Resilience in Safety Engineering:
Long-Term Cooling in Nuclear Power Plants
Generation I
Early PrototypeReactors

Generation II
Commercial PowerReactors

LWR: PWR/BWR
CANDU, VVER

Gen IGen II

1960

Generation IV
Enhance safety
Reduce costs
Minimal waste
Prolif. resistant

Shippingport
Dresden Fermi-I
Magnox AVR MSBR

1950

Generation III
Advanced
LWRs

1970

1980

ABWR
EPR

AP1000ESBWRGen III

1990

2000

2010

Gen IV
2020

2030

Technical Perspective The inherent nature of a nuclear power plant design
recognizes that after the fission process stops, thermalheat is still produced by the decay of fission productsthat remain and must be removed to a heat sink
 This ‘decay heat’ while small (<1% of PO) is still
substantial enough that safety systems must be
designed and operational procedures must be
developed to assure long-term heat removal
 Resilience in safety engineering is a key objective

Michael Corradini

Technical Perspective

Safety Actions after Fukushima USNRC (2008) began to evaluate the design basis forthe long-term core cooling approach for each newreactor design considering extended time periods (days)
 Fukushima only sharpened the focus on the need toassure long-term cooling for beyond design basis events
 Finally, in all advanced nuclear plant designs, so-called
Generation IV plants, this concept of long-term coolingis imbedded in the inherent plant design.

4NAS Fukushima Study

NAS Fukushima Recommendations

NAS Study commissioned by Congress 2012: Task Statement
1.Causes of the Fukushima nuclear accident.
2.Re-evaluation of conclusions from previous NAS studies onsafety and security of spent nuclear fuel and high-level
radioactive waste storage.
3.Lessons that can be learned from the accident to improvecommercial nuclear plant safety and security systems andoperations.
4.Lessons that can be learned from the accident to improvecommercial nuclear plant safety and security regulations

USNRC & US nuclear industry should improve nuclear plant systems:

Note: Most findings and recommendations in NAS report mirror thosemade by other organizations, including the USNRC Near-Term TaskForce. But, NAS report provides different perspectives on some issues.

Additional recommendation were in the areas Operator Training, Offsite
Emergency Response and Risk Assessment; e.g., beyond design base analysis5•DC power for instrumentation and safety system control.
•Tools for estimating real-time plant status during loss of power.
•Long-term Decay-heat removal and reactor depressurization and containment
venting systems and protocols.
•Hydrogen monitoring and mitigation.
•Instrumentation for monitoring critical thermodynamic parameters in reactors,containments, and spent fuel pools as well as offsite radiation monitoring.
•Communications and real-time information systems to support communication andcoordination between control rooms and technical support centers.

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AP1000

7Advanced Reactor Systems
Near-Term LWR Designs•Well understood Technology•Fuel <5% U-235 oxide fuel•Regulatory & operating experience•Deployment in <10 years
Longer-Term Gen IV Designs•New innovative technologies•Mostly non-LWR based designs•Deployment 20+ years•Broader applications•Process heat applications•Transportable/mobile•Long-lived coresWestinghouse
200 MWeGE PRISM

GA MHTR

Holtec HI-SMUR
140 MWe

Hyperion10

Very-High-Temperature Reactor (VHTR)
Fluoride Salt-Cooled
High-Temperature
Reactor (FHR)

EPACT 2005
Authorized
General Electric SPRISM

Characteristics
o Helium cooled
o 900°C temp.
o 600 MWthPassively-SafeReactor

Key Benefito High thermal
efficiency
o Hi-Temp
Process Heat

GE Power Systems MS7001FB

Nuclear Brayton
Combined Cycle
9Hi-Temperature
Coated-Particle
FuelHigh-Temp, LowPressure LiquidSalt Coolant

NEEP 231 - Survey of Nuclear Engineering

SMR Long-term cooling issues:
Natural Circulation and Condensation

High-Temp Reactor Long-term Cooling:
Natural Circulation & Flow Instabilities

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UW Scaled Air Cooled RCCSUW Scaled Water-Cooled RCCS
Data Acquisition
- x60
- x1
- x3
- x4
- x4

Thermocouples
Magnetic mass flow
UDV velocity TDXHeat flux sensors
X-ray void fraction

Facility- Variable scale
1:4 distorted
1:6 true- 2 bar max- 350 gal. capacity

Test Section

Test Section- 3 risers- 3 radiant fins- 18.5' total- 12.0' heatedPower- 34 heaters- 6 control zones- 42.5 kW max
3 story facility. 24' total height13

Current Observations on Resilience Fukushima events reminded us that the key objectiveof nuclear safety engineering is to demonstrate longterm cooling of decay heat to an ultimate heat sink.
 Current plants need to show this ability by upgradeddecay heat removal systems (e.g., FLEX approach) Advanced LWR plants are designed to use passive
safety systems with minimal operator action
 Generation IV plants need to be designed and tested
to demonstrate this ability.

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