the scenario unlikely given additional geological studies that invalidated the predictions [4].
Furthermore, how the accident was managed in the first days following the
earthquake illustrates how decisions were taken in a context of crisis. The Japanese
government’s Investigation Committee was particularly interested in the circumstances in which Reactor 1 exploded on the afternoon of 12 March, 2011, when
on-site teams thought they had vented it and cooling via the injection of seawater
was about to begin [5]. Investigators asked the superintendent of the plant about his
decision-making process given the information available to him [2]. To understand
their approach, it is useful to recall certain facts.
On 11 March, the superintendent, Masao Yoshida, ordered preparations to begin
for the injection of water into Reactor 1 using fire conduits and fire engines, to
ensure cooling when the isolation condenser (IC)
4 stopped working because of
electrical failure. The water level in the tank was checked by reading an indicator.
The level indication was normal, which supported the belief of operators that the
reactor was correctly cooled. The level, however, could not be constantly monitored. At around 02:00 on 12 March, the indicator showed a stable or slightly rising
water level, while at the same time the pressure inside the tank fell. Communication
between the control room and the crisis room was difficult and the superintendent
had not been informed of problems in the IC conduit. Perplexed by the rise in
radioactivity, he concluded that the water level indicator was malfunctioning, that
the IC had potentially been non-operational for several hours and that the core was
probably exposed [2]. This was confirmed by measuring the increase in pressure in
the containment vessel, which had exceeded its structural limits.
The plant’s superintendent said that he regretted having placed too much confidence in the water level indicator and not having asked the control room about the
IC conduit. For their part, investigators expressed their surprise at the apparent
passivity of operators, given that an IC valve had been closed for no apparent
reason and that the injection of water was impossible, with the result that the reactor
was not cooled between 18:25 and 21:30. It appeared that none of the shift leaders
had alerted the crisis cell.
Yoshida also stated that, “anyway, in terms of solutions, we did not have anything much better than the diesel pump, injecting with the fire pump and using the
fire engine, which we finally did. Could we have reacted more quickly if we had
known? I think that physically, we could not have gone faster” [2] (our translation).
Faced with pressure that exceeded the structural limits of the containment vessel,
the superintendent asked for Reactor 1 to be vented. This operation required the
activation of a valve, which proved particularly difficult and dangerous because of
the high levels of radioactivity, the lack of electricity or pneumatic equipment, and
the lack of indicators or light in the control room. As none of the operators had
4
A backup system in some boiling water reactors. It cools the core when power cannot be
evacuated by the main condenser. The system condenses the steam produced in a heat exchanger,
and then re-injects it into the tank using gravity.
Decision-Making in Extreme Situations …
171
Furthermore, how the accident was managed in the first days following the
earthquake illustrates how decisions were taken in a context of crisis. The Japanese
government’s Investigation Committee was particularly interested in the circumstances in which Reactor 1 exploded on the afternoon of 12 March, 2011, when
on-site teams thought they had vented it and cooling via the injection of seawater
was about to begin [5]. Investigators asked the superintendent of the plant about his
decision-making process given the information available to him [2]. To understand
their approach, it is useful to recall certain facts.
On 11 March, the superintendent, Masao Yoshida, ordered preparations to begin
for the injection of water into Reactor 1 using fire conduits and fire engines, to
ensure cooling when the isolation condenser (IC)
4 stopped working because of
electrical failure. The water level in the tank was checked by reading an indicator.
The level indication was normal, which supported the belief of operators that the
reactor was correctly cooled. The level, however, could not be constantly monitored. At around 02:00 on 12 March, the indicator showed a stable or slightly rising
water level, while at the same time the pressure inside the tank fell. Communication
between the control room and the crisis room was difficult and the superintendent
had not been informed of problems in the IC conduit. Perplexed by the rise in
radioactivity, he concluded that the water level indicator was malfunctioning, that
the IC had potentially been non-operational for several hours and that the core was
probably exposed [2]. This was confirmed by measuring the increase in pressure in
the containment vessel, which had exceeded its structural limits.
The plant’s superintendent said that he regretted having placed too much confidence in the water level indicator and not having asked the control room about the
IC conduit. For their part, investigators expressed their surprise at the apparent
passivity of operators, given that an IC valve had been closed for no apparent
reason and that the injection of water was impossible, with the result that the reactor
was not cooled between 18:25 and 21:30. It appeared that none of the shift leaders
had alerted the crisis cell.
Yoshida also stated that, “anyway, in terms of solutions, we did not have anything much better than the diesel pump, injecting with the fire pump and using the
fire engine, which we finally did. Could we have reacted more quickly if we had
known? I think that physically, we could not have gone faster” [2] (our translation).
Faced with pressure that exceeded the structural limits of the containment vessel,
the superintendent asked for Reactor 1 to be vented. This operation required the
activation of a valve, which proved particularly difficult and dangerous because of
the high levels of radioactivity, the lack of electricity or pneumatic equipment, and
the lack of indicators or light in the control room. As none of the operators had
4
A backup system in some boiling water reactors. It cools the core when power cannot be
evacuated by the main condenser. The system condenses the steam produced in a heat exchanger,
and then re-injects it into the tank using gravity.
Decision-Making in Extreme Situations …
171