Failure and Accident Analysis

Ioannis Bitharas

Fukushima Nuclear Disaster

2011 Tōhoku Earthquake

9 on Richter scale, with duration 140-160s

Fukushima is 178 km from the earthquake’s epicentre

Power plants sustain minor damage and go into shutdown (scram)

Power lines are destroyed by the earthquake

Anti-Seismic design

Design basis was for 7.9 Richters

Historically, earthquakes greater than the design values had been

recorded in the area

Damage from earthquake cannot be estimated due to ensuing events

Fukushima Daiichi Overview

Earthquake’s Aftermath

Workers evacuate plants after nationwide alert

Skeleton crew of 50 is left on Daiichi site to manage crisis

Devastating tsunami follow

7 waves of ~70mph

Peak wave height ~14m

Wave barriers (10m high) could not completely stop waves

Emergency backup power is lost due to flooding

Tsunami vs Wall

Tsunami vs Car

Affected Power Plants

BWR Mk.I Layout Operating

conditions

600K 70 bar

Pictures source:

GE Hitachi Nuclear Energy

BWR Mk.I Layout Operating

conditions

600K 70 bar

Pictures source:

GE Hitachi Nuclear Energy

BWR Mk.I Layout Operating

conditions

600K 70 bar

Pictures source:

GE Hitachi Nuclear Energy

Reactor loss of cooling

Radioactive rods inside reactor heat up

The low-pressure core spray, residual

heat removal, low-pressure coolant

injection system main pumps and the

automatic depressurization systems all

require AC power

Reactor cannot contain

pressure/temperature and leaks in

several points

Release valves were assumed to be

working

Primary containment failure and

gradual core meltdown Unit 1 Units 2-3

The Fukushima 50

The Fukushima 50

Spent fuel assemblies

• 1000-1500 tonnes of water required to fill

each pool

• The heat from each pool evaporates 70

tons per day

• Cladding triggers hydrogen explosions

after 500oC

Hydrogen-Air explosions

Hydrogen-Air explosions

Radioactive elements release

Iodine-131

Caesium-137

2012 Estimation: 9x1017 Bq

84,000 evacuated on 20km radius

Affected Power Plants

Lack of H&S from operator

Lack of seismic and tsunami protection in Design Basis

Probabilistic Safety Analyses (PSA) underestimated dangers

Reactor upgrades were recommended by regulatory authorities,

including the Japanese government

Numerous studies found Fukushima prefecture power plants

inadequately protected

The company’s own engineers, nuclear safety experts and even

court orders were ignored, claiming all hazard reports were

unrealistic

Cause: deliberate oversight

TEPCO claimed that they had been afraid to consider the

risk of such a large tsunami, fearing admissions of risk could

result in public pressure to shut plants down

“There were concerns that if new countermeasures against severe

accidents were installed, concern would spread in host communities that

the current plants had safety problems,” the report said.

Nuclear & Industrial Safety Agency

NISA had deemed the plant operations as safe

Part of the ministry of trade, economy and industry

Ministry also responsible for promoting Nuclear Energy

Conflict of interests

"NISA’s lack of independence from the trade ministry, which promotes

the use of atomic power, hampered a quick response to the disaster at

Tokyo Electric Power Co.’s Fukushima Dai-Ichi plant this year“

Key people fired and NISA was disbanded on 2012

Nuclear Regulation Authority formed September 2012

References

Fukushima Nuclear Accident Interim Report, TEPCO, November 2011

Fukushima Dai-ichi NPP Accident, International Atomic Energy

Agency, June 2011

Lessons Learned and Recommendations from the Fukushima Dai‐ichi

Nuclear Accident, National Nuclear Security Administration, May

2012

Japanese earthquake and tsunami: Implications for the UK nuclear

industry Final Report, HSE, September 2011

Executive Summary of the Interim Report, Investigation Committee

on the Accidents at Fukushima Nuclear Power Stations of TEPCO,

December 2011

Reuters, NY Times

Allthingsnuclear.org, Wikipedia

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