Nuclear Spent Fuel Expert Describes Vermont Yankee Dry Cask Safety
By Guy Page
By 2020, the spent fuel left over from all 42 years of Vermont Yankee’s operation is scheduled to be stored in huge steel “dry casks” on pads at the plant site in Vernon. Just how strong and reliable are Vermont Yankee’s “dry cask” spent nuclear fuel containers?
Consider the following dry cask testing conducted at Sandia National Lab:
- A tractor-trailer carrying a container ran into a 700-ton concrete wall at 80 MPH.
- A container was broadsided by a 120-ton train locomotive traveling 80 MPH.
- A container was dropped 2,000 feet onto soil as hard as concrete, traveling 235 MPH at impact.
- A container was subjected to a device 30 times more powerful than a typical anti-tank weapon.
- A container was subjected to a simulated crash of a jet airliner and the armament of an F-16.
In each case, post-incident assessments demonstrated that the containers would not have released their contents.
All of the information shared above was reported Jay Tarzia, Principal of Radiation Safety and Control Services Inc. and chair of the New Hampshire State Radiation Advisory Committee, on March 26 to the Vermont Nuclear Decommissioning Citizen’s Advisory Panel at Brattleboro Union High School.
Dry casks are designed to resist floods, earthquakes, tornadoes, projectiles, and temperature extremes. Tipped over, they will stay intact. And of course, heavy shielding prevents radiation leakage. They also remained intact after being submerged in water for eight hours and exposed to a 1,475 degree fire for 30 minutes. There have been no known or suspected sabotage attempts or releases of radiation since the first dry cask system was licensed in 1986. At Fukushima, 400 dry casks were exposed to earthquake and tsunami. Although knocked over and tossed around, none were breached.
The U.S. Nuclear Regultory Commission (NRC) licensing allows fuel to be stored for up to 100 years and the NRC is developing an extended storage program for up to 300 years. After 100 years, the fuel’s radioactivity will have shrunk to about one percent of its beginning total radioactivity. Stress on the canister will be greatly reduced. But Mr. Tarzia did not minimize the longterm nature of dry cask management. After about 4,000 years, the fuel’s radioactivity will return to the level of the original uranium ore. “The fuel will be radioactive for a long time. We need to manage it,” he said. “The security doesn’t go away when the plant goes away, when there’s a long-term storage site.” The industry is running computer models now showing the outer limits of how long the canisters will last. Ultimately, a long-term storage process or facility will make dry cask storage unnecessary, he predicted.
In closing, Mr. Tarzia predicted that within decades, waste-free nuclear fusion will produce limitless electricity.
Editor’s note: Notwithstanding our disagreement with the prediction in the final sentence, the above information is worth sharing to people who express their deep concerns about “nuclear waste,” what we prefer to call reusable nuclear fuel.
This post first appeared on the site of the Vermont Energy Partnership and is reprinted here with permission.
My problem with explaining the half-life waste storage issue is that to the lay public it sounds like you’re trying to cage a very dangerous monster that’ll take thousands of years to calm down. DON’T do the longevity thing! Ask people in cities when was the last time you visited the city dump? Isn’t the urban creedo once the garbage truck leaves your street your trash is out of sight and out of mind? Why must the public be hammered with radioactive lifetimes of stuff buried thousands of feet down — it’s not like anyone’s going to be building condos down there — or in casks hundreds of times thicker than the linings of tanks storing massive chlorine and chemical stocks? Yes, push that the stuff is well isolated, but push way MORE that it’s STILL good useful fuel that can be tapped and eagerly used and well-handled and isn’t like some forbidden crawling goo out of Homer Simpson.
Additional point about the longevity of waste, the strong gamma emitters are almost all short lived. The long lived elements are mostly alpha emitters, which means that after a while the waste is only dangerous if you eat or drink it, which you’re even less likely to do than visiting it.
And people claiming they are very concerned about the idea of some people in a very far future digging a deep hole and poisoning themselves with some product hidden inside it should consider this is something that requires neither nuclear waste to happen, nor to wait for that distant future : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3191694/ or http://science.time.com/2010/06/19/study-says-arsenic-poisons-millions-in-bangladesh%E2%80%94but-theyre-not-the-only-ones/
Here is a favored clip from a couple of skeptical magicians illustrating the safety of a container broadsided by the locomotive and set afire for 90 minutes:
(clip contains vulgar language satirizing the hysteria surrounding storage)
Question: If a new container was hypothetically sawed in half down the middle and opened, what type of exposure (proximity and duration to an open container) would it take before a person would be subjected to any meaningful increased epidemiological risks?
I think a more meaningful question, hypothetically, would be what tools would it take, and for how long, to drill into or saw open a cask. And would a Darwin be awarded the successful applicant?
Other than just unscrewing the top. Supposedly, there’s got to be some way to get at the valuable contents for recycling.
The videos I’ve seen say the inner casks are welded shut.
Just getting the concrete overpack out of the way would be an involved process, requiring either heavy equipment or measures like shaped charges.
Here at Columbia, the inner cask is welded shut, all moisture and air is then removed and the cask is filled with helium for cooling. The inner cask is then lowered into another massive cask (concrete and steel) and heavily bolted shut. They are then transferred out to our ISFSI pad via a “crawler” that moves about 1 mph. There they sit self cooling (natural convection) and giving off dose rates of <1-2 mrem/hr gamma and <1 mrem/hr neutron. We use Holtec HI-STORM casks.
Thank you for sharing first hand knowledge. I have a gentle quibble with the following:
…giving off dose rates of <1-2 mrem/hr gamma and <1 mrem/hr neutron.
