Chernobyl vs Fukushima

Understanding the Scale and Mechanics of the Disasters

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INES Level 7 Accidents

The only two in history

Chernobyl

place April 26, 1986 | Ukraine (USSR)
Reactor Design
RBMK-1000
Graphite-moderated
Containment
None
No protective vessel
Fatal Flaw
Positive void coeff.
Runaway reactions
format_list_numbered Accident Sequence
1
Operators bypass safety systems for turbine test
2
Power surge causes rapid water boiling in reactor
3
Emergency SCRAM fails, causing massive power spike
4
Steam/hydrogen explosion INSIDE core ignites graphite
5
Exposed graphite burns for 10 days, spewing radiation
335k
Evacuated
30 km
Exclusion Zone
Deaths
Direct ~30
Long-term est.* 4k–16k
*Estimates vary widely

Fukushima

place March 11, 2011 | Japan
Reactor Design
BWR Mark I
Boiling water reactor
Containment
Primary
Outer bldg. destroyed
Fatal Flaw
Vulnerable Backup
Low-lying generators
format_list_numbered Accident Sequence
1
9.0 Quake triggers successful automatic SCRAM
2
14m Tsunami floods low-lying backup diesel generators
3
Total station blackout stops cooling water circulation
4
Core melts; primary containment initially holds but leaks
5
Hydrogen vents and explodes OUTSIDE primary containment
154k
Evacuated
20 km
Exclusion Zone
Deaths
Direct radiation 0
Rad. overdose years later 1
Evacuation-related ~2.3k

bar_chart Total Radiation Released (Iodine-131 Equivalent)

Chernobyl
5,300 PBq
Spread across 1000+ km of Europe
Fukushima
530 PBq
~80% blown out over the Pacific