Fukushima-Daiichi - a radiochemical view of the evolving situation in Summer 2011.

Transcription

1 Fukushima-Daiichi - a radiochemical view of the evolving situation in Summer Kath Morris. Research Centre for Radwaste and Decommissioning The University of Manchester With thanks to Dr Edward Blandford, Stanford University. Prof. Francis Livens & Dr John Roberts, The University of Manchester.

2 Nuclear reactors The Great East Japan Earthquake and Tsunami The series of evolving events as we understand them at Fukushima- Daiichi Environmental information Implications Talk Structure.

3 Nuclear Reactor UO 2 MP 2865 C Zircaloy MP 1850 C

4 BWR Fukushima Daiichi Units 1, 2, 3, 4, 5, 6

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6 Fuel storage pond Principal Containment 3. Drywell containment structure ( cm concrete) 2. Reactor Vessel (15 cm steel) 1. Zircaloy cladding Suppression pool Zircaloy MP 1850 C UO 2 MP 2865 C

7 Courtesy Edward Blandford The Earthquake Aerial view of Fukushima-Daiichi NPP - before & after Before the Earthquake and Tsunami After the Earthquake and Tsunami Unit 5 Unit 6 Unit 1 Unit 4 Unit 3 Unit 2 Photo Source: TEPCO Photo Source: Air Photo Service Inc (Myoko, Niigata Japan)

8 Earthquake and aftershocks Ground motion of Fukushima NPP Earthquake time: 2:46 pm March 11, 2011 Location: Offshore Sanriku coast, 24 km in depth, M9.0 Earthquakes: M quake (March 11) M - 7 class 5 times M - 6 class 72 times M - 5 class 423 times Unit MWe Observed (max. gal) Design Basis (max. gal) N-S E-W Vert. N-S E-W Vert TOKYO tokyo.ac.jp/eqvolc/201103_to hoku/eng/#mesonet Earthquake Research Institute, University of Tokyo, Prof. Takashi Furumura and Project Researcher Takuto Maeda F-D NOTE: Scram set points by acceleration Horizontal= gal, Vertical=100 gal Seismometers were located in the basement of reactor building gal is a unit of acceleration cm / s 2 Courtesy Edward Blandford

9 14 NPPs along eastern Honshu coast affected by Tsunami Time sequence of Units 1-3 immediately following earthquake: Earthquake followed by Reactor SCRAM, LOOP, EDGs start, IC/RCIC in operation Tsunami followed by complete (AC/DC) blackout and (mostly) isolation from the Ultimate Heat Sink Earthquake Research Institute, University of Tokyo, Prof. Takashi Furumura and Project Researcher Takuto Maeda Source: A. Omoto, Fukushima Accident : An overview, ICAPP 2011, 3 May 2011; Courtesy Edward Blandford

10 Initial impact on plant reactor safety systems Shutdown was secured by automatic shutdown of all control rods Transmission line was damaged by the earthquake Emergency diesel generators started but subsequently were lost due to Tsunami Station blackout Most of the cooling function of reactor and spent fuel pool were lost by the loss of power supply caused by Tsunami High level contaminated water found in turbine buildings loss of containment function Source: TEPCO presentation, The Great East Japan Earthquake and Current Status of Nuclear Power Stations, April 25, 2011

11 Intense heating (10 days ), steam, contamination Dumping Excess Heat

12 Sequence of Events: Unit 1 Unit 1 Sequence of Events March 11 14:47 Earthquake, loss of offsite ac power, and plant trip 14:52 Isolation condenser operated to cool reactor 15:03 Isolation condenser stopped operating 15:37 Tsunami and total loss of ac power SBO 15:37 Loss of ability to inject water to the reactor ~17:00 Water level below top of fuel --:-- Partial core damage (several hours after tsunami) March 12 14:30 Vent primary containment 15:36 Explosion results in damage to the reactor building At high T: Zr + 2H 2 O ZrO 2 + 2H 2 + HEAT Onwards Inject seawater / freshwater to cool

13 Unit 2 & Unit 3 Unit 2 explosion 15 th March 6.20am coupled to pressure loss in TORUS Containment damage assumed (Weightman, May 2011) Unit 3 explosion 14 th March 11.01am Damage is extensive - containment?

14 Unit 4, 5 and 6 TEPCO. Unit 4 reactor de-fuelled, SNF in storage pond. Active cooling required / explosion (hydrogen) possibly from Reactor 3 (venting) Unit 5 and 6 Sequence of Events (both units were shut down for periodic inspection) March 11 14:46 15:41 March 20 Earthquake and loss of offsite ac power Tsunami and total loss of ac power at site SBO 14:30 Unit 5 enters cold shutdown 19:27 Unit 6 enters cold shutdown

15 Source of hydrogen Delayed Release of Heat After Shutdown Zirconium cladding reaction with steam to produce hydrogen becomes substantial at temperatures above 1000 C Volatile fission products released as noble gases (e.g. Kr) or aerosols (e.g. I, Cs) Fuel pellets melt at 2600 C Zr, Fe, UO 2 melt - corium Flammability limit of hydrogen gas Source: 1) TEPCO presentation, The Great East Japan Earthquake and Current Status of Nuclear Power Stations, April 25, 2011, 2) MIT NSE webpage

16 Situation After Explosions Sea water (then fresh water) pumped into the core to lower the temperature Situation steady state injection stable - highly radioactive cooling water top up needed to maintain level and minimise further damage The earthquake has damaged containment leading to release of some radioactivity Ongoing effort on dust inhibition / water control / containment

17 Current status according to TEPCO as of 17/7 Source: TEPCO Roadmap Towards Restoration from the Accident at Fukushima Daiichi Nuclear Power Station Revised Version, Append 1-3,July 19, 2011

18 Unit 1 current situation Image:TEPCO

19 Environmental Situation Fukushima INES Level 7 People & Environment Chernobyl, 1986 External release of a significant fraction of reactor core inventory Consequence Major release of radioactive material with widespread health and environmental effects 6 Kyshtym, Russia, 1957 Significant release of radioactive material to environment from explosion of high activity waste tank Significant release of radioactive material Fukushima 5 Windscale Pile, UK, 1957 Radioactive material release to environment following fire in the core Limited release of radioactive materials 4 Tokai Mura, Japan 1999 Criticality event led to fatal overexposures of workers Minor release of radioactive materials Source: OECD Nuclear Energy Agency

20 Environmental Situation Source: OECD Nuclear Energy Agency

21 Environmental Situation Source: Nature Web Blog, Sept 7 th 2011 Source: TEPCO The Great East Japan Earthquake and Current Status, of Nuclear Power Stations, Sept 2011

22 Environmental Situation

23 Implications One in a thousand year events are possible Ongoing effort by Japanese to deal with consequences of earthquake and tsunami Fukushima-Daiitchi one aspect of that: Total = $300 billion Fukushima Daiitchi = $100 billion Global reassessment of nuclear - stress-tests Germany no; Switzerland no(ish); UK proceed Decommissioning and waste management radiochemistry (again) needed to assist

24 Thank you for your attention