Monday, May 14, 2012

12. Spent Fuel Pools? -- More Like Vaults

Initially Posted on May 14th, 2012

Back in the far earlier days of Nuclear Power Plant design, I am afraid that the designers made an inadvertent mistake in naming a vital portion of their plants.

They named the interim storage areas for irradiated fuel assemblies Spent Fuel Pools. Here is a picture of one, I think from Catawba.

Recently, scaremongers have have been trumpeting outlandish imaginary scenarios relating to the Unit 4 Spent Fuel Pool at Fukushima Daiichi.  These postulated scenarios defy the laws of physics, to put things bluntly and simply.

Rod Adams has covered the issue here, and again a few days ago here with the video just below.

Leslie Corrice at Hiroshima Syndrome has also mentioned it.
Dan Yurman has talked about it.
And so has Steve Skutnik (both at his site The Neutron Economy and re-published at The Energy Collective)

UPDATE (May 16th lunchtime):
Will Davis has posted about the absence of the danger at the ANS Nuclear Cafe.
That brings me to the mistake that I think was made during the original design phase in regards to naming a portion of a nuclear power plant, The Spent Fuel Pool.

The term "Pool" very likely puts mental images like this into people's heads.

When you see a kiddie pool, I would bet that strength is far, far down the list of terms that would be associated with such a structure. The fact that mental images of weak structures like this can be so easily recalled is a primary reason that the fables ignoring physics that have been propagated by anti-nuclear activists in regards to Spent Fuel Pools can gain some traction with relative ease.

A more appropriate mental image for the robustness of the design of an actual Spent Fuel Pool could better be conveyed by the term VAULT.
No, not that Vault. Besides, Surge was always considerably better anyway.Non-nuclear digression: Surge was likely the leading edge of the energy drink boom in America, which could be an interesting little business case study for someone. /End digression.  

This type of Vault is more what I was thinking of.
This type of vault conveys the strength that is inherent in the designs of nuclear power plant's spent fuel pools. Also, take a look at this picture of a pad of spent fuel casks (dry storage).
 Pretty Vault-like, huh?

How much more difficult would it have been to cause people to be concerned about the Fukushima Daiichi Spent Fuel Pools if they had been named Vaults from the beginning, rather than merely Pools? My guess is that it would have been a bit more difficult. 

The strength of the design is not the only reason that I think the term "VAULT" is apt for the interim storage locations for what I prefer to call partially-utilized spent fuel assemblies. The second reason is that the remaining energy content in fuel assemblies could potentially be extremely valuable someday. The presently typical "once-through" fuel cycle does not utilize anywhere close to the fuel energy potential of either the material within the fuel itself, nor especially of the mined uranium that the assemblies were made of. The term vault would help to convey that the PARTIALLY Spent Fuel Assemblies possess immense potential future value, possibly enough value to make the contents of the fortified structure pictured below pale in comparison (click on the picture if you don't recognize what it is).

I would like to propose a method of remedying this historical oversight. As part of the mandated spent fuel changes as follow-up to the Fukushima-Daiichi incident, utilities can choose to "upgrade" existing SFPs to "vaults". In most cases, I would guess that this would require little, if any, physical changes, but would be a documentation only change. Perhaps the NEI or NRC might decide to set some standards/requirements for allowing utility to use the term "vault" in regards to a specific pool. Such a validation of the use of this revised terminology could provide a level of robustness, similar to the existing designs of these Spent Fuel Pools.

Making such a change could have a small effect of enhancing the public perception of safety, even if not appreciably increasing safety above the present level (how do you top zero spent fuel-related incidences at commercial plants?).

A further enhancement that I would like to see, but may fit better under the topic of a future post, is revising the "spent" part of the pools' name to "partially used". This would help convey the presence of the remaining energy potential of the fuel assemblies (which very likely would have already been put to use effectively, if not for the Jimmy Carter years).

In summary, the term Vault would convey two primary thoughts:

1. That the enclosed material is secure


2. That the material is still extremely valuable


  1. Good point --- and since the fuel is only "spent" if wasted and not recycled, how about a "UFV," or "Used Fuel Vault." Could also be an "FFV," or "Future Fuel Vault."

  2. To get the unwashed masses onboard, call the pools "Decay heat powered hot tubs" and start a promotional ad campaign with celebrities swimming around in the SFPs. Have some model exclaiming how the boric acid makes her skin feel so smoothe.

  3. They are pools fool! We do not change the accurate description of something because you have a silly perception. New fuel is stored dry in a vault because it does not need to be cooled by water.

    Spent fuel pools are made of stainless steel and supported by concrete structures designed to withstand earthquakes and none have ever been damaged. Spent fuel pools are designed not be drained. There is no connection at the bottom to drain it. Cooling system take a suction from the top of the pool.

    The primary function of the water is to provide shielding. Spent fuel pools therefore contain large amounts of water as a result. It takes a long time for them to heat up even shortly after fuel is taken out of the core. Then it takes an even longer time for the water to boil off.

    By the time the fuel is out of the core for a month, I am not sure you could make it all boil away anyhow. Just today I was looking at calculation for the decay heat load at work. One of those what if this and what if that scenarios.

    Many years ago, I ran a test where I turned off the decay heat removal system to see how much time I had to perform maintenance. Core temperature deceased because the 200 kw or energy that was being put in was more than decay heat in the core. Ambient heat loses would cool the core. Did the same thing in the navy.

    Removing the decay heat from the core immediately after shutdown take about 100 gpm if you are boiling out relief valves. The systems are sized not just to remove decay heat but to cool down the plan as fast as possible withing thermal limits. Time is money. Getting to cold shut down and replacing the fuel is done so we can start making power again

    In fifty years we have never had a problem keeping spent fuel pool cool. Not even after a 1000 year natural disaster.

  4. Kit, I will read your comment later and provide a reply, but dinner is first.

    Glad to see you found my blog since you couldn't stay around at Atomic Insights.

  5. This comment has been removed by the author.

  6. The acreage around those casks is just begging for a fuel recycling plant on that site! I'm no expert, but maybe this is the way to go to keep nuclear viable and more economical in the U.S.; construct new plants/refit (or Thoriumize) than decommission plants in existing nuke plant sites in already nuclear friendly communities along with a sister recycling plant, and to handle the far smaller waste volume later just drill a couple of thousand foot deep holes into the solid bedrock there (since plants have to be okayed regarding water tables anyway). I mean why truck waste way to Yucca when the stuff's in a deep local place the sun won't shine for a hundred million years? Nuclear plant sites would be like a roach motel; nuclear fuel check in but don't check out!

    James Greenidge
    Queens NY

  7. OK Kit, I have to presume from your comment that you read far from the entirety of the above post. Yet you still used the word fool. That is not a great start for you here. You have completely missed the points I was going for. My suspicion is that you only read as far as "designers made an inadvertent mistake" when your blood started boiling, which is much, much faster than the 23 feet of water above the ~13 foot tall/long fuel assemblies in a "Wet Future Fuel Vault" could boil away.

    Kit, please conduct yourself in a manner here that will allow you to stick around.

    James, I would guess that the economics of building distributed reprocessing sites at existing plants would be uneconomical, and extremely unlikely due to politics. I plan to post sometime in the future about an "X-Prize" type of idea regarding what should be done with the U.S.'s existing "once and future fuel".