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Safety design features

What is targeted?

1

Integral primary circuit

Elimination of large break LOCA

2

Integral primary circuit

Increased coolant inventory/larger thermal inertia

3

Internal CRDMs

Elimination of rod ejection

4

Internal CRDMs

Elimination of vessel head penetrations or reduction of their size

5

Soluble boron free core

Elimination of boron dilution

6

Increased level of natural circulation

Passive decay heat removal in LOFA

7

Pressure suppression containment

Fission product retention increase

8

Inerted containment

Prevention of hydrogen explosion

9

Reduced core power density

Slower progression of accidents

10

Soluble boron free core and reduced core power density

Mitigation of ATWS

TABLE IV-5. QUESTIONNAIRE 2 — LIST OF INTERNAL HAZARDS

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Specific hazards that are of concern for a reactor line

Explain how these hazards are addressed in an SMR

1

Prevent unacceptable reactivity transients

Internal CRDMs (no control rod ejection); boron-free core (no boron dilution); (limited) negative moderator reactivity coefficient

2

Avoid loss of coolant

-Integral design of the primary circuit (no large break LOCA, minimized vessel penetrations due to internal CRDMs)

-Grace period increased due to large coolant inventory and reduced core power density

3

Avoid loss of heat removal

— Diverse and redundant passive decay heat removal systems with heat exchanges integrated in the primary coolant system

-Diverse ultimate heat sinks with the air cooling tower having infinite autonomy

-In-vessel retention achieved via RPV cooling by natural convection of water in the reactor cavity

-Large heat capacity of the primary circuit

4

Avoid loss of flow

-Increased level of natural circulation in the primary coolant system; reduced power density in the core

5

Avoid exothermic chemical reactions

-Inerted containment

-Reduced core power density, providing an increased margin to Zr-steam reaction

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List of initiating events for AOO/DBA/BDBA typical for a reactor line (PWRs)

Design features of SCOR used to prevent progression of the initiating events to AOO/DBA/BDBA, to control DBA, to mitigate BDBA consequences, etc.

Initiating events specific to this particular SMR

1

LOCA

-Integral primary circuit eliminates large break LOCA — Increased coolant inventory extends grace period — Containment with high design pressure — Pressure suppression system

Nothing specified here

2

Steam generator tube rupture

-Steam generator designed for full system pressure

3

Steam line rupture

-Steam is discharged to a dedicated water pool

4

Control rod ejection

Internal CRDMs eliminate an option of control rod ejection

5

Boron dilution by the ingress of boron free water from the secondary circuit

-Soluble boron free core design

6

LOFA

-Increased level of natural circulation — Reduced core power density

Passive safety design features

Positive effects on economics, physical protection, etc.

Negative effects on economics, physical protection, etc.

Integrated primary circuit

Allows for a reduction in containment volume (see below)

Increased RPV cost per unit of energy produced; unit power limited by 2000 MW(th) for the original SCOR steam generator concept

Increased reliance on natural circulation

Simplifies design and maintenance, contributing to reduced costs

RPV cost increased due to larger vessel size; may increase complexity of reactor operation (startup phase, etc.)

Compact primary circuit

Containment volume could be reduced with a positive effect on plant economy

Soluble boron free core

Relaxes concerns related to human actions of malevolent character