1.) It sunk. Given the technical sophistication of submarines, I imagine one would be hesitant to reproduce a design in which the only example sank (i.e., the assumption that it was flawed).
2.) It had a liquid-metal reactor, a design the Soviets experimented heavily with but gave them a lot of trouble (see the Alpha-class, which also used liquid-metal reactors. I believe one of them sank as well).
K-278 was an advanced combat submarine (primarily a development ship but fully combat capable) to evaluate new technologies for 4th Generation Soviet SSN: titanium hulls, 1000 m depth, max speed in excess of 30 knots, advanced sonar, highly automated...Propulsion was provided by a single OK-650b-3 reactor.
Design started by late 60's leaded by N.A. Klimov and, after his dead in 1977, Yu. N. Kormilitsin. K-278 entered service in 1984.
Several times the management of the Rubin design bureau proposed building additional Project 685 submarines but that proposals were not accepted. Northern Fleet command was in favor of additional units said deputy chief designer D.A. Romanov. The accident cancelled any possibility for a series production.
The OK-650 reactor is the nuclear fission reactor used singly to power the Soviet Navy's Project 685 Плавник (Mike), Project 971 Щука-Б (Akula), and Project 945 Барракуда, Кондор, and Марс (Sierra) submarines, and in pairs to power the Project 941 Акула (Typhoon) and Project 949 Гранит and Антей (Oscar) third generation submarines. It is a pressurized water reactor (PWR), using 20-45% enriched uranium-235 fuel to produce 190 MWt of power.
hey thanks for the replies. However I do not think any alfa was lost. The reason I brought this up , because, I think we may see a lot of the komsomolets resurrected as the Yasen. that liquid metal coolant concept is not dead yet.