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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/thermal inertia

3

Internal CRDMs

Elimination of rod ejection

4

Internal CRDMs

Elimination of vessel head penetrations

5

Increased natural circulation

Downgraded LOFA

6

Reduced size, high design pressure containment

Small break LOCA mitigation

7

Pressure suppression containment

Fission product retention improvement

8

Inerted containment

Prevention of hydrogen explosion

9

Reduced core power density

Slower progression of accidents

10

Integral steam generators, designed for full system pressure and with tubes in compression

Prevention or downgrading of:

— SG tube rupture

— Steam line break

— Feed line break

Elimination of tensile stress induced cracking

11

Internal (fully immersed) axial design pumps

Elimination of:

— Shaft seizure

— Locked rotor

12

Thick downcomer acting as internal neutron shield

No vessel embrittlement, and no need for surveillance resulting from a reduction of fast neutron fluence on the reactor vessel

13

Large volume integral pressurizer

Prevention of overheating events, elimination of sprays

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

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

Initiating events specific to this particular SMR

Large break LOCA

-Integral primary circuit eliminates large break LOCA

Small break LOCA

Coupled response of reactor vessel and containment to small break LOCA limits loss of coolant and prevents

core uncovery

LOCA

Steam generator tube rupture

-Integral primary system — High design pressure containment — Increased coolant inventory extends grace period — Pressure suppression system

-Because the primary coolant is on the shell side of the steam generators, the tubes are compressed and the possibility of a steam generator tube rupture (e. g., by stress corrosion cracking) is greatly reduced — SG designed for full primary system pressure, up to main isolation valves (MIV)

Nothing in particular specified here

Rod ejection

Internal CRDMs

LOFA

-Multiple (8) main circulating pumps (MCPs) — Increased natural circulation fraction because of a large, tall vessel

Passive safety design features

Positive effects on economics, physical protection, etc.

Negative effects on economics, physical protection, etc.

Integral primary circuit with safety-by-design™

-Core damage frequency (CDF) and large early release frequency (LERF) are reduced, allowing for twin unit or multiunit power plants; potential economic benefits from reduced or eliminated emergency planning — Allows use of a compact steel containment, minimizing the siting area and improving protection from external events, such as aircraft crash

— Safety-by-design™ results in a reduced complexity of the plant and its safety systems, contributing to reduced costs — Intrinsic security (‘security by design’) contributes to reduced costs

-Limits power of a single module (counteracted by modular construction of multiple units at site)

— Increases reactor pressure vessel size (however, containment and overall footprint are decreased)

All safety grade systems are passive

-Results in reduced complexity and improved reliability of the plant, contributing to reduced capital and maintenance costs

-Added resilience to sabotage and other malevolent acts

None identified