The Nuclear Power Corporation of India expanded the Tarapur Atomic Power Plant with Units 3 and 4, each with a 540 MWe capacity, marking India’s first units over 500 MWe. TCE provided comprehensive engineering services for these Pressurised Heavy Water Reactors (PHWR), employing a standardised twin unit design. Safety was a priority, with features like the Reactor Auxiliary Building (RAB), Safety Auxiliary Buildings (SABs), and a supplementary control room. TCE designed structures, pipework, and ventilation systems to withstand high seismic activity. An emergency feed water system was implemented to prevent coolant loss accidents. TCE also obtained approval to declassify non-nuclear structures from nuclear safety considerations, simplifying designs and reducing costs. The plant incorporated innovative elements such as concrete-volute condenser cooling water pumps and titanium tubed condensers. TCE conducted extensive modelling and simulation tests to design the sea water cooling system, preventing thermal pollution and protecting marine ecology. TCE’s services also included detailed procurement specifications and post-contract engineering support.