"An academic reactor or reactor plant almost always has the following basic characteristics: (1) It is simple. (2) It is small. (3) It is cheap (4) It is light. (5) It can be built very quickly. (6) It is very flexible in purpose (’omnibus reactor’). (7) Very little development is required. It will use mostly off-the-shelf components. (8) The reactor is in the study phase. It is not being built now."
Link to the other thread here: https://news.ycombinator.com/item?id=22851622
Link to the recent HN discussion of said letter by Admiral Rickover here: https://news.ycombinator.com/item?id=22715730