Proportional mathematics shows that Holtec’s nuclear waste trash cans are proportionally not much thicker than an egg shell
Last year, we asked Carlsbad computer programmer and nuclear safety advocate, Ace Hoffman to evaluate the “thin-walled” nuclear trash cans that Southern California Edison is using at its beachfront nuclear wast dump at San Onofre using proportional mathematics. Ace is the author of a popular intensively illustrated book on radiation, The Code Killers which is available for free at his Web site The title of the book refers to the destruction of DNA by radioactive substances. Ace has spent a lifetime studying nuclear waste but has significant math cred from writing programs for straight, circular, spiral and cylindrical slide rules. Ace is also a member of the Oughtred Society
Our question: If you shrunk down a Holtec can to the size of an egg, would the walls on the cans be thicker than an eggshell? The answer is that the cans are eggshell thin.
We know that the nuclear waste trash cans at San Onofre will carry an average of 38,000 pounds of high-level radioactive waste that is deadly to all human life for the next 250,000 years. Some of these cans may weigh as much as 110,000 pounds. We also know that the cans are roughly 18 feet tall. What’s more, given the eternally lethal nature of the payload in each can, we were shocked to learn that each can is only 5/8′ thick stainless steel – less than the width of a dime (see illustration below). Shockingly, the Holtec cans are only guaranteed to last 25 years, and the entire system which includes a concrete bunker with silos to hold the cans is only guaranteed for ten years.
To us this all sounds reckless, cheap, and irresponsible.
But what concerns us the most is the thickness of the stainless steel walls on each can. Only 5/8 of an inch stands between the public and a nuclear waste disaster. Below the pictures are the criterion variables that Ace Hoffman used to arrive at the conclusion that Holtec’s cans are “eggshell thin.”
The wall thickness on the 18 foot high cans at San Onofre is 5/8″ inch – thinner than the width of a dime.
This illustration from our report Earthquake Bay
For a 5/8″ shell, I calculated the % of the shell compared to overall diameter to be about 1.6 % of the total diameter.
For a chicken egg shell, the % (across the widest part, not the longest part) is about 1.25% of the total diameter. Less for the longer dimension, of course.
So they are pretty similar: Less than half a percentage point difference.
For a 1/2 inch thick dry cask shell, they’re even closer.
The cask, however, must carry about 3 times the density (including its own weight) than an egg (including the shell weight).
I therefore conclude a dry cask is little more protection than an egg shell and perhaps less.
An actual comparison is impossible because there are so many factors to consider: Deformation capabilities of the materials (i.e., rigidity), imperfections in the materials (due to manufacturing errors, or increases with time due to hydride formation on the dry cask), heat load (more heat will tend to make the dry cask more elastic), ambient temperature (colder outside air will tend to make the outer parts of the dry cask more brittle, and cause internal stress due to the difference in temperature between the outside and inside of the dry cask), etc. etc.
Below are the values used for my calculations. Dimensions and weights of the casks are from Holtec documentation, for the egg it’s from half a dozen different online sources which tended to comport with each other. Calculations were mostly done with Google online calculators.
Overall Height of MPC-37 cask: 213 inches maximum (depends of fuel length to be stored. I think SanO’s are at or near the maximum length).
Outer Diameter of MPC-37 cask: 75.5 inches
Maximum weight of MPC-37 cask: 110,000 lbs
(Maximum fuel assembly weight (37 per cask) is less than or equal to 2,050 lbs.
Density of UO2: 10.52 grams per cubic centimeter
Density of DU (U238): 19.28 grams per cubic centimeter
Weight of U (PWR): 469 Kilograms (Not sure if that’s per fuel assembly or the total weight of U-235 per MPC-37)
Density of lead: 11.34 grams per cubic centimeter
Up to 12 of the 37 fuel assemblies can have damaged fuel.
Volume of an MPC-37: 3,810,000 cubic inches = 62,434,710 cubic centimeters
Volume in gallons (US): 4,128.11 gallons.
Density of an MPC-37 cask:
weight of a gallon of water is: 8.34 pounds (3.78 kilograms)
Weight of MPC-37 if filled and made of water: 34,427.52 lbs.
% of diameter of shell: 0.828 (for one side of a 5/8ths inch shell)
Large chicken egg:
Shell thickness: 0.3 mm
Weight of shell is about 13% of total weight of chicken egg.
Diameter of a chicken egg: 2 1/4 inches long and 1 3/4 inches wide (at their longest and widest parts). 57.15 mm by 44.45 mm
Weight of a chicken egg: 57 grams
Volume of a chicken egg: 51 cubic centimeters (46 ml (3.25 tbsp) (cooking yield))
% of diameter (shorter diameter) of shell: 0.675% (for one side of the shell)
Density of a chicken egg: about 1.1 grams per cubic centimeter