following the reactor scram, operators activated the reactor core isolation cooling system (rcic) and the residual heat removal system and core spray systems were made available to cool the suppression pool; whether they were activated prior to the tsunami has not been made clear. the rhrs and cs pumps were knocked out of commission by the tsunami. with dc battery power remaining, the rcic continued to keep the water level stable, and the operators switched to the high-pressure coolant injection (hpci) system when water level began to drop. on 13 march, the hpci system failed, the reason for which is not completely clear due to instrumentation not being available. it is believed to be either due to loss of dc power due to depletion of batteries or to reactor pressure dropping below the level at which it can operate. operators were unable to restart it as batteries were exhausted. after this, the operators were unable to start the rcic system and began injecting seawater. although it was not clear at the time, some of the fuel in reactor 3 apparently melted around sixty hours after the earthquake (the night of the 12th to 13th).