The contract is intended to help protect against the equipment obsolescence risk by ensuring continuous operations of high-integrity control system and the primary protection system at the facility for the next four decades.
The two systems are Westinghouse Eagle Series 2 equipment, a platform based on 1980s digital technology.
Westinghouse UK, Middle East and Egypt vice-president and managing director Dave Unsworth said: "This program, which has been carefully formulated over the last 18 months, is designed to give our customer an alternative by preserving the ability to maintain the Eagle platform."
In particular, the company will keep operating the specialist nuclear equipment systems through the end of the operational life of the power station including during decommissioning.
Westinghouse UK, Middle East and Egypt vice-president and managing director Dave Unsworth said: "Our aim isn’t simply to stockpile parts for the future, but to keep an active, working knowledge of the platform and its design.
"This knowledge can then be deployed to troubleshoot or redesign aspects of the system as required.
"Being able to rely on a service that will guard against significant vulnerabilities is hugely advantageous to our customers, helping them ensure continued operational safety and plant economy, both in terms of electricity production and in avoiding unplanned equipment upgrades."
Westinghouse will undertake component lifecycle reviews of all individual parts and pieces of the equipment following which mitigation strategies will be developed upon finding potential obsolescence issues.
Although the power plant is currently planned for decommissioning in 2035, the company expects to operate the facility till 2055.
The Westinghouse-designed Sizewell B plant is claimed to be the only pressurized water reactor in the country.
