Plutonium is much rarer in nature than uranium and is more commonly used for bombs rather than as reactor fuel. Like uranium, it comes in various isotope forms, with plutonium 239 the most commonly used. It is mixed with the much more unstable plutonium 240 to generate power.
It's my understanding that a horse's knees close around age 2- 2 1/2. My gelding JUST turned 3. A couple days ago in fact. Will a horse's knees almost certainly be closed by that age?
Regardless of the age of the horse, it is essential that you do not ride a horse whose knees have not finished closing. If your horse's knees have not closed, it means that the knees have not fully developed and are extremely vulnerable to damage that can occur as a result of putting too much pressure on the joints.