National Secretary Alan Leighton said: "Prospect welcomes this move because it will continue to provide vital, safe, low-carbon energy while at the same time maintaining a base of nuclear expertise and sustaining local economies.
"Prospect believes that nuclear power is a vital component of a balanced energy policy. This decision will safeguard the jobs and skills of more than 1,500 employees and contractors in the affected areas - Somerset and North Ayrshire.
"It will also provide important training opportunities, and play a major role in building a bridge to the construction and operation of the new generation of nuclear power stations that we so urgently need, and to which EDF Energy has committed itself, subject to the right investment framework."
The news was announced by EDF Energy as its chief executive officer Vincent de Rivaz opened a visitor centre at Hinkley Point B.
Prospect represents more than 2,700 engineers, managers and specialists at eight existing EDF Energy nuclear power stations across the UK.