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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Water cooled SMRs (Only Examples)

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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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Power Range of SMRs

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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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4

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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SMR – iPWR type: integration of NSSS

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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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Key Design Features of Water-

cooled SMR Contributing to

Level 1 of

Defense-in-Depth

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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

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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

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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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Key Design Features of Water-

cooled SMR Contributing to

Level 2 of

Defense-in-Depth

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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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Key Design Features of Water-

cooled SMR Contributing to

Level 3 of

Defense-in-Depth

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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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Key Design Features of Water-

cooled SMR Contributing to

Level 4 of

Defense-in-Depth

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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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Key Design Features of Water-

cooled SMR Contributing to

Level 5 of

Defense-in-Depth

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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 <M.Subki@iaea.org>

Questions & Comments?

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