New Delhi: The work of loading reactor fuel into the second unit of the Kudankulam nuclear power plant in Tamil Nadu has begun successfully, a source at the KNPP said on Thursday. "On May 11, the first fuels assembly was loaded successfully into the reactor of Unit 2 of KNPP. This means the commencement of the physical start-up stage at the unit," a source at the project said over telephone. "A total of 163 fuel assemblies will be loaded at the reactor, on completion of which and of a number of required tests, the unit will be brought to the first criticality status," the source added. Criticality for a nuclear reactor denotes the start of the fission process. The 1,000 MW second unit is expected to go critical by the mid-2016. Russia's state-run nuclear power corporation Rosatom are the builders of the KNPP being operated by the Nuclear Power Corporation of India (NPCIL). This first 1000 MW unit at Kudankulam has already been commissioned. Start of work on Units 3 and 4 was delayed due to concerns among foreign nuclear plant suppliers about India's nuclear damage liability law. They were reluctant to sell to India, citing the provisions of the Civil Liability for Nuclear Damage Act (CLND) 2010, that provides the right of recourse by Indian operator NPCIL against the vendors for compensation in case of an accident. The Indian government last year launched an insurance pool of Rs.1,500 crore ($220 million) to be managed by national reinsurer GIC Re. "This is the world's first nuclear power plant which has implemented and successfully operated the tightened security measures post-Fukushima," the source said. The Kudankulam nuclear power plant is equipped with state-of-the-art safety mechanisms with unique features that make them foolproof. In an interview earlier, Denis Kolchinskiy, chief project engineer of SPbAEP, the developers of the AES 92 nuclear reactor installed at Kudankulam, had said modern Russian designs - developed over a decade - have an optimised balance of active and passive safety systems to provide two layers of protection. The key to preventing an apocalypse in the event of a core meltdown, said Kolchinskiy, is the "molten-core catcher" - a mandatory safety system included in the Kudankulam project's basic supply package.