A total of 11 incidents were recorded at Faslane naval base on the Clyde and Devonport in Plymouth, with radioactive waste being spilled, workers exposed to radiation, power supplies lost, safety valves wrongly operated and a bag of waste mistakenly dropped overboard.
The incidents have been admitted by UK defence minister, Philip Dunne, in response to a parliamentary question from Angus Robertson MP, the SNP's defence spokesman.
Mr Robertson said it was "frightening reading". "They concern the most serious types of incident and would not even be in the public domain without asking for the information. Safety has to be paramount at Faslane and Devonport and some of the reported incidents that we do know about do not inspire confidence."
The MoD said six incidents since 2008 at Faslane have been defined as "category B". This is the second-worst rating, involving "actual or high potential for a contained release within building or submarine or unplanned exposure to radiation".
Last year, maintenance workers entered an area next to a reactor compartment "without the proper radiological controls in place and hence received an unplanned exposure to a radiological dose," the MoD said.
Although the MoD described what happened in 10 instances, it refused to give details of one event at Devonport as "disclosure would be likely to prejudice the capability, effectiveness or security of the armed forces".
UK defence minister Mr Dunne said radioactive contamination had not caused a danger to the environment or human health.
But John Ainslie, co-ordinator of the Scottish Campaign for Nuclear Disarmament, said: "This catalogue of safety errors shows there is always the risk that something can go catastrophically wrong so long as nuclear submarines remain in Scotland."