ML12146A367

0752 - G112 - Seminar for Oig & OI Personnel - 06 - Boiling Water Reactors

ML12146A367
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Issue date:	05/25/2012
From:	NRC/OI, NRC/OIG
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OI/OIG SEMINAR March 2010 Boiling Water Reactors 1

Objectives:

1. Become familiar with boiling water reactor basic theory of operations

2. Become familiar with basic accident sequences 2

z Boiling Water Reactors (35) z Pressurized Water Reactors (69) 3

Boiling water reactor basics:

1. Light water cooled and moderated

2. Designed for boiling in the reactor vessel 3 Designed

3. D i d to t keep k all ll reactor t coolant l t iin the containment building when warranted

4. Produced by General Electric 4

Boiling water reactor basic operation 5

The major components of any BWR are:

• REACTOR VESSEL AND INTERNALS

• REACTIVITY CONTROL SYSTEMS

• SEMI-CONVENTIONAL STEAM PLANT

• EMERGENCY CORE COOLING SYSTEMS

• PRESSURE SUPPRESSION CONTAINMENT 6

REACTOR VESSEL AND INTERNALS Steam Feedwater Core 7

REACTOR VESSEL 8

CORE SHROUD Core 9

REACTOR CORE (FUEL)

About 100 tons of fuel in the core 10

REACTOR CORE (FUEL)

Neutrons striking certain uranium and plutonium atoms causes them to become unstable. They split, or fission, releasing energy, slighting more than two neutrons and two fission products (smaller atoms).

In a reactor at power, the freed neutrons cause more fissions in a nuclear chain reaction.

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PRIMARY & SECONDARY CONTAINMENT It is the radioactivity from fission products rather than from fresh fuel that can be hazardous to workers and the public.

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REACTOR CORE (FUEL) 177 in 660 lbs Active Fuel Length 144 inches 13

REACTOR CORE (FUEL)

Plenum Spring Fuel Rod Fuel Pellet 14

Looking Down Removed 15

STEAM SEPARATOR & STEAM DRYER Water vapor leaving the reactor core passes through holes in the shroud head into the steam separator. The vertical tubes force the flow to spin, with water droplets returned to the topside of the shroud head and steam sent along to the steam dryer.

The steam dryer forces the flow along an S-shaped route, again separating water droplets from steam. Dry steam leaves the vessel while the water drains back to the annulus.

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REACTIVITY CONTROL SYSTEMS

• CONTROL RODS 9 NORMAL INSERTION AND WITHDRAWAL 9 RAPID INSERTION (SCRAM)

• RECIRCULATION FLOW 9 NORMAL POWER INCREASES/DECREASES 9 RAPID POWER REDUCTIONS

• STANDBY LIQUID CONTROL 9 EMERGENCY SHUT DOWN 17

CONTROL RODS Control rod drive mechanisms apply water pressure to one side of a hydraulic piston and vent water from the opposite side of the piston to move control rod(s).

• NORMAL INSERTION AND WITHDRAWAL An individual d d l controll rod d can b be movedd in 6-inch increments or full length in 48 seconds

• RAPID INSERTION (SCRAM)

All control rods inserted in 3 to 5 seconds 18

CONTROL RODS 19

CONTROL RODS 20

CONTROL RODS Cutaway Fuel Bundles Top of Control Rod 21

CONTROL RODS Control rods contain boron, which acts like neutron glue.

Inserting a control rod soaks up free neutrons, slowing the nuclear chain reaction. 22

CONTROL RODS Normal insertion: Valves open for a single control rod to admit water to the bottom of the DRIVE PISTON and vent water from above it. About 260 pounds differential pressure move the control rod into the reactor core.

Normal withdrawal: Valves open for a single control rod to admit water to th top the t off the th DRIVE PISTON and d vent water from below it. About 260 pounds differential pressure move the rod out of the reactor core.

Scram: Valves open for all control rods to admit water to the bottom of the DRIVE PISTON and vent water from above it. About 1,200 pounds differential pressure moves the rods into the reactor core.

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STANDBY LIQUID CONTROL If the control rods fail to shut down the reactor, the operators can manually start pump(s) to inject boron in liquid form into the reactor vessel.

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RECIRCULATION FLOW Two motor-driven pumps draw water from the reactor vessel and return it through jet pumps located between the shroud and the reactor vessel wall. High velocity water in the jet pump nozzles pulls water from the annulus. The combination of drive and driven flow passes through the reactor core.

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RECIRCULATION FLOW Jet Pump Nozzle High velocity drive flow from recirculation pumps pulls flow from annulus region to force about 3 times as much flow through reactor core.

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RECIRCULATION FLOW Varying the flow rate through the reactor core affects the formation of steam bubbles (voids) and thereby the power level. Increasing the flow rate sweeps bubbles away faster, increasing the reactor power level.

Operators can change the reactor power level from about 40% to 100% rated output by regulating the recirculation flow rate.

When conditions warrant pump or core protection, the recirculation pumps output will be automatically reduced, rapidly dropping the reactor power level.

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RECIRCULATION FLOW 28

Semi-Conventional Steam Plant Because steam is radioactive, gas pulled from condenser is treated before release.

