Institut »Jožef Stefan«Odsek za reaktorsko tehniko

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Nuclear energy - four monthsafter Fukushima

Iztok Tiselj

"Jožef Stefan Institute", Reactor Engineering Division &

Chair of Nuclear Engineering, Faculty of Mathematics and Physics

Contents

•"Great East JapanEarthquake"• Nuclear power plants in the earthquake zone• Accident in NPP Fukushima Daiichi

• Basics of reactor engineering

• Key events,core melt

• Cooling• Restoration plans• Releases of

radioactivity•Local and

global consequences

UPI/Air Photo Service

5,6

2

3

4

1

500 m

"Great East Japan Earthquake" max acc.: Miyagi prefecture

http://earthquake.usgs.gov/U.S. Geological Service

acceleration

(g)measured(basement)

project

N-S 0.35 0.45

E-W 0.56 0.45

Up-Down 0.31 0.43

Max. accelerations in NPP Fukushima - Daiichi -reactor #2

time (s)

NS

reactor shutdown at 0.135g

source: JAIF

Japan nuclear power plants - earthquake

Earthquake: - automatic shut down of 11 operating reactors (control rods inserted).- cooling systems remove the residual heat from the cores.

Japan: 54 (+ 2 - 4 - X) nuc. power plants

48 GW electric (~27 %)(before quake: plans for

increase to 50% by 2030)

Boiling water reactor - BWR

pump

river/sea

generator

condenser

turbine

turbine building

containment suppression chamber

containment drywell

steam dryer & moisture separator

jet pumpreactor core

recirculation pump

steam linereactor vessel

~20% of world power reactors.

Cooling system: p~70 bar, T~285 oC

source: NRCNuclear Regulatory Commission

BWR reactor vessel

h=20m

diam.=5-6 m

fuel assembly

h=4m

source: General Electric

Containment:

volume ~10000 m3

filled with N2

pressure: - design 5 bar - rupture ~8-9 bar

3000 tons of water in suppression chamber (Daiichi 2,3)

Spent fuel pool

Nuclear physics and engineering - fundamentals ...

Fission ~200 MeV energy

Out of that ~15 MeV due to the radioactive decay of fission products!

235Un

fission products:I, Cs, Sr, Xe...

Decay heat in MW

0

10

20

30

40

50

0 5 10time after shutdown (hours)

Fukushima-Daiichi-1

Fukushima-Daiichi-2,3

0

4

8

0 7 14 21 28 35 42 49 56

time after shutdown (days)

Thermal power:

Daiichi 1 - 1380 MW

Daiichi 2,3 - 2380 MW

RHR:

Residual Heat Removal System

Residual Heat Removal systems cool the reactors. Fukushima Daiichi - RHRs powered by diesel generators cool the cores.Fukushima Daini, Onagawa - RHRs powered by external electricity.

1st hour after earthquake:

Accident -Earthquake

Loss of all power in Fukushima Daiichi 1-4 (blocks 5,6 slightly higher elevation)

Accident - Tsunami

D/G

source: TEPCO - Tokyo Electric Power COrporation

Accident -Fukushima Daiichi

Cooling after Tsunami - with systems working with (almost) no electricity

Daiichi 1 ~ 8h (ICC)

Daiichi 2 ~70 h (RCIC)

Daiichi 3 ~40 h (ECCS/RCIC)

RCIC - Reactor Core Isolation Cooling System, ICC - Isolation Condenser Cooling System

Scheme of High pressure Emergency Core Cooling System (ECCS)

Sever accident - core melting

Energy balance (boiling water reactor ~700 MW electric power):

1) Decay heat 10-20 MWh/h2) Above 1500 K - rapid Zirconium-water reaction (50 ton):

Zr + 2H2O -> ZrO2 + 2H2 + ~20 MWh/10 ton Zr

3) H2 combustion ~20 MWh/10 ton Zr

-1) Vaporization of H2O ~5 MWh/10 ton (3 h ~ 100 ton)unknown mass ~100-200 ton, unknown leak rate

-2) Heating and melting of fuel and internal structures of the reactor ~20 MWh/100 ton UO2

Three Mile Island core (PWR) 1979, core status known after few years.

source: NRC

Reactor #1 :

~ 1 day without cooling

- largest core damaged

(estimates by TEPCO, NRC)

Source: NISA - Nuclear and Industrial Safety Agency

Containment vessel of Reactor #1 not damaged.

Accident - Fukushima Daiichi - Reactor #124 h after quake

Source: NISASea water replaced with fresh water after 2 weeks (electricity in plant after 1 week)

Cooling restoredAccident - Fukushima Daiichi - Reactor #1 - cooling restored

30 h after quake

Fukushima Daiichi Reactor 3similar events - strong explosion

Fukushima Daiichi Reactor 2

hydrogen(?) explosion near the suppression chamber ruptured the containment.

#2 Probably responsible for the majority of the radioactive releases!

Problems with Spent Fuel Pools

Major problem - Reactor #4

Reactor #4 stopped in Nov. 29, 2010 -all fuel moved to Spent fuel pool.

Reactors #5 and #6 -stopped at time of earthquake - fuel in reactors and SFPools. No problems with cooling.

No problems with cooling of commonSFPool

Spent fuel pool

Explosion

Containment vessel

Reactor vessel

1500 m3 water

~ 4 MW heat

Boiling acceptable in emergency conditions

Water level "low" 4 days after the earthquake.

H2 explosion & fire in unit 4 (after ~90 hours).

Spent fuel pool - Reactor #4 source: NRC, General Electric

TEPCO 16.5: H2 came from Reactor #3 !

Current cooling of Spent fuel poolsExternal water spray in pools #1 & #4 - sea water in the first 2 weeks, fresh water later.

Concrete pump trucks used today. Structural integrity of pool #4 questionable. Reinforcement of the pool #4 (steel & concrete) by the end of July.

"Standard" path of water injection in spent fuel pool #2 and #3 since May.

Pools of reactors #5 and #6 and common spent fuel pool: operating cooling systems.

pool#3 10.5.

pool#4 8.5.

Current status of Fukushima Daiichi reactors- Reactors 1,2,3 - water injected into reactor vessels ~3-9 m3/h - Evaporative cooling, cores solid, partially uncovered,

Tvessel~100-160 0C, p~1 bar (reactor #1 p ~2-3 bar)- Closed cooling circuits established in June - leaking water

decontaminated/desalinated and injected back into reactors

source: TEPCO 19.7.2011

Nitrogen injected into containment vessels of #1, #2, #3 reactors

Radiological consequences (quantities, units, orders of magnitude)

Activity - basic unit: Bq - decay/s

~100 EBq - activity of power reactor (E - Exa - 1018)

~0.1 mBq - activity I-131 per m3 in Slovenia in March 2011 (m - mili - 10-3)Fukushima reports - units used (no prefixes): Bq/m2, Bq/m3, Bq/cm3, Bq/l , Bq/kg

Activity in US: [Ci] (1 Curie - 1 g radium-226 = 3.7*1010 Bq)

Biological radiation effects - activities and doses:

1 Bq element A ≠ 1 Bq element B

1 Bq elem. A on the ground ≠ 1 Bq A inhaled ≠ 1 Bq A ingested

Dose:

Absorbed Gy (Gray, J/kg) - for acute consequences of radiation (USA: rad=0.01 Gy)

Equivalent Sv (Sievert) - for stochastic consequences (USA: rem =0.01 Sv)

Effective (Sv) - for non-uniform irradiation (weighted sum of equivalent doses per tissue)

1 Sv ~ 1 Gy for gamma in beta radiation

Fukushima - orders of mag.: ~ 0.1 μSv/h (natural background without Radon)

~ 0.01 - 1 mSv/h (Fukushima site)

~ 10-100 mSv/h (Reactors 1,2,3,4 rooms)

~ 10 Sv/h (inside containment buildings)

Limitations: public 1 mSv/yearprofessionals 20 mSv/yearemergency 500 mSv

Radiation sickness ~ 0.5-1 Gy (Sv) in short time,

lethal ~2-5 Gy

This slide intentionally made complex!

human body ~100 Bq/kg

Radon

~0.2 μSv/h

natural background dose ~2-3 mSv/year

Dose rate (microSv/h) at the NPP site - Main entrance

Releases:

cumulative ~5*1017 Bq

(~10% Chernobyl)

End of April ~1012 Bq/h

Limitations: public 1 mSv/yearprofessionals 20 mSv/yearemergency 500 mSv

Gesellschaft für Anlagen- und Reaktorsicherheit

source: TEPCO

~500 m

Background: 0.1 micro Sv/h

TEPCO

24

U.S. Department of Energy, 6.5.2011

DOE (Dept. of Energy) - measurements and predictions

First year dose (19.April)

mSv>2010-205-101-5<1

natural background dose ~2-3 mSv/year

Average Slovenian -~1 mSv from Chernobyl

Rough estimate: 3000 Fukushima workers, average 20 mSv:Collective dose = 60 man-Sv ... 5% -> 3 additional cancer fatalities in the next

decades ... (1003 instead of 1000)...

ICRP recommendations 2007

Radiological consequences

(LNT - Linear-No-Treshold model)

Dose => Deaths:

Fatalities, DamageEarthquake & tsunami fatalities ~23,000 (111.000 people lost homes, 37.000 new house built 11.7.2011)Fukushima accident ~100 (ICRP methodology)

Damage:Total earthquake and tsunami damage ~200-300 G$ (sources: World Bank. 21.March, 122-235 G$,

newspapers)

Sum ~ nuclear damage - without compensations for land and evacuated residents ~50-100 G$

Nuclear power - global impact:- Extensive re-assessment of nuclear safety and risks.- Setback to "Nuclear renaissance".

- Germany - nuclear phase-out in ~10 years, Italy - remains non nuclear, Japan - unclear?- UK - no change of energy plans - Nuclear energy - important part, Finland - call for new reactor, USA - nu

Institut »Jožef Stefan«Odsek za reaktorsko tehniko

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Thanks: colleagues of R4, F8, RPU

Sources:- NISA - Nuclear and Industrial Safety Agency

http://www.nisa.meti.go.jp/english/- TEPCO - Tokyo Electric Power COrporation

http://www.tepco.co.jp/en/index-e.html- JAIF - Japan Atomic Industrial Forum

http://www.jaif.or.jp/english/index.php- DoE - Dept. of Energy (USA)

http://www.energy.gov/news/10194.htm

- World Nuclear Associationhttp://www.world-nuclear.org/info/fukushima_accident_inf129.html

- IAEA - International Atomic Energy Agencyhttp://www.iaea.org/

- NRC - Nuclear Regulatory Commission (USA)http://www.nrc.gov