Marc, The NR-1 hull was extended by 30 feet later in its life which allowed room for greater habitability and more scientific missions. The core was about the size of an office desk round metal trash can and was composed of 4 shortened S5W core modules with highly-enriched fuel. As you note, a smaller reactor compartment will require less shielding due to the overall smaller volume but the thickness of the shielding cannot be reduced. While the reactor is critical and undersea, the typical radiation exposure is less than while on the surface as the cosmic ray exposure is shielded by the seawater. There was a reactor vessel system built for an NR-2 but after our Congress got wind of this sub that was funded outside of Congressional oversight, further development was halted. The decommissioning of this national resource due to its expensive operating budget and the need for refueling/replacement of the reactor vessel was a loss to both the Navy and to the scientific community. R/Jay -----Original Message----- I don't doubt that. Still, it is amazing that they were able to shoehorn a conventional two-loop, light-water reactor and its auxiliaries into such a small package. Now imagine a reactor running on highly-enriched fuel, with a much smaller core size. Perhaps gas cooled, so only one coolant loop is needed. And shield weight and volume drops rapidly with shrinking core size. Marc |