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Semi-Conventional Steam Plant Unlike Same as fossil-fired Similar steam plant to 30

PRIMARY & SECONDARY CONTAINMENT 31

BWR Containments MARK II Containment MARK I Containment MARK lll Containment 32

Mark I Containment 33

DRYWELL HEAD DRYWELL FLANGE DRYWELL SHEAR LUG SUPPORT REACTOR PRESSURE VESSEL DRYWELL SHIELD WALL CORE RADIAL BEAM RADIAL BEAM VENT JET DEFLECTOR MANWAY VENT HEADER VACCUM BREAKER DOWNCOMER PIPE DWFDS DWEDS WATER LEVEL PRESSURE SUPPRESSION CHAMBER 34 Figure 6.5-1 Mark Containment

35 T-Quencher Downcomer HPCI Steam Exhaust 36

MARK II Containment 37

DRYWELL HEAD Pressure Suppression DRYWE LL RE ACTO R VES S EL S ACRIFICIAL S HIELD WALL S TEEL LINER REACTO R P EDE S TAL S /R VALVE TAILP IP E (18)

E QUIP MENT HANDLING DRYWELL P LATF OR M DECK DOWNCO MER (VENT)

VACUUM BREAKERS P RES S URE S UP P RE S S IO N (5) CHAMBER S UP P O RT CO LUMN (12) WATER LEVEL QUENCHER (18)

REINFO RCED CONCRETE 38 Figure 6.5-3 Mark II Containment

39 40 CONTAINMENT S P RAY S HIELD BUILDING 125 TON CRANE W/15 TON AUX HOOK Pressure Suppression CONTAINMENT UP P ER P OOL DRYWELL HEAD FUEL TRANS FER P OOL REACTOR VES S EL REACTOR S HIELD DRYWELL BOUNDRY WEIR WALL DRYWELL FUEL TRANS FER S /R VALVE LINE TUBE S UP RES S ION P OOL HORIZONTAL VENT 41 Figure 6.5-5 Mark III Containment

42 43 Mark I Mark II Mark III (BFNP) (LaSalle) (Perry)

Drywell Material Steel Concrete Concrete Drywell Thickness (ft) .17 6 6 Drywell Upper Diameter (ft) 39 31 73 Drywell Lower Diameter (ft) 67 73 73 Drywell Height (ft) 115 91 89 Drywell Free Air Volume (ft )

3 159,000 209,300 277,685 Drywell Design Internal Pressure (psig) 56 45 30 Drywell Design External Pressure (psig) 2 5 21 Drywell Deck Design d/p (psid) N/A 25 N/A Drywell Design Temperature ( F) o 281 340 330 Drywell max. Calculated LOCA Pressure (psig) 49.6 34 22.1 Shield above RPV Head Concrete Concrete W ater Suppression Chamber (or Containment ) Thickness (ft) .17 4 .15 Suppression Chamber (or Containment ) Steel Liner N/A .25 N/A Suppression Chamber (or Containment ) Diameter ft) 111 87 120 Suppression Chamber (or Containment ) Height (ft) 31 67 183 Suppression Chamber (or Containment ) Free Air 119,000 164,500 1,141,014 Suppression Pool Volume in Drywell (ft )

3 N/A N/A 11,215 1 ft3 = 7.48 gal Total Suppression Pool Volume (ft3) 135,000 124,000 129,550 Upper Pool Makeup to Suppression Pool (ft )

33 N/A N/A 32,830 Suppression Chamber (or Containment) Design Internal 56 45 15 Pressure (psig)

Suppression Chamber (or Containment) Design External 2 5 0.8 Pressure (psig)

Suppression Chamber (or Containment) Design 281 275 185 Suppression Chamber (or Containment) max. Calculated 27 28 11.31 Suppression Chamber (or Containment) design Leak Rate .5 .5 .2

(% of vol/Day)

Number of Drywell to Suppression Chamber (or 8 98 120 Containment) vents Total Vent Area (ft3) 286 308 512 Drywell Atmosphere N2 N2 Air 44

EMERGENCY CORE COOLING SYSTEMS Low Pressure ECCS High Pressure ECCS The motor-driven Residua Heat Removal (RHR) and Core Spray (CS) pumps The steam-driven High can transfer water from Pressure Coolant Injection the suppression pool to (HPCI) system and the reactor vessel vessel.

steam-driven non-ECCS Reactor Core Isolation Cooling (RCIC) system can transfer water from the Condensate Storage Tank to the reactor vessel.

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EMERGENCY CORE COOLING SYSTEMS Design, assuming single failure, provides a success path for adequate core cooling.

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EMERGENCY CORE COOLING SYSTEMS View down into reactor vessel with steam dryer and steam separator removed showing spray pattern above reactor core from Core Spray system operation.

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DESIGN BASES ACCIDENTS Control rod drop accident (CRDA)

A control rod is uncoupled from its mechanism and sticks fully inserted as the mechanism is fully withdrawn. The uncoupled control rod then falls freely to the fully withdrawn position.

Loss of coolant accident (LOCA)

The largest g diameter m pipe p p connected to the vessel ruptures, p ,

allowing cooling water to leak from the vessel at the fastest rate.

Main steam line break accident (MSLBA)

A main steam line break inside primary containment deposits energy into containment at the fastest rate.

Fuel handling accident (FHA)

A spent fuel bundle is dropped in transit and falls freely to strike irradiated fuel bundles in the reactor core (or spent fuel pool).

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Accidents MSLBA LOCA 49

ACCIDENTS FHA CRDA 50

QUESTIONS?

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