Why isn't the cooling system power-independent?

[Passiday]

Hello,

I am far from nuclear plant engineering, so I might be asking irrelevant question... But I was wondering, why the Fukushima power plant reactor cooling system was designed to be dependent on external power? That sounds like planning for failure to me, especially in the environment where they regularly would shut the plan down in case of earthquakes. I mean, there are engine types that run on heat, like Stirling engine - couldn't these be used to power the pumps that move the cooling water around? All that is needed here is stable supply of cool gas and source of heat. The cool gas could be air, or if there is a risk of contamination, then perhaps a dedicated gas, and the source of heat is the coolant itself. Then the cooling system would work while there is the hot water in the system, what is exactly what's required.

Perhaps I am proposing naïve solution to a complex engineering problem, just wanted to hear some comment from more experienced people.

[uart]

Apparently there was an extensive system of diesel backups and there worked perfectly after the quake took out the power, but only for 30 minutes until the tsunami hit and took them all out.

It then switched to battery backup to the backup, and that also worked as designed, but unfortunately it was only designed to run for 8 hours. After that they were stuffed.

[Astronuc]

Hello,

I am far from nuclear plant engineering, so I might be asking irrelevant question... But I was wondering, why the Fukushima power plant reactor cooling system was designed to be dependent on external power? That sounds like planning for failure to me, especially in the environment where they regularly would shut the plan down in case of earthquakes. I mean, there are engine types that run on heat, like Stirling engine - couldn't these be used to power the pumps that move the cooling water around? All that is needed here is stable supply of cool gas and source of heat. The cool gas could be air, or if there is a risk of contamination, then perhaps a dedicated gas, and the source of heat is the coolant itself. Then the cooling system would work while there is the hot water in the system, what is exactly what's required.

Perhaps I am proposing naïve solution to a complex engineering problem, just wanted to hear some comment from more experienced people. New plant designs are more passive with respect to cooling in an emergency.

It was not expected that the EDGs would be destroyed or otherwise incapacitated, or that the batteries would have to support the cooling systems and other plant services for as long as they did. The event was 'beyond design basis'.

Please realize that the systems were designed and contructed during the early to mid-1960s, without the benefit of lessons learned over the last 40+ years, especially post TMI-2 and Chernobyl.

Utilities with the same or similar designs are reviewing their system and plant designs, as well as their emergency operating procedures (EOPs) to ensure the adequacy of designs and plans.

[Reno Deano]

Currently, advanced designs of reactors (some of which are being built or authorized for construction in the US and Foriegn countries) are of the "passive" type. Here are some links to information on them:

Westinghouse AP 1000 PWR: http://www.ap1000.westinghousenuclear.com/

GE Advanced BWR: http://www.gepower.com/prod_serv/products/nuclear_energy/en/new_reactors.htm

Peblebed Reactor:
http://pebblebedreactor.blogspot.com/
http://en.wikipedia.org/wiki/Pebble_bed_reactor

NRC Advanced Reactor Certification:
http://www.nrc.gov/reactors/advanced.html

http://www.nrc.gov/reactors/new-reactors/design-cert.html

Additional information can be gleamed from Links within the above sites.

For small out put reactors the pebble bed type is by far the most unique, simple and safest.

[BishopUser]

The emergency core cooling systems of a nuclear plant are not designed to run on external power. All events/accidents are postulated with a coincident loss of offsite power (one cannot credit offsite power in accident analysis). Therefore, the emergency core cooling system power must come from a combination of passive systems as well as those powered typically by diesel generators. There should be at least two diesel generators per unit. Even if there is a loss of offsite power and loss of both diesels (station blackout) a nuclear plant should have other measures in place such as emergency pumps that are driven by steam or by diesel fuel (motor driven pumps).

Like others have mentioned the event was beyond the design basis. You had a beyond design basis earthquake coincident with massive flooding. Generators and pumps (electrical or diesel driven) don't do very well when underwater. It is unclear what type of flooding the plant was designed to handle, but I can't imagine it was designed with a tsunami of this scale in mind.