The old rusty pipes at Daiichi? They may not last the entire decade TEPCO says they need to cool the melted fuel. The SimplyInfo.org research team looked at various factors involved in the accident and the long term use of out of balance water to cool both the reactors and the spent fuel pools.
TEPCO's best case scenario to remove all the fuel from the spent fuel pools is ten years. Two unused fuel assemblies removed from unit 4's spent fuel pool showed signs of moderate corrosion. Older used assemblies and other parts of the pool may not be even faring that well as various factors such as circulation and sediment cause uneven corrosion within the pool.
The research found accelerated corrosion from the injected seawater, age of the metal in the reactors (34-42 years) and the ongoing out of range water chemistry. This could cause metal pipes or other critical metal parts to fail in as little as 3 years under certain circumstances.
Since TEPCO can not send human workers deep into the reactors now or at any point in the near future, replacing reactor vessel pipes is not possible. Degraded metal on fuel assemblies or other critical parts of the spent fuel pools could drastically increase the risks and complexity of trying to remove the used fuel from the pools.
While TEPCO has taken steps to lower the salt levels in the water being used to cool the reactors and fuel pools, extremely high salt levels existed for a considerable amount of time. Other factors of the water chemistry remain seriously out of spec adding to the ongoing degradation.
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