Remember that power outage? TEPCO released the result of their investigation on March 25, 2013.
The mouse has a mark in the stomach from an electric shock.
From TEPCO's Photos and Videos Library, 3/25/2013, "Progress of Investigation of Power Supply Facilities Failure at Fukushima Daiichi Nuclear Power Station":
The regular M/C was receiving power from the temporary M/C because of the ongoing renovation work:
[Power supply system structure]
Since power receiving cable renovation for the regular M/C in the Process Building (as part of Tsunami countermeasures) was ongoing at the time of the incident, the regular M/C was temporarily receiving power from the
backup M/C in the Process Building.
1. The ground relay in B system operated: The failure is assumed to have occurred in B system and high voltage power supply system.
2. The circuit breakers of the regular M/C (3A) and (4A) in the Process Building and the backup M/C in the Process
Building (3A) tripped due to overcurrent. : The failure is assumed to have occurred in the downstream of the regular M/C in the Process Building (4A).
3. The ground directional relays and the circuit breakers of Units 3-4 temporary M/C (4A), (5A) and (10A) did not
operate. : The failure is assumed to hav
e occurred in the upstreamof the load systems of Units 3-4 temporary M/C.
4. Fault current was found in Units 3-4 temporary M/C (A)(5B). : The failure is assumed to have occurred in the
downstream of Units 3-4 temporary M/C (A) (5B).
TEPCO will install mouse traps as countermeasure.