The three appointments are with Babcock International Group, Dounreay Site Restoration Ltd and NNB Generation Company (part of EDF Energy).
The appointment with Babcock is to provide quantity surveying and commercial services on the engineering firm's UK nuclear decommissioning projects, including major works at Sellafield and Berkeley as part of a three-year framework.
Working with Dounreay Site Restoration over a four-year period, Sweett will provide cost estimating services, predominantly from its offices in Edinburgh and Glasgow, on the decommissioning of the site which formerly housed the UK's centre of fast reactor research and development.
In the nuclear new-build field, Sweett has been appointed by EDF Energy to provide commercial support services as part of a 30-month framework for the construction of a proposed new nuclear power station at Hinkley Point C.
Sweett CEO Dean Webster said: "Investing in growth sectors such as energy infrastructure is one of the key components of our strategy to diversify our UK business. Our UK order book has continued to develop positively since the start of the financial year, a clear sign that we are winning greater market share in an increasingly competitive market."