10 Loss Coolant1

7/29/2019 10 Loss Coolant1

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Loss of Coolant

PWR, BWR, CANDU

Gas-Cooled, Na-CooledPebble Bed, GEN IV


2/19


3/19

Complexity More Breakdowns


4/19

Loss of Coolant Accident (LOCA)

Component(s)

breakdown

Interruption of normal

coolant flow

Reactor shutdown

Decay heat buildup

Alternative systemsneeded to prevent

damage to reactor


5/19

Operational States

Normal Operation

Continuous Power

Generation

Operational Transients ~10 per reactor year

Shifts in steady-state

conditions

Startup

Shutdown

Maintenance Routines

Upset Conditions

~1 per reactor year

Not normal operating

event Expected occurrence

Lightning strike

Power lines broken

Pump failure

Loss of feedwater

Little or no damage

No radiation release


6/19

Operational States

Emergency Events 1 in 100 reactor years

Some damage to power

plant components Break in reactor pipes

Relief valves stuck open

Electrical Fires

No radiation release

Limiting Fault 1 in 10,000 reactor

years

Design Basis Accident Radiation releasepossible Earthquake

Plane impact

Unprotected, BeyondDBA Asteroid impact

Act of God


7/19

Engineered Safety Systems

Main safety systems

tripping the fission

reaction

Emergency corecooling system (ECCS)

Safety achievement

Duplication

Multiple sensors,

processors, and controldevices to monitor

reactor

Multiple safety systems

to prevent and/or contain

accidents Diversity

Monitoring different

parameters to confirm

results


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Design Basis Accident

Postulated events that

cause limiting faults

Earthquake

Plane impact

Flood

Terrorist activities

Volcanic eruption

Beyond DBA

Events too unlikely to

occur for that reactor

Simultaneous DBA

events

Asteroid impact

Geological upset in an

area without history for

that type of event

Dinosaur stampede


9/19

LWR Conditions

Upsets

Loss of coolant through relief

valve

Addition of extra coolant

through pump

Changes in feedwater

conditions

Improper operation of

reactor controls

Emergency events

Valves stuck open

Small breaks in steam line

Loss of flow from all reactor

coolant pumps

Limiting faults

Large break in steam line

Large break in coolant pipe

Steam generator rupture

Main coolant pump failure

Failure of control rods


10/19

PWR Heat Regulators

Accumulators

Pressurized water vessels

High-Pressure Injection

System (HPIS) Low injection rate of highpressure water

Low-Pressure Injection

System (LPIS)

High injection rate of low

pressure water

ECCS Sumps

Recirculate water which has

escaped from the primary

circuit

Power-Operated ReliefValve (PORV)

Release valve to release

built up steam and energy

from the reactor Depressurize vessel


11/19

BWR Heat Regulators

High-Pressure Corespray

System (HPCS)

Regularly spray water from

storage tank or suppression

pool onto core and fuel forany pressure level

Automatic

Depressurization System

(ADS) Release vessel water into a

suppression pool

Lowers vessel pressure

Low-Pressure Corespray

System (LPCS)

Spray water from

suppression pool to remove

heat at low pressures

Low-Pressure Coolant

Injection System (LPCI)

Pump water from

suppression pool for long-term heat removal


12/19

CANDU

Headers Distributors of D2O to

and from core

Emergency CoolantInjection System (ECI) Separate system to

supply H2O to thereactor

Similar HPIS and LPISdesigns

Disadvantages Horizontal tubes can

get steam bubbles

Reactivity increases inareas where no coolantis present

Advantages Lower operational

temperature andpressure

Significant heat transferto moderator (when

present)


13/19

Gas-Cooled Conditions

Operational Transients Startup and Shutdown

Online refueling

Upsets Loss of site power

Turbine trip

Steam fault

Failure of gascirculators

Emergency Conditions Interruption of electricity

supply to power station

Reactor trip Loss of boiler feedwater

Steam line break

Water entering reactor

Limiting Fault Rupture of containment

Loss of control rods

Blocked channel flow


14/19

Sodium-Cooled Fast Reactor

Operational Transients

Slow response of molten sodium to heat input

Upsets Similar to water- and gas-cooled reactors

Emergency Conditions

Similar to water- and gas-cooled reactors


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Gen IV Reactors

LOCA concerns are vital in the design and

construction of new nuclear power plants

Extra safety features are implemented intothe Gen III+ and Gen IV reactor designs to

protect against LOCA accidents and prevent

reactor core meltdown


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Examples and Problems 4.1

LOCA in a PWR


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Inlet Pipe Rupture in a Magnox Reactor


18/19


Pumps On or Pumps Off? What Events Occur When the Main Circulating

Pumps are Stopped (Path 1) or Left Operating(Path 2) During a Small LOCA Event?

Core Coverage

Core Damage

Heat Transfer

What ShouldYou Do?


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Other Problems

What about a large LOCA event?

What could you do to prevent the core from

melting?

Additional Analysis

If you had knowledge of the location of the

break, how would that affect your decision? What measures could be taken to avoid futureLOCA events of the same type?

10 Loss Coolant1

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