August 25, 2008. The Department of the Interior along with the Department of Energy has announced that the Hanford B Reactor has been designated as a National Historic Landmark.
A pdf download details the history of area 100-B. In this document there is a figure that shows how new fuel elements were pushed in one side and how the spent elements came out the other side into a water basin with the aid of the local (and free) gravitational field.
This seems very clever. I fear that a modern solution would involve 10 years of studies and would result in a half billion dollar high tech solution. Contractors would lock on to the DOE tit and hang there for decades with service contracts and spec’d in consumables.
Lamentations on Chemistry 
$50 million in studies just to determine whether fuel element insertion should be serial or parallel. The initial answer will be a horrendous Poisson distribution parameterized for average velocity weighted by core position and corrected for empirical anomalies plus “more studies are needed”. Top Secret/Special Access Required.
The Top Secret/Lotus Eater alternative: It’s built on land not operated in a submarine. Make it as large as you want so it’s safe.
What will be used as lubricant as those puppies centimeter their way through? I know! Let’s start with h-BN and do optimization studies when it craps out. (Graphite is messy black – can’t have that in a PBS documenary.)
So, you have experience in this field, eh?