Nuclear energy - four months after Fukushima

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1 Institut»Jožef Stefan«Odsek za reaktorsko tehniko Nuclear energy - four months after Fukushima Iztok Tiselj "Jožef Stefan Institute", Reactor Engineering Division & Chair of Nuclear Engineering, Faculty of Mathematics and Physics 1

2 Contents "Great East Japan Earthquake" 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 500 m ,6 UPI/Air Photo Service

3 U.S. Geological Service "Great East Japan Earthquake" max acc.: Miyagi prefecture NS time (s) Max. accelerations in NPP Fukushima - Daiichi - reactor #2 acceleration (g) measured (basement) project N-S E-W Up-Down reactor shutdown at 0.135g

4 Japan nuclear power plants - earthquake Japan: 54 ( X) nuc. power plants 48 GW electric (~27 %) (before quake: plans for increase to 50% by 2030) source: JAIF Earthquake: - automatic shut down of 11 operating reactors (control rods inserted). - cooling systems remove the residual heat from the cores.

5 Boiling water reactor - BWR ~20% of world power reactors. Cooling system: p~70 bar, T~285 o C containment drywell steam dryer & moisture separator reactor vessel steam line turbine building turbine generator reactor core condenser jet pump recirculation pump pump river/ sea containment suppression chamber source: NRC Nuclear Regulatory Commission

6 BWR reactor vessel h=20m diam.=5-6 m fuel assembly h=4m source: General Electric

7 3000 tons of water in suppression chamber (Daiichi 2,3) Containment: volume ~10000 m 3 filled with N 2 pressure: - design 5 bar - rupture ~8-9 bar Spent fuel pool

8 Nuclear physics and engineering - fundamentals... n 235 U fission products: I, Cs, Sr, Xe... Fission ~200 MeV energy Out of that ~15 MeV due to the radioactive decay of fission products! Decay heat in MW Fukushima-Daiichi-1 Fukushima-Daiichi-2, Thermal power: 20 4 Daiichi MW 10 Daiichi 2, MW time after shutdown (hours) time after shutdown (days)

9 Accident - Earthquake RHR: Residual Heat Removal System 1st hour after earthquake: 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.

10 Accident - Tsunami D/G Loss of all power in Fukushima Daiichi 1-4 (blocks 5,6 slightly higher elevation) source: TEPCO - Tokyo Electric Power COrporation

11 RCIC - Reactor Core Isolation Cooling System, ICC - Isolation Condenser Cooling System 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) Scheme of High pressure Emergency Core Cooling System (ECCS)

12 Sever accident - core melting Energy balance (boiling water reactor ~700 MW electric power): 1) Decay heat MWh/h 2) Above 1500 K - rapid Zirconium-water reaction (50 ton): Zr + 2H 2 O -> ZrO 2 + 2H + 2 ~20 MWh/10 ton Zr 3) H 2 combustion ~20 MWh/10 ton Zr -1) Vaporization of H 2 O ~5 MWh/10 ton (3 h ~ 100 ton) unknown mass ~ ton, unknown leak rate -2) Heating and melting of fuel and internal structures of the reactor ~20 MWh/100 ton UO 2 Reactor #1 : ~ 1 day without cooling - largest core damaged (estimates by TEPCO, NRC) Three Mile Island core (PWR) 1979, core status known after few years. source: NRC

13 Source: NISA - Nuclear and Industrial Safety Agency Accident - Fukushima Daiichi - Reactor #1 Containment vessel of Reactor #1 not damaged. 24 h after quake

14 Cooling restored Accident - Fukushima Daiichi - Reactor #1 - cooling restored 30 h after quake Sea water replaced with fresh water after 2 weeks (electricity in plant after 1 week) Source: NISA

15 #2 Probably responsible for the majority of the radioactive releases! Fukushima Daiichi Reactor 3 similar events - strong explosion Fukushima Daiichi Reactor 2 hydrogen(?) explosion near the suppression chamber ruptured the containment.

16 Problems with Spent Fuel Pools Major problem - Reactor #4 Reactor #4 stopped in Nov. 29, 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 common SFPool

17 Spent fuel pool - Reactor #4 source: NRC, General Electric 1500 m 3 water ~ 4 MW heat Boiling acceptable in emergency conditions Explosion Spent fuel pool Water level "low" 4 days after the earthquake. H 2 explosion & fire in unit 4 (after ~90 hours). Containment vessel Reactor vessel TEPCO 16.5: H 2 came from Reactor #3!

18 Current cooling of Spent fuel pools External 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. pool# pool# "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.

19 Current status of Fukushima Daiichi reactors - Reactors 1,2,3 - water injected into reactor vessels ~3-9 m 3 /h - Evaporative cooling, cores solid, partially uncovered, T vessel ~ C, p~1 bar (reactor #1 p ~2-3 bar) - Closed cooling circuits established in June - leaking water decontaminated/desalinated and injected back into reactors Nitrogen injected into containment vessels of #1, #2, #3 reactors source: TEPCO

20 Radiological consequences (quantities, units, orders of magnitude) Activity - basic unit: Bq - decay/s ~100 EBq - activity of power reactor (E - Exa ) ~0.1 mbq - activity I-131 per m 3 in Slovenia in March 2011 (m - mili ) Fukushima reports - units used (no prefixes): Bq/m 2, Bq/m 3, Bq/cm 3, Bq/l, Bq/kg Activity in US: [Ci] (1 Curie - 1 g radium-226 = 3.7*10 10 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 human body ~100 Bq/kg This slide intentionally made complex! Radiation sickness ~ Gy (Sv) in short time, lethal ~2-5 Gy 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) Limitations: ~ msv/h (Fukushima site) public 1 msv/year professionals 20 msv/year ~ msv/h (Reactors 1,2,3,4 rooms) emergency 500 msv ~ 10 Sv/h (inside containment buildings) Radon ~0.2 μsv/h natural background dose ~2-3 msv/year

21 Dose rate (microsv/h) at the NPP site - Main entrance Gesellschaft für Anlagen- und Reaktorsicherheit Releases: cumulative ~5*10 17 Bq (~10% Chernobyl) End of April ~10 12 Bq/h Limitations: public 1 msv/year professionals 20 msv/year emergency 500 msv

22 source: TEPCO Background: 0.1 micro Sv/h ~500 m

23 TEPCO

24 U.S. Department of Energy,

25 DOE (Dept. of Energy) - measurements and predictions First year dose (19.April) msv > <1 natural background dose ~2-3 msv/year Average Slovenian - ~1 msv from Chernobyl

26 Radiological consequences Dose => Deaths: ICRP recommendations 2007 (LNT - Linear-No-Treshold model) 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)...

27 Fatalities, Damage Earthquake & tsunami fatalities ~23,000 ( people lost homes, new house built ) Fukushima accident ~100 (ICRP methodology) Damage: Total earthquake and tsunami damage ~ G$ (sources: World Bank. 21.March, G$, newspapers) Sum ~ nuclear damage - without compensations for land and evacuated residents ~ G$ 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

28 Institut»Jožef Stefan«Odsek za reaktorsko tehniko Thanks: colleagues of R4, F8, RPU Sources: - NISA - Nuclear and Industrial Safety Agency - TEPCO - Tokyo Electric Power COrporation - JAIF - Japan Atomic Industrial Forum - DoE - Dept. of Energy (USA) - World Nuclear Association - IAEA - International Atomic Energy Agency - NRC - Nuclear Regulatory Commission (USA) 28