Chemistry fans often refer to Oct. 23 as “Mole Day,” since the numbers 10 and 23 are part of a basic constant in chemistry, the mole. This unit describes how many atoms exist in a given sample of any substance, so scientists use moles to simplify lots of calculations. For example, when an average nuclear reactor first starts up its core has about 120,000 kilograms of uranium in its fuel. A mole of uranium weighs about 238 grams, so a brand-new core has about 504,000 moles of uranium. A plant scientist or NRC specialist would base some core calculations on a more exact definition of moles in the core.
U.S. NRC Blog 
The “Public Pit Bull” brings forth a bit of info that extends out into other realms in our world of internet media about Avogadro Amedeo, the mole, the science and math of it all. http://www.wired.com/2015/10/mole-day-avogadro-didnt-even-know-avogadros-number/
Holy Moly is right! Deceitful people in high places. Scary thought! Now even Japan admits to its first radiation death from the Fukushima disaster. The tally now from deaths due to the Fukushima disaster is well over 1,000 just from the adverse affects of being evacuated with no hope of returning to your home. Now we can add a death from radiation. Sadly this is probably the tip of the nuclear tombstone iceberg. Nuclear icebergs are now much more deadly than the iceberg that sunk the Titanic. High time for a moratorium on new nuclear plants in this country and no more license extensions on existing plants.
around 119,997 kg
Holy Mole Gary — You are right on many levels and especially about saying that anything that is radioactive can be used as a weapon, if only as a threat to all those that want no part of living with “additional” radiation, that once scattered becomes almost impossible to get rid of, the wide spread radioactive waste now found all around Fukushima and the DU now located in many places in the middle east are both good perfect examples of what happens when Nuclear goes BAD.
Thanks for your comment and I hope to read many more for you.
using 120,000 kG as the starting point, what is the ending weight of the same core on a normal burnup cycle? TY!
Informative article, thank you. More about the 120,000kg of nuclear reactor fuel and “moles.”
When the120,000kg of nuclear fuel is finished with its’ useful cycle, it becomes 264,000 pounds of highly radioactive spent fuel, suitable for various types of nuclear weapons, if processed or unprocessed ( https://en.wikipedia.org/wiki/Nuclear_weapon_design or a dirty bomb https://en.wikipedia.org/wiki/Dirty_bomb ) – “Used fuel will typically have about 0.9% U-235 and 0.6% fissile plutonium (almost 1% Pu total), with around 95% U-238.” http://www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Introduction/Nuclear-Fuel-Cycle-Overview/
Nuclear Reactors are critical to nuclear weapons materials. Those who claim a nuclear weapon cannot be built from spent reactor fuel are not telling the truth. Those who convey such nonsense are aware of their deceit or flunked nuclear physics and/or their class on nuclear materials security. To demonstrate the fallacy that spent nuclear fuel assemblies may not be utilized as a nuclear weapon I would suggest the reading of the study regarding nuclear criticality explosions at this link – http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/27/063/27063492.pdf A nuclear weapon is more than a fission device.
“Mole” has several meanings, one of those meanings is that of an unscrupulous, disloyal person in an organization. You have described for us the amount of uranium which makes up 1 mole. It only takes 1 unscrupulous organizational mole in a high level position or a position which facilitates public deceit to destroy the credibility of an organization. In that realm, the nuclear energy industry has many moles facilitating deceit and destroying the concept of Human Reliability and public trust.
I knew about Groundhog Day but not Mole Day. Thanks for informing me. This 10 to the 23rd power is a mind-boggling huge number, a 10 with 23 zeroes added on. That huge number represents the number of atoms in just 12 grams of carbon. Incredible. This number is called Avogadro’s number or constant. Did Avogadro determine it? Who was he?