Workers at the Atomic Weapons Establishment at Aldermaston and Burghfield are to stage two more 24 hour strikes.
Their walk-out on May 10 and 18 will follow two other days of action already announced for May 4 and 8.
It brings the total number of strikes by more than 700 workers to 18 since a dispute began in November last year when the pensions were moved from the Ministry of Defence to the private sector.
Unite, the country’s largest trade union, claim that that the closure of the defined benefit scheme by AWE bosses will result in employees having thousands of pounds slashed from their retirement incomes.
The union also says it came up with suggestions to find a solution to the long- running dispute but they have been ignored.
Next month’s strike on May 10 will coincide with the regulatory site exercise day, when AWE and local councils run through the scenario of a nuclear incident on site.
Unite regional officer Bob Middleton said: “We have not received a response or even an acknowledgement to the pension proposals that we sent to AWE management on April 13. We put forward these proposals in good faith but our members feel that they have now been snubbed.”
An AWE spokesman said they had offered a significantly improved scheme and enhanced benefits.