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BTW, units 5 and 6 are using their normal cooling process to cool the spent fuel pools as well as the main reactor cores. They may be salvageable.

Not if they used salt water to cool them. There is going to be scale all over everything in the reactor Bessel and nobody is going to crawl in there to scrape it off. Once you get salt water into a system like this it isn't coming back. And heck the things were due to be taken out of service in less than a year anyways. No reason to take the risk of restarting a possibly damaged reactor. Just finish the shutdown.

Not if they used salt water to cool them. There is going to be scale all over everything in the reactor Bessel and nobody is going to crawl in there to scrape it off. Once you get salt water into a system like this it isn't coming back. And heck the things were due to be taken out of service in less than a year anyways. No reason to take the risk of restarting a possibly damaged reactor. Just finish the shutdown.

They have not, as far as I know, used salt water on 5 and 6. The backup diesel for unit 6 either survived the tsunami or was brought back on line shortly after so they were able to maintain normal circulation of cooling water on those units, at least at a modest level. Also, while the fuel storage pools got up to 65-70 C., once they got the backup generator for unit 5 back on line, they were able to provide full cooling capacity for both units and their spent fuel ponds.

I'll note that both units 5 and 6 are several hundred meters to the north of units 1 through 4, and probably were added to the plant beyond its original design. They are also the newest of the 6, and may have benefitted from improved design and construction methods.

As far as I know, only unit 1 was destined to be removed from service this year. It is the oldest of the units, having gone commercial in 1971, whereas units 5 and 6 went commercial in 1978 and 1979 respectively. Also, while 5 is similar to 2, 3, and 4 (BWR-4), unit 6 is a BWR-5.

Not if they used salt water to cool them.

Reactors 5 and 6 were further away and I don't believe salt water was used to cool them.

And heck the things were due to be taken out of service in less than a year anyways.

Prior to this disaster, the plant's operating certificate was renewed for another decade. They were not planning on decommissioning any reactors this year.

Reactors 5 and 6 were several years newer than 1-3, and another two reactors were scheduled to be built at the plant.

Use of seawater in and of itself is not a deal breaker. Saltwater corrosion occurs in susceptible materials over a relatively long time. Materials used in the pressure vessel and vessel internals are very resistant to most corrosion mechanisms. If they want to salvage these reactors they will have to go through a cleanout procedure to remove residual minerals, sodium chloride, and other things, but chemical engineers know how to do that. The cleanup of the K-25 GDP in Oak Ridge was a greater challenge in many ways. You had things building up in that diffusion cascade for decades that had to be flushed out.

Lets calm down and see how this plays out. In the end, it is almost certain they will restart units 5 and 6. Unit 4 had the SFP problem and they will have to get that settled down. The Unit 4 reactor was probably not too badly damaged and probably can be salvaged. Units 2 and 3 had fuel in the core and they will have to get in there and check the extent of the damage prior to making a restart decision. Unit 1 was the oldest and had core damage so of all of them this is the one they will probably retire, most likely doing a SAFSTOR, like we did with TMI-2.