INDICATIONS ARE THAT THE PROTOTYPE Fast Breeder Reactor (PFBR) will reach first criticality in late 2018. The PFBR in Kalpakkam, which begun construction in October 2004, has been on the verge of commissioning for some time, but the expected date of commissioning keeps being pushed back.

The delay, according to India’s Department of Atomic Energy (DAE), “is primarily owing to the augmentation of certain additional assessments and checks on the installed equipment prior to commencement of their commissioning, which have essentially emanated owing to both increased regulatory requirements and as a matter of abundant caution”. DAE’s ‘abundant caution’ stems not only from a tougher post-Fukushima regulatory environment, or the experience of sodium-cooled FBRs elsewhere, but also the fact that the PFBR is a lodestone for the second stage of India’s three-stage nuclear programme (TNSP) which envisages the creation of at least 300GWe generation capacity via FBRs.

It was back in 2004 that construction of the sodium-cooled pool-type 500MWe PFBR was begun, by Bhavini, a special purpose vehicle set up by DAE to realise the project and to act as a utility overseeing the construction and operation of future FBRs in India. Working alongside Bhavini, as the design, research & development (R&D) agency for the PFBR, has been the Indira Gandhi Centre For Atomic Research (IGCAR), Kalapakkam, also a part of DAE.

The PFBR development project has been a significant learning experience for both IGCAR and Bhavini given that a lot of equipment going into the reactor is ‘first of a kind’ (FOAK) and has been created from the ground-up in India via domestic production, and this has been a primary reason for the delays. After Fukushima, tougher standards from India’s Atomic Energy Regulatory Board (AERB), also required additional safety features, more conservative design parameters for external events and an emphasis on in-service inspection, which contributed to further delays.

For instance, the mechanical harfaced seal arrangement at the interface of the IHX outer shell and the inner vessel standpipe in the PFBR, rather than using traditional cobalt-based stellite alloy, is now made of a more wear-resistant nickel-based hard facing alloy (Colmonoy-5), because of the expected radiation dose rate to be experienced during the lifetime of the reactor. A computational-intelligence-based welding system for online monitoring and control during welding was also developed for obtaining zero-defect welded PFBR components, which is a key safety requirement.

As far as physical construction is concerned, the PFBR is complete, with various pre-commissioning tests underway. The boxing up and pre-heating of the main vessel, completion of the integrated leak rate test, deflection measurements of the reactor containment building, completion of fabrication of the pump intermediate heat exchanger (IHX) flask and demonstration of lifting the primary sodium pump were all completed by the end of last year.

So was the subsequent sodium filling and commissioning of both the secondary loops. But hydraulic problems in the secondary circuits led to flow oscillations, which made it impossible to operate the secondary sodium pumps at full speed. Even as this was being studied, Bhavini decided to progress testing of the fuel handling systems under ‘hot’ conditions along with the verification and validation of the software for the associated computer control systems. The sodium filling of the vessel and the primary loops were due to start after the completion of the fuel handling system trials, purification of the sodium to be loaded and the starting of the sodium pumps.

Sodium filling is also subject to the AERB granting appropriate clearances and approvals. After filling the main vessel and primary loops, isothermal tests will be carried out, after which the PFBR’s uranium-plutonim MOX fuel will be loaded into the core. According to Bhavini, fuel loading will take about two months, and attempts to reduce flow instability in the secondary loops will be made during this period.

A lot hinges on the successful commissioning of the PFBR for India, given that the reactor is an industrial scale demonstrator that is intended to validate its design concept and provide critical experience for operations and maintenance in a sodium environment with an operating temperature of 550°C. This experience will prove vital to the future expansion of Bhavini, which plans to construct two 600MWe FBRs of improved design on a site adjoining the present PFBR.

IGCAR and Bhavini are currently progressing detailed engineering studies for this new 600MWe ‘commercial’ FBR (CFBR) design. DAE believes that construction of these reactors could begin in early 2022/23, by which time it is hoped that enough feedback on full power operations from the PFBR can be incorporated into the design.

To prepare for the construction of the two commercial FBRs, a site assembly workshop and electrical substation are being built on-site. In addition to these two reactors, DAE also intends to develop four more FBRs at a different site and a ‘site-selection committee’ has been formed for this purpose.

The timelines for these plans will, of course, depend to a great degree on the actual commissioning and smooth full-power operations of the PFBR.  

Author information: Saurav Jha, Author and commentator on energy and security, based in New Delhi