Now, December 2021 - India's Prototype Fast Breeder Reactor [PFBR] To Go Critical

Major Erection activities in India's much overdue Prototype Fast Breeder Reactor [PFBR] programme are complete. Having entered the Commissioning phase, it is, currently, undergoing subsystem trials. Located within the facilities of the Indira Gandhi Centre for Atomic Research [IGCAR], this Bharatiya Nabhikiya Vidyut Nigam Limited [BHAVINI] run facility would constitute a meaningful step into the critical Stage II of India's far-reaching, long-stretching, 3-Stage Nuclear Programme ambitions.

Responding to a question raised in the Rajya Sabha, Parliamentarian Dr. Jitendra Singh informed the Upper House that the PFBR, conceived in 1992, is now scheduled to become operational only by December 2021 [above]. That said, of the Kakrapar 700 MWe PHWR facility, which attained Criticality on July 22, 2020, he informed October 2020 as the date. So, take this information, & apply to it a sweeping ±tolerance limit.

Subsequently, the latest IGCAR Annual Report details the PFBR's current development status. A major take-away, it reported resumption of trials of it's Secondary Sodium Coolant [SSC] Pump. More on that later. Trials of a redesigned Transfer Arm [TA], modifying it's Gripper end to enable correct Fuel Rod handling is underway. It's Rotatable Plugs - the Large Rotatable Plug [LRP] & Small Rotatable Plug [SRP] have thrown up some deviations, during commissioning, requiring a re-look of it's Bearing Assembly. BHAVINI authorities expect to commence Nuclear Fuel loading, that have been moved in the vicinity, once they complete a prior series of sequential activities. This includes achieving stable, reliable performance of Coolant Pumps & filling the Circuit with Sodium. Fuel loading, would be followed by pursuing attainment of the Holy Grail - Criticality.

The 500 MWe PFBR follows on the trails of the highly successful 40 MWth Fast Breeder Test Reactor [FBTR], that IGCAR has been operating since 1985 [above]. While the FBTR has a loop configuration, the PFBR adopts a pool-type design, in keeping with it's larger capacity. To begin on a firm footing, the PFBR would first use the well-proven Mixed Oxide [MOX] Fuel [PuO2+UO2] for the Chain Reaction. With time, plans are on to trial the PFBR with the less tested, but better breeding Metallic Fuel into the Core. Initial Indian plans envisaged setting up purely Metal Fuelled Fast Breeder Reactor [FBR] in around 2030. Safe to add a few more decades now.

The Fission Chain Reaction liberates heat energy, that first transfers to the Primary Sodium Circuit [PSC]. At the Intermediate Heat Exchanger [IHX], the PSC transfers energy to the 2 Nos. Secondary Sodium Main Circuit [SSMC]. This, in turn, flows through it's 8 Nos. of Steam Generator [SG], passing on the heat to the Steam/Water Circuit [SWC].

This Superheated Steam flows over the Turbine, turning heat into Mechanical Energy. An Alternator, coupled to this rotating Turbine, would generate the electricity.

During this process, a blanket of fertile Thorium-232 [Th-232] placed around the Fuel Core would be irradiated to fissile Uranium-233 [U-233], whereas radioactive Plutonium-239 [Pu-239] can be bred from a blanket of non-radioactive Uranium-238 [U-238]. U-233, as fuel, would be the 'Wonder Metal' powering India's Stage III commercial-scale Nuclear Power Plants, plus breeding more U-233. As one can see, a Breeder Reactor, in addition to generating electricity, also produces more fuel to fuel itself. The Physics, Chemistry & Engineering involved towards achieving a practical, sustainable path towards this is the stuff of "path-breaking".

In keeping with the dictum of 'Waste Not, Want Not', India, right at the outset, had adopt a closed-cycle Nuclear Programme. It means, that the Reactor Fuel Rods, after it reaches end of life, would be "broken down", to extract all the goodies it continues to hold. To handle the PFBR fuel through it's entire cycle, the Fast Reactor Fuel Cycle Facility [FRFCF] is in the process of completion. For the pre-loading, it would include a Core Subassembly Plant [CSP] & Fuel Fabrication Plant [FFP]. Spent Fuel Reprocessing would be done at the Fuel Reprocessing Plant [FRP] & Reprocessed Uranium Oxide Plant [RUP], with safe disposal of non-salvageable elements such as actinides being carried out at the Waste Management Plant [WMP].

All said, India's 3-Stage Nuclear Programme, in general, and the PFBR, in particular, has suffered endemic delays in deadlines. A major contributing factor is the relatively scarce global empirical knowledgebase in Fast Reactor Technology. That is because, as noted in the picture above, a Fast Reactor, utilising Th-232, transmutes to U-233 isotope. Owing to the trace amount of Uranium-232 [U-232] generated during the above process, it is not preferred for use in Military application. High doses of the strong Gamma Rays, emitted during U-232 decay would "Fry" any electronic circuitry onboard a weapon & adversely affect any Biological tissue in vicinity. Proponent like to refer to Thorium as a 'Proliferation Proof' Metal. The SOP for U-232 demands remote-handling, with sufficient physical barrier - think 1750 mm thick Concrete wall [1000 mm Outer Wall; 750 mm inner wall]. These can be conveniently fulfilled in a Stationary Power Rector. Thus, the early momentum of Military-driven end use Nuclear Research, saw relegation of Fast Reactor Technology to the proverbial back-burners.

Not many currently operational Fast Reactors. Some of those built earlier have now ceased operation [Superphénix, above], while some concepts never attained "Critical Mass" [pun intended]. Compared to 448 Thermal Reactors in operation worldwide, only around 20-odd Fast Reactors were built. Adding to sensitivities surrounding Fast Reactors, is the need to introduce Plutonium into the mix, a scarce resource with high demand in Strategic applications. Everything considered global co-operation in Fast Reactor technology isn't very vibrant.

As per a response tabled in the Parliament in 2013, India has 11.93 Million MT of proven Monazite Ore reserves, yielding 1.07 Million MT of Thorium Oxide. This roughly translate to it's ability to fulfil India's Electricity requirement for almost 200 years. So, pursuing a path that would lead to a solution guaranteeing self-sustaining, cost-effective Thorium-powered Power Generation is the elixir to aspirations of explosive Economic empowerment & Energy Independence.

It is to the testament of the far-sightedness of India's Foundation-layers, that a decision to this effect, they took, way back in the 50s, at the infancy of India's democratic experiment, the fruits of which, they knew, would be borne many many decades after their physical existence would have become one with Nature.

To that end, India's Fast Reactor programme is pioneering & amongst the most advanced in the world & ambitious in the scope of it's goals. One of the most challenging aspects has been Sodium handling proficiency validation. A Fast Reactor has around 6800% higher heat density than a Conventional Reactor. A 600 MWe Fast Reactor, for example, would liberate 550 MWth/m³ of heat. Compared to that, a similarly-sized mainstream Nuclear Reactor would give out only about 8 MWth/m³ heat. To put it simply, it is 6800% more critical that Designers implement an effective heat removal arrangement in the PFBR.

Sodium demonstrates the desired properties sought for in a Fast Reactor Coolant. It is an excellent heat conductor, with a high boiling point & acceptable specific heat. This permits it's operational use over a wide temperature range, at almost atmospheric pressure. Most critically, