I found the following expression in New York Times:
On the International Nuclear Event Scale, a Level 7 nuclear accident involves "widespread health and environmental effects" and the "external release of a significant fraction of the reactor core inventory."
In this sentence, I couldn't understand what "a significant fraction of the reactor core inventory" means. I think this refers to radioactive materials. Is that right? But if so, I don't know why such an expression is used.
According to Longman dictionary, "inventory" means "a list of all the things in a place". And "fraction" means "a very small amount of something".
Then, it follows that the phrase in question means "a small significant amount of a list of all the things in the reactor core". Is it correct to interpret this means "radioactive materials". If not, could you tell me "a significant fraction of the reactor core inventory"?
Also, significant modifies not "its amount" but "its quality". Is that right?