Most nukes are people of few words, so they often neglect to include “on contact” or “general area” when they mention dose rates. When dealing with specific sources like dry casks, or hot spots in a lightly contaminated area, it makes a world of difference. We need to keep reminding people of the inverse square (or inverse cube, depending on the size of the source) relationship of dose rate and distance.
Please correct me if needed, but aren’t the dose rates you mention “on contact” with the dry cask?
In the spirit of, would happen if someone jumped into a nuclear spent fuel pool [I don’t appear to be the only one who has wondered this] this write up explains a person would be unharmed (except for the gunshot wounds from security) as water is an excellent radiation shield https://what-if.xkcd.com/29/
Per Bonds 25 response below, it appears exposed/unshielded cooled spent fuel rods still emit a lethal dose of radiation of millions of rem/hour.
If they could get into the pool (and deep enough) fast enough, the water would shield them from bullets too.
How to do a super-Olympic sprint while carrying SCUBA gear is an exercise for the student.
A high-pressure water jet “laser” would do the cask cutting job quickly and cleanly.
You wouldn’t be able to get very close before lethal dose rates would stop your momentum. We are talking millions of rem/hr (unshielded “spent” fuel)
Shielded “spent” fuel……..<1-2 mrem/hr
Sorry for the lack of detail on my part. The dose rates I gave are indeed on contact and are actually found at the top and bottom vent locations. All dose rates are <1 mrem/hr at 30cm (general area). Dose rates around our ISFSI pad perimeter (Security)fence are 12-50 microRem/hr. Our pad has 36 casks and is full, so before our next ISFSI campaign we will be building another pad.
That reminded me of my first outage ever, Calvert Cliffs Spring 1997. A diver working in the SFP decided to wonder off and check out another job that was going to be performed and lets just say if it wasn’t for his teledosimetry instantly alarming and the HP frantically pulling his tether…….he might not have made it out of the pool alive. Believe he received 900 mrem very quickly from coming a couple yards away from a bundle. Things have changed now, the divers are on a tight leash…..if you will. Every time I look in the SFP (less than an hour ago actually) Im amazed how awesome of a shield H2O is…….and just how much energy remains in those “spent” fuel bundles.
Not sure if diving into the SFP warrants being shot by Security, but they will happily escort you off site and into the back of a police car…….after you are pressure washed and scrubbed with a wire brush by HP.
Much more likely: within decades very low waste-producing fast neutron reactors and/or thorium reactors will produce limitless electricity.
The comments in this thread remind me of the talks given by Galen Windsor about his experiences with used nuclear fuel and spent fuel pools.
“We are talking millions of rem/hr (unshielded “spent” fuel)” — according to Table 1 in informal 1994 LLNL publication “Dose Rate Estimates from Irradiated Light-Water-Reactor Fuel Assemblies in Air”, for one LWR fuel rod, burnup 35000 MWd/t, distance 5 m, cooling time ten years, it’s 274 rem/h, not millions.
If a used fuel container has 25 assemblies inside, the dose rate might add up to “millions of R/hr” when closer than 5 m away.
Each assembly contains approximately 275 rods (17×17 array with some spaces used for control rods).
For those who wonder about the resistance to hypothesized vulnerabilities, here is a pretty good presentation.
I should have said “fuel assembly”. I was thinking of the big square bundle shown in Figure 1 of “Dose Rate Estimates from Irradiated Light-Water-Reactor Fuel Assemblies in Air” as a single rod, but they and you use the same term.
Take 2: according to Table 1 in informal 1994 LLNL publication “Dose Rate Estimates from Irradiated Light-Water-Reactor Fuel Assemblies in Air”, for one LWR fuel assembly, burnup 35000 MWd/t, distance 5 m, cooling time ten years, it’s 274 rem/h, not millions.
At 1 m and 5 years, 6561 rem/h.
Does anyone have a more recent and/or more formal link for data of this kind?
This broadly agrees with this report from the IPFM (pdf page 13) which gives around 25Sv/h (2500 rem/h) at 1m from a 5yo 33GWd/THM PWR fuel assembly.
I think the key is to take self-shielding into account. Uranium is a damn good shielding material for gammas. The IPFM guys do a full Origen calculation of the whole assembly, which seems the proper way of doing it. I guess the millions of rems per hour estimates come from naively summing up the whole gamma power of the assembly, ignoring self-shielding.
Shielding also means that the dose rate from N assemblies will be less that N times that of a single assembly.
Sorry, I said millions because I was talking about all the bundles being exposed from the cask being cut in half. I guess I should have said >20,000 rem/hr because I have indeed seen the high range detector of an RO-7 pegged from a spent bundle……underwater and it didn’t seem to be within a meter. So , honestly I don’t know what kind of dose rates are on a bundle because we don’t have any instruments that go above 20,000 rem/hr. 274 rem/hr isn’t scary at all……
Not getting off the track, but a partially related issue since some are talking about the bio effects of being exposed to raw cask core material. Google doesn’t have any info on this so I’m hanging on your pro guesses re: that natural uranium “atomic pile” strata in Africa. How high would’ve the exposure rates been for any wildlife around at that area during its maximum output, and do you think there are today any traceable mutations from it?
Thanks for any leads!
The reactor at Oklo is more than 3 times as old as the Cambrian explosion, and more than 4 times as old as the Carboniferous era. With little or no land life beyond perhaps lichens (vascular plants were far in the future), the likelihood of any mutations occurring and persisting to the present is infinitesimal.
Life before meat.
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