REACTOR FACILITIES GROUP

FAST BREEDER TEST REACTOR (FBTR)

Description Components Safety Radiological Safety Construction, Commissioning & Operation Summary Reactor Vessel Internal Inspection History of FBTR

History of FBTR

    Fast Breeder Test Reactor (FBTR) at Indira Gandhi Centre for Atomic Research (IGCAR), Kalpakkam is a sodium cooled, loop type fast reactor which serves as a valuable test bed for development of fuel and structural material for future fast reactors in India. FBTR has completed 32 years of operation. The knowledge gained through successful operation of FBTR for the last 32 years has provided vital inputs for the commercialization of fast breeder programme through the construction of 500MWe Prototype fast breeder reactor.

    Heat generated in the reactor is removed by two primary sodium loops and transferred to the corresponding secondary sodium loops through Intermediate Heat Exchangers (IHX). Each secondary sodium loop is provided with two once-through steam generator modules. Steam from the four modules is fed to turbine-generator (TG). A Dump Condenser of 100% capacity is also provided in the steam water circuit for continued reactor operation when TG is not available. FBTR uses an internationally unique fuel in the form of Pu rich carbide, and the fuel has logged a record level of burn-up-i.e. energy generated per ton of fuel. The carbide fuel of FBTR has seen a burn-up of 155 MWd/kg, setting an international record for this fuel. The current core is rated for 30 MWt. FBTR has successfully completed 25 irradiation campaigns and the 26th irradiation campaign is in progress. The term “irradiation campaign” refers to the period of operation with a specific core configuration. Steam at the highest temperature and pressure among any nuclear plants is being generated in FBTR (125 bars & 460 deg.C)

        The reactor core consists of 745 closely packed locations, with fuel at the centre, surrounded by nickel reflectors, thoria blankets and steel reflectors. There are 23 storage locations in the outermost steel reflector row. The core is vertical and freestanding, with the subassemblies supported at the bottom by the grid Plate and held on to the latter by collapsible hold-down springs. The subassemblies are hexagonally shaped. The fissile zone of the current core, as of March 2018 has 52 fuel subassemblies. The driver fuel for FBTR is a unique high Pu carbide (called MK-I fuel, of 70%PuC+30%UC composition). Each subassembly has 61 fuel pins of F 5.1 mm. The current core has 38 MK-I fuel subassemblies. In addition, there are 5 subassemblies of MK-II (55%PuC+54%UC), eight subassemblies of high Pu MOX (44%PuO2) and one special subassembly of 1 IFZ100. Irradiation of sodium bonded metallic fuel pins and structural materials is in progress presently. Reactor control is by six control rods of 90% enriched boron carbide. The major components of the primary system are the reactor assembly, two intermediate heat exchangers and two sodium pumps. The entire primary system including the piping is provided with a concentric outer jacket called `Double Envelope’ designed to keep the level of sodium in the reactor above the core in the event of any possible leak from the main walls.

    Over the years, several major retro fitting measures and modifications were carried out based the operating experience. These were required for improving the plant safety, reliability, operator convenience, to achieve the design sodium temperature at the reactor outlet and to take care of obsolescence. Some of the modifications were to overcome the deficiencies observed during the commissioning stage and some were based on the review of incidents in the plant. FBTR is the mother of fast reactors in India. Operational feedback from FBTR went into the design of PFBR. The safe operation FBTR was instrumental in the sanction for PFBR project.

    FBTR, in operation since 1985, is the flag-ship of IGCAR and is the test bed for fast reactor fuels and materials. 25 irradiation campaigns were completed so far for various irradiation programs. Review of the PSR documents by AERB has been completed and FBTR has been licensed for operation upto June 2018.

Salient Features of recent irradiation Campaigns

* Irradiation of enriched U based and Plutonium based sodium bonded metallic fuel pins.
* Irradiation of TRISO coated particles being developed by BARC for Compact High Temperature Reactor (CHTR) and disc specimens of CHTR structural materials (Nb-1% Zr 0.1% C) were completed.
* Irradiation of structural materials for low dose irradiation for future Fast Reactors.
* Testing of High Temperature neutron detectors developed by BARC for PFBR
* Production of Strontium isotope for medical purposes

Seismic re evaluation

Seismic re evaluation of FBTR has been carried out. The seismic margin assessment indicates that the plant, in the current condition, is safe for 0.09g. With the retro-fittings recommended by the Review Committee, the Seismic Margin will improve to 0.3 g. Retrofitting work was completed.

Modification in the plant to take care of Tsunami incident

Subsequent to the Tsunami of Dec 2004, a study was carried out by IIT Madras for Kalpakkam site. FBTR being far away from the coast (~1 km) the Design Based Flood Level for tsunami has been estimated to be less compared to the cost. This is also borne out by the fact that there was no water ingress in FBTR-RML complex during the tsunami of 2004. However modifications were completed to avoid direct entry of water into the complex. Earth Quake Notification system (ENS) is installed in FBTR control room, MAPS control room and KARP control room which will alert the operator about possibility of Tsunami. Sufficient warning time is available to shutdown the reactor and cool the core.

Modification in the plant to take care of Flood

The study by IIT Madras indicates that under the cyclonic conditions combined with heavy precipitation and high tide, the flood level can reach 600 mm above the Finished Floor Level of FBTR. To avoid water entry to FBTR, all entry points to FBTR have been elevated by 600 mm.

Modification in the plant to take care of extended Black-out scenario

FBTR is procuring two additional air cooled DG sets to meet the power requirements in case of Extended Black-out scenario. These DGs were located around 2 meters above ground floor so that flood and Tsunami will not affect their performance. In addition, mobile DGs are being procured which were located in the first floor of the buildings.