# Prototype Fast Breeder Reactor

The Prototype Fast Breeder Reactor (PFBR) is a 500 MWe sodium-cooled, fast breeder reactor that is being constructed at Kokkilamedu, near Kalpakkam, in Tamil Nadu state, India. The Indira Gandhi Centre for Atomic Research (IGCAR) is responsible for the design of this reactor, the Advanced Fuel Fabrication Facility at the Bhabha Atomic Research Centre in Tarapur is responsible for MOX fuel fabrication and BHEL is providing technology and equipment for construction of the reactor. The facility builds on the decades of experience gained from operating the lower power Fast Breeder Test Reactor (FBTR). At first, the reactor's construction was supposed to be completed in September 2010, but there were several delays. The Prototype Fast Breeder Reactor is scheduled to be put into service in December 2024, which is more than 20 years after construction began and 14 years after the original commissioning date, as of December 2023. The project's cost has doubled from ₹3,500 crore to ₹7,700 crore due to the multiple delays. The construction was completed on 4th March 2024 with commencement of core loading of the reactor hence paving the way for the eventual full utilization of India’s abundant thorium reserves.

## Background

The Kalpakkam PFBR is designed to use uranium-238 to breed plutonium in a sodium-cooled fast reactor design. The use of thorium-232, which in itself is not a fissile material, as a blanket is also envisaged in this stage. By transmutation, thorium will create fissile uranium-233 which will be used as fuel in the third stage. FBR is thus a stepping stone for the third stage of the program paving the way for the eventual full utilization of India's abundant thorium reserves. The surplus plutonium (or uranium-233 for thorium reactors) from each fast reactor can be used to set up more such reactors and grow the nuclear capacity in tune with India's needs for power. The PFBR is a part of the three-stage nuclear power program.
PFBR, with closed fuel cycle as the energy resource, is capable of generating a large amount of U-233 (a fissile isotope) from the abundant available thorium-232 within the country, to launch the third stage nuclear energy programme based on U-233 fuel cycle.
The fuel for the PFBR will initially be Uranium-Plutonium mixed oxide (MOX).
India has the capability to use thorium cycle based processes to extract nuclear fuel. This is of special significance to the Indian nuclear power generation strategy as India has one of the world's largest reserves of thorium, which could provide power for perhaps as long as 60,000 years.

## Design and construction

The design of this reactor was started in the 1980s, as a prototype for a 600 MW FBR. Construction of the first two FBR are planned at Kalpakkam, after a year of successful operation of the PFBR. Other four FBR are planned to follow beyond 2030, at sites to be defined.
In 2007, the reactor was planned to begin its operation in 2010, but as of 2019, it was expected to reach first criticality in 2020.
In July 2017, it was reported that the reactor is in final preparation to go critical. However in August 2020, it was reported that the reactor might go critical only in December 2021.
As of February 2021, around ₹6,840 crore (equivalent to ₹77 billion or US$878.35 million in 2023) have been spent in the construction and commissioning of the reactor. The reactor is now expected to be operational by October 2022.
Prime Minister Narendra Modi was in Kalpakkam on 4 March 2024 to witness the initiation of its first core loading. A press release described the PFBR as marking the second stage of India's three-stage nuclear power program.
On 31 July 2024, the Atomic Energy Regulatory Board (AERB) approved adding nuclear fuel and starting the chain reaction. It is expected to be operational by end of 2025. A few lower power physics experiments will be carried out once sustained nuclear chain reaction is achieved. The next step will link the reactor to electrical grid and start producing power on a commercial basis, pending approval from AERB. Kalpakkam will see the construction of two more fast breeder reactors after the Department of Atomic Energy (DAE) is satisfied with the reactor's performance.

### Technical details

The reactor is a pool type LMFBR with 1,750 tonnes of sodium as coolant. Designed to generate 500 MWe of electrical power, with an operational life of 40 years, it will burn a mixed uranium-plutonium MOX fuel, a mixture of PuO $_2$ and UO $_2$. A fuel burnup of 100 GWd/t is expected. The Fuel Fabrication Facility (FFF), under the direction of Bhabha Atomic Research Centre (BARC), Tarapur is responsible for the fuel rods manufacturing. FFF comes under "Nuclear Recycle Board" of Bhabha Atomic Research Center and has been responsible for fuel rod manufacturing of various types in the past. FFF Tarapur in early 2023 had successfully completed fabrication of 100,000 PFBR fuel elements.

### Safety considerations

The prototype fast breeder reactor has a negative void coefficient, thus ensuring a high level of passive nuclear safety. This means that when the reactor overheats (below the boiling point of sodium) the speed of the fission chain reaction decreases, lowering the power level and the temperature. Similarly, before such a potential positive void condition may form from a complete loss of coolant accident, sufficient coolant flow rates are made possible by the use of conventional pump inertia, alongside multiple inlet-perforations, to prevent the possible accident scenario of a single blockage halting coolant flow.
The active-safety reactor decay heat removal system consists of four independent coolant circuits of 8MWt capacity each. Further active defenses against the positive feedback possibility include two independent SCRAM shutdown systems, designed to shut the fission reactions down effectively within a second, with the remaining decay heat then needing to be cooled for a number of hours by the four independent circuits.
The fact that the PFBR is cooled by liquid sodium creates additional safety requirements to isolate the coolant from the environment, especially in a loss of coolant accident scenario, since sodium explodes if it comes into contact with water and burns when in contact with air. This latter event occurred in the Monju reactor in Japan in 1995. Another consideration with the use of sodium as a coolant is the absorption of neutrons to generate the radioactive isotope $^{24}$ Na, which has a 15-hour half life.