hindsight- how to avoid repeat of Fukushima 4

[davefitz]

In anticipation of the need to incorporate "lessons not quite learned" from the last 3 meltdowns, here is my list economically and technically achievable means to avoid repeats:

a)add a hardwired, remote , backup operating room 0.7 km away from the reactor.
b)spent fuel storage pool located at least 0.5 km away from reactor
c)backup diesel genset at ALL coastal plants to have inlet air snorkel be at least 10 M above sea level. Ditto exhaust discharge nozzle.
d)use geopolymer concrete for containment dome- at least for the foundation- tolerates much higher temperatures than ordinary portland cement concrete.
e) (??) develop and implement a stirling engine based backup circ pump that is driven by primary coolant discharge , air cooled at cold end
f)(??) onsite mandatory storage of sufficient boric acid for loss of coolnat events- perhaps stored in a pressurized local accumulator that can be immeidiately discharged to the core , based on 2 independent keyed switches plus control system confirmation loss of coolant for ( XXX minutes).

 

[davefitz]

"The Licensee has no motivation to move fuel into a safer onsite storage location" + Yucca canceled + 20 yr license renewal = formula for open-ended increase in SPF inventory.

Sounds like the foxes are guarding the chicken coop.Why is it that there is no assessment of the risk due this accumulation?

 

[trottiey]

rmw,
I just wanted to say that I appreciate your post of April 3rd for its professionalism and care with facts. I'm glad we got over that bump in the conversation.

If you don't mind, I would point out that referring to "this country" is ambiguous when writing on an internet forum. From your figure of 20%, I can guess you mean the USA, but that is not representative of my country nor of several other posters on this forum.

 

[mauner]

Thankyou davefitz for being someone who understands the point of my lesson learned.

How do we get these concerns to the NRC task force investigating the Fukushima event for U.S. plants?

 

[Spartan5]

{quote]I know that Spent Fuel Pools will get a lot of attention in the next few months ... but first we need to understand why the Fukishima pools lost their water. I don't think it was because of the earthquake or the tsunami. I think it was because of the containment design of Fukushima with the pool in very close proximity to the reactor where it could be damaged by the hydrogen explosions. If this does turn out to be the case, then plants who have their pools in a separate building won't have this problem. This is the case for all PWRs in the US. [/quote]
Reactor 4 loss its water before the explosion. If I'm not mistaken, it was the loss of water that allowed the fuel to be exposed which caused the explosion. That reactor was completely shut down and defueled at the time.

Where did the water go? There are some good ideas here:

http://allthingsnuclear.org/post/3964225685/possible-source-of-leaks-at-spent-fuel-pools-at

and here

http://allthingsnuclear.org/post/4133270698/where-did-the-water-in-the-spent-fuel-pools-go

A significant problem may have been identified!

A possible source of the leak in the Unit 4 pool may be the seals around the doors (or “gates”) on one side of the spent fuel pool. These gates are shown in the diagram below. They are located between the pool and the area above the reactor vessel. They are concrete with metal liners, and are roughly 20’x 3’.

When fuel is moved between the pool and vessel, this whole region is filled with water, the gates are opened, and the fuel can be moved to or from the reactor core while remaining under water. The water not only keeps the fuel rods cool but acts as a radiation shield.

When the gates are closed, they are made watertight by an inflatable seal, similar to a bicycle innertube, that runs around the sides and bottom of the gates. Electric air pumps are used to inflate these seals and keep them inflated as air leaks out of them over time.

These pumps are powered by electricity from the power grid, and not by backup diesel power or batteries. So once the power grid in Japan was knocked out, these seals could not be inflated if they lost air over time. If these seals lost air they could lead to significant water loss from the pool, even if there were no direct physical damage to the pool from the earthquake or tsunami. This may be what happened at pool 4, and could affect the other pools as well.

We saw an example of this in the US at the Hatch nuclear plant in Georgia in December 1986. This reactor is very similar to the reactors at Fukushima. In the Hatch case, the line supplying air to the inflatable seal was accidentally closed, the seal lost pressure and created a leak, and by the time the problem was identified several hours later some 141,000 gallons of water leaked from the pool—about half the water in the pool Fortunately, the source of the problem was discovered and fixed before the water level uncovered the fuel.

An NRC document on the leak gave this description of the event:

A valve in the single air supply line to the seals was mistakenly closed. Although water level dropped about 5 feet and low-level alarms in the spent fuel pool worked, the leak was not specifically identified for several hours because a leak detection device was valved out and none of the seals were instrumented to alarm on loss of air pressure.

The NRC document goes on to note that if the water level had gotten low enough to expose the fuel the high radiation level around the pool would have made it difficult for workers to fix the problem.

The closed air line in the Hatch case had the same result that lack of electric power the air pump inflating the seals in Japan could have.

See also this entry for the current state of gauges and controls at the stricken reactors:

http://allthingsnuclear.org/post/4136147791/how-much-does-japan-know-about-the-status-of-its

 

[itsmoked]

Wow.. Thanks for quoting that Spartan5.

That needs some fail-safe work.

Keith Cress
kcress -

http://www.flaminsystems.com