relevant
safety
requirements
4. Use of digital
technology
Proven reliability of
I&C system
Most designs Requirement
20, Paragraph
4.11 [(a) and
(c)] and
relevant
Paragraphs
5. Improved human-
machine interface
Most designs
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LEVEL 3 of Defense-in-Depth
SI.
No.
Design features Design objectives SMR designs Relevant
safety
requirements
1. Use of once-through
steam generators
Limitation of heat rate
removal in a steam
line break accident
KLT-40S Requirement
20, Paragraph
4.11 [(a) and
(d)] and
relevant
Paragraphs
2. Self-pressurization,
large pressurizer
volume, elimination
of sprinklers, etc.
Damping pressure
perturbations in
design basis
accidents
CAREM25,
DMS, mPower,
NuScale,
SMR-160
3. Gravity driven high
pressure borated
water injection
device (as a second
shutdown system)
Reactor shutdown CAREM25 and
AHWR300
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LEVEL 3 of Defense-in-Depth
SI.
No.
Design features Design objectives SMR designs Relevant
safety
requirements
4. Natural convection
core cooling in all
modes
Passive heat removal CAREM25,
AHWR-300,
DMS, IMR,
ABV-6M,
NuScale, SMR-
160
Requirement
20, Paragraph
4.11 [(a) and
(d)] and
relevant
Paragraphs5. Safety (relief) valves Protection of reactor
vessel from over
pressurization
IRIS,
CAREM25, it
should be
available in all
designs
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LEVEL 4 of Defense-in-Depth
SI.
No.
Design features Design objectives SMR designs Relevant
safety
requirements
1. Relatively low core
power density
Limitation or
postponement of
core melting
IRIS,
CAREM25,
NuScale and
mPower
Requirement
20, Paragraph
4.11 [(a) and
(e)] and
relevant
Paragraphs2. Passive system of
reactor vessel
bottom cooling
In-vessel retention
of core melt
KLT-40S,
CAREM25
and Flexblue
3. Passive flooding of
the reactor cavity
following a small
LOCA
Prevention of core
melting due to core
uncovery; in-vessel
retention
IRIS, VBER-
300, mPower
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LEVEL 4 of Defense-in-Depth
SI.
No.
Design features Design
objectives
SMR designs Relevant
safety
requirements
4. Containment and
protective
enclosure or
Double
containment
Protection
against
radioactive
release in severe
accidents and
external event
(like aircraft
crash, missiles)
CAREM25, KLT-
40S, IRIS,
mPower,
NuScale, W-
SMR and SMR-
160
Requirement
20, Paragraph
4.11 [(a) and
(e)] and
relevant
Paragraphs
5. Reduction of
hydrogen
concentration in
the containment by
catalytic re-
combiners
Prevention of
hydrogen
combustion
CAREM25,
AHWR300,
SMR-160
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LEVEL 5 of Defense-in-Depth
SI.
No.
Design features Design objectives SMR designs Relevant
safety
requirements
1. Mainly
administrative
measures
Mitigation of
radiological
consequences
resulting in
significant release
of radioactive
materials
KLT-40S IAEA SSR–
2/1 (Rev. 1)
Requirement
20, Paragraph
4.11 [(a) and
(f)] and
relevant
Paragraphs 2. Relatively small
fuel inventory, less
non-nuclear
energy stored in
the reactor, and
lower decay heat
rate
Smaller source
term, smaller
emergency
planning zone
(EPZ)
All design
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Lessons learned from the Fukushima
Daiichi accident
• As many as 94 individual lessons and
recommendations on Fukushima Daiichi Accident
These are categorized into four (4) main areas:
1. Design and Siting
2. Accident Management and on-site emergency
preparedness and response
3. Off-site emergency preparedness and
response
4. Nuclear safety infrastructures
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Key features in Design and Siting
• Strengthen measures against extreme natural
hazards and consequential effects
• Consider issues concerning multiple reactor sites
and multiple sites
• Ensure measures for prevention and mitigation of
hydrogen explosions
• Enhance containment venting and filtering system
• Enhance robustness of spent fuel cooling
• Use PSA effectively for risk assessment and
management
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Accident Management and on-site
emergency preparedness and response
• Ensure on-site emergency response
facilities, equipment and procedures
• Enhance human resource, skill and
capabilities
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Off-site emergency preparedness and
response
• Strengthen off-site infrastructure and
capability
• Strengthen national arrangements for
emergency preparedness and response
• Enhance interaction and communication with
the international communities
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CRPs to start in 2017 and 2018
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Launch a new CRP in 2017
CRP I3 2010 on “Design and Performance
Assessment of Passive Engineered Safety Features in
Small Modular Reactors” with 1st RCM in October
2017
Objectives:
1. Propose a common novel approach for designing
passive safety features for SMRs and provide
methods for assessing their performance and
reliability
2. Report validation of methodologies for SMR’s
engineered safety features performance assessment
using experimental test facilities
Launch a new CRP in 2018
CRP I3 1029 on “Development of Approaches
and Criteria for Determining Technical Basis
for Emergency Planning Zone for SMR
Deployment” with 1st RCM in March 2018
Background:
• SMRs may be deployed for sites located
nearer to the intended users
• SMRs characteristics: small power/source
term, enhanced safety
• Emergency Plan required to assure that on-
site & off-site emergency preparedness
provides assurance of adequate measures be
exercised in the event of a nuclear
incident/accident
Objectives:
1. Review implementation of DiD in SMRs
2. Develop approach and formulate technical
basis for guidance on emergency
preparedness & response focusing on EPZ
sizeUS Emergency Planning Zone: 10
miles
CAORSO site
France Evacuation Zone:
5 km
IRIS: 1 km
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Technical Summary (1)
Various extreme natural hazards (specific to the site) occurring simultaneously have to be considered in the design
For multiple unit plant, ensure un-precedented accident scenario and common cause failures are considered, and counter measures can be carried out on the site if meltdown occurs.
Consider electrical power unavailability and ensure core cooling and decay heat removal.
At least one success path to cope with accident to cool down the reactor core by active, passive, manually aligned systems or suitable combination.
The Fukushima daiichi accident has unveiled many issues regarding the
weakness of the existing plant design especially regading the design of
engineered safety features in order to withstand extreem natural hazards
and cope with the emergency situation of extended station blackout
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Technical Summary (2)
Assure containment vessel integrity, diverse shutdown, core cooling and decay heat removal.
Provide diverse cooling system for containment and provision for connecting portable equipment.
Survivability of emergency power supply system should be assured to cope with extreem natural hazards
Hydrogen concentration must be controlled by adopting appropriate technology. The vent system should be
able to prevent catastrophic failure of containment and reduce pressure with filtering capabilities.
Ensure DC power availability for post accident monitoring system.
Designs should prevent failure of safety related SSC and accommodate failure with compensatory measure
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THANK YOU VERY MUCH
For inquiries on SMR, contact:
Dr. M. Hadid Subki <[email protected]>
Questions & Comments?
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