1

Fukushima accident

Kosmidis Konstantinos2014

Presentation on Experimental Research on Nuclear Waste Disposal

Czech Technical University in PragueFaculty of Civil Engineering

Centre of Experimental Geotechnics

2

Introduction

3

Introduction• Tokyo Electric Power Company (TEPCO) operates the Fukushima nuclear

power complex in the Futaba district of Fukushima prefecture in Northern Japan, consisting of six nuclear units at the Fukushima Daiichi station and four nuclear units at the Fukushima Daini station

• All the units at the Fukushima complex are boiling water reactors, with reactors 1 to 5 at the Fukushima Daiichi site being the General Electric Mark I design

4

Introduction• The Daiichi (first) and Daini (second) Fukushima plants are sited about 11

km apart on the coast, Daini to the south.• The original design basis tsunami height was 3.1 m for Daiichi based on

assessment of the 1960 Chile tsunami and so the plant had been built about 10 metres above sea level with the seawater pumps 4 m above sea level.

• The Daini plant was built 13 metres above sea level. In 2002 the design basis was revised to 5.7 metres above, and the seawater pumps were sealed

5

Introduction

6

The accident• The Great East Japan Earthquake of magnitude 9.0 at 2.46 pm on Friday

11 March 2011 did considerable damage in the region, and the large tsunami it created caused very much more.

• The earthquake was centred 130 km offshore the city of Sendai in Miyagi prefecture on the eastern cost of Honshu Island (the main part of Japan), and was a rare and complex double quake giving a severe duration of about 3 minutes.

• Japan moved a few metres east and the local coastline subsided half a metre.

7

The accident

• The tsunami inundated about 560 sq km and resulted in a human death toll of over 19,000 and much damage to coastal ports and towns with over a million buildings destroyed or partly collapsed.

• 41 minutes later the first tsunami wave hit, followed by a second 8 minutes later

8

The accident• No serious damage was done to the reactors by the earthquake, and the

operating units 1-3 were automatically shut down in response to it, as designed

• All six external power supply sources were lost due to earthquake damage, so the emergency diesel generators located in the basements of the turbine buildings started up. Initially cooling would have been maintained through the main steam circuit bypassing the turbine and going through the condensers.

• Tsunamis submerged and damaged the seawater pumps for both the main condenser circuits and the auxiliary cooling circuits, notably the Residual Heat Removal (RHR) cooling system.

• They also drowned the diesel generators and inundated the electrical switchgear and batteries, all located in the basements of the turbine buildings (the one surviving air-cooled generator was serving units 5 & 6).

• Station blackout, and the reactors were isolated from their ultimate heat sink. The tsunamis also damaged and obstructed roads, making outside access difficult.

9

The accident• All this put those reactors 1-3 in a dire situation and led the authorities to

order, and subsequently extend, an evacuation while engineers worked to restore power and cooling.

• The 125-volt DC batteries for units 1 & 2 were flooded and failed, leaving them without instrumentation, control or lighting. Unit 3 had battery power for about 30 hours.

• At 7.03 pm Friday 11 March a Nuclear Emergency was declared, and at 8.50pm the Fukushima Prefecture issued an evacuation order for people within 2 km of the plant. At 9.23 pm the Prime Minister extended this to 3 km, and at 5.44 am on 12th he extended it to 10 km. He visited the plant soon after. On Saturday 12th he extended the evacuation zone to 20 km.

10

The accident

11

The accident• The accident was rated 7 on the INES scale, due to high radioactive

releases over days 4 to 6, eventually a total of some 940 PBq (I-131 eq). • Four reactors were written off due to damage in the accident – 2719 MWe

net. • After two weeks, the three reactors (units 1-3) were stable with water

addition and by July they were being cooled with recycled water from the new treatment plant.

• Official 'cold shutdown condition' was announced in mid-December.• Apart from cooling, the basic ongoing task was to prevent release of

radioactive materials, particularly in contaminated water leaked from the three units. This task became newsworthy in August 2013.

12

Consequences• There have been no deaths or cases of radiation sickness from the nuclear

accident, but over 100,000 people had to be evacuated from their homes to ensure this. Government nervousness delays their return.

• Official figures show that there have been well over 1000 deaths from maintaining the evacuation, in contrast to little risk from radiation if early return had been allowed.

13

Consequences• The main radionuclide from among the many kinds of fission products in

the fuel was volatile iodine-131, which has a half-life of 8 days. • The other main radionuclide is caesium-137, which has a 30-year half-life,

is easily carried in a plume, and when it lands it may contaminate land for some time. It is a strong gamma-emitter in its decay.

• Cs-134 is also produced and dispersed, it has a two-year half-life. Caesium is soluble and can be taken into the body, but does not concentrate in any particular organs, and has a biological half-life of about 70 days

14

Consequences

15

Consequences• A significant problem in tracking radioactive release was that 23 out of the

24 radiation monitoring stations on the plant site were disabled by the tsunami.

• No convincing results found ,only estimations that vary a lot between them

• By 31 December 2011, Tepco had checked the radiation exposure of 19,594 people who had worked on the site since 11 March. For many of these both external dose and internal doses (measured with whole-body counters) were considered. It reported that 167 workers had received doses over 100 mSv. Of these 135 had received 100 to 150 mSv, 23 150-200 mSv, three more 200-250 mSv, and six had received over 250 mSv (309 to 678 mSv) apparently due to inhaling iodine-131 fume early on

16

Consequences

17

Consequences

18

Official report• A Japanese parliamentary panel has delivered a damning verdict after

investigating the accident at the Fukushima nuclear plant • Although such an event should have been predicted and planned for, the

panel said, it found gaping holes in safety standards and emergency procedures.

• Disaster 'manmade' - chairman's message (Kiyoshi Kurokawa)

19

Official report• Collusion and lack of governance • Organisational problems within Tepco• Emergency response issues• Evacuation issues• Continuing public health and welfare issues- Approximately 150,000

people were evacuated in response to the accident... Insufficient evacuation planning led to many residents receiving unnecessary radiation exposure

• Regulator failures• Operator failures• Shortcomings in laws and regulations• No 'cosmetic solutions‘ - Replacing people or changing the names of

institutions will not solve the problems. Unless these root causes are resolved, preventive measures against future similar accidents will never be complete

20

Official reportSolutions:

• Permanent committee in National Diet [parliament] to oversee the regulators, with regular investigations and hearings

• Reform of the crisis management system• Establishment of system to deal with long-term public health effects,

including monitoring and decontaminating radiation-affected areas• Dramatic corporate reform of Tepco• New regulatory body• Reform of laws related to nuclear energy to meet global standards of

safety, public health and welfare• Develop a system of independent investigation commissions

21

Bibliography• Fukushima report: Key points in nuclear disaster report ,BBC,5 July 2012• International Atomic Energy Agency- IAEA Briefing on Fukushima Nuclear

Accident • Fukushima Accident-World Nuclear Association• Fukushima Nuclear Disaster-Congressional Research Service• Lessons from Fukushima-Greenpeace• American Nuclear Society Special Committee-Report on Fukushima