The world’s first nuclear icebreaker Lenin was in operation from 1959 until 1989. During that time, there have been two seriuos accidents onboard.
The first nuclear propulsion unit (OK-150) on Lenin had three identical pressurised water reactors (PWR) with a maximum heat output of 90 MWt. The shaft power was 44 ,000 horsepower. Enriched uranium was used as fuel (the content of U-235 was equivalent 85 kg), and distillate water was used as a moderator and for heat transfer.The reactor core was 1.6 meters high and measured one meter in diameter.The core consisted of 7,704 fuel pins in 219 fuel assemblies.
There have been two accidents onboard the nuclear powered icebreaker Lenin. The first took place in February 1965, when Lenin was undergoing repairs and refuelling. The vessel sustained severe mechanical damages to the fuel assemblies, some of which were broken in two pieces, and were detected during the unloading of fuel from reactor number two. About 95 spent nuclear fuel assemblies were transferred to the nuclear service ship Lepse and unloading was halted after that.
After investigations as to why the spent nuclear fuel assemblies were deformed, it was established that the nuclear reactor operators had made an error that left the reactor core without cooling water. The partial deformation of the fuel assemblies had occurred due to overheating of the reactor core. About 60% of the assemblies were damaged.
The decision was made to unload the remaining 124 spent nuclear fuel assemblies together with the neutron absorbing rods and control grid.
A special cask was built onshore to implement this operation. A part of the reactor containing spent nuclear fuel (SNF) was placed into the cask and filled with furfurolbased solidifying matter. This cask was then stored for two years. In 1967, it was reloaded onto a pontoon, towed by a tug to the eastern coast of the Novaya Zemlya Archipelago and dumped in Tsivolki Bay.
The second accident aboard the Lenin took place in 1967, when the pipe system of the third circuit sprung a leak following the loading of fresh nuclear fuel. In this instance it was necessary to open the biological shield of the reactor compartment in order to locate the leakage. This protection was made of concrete mixed with metal shavings and it required the use of sledgehammers to break through the shield.This led to further damage of the reactor installation. Upon later examination, it became clear that it would be impossible to repair the damage incurred to the reactor installation by the sledghammers.