Why+did+the+back-up+plans+not+work?

Sagar's group

One of the plans to protect the reactor was to make it Earthquake and Tsunami proof. However, during the disaster, it suffers from both an Earthquake and a tsunami which results in the shut down of most of the emergency systems. The reason was that the systems wasn't designed good enough to withstand a real strong Earthquake or a Tsunami.

Recognizing that information is still not complete due to the destruction of the communication infrastructure, producing reports that are conflicting, here is our best understanding of the sequence of events at the Fukushima I‐1 power station. - The plant was immediately shut down (scrammed) when the earthquake first hit. The automatic power system worked. - All external power to the station was lost when the sea water swept away the power lines. - Diesel generators started to provide backup electrical power to the plant’s backup cooling system. The backup worked. - The diesel generators ceased functioning after approximately one hour due to tsunami induced damage, reportedly to their fuel supply. - An Isolation condenser was used to remove the decay heat from the shutdown reactor. - Apparently the plant then experienced a small loss of coolant from the reactor. - Reactor Core Isolation Cooling (RCIC) pumps, which operate on steam from the reactor, were used to replace reactor core water inventory, however, the battery‐supplied control valves lost DC power after the prolonged use. - DC power from batteries was consumed after approximately 8 hours. - At that point, the plant experienced a complete blackout (no electric power at all). - Hours passed as primary water inventory was lost and core degradation occurred (through some combination of zirconium oxidation and clad failure). - Portable diesel generators were delivered to the plant site. - AC power was restored allowing for a different backup pumping system to replace inventory in reactor pressure vessel (RPV). - Pressure in the containment drywell rose as wetwell became hotter. - The Drywell containment was vented to outside reactor building which surrounds the <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">containment. <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">- Hydrogen produced from zirconium oxidation was vented from the containment into the reactor building. <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">- Hydrogen in reactor building exploded causing it to collapse around the containment. <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">- The containment around the reactor and RPV were reported to be intact. <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">- The decision was made to inject seawater into the RPV to continue to the cooling process, <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">another backup system that was designed into the plant from inception. <span style="background-clip: initial; background-color: transparent; background-origin: initial; border-bottom-width: 0px; border-left-width: 0px; border-right-width: 0px; border-top-width: 0px; margin: 0px 0px 24px; padding-bottom: 0px; padding-left: 0px; padding-right: 0px; padding-top: 0px; vertical-align: baseline;">- Radioactivity releases from operator initiated venting appear to be decreasing.

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