Not necessarily required it was done to provide the structure or scaffolding if you wish for the cells to grow on, it was a faster method this time around rather than having to make one artificially from scratch.

While I do not directly work in the industry I've been contracted in at various points and have brought up thorium reactors in conversation more than once. It basically goes like this. "For an efficient thorium reactor you need completely new hardware for it to perform well. It would cost far to much to retrofit an existing system to be used as a thorium reactor and even then it wouldn't be as efficient as what we're using or nearly as efficient as a newly built system" Basically it comes down to the all mighty dollar, they do not want to spend the money even if it's safer/better.

King Arthur: Consult the Book of Armaments.

Brother Maynard: Armaments, chapter two, verses nine through twenty-one.
Cleric: [reading] And Saint Attila raised the hand grenade up on high, saying, "O Lord, bless this thy hand grenade, that with it thou mayst blow thine enemies to tiny bits, in thy mercy." And the Lord did grin. And the people did feast upon the lambs and sloths, and carp and anchovies, and orangutans and breakfast cereals, and fruit-bats and large chu...

Brother Maynard: Skip a bit, Brother...

Cleric: And the Lord spake, saying, "First shalt thou take out the Holy Pin. Then shalt thou count to three, no more, no less. Three shall be the number thou shalt count, and the number of the counting shall be three. Four shalt thou not count, neither count thou two, excepting that thou then proceed to three. Five is right out. Once the number three, being the third number, be reached, then lobbest thou thy Holy Hand Grenade of Antioch towards thy foe, who, being naughty in my sight, shall snuff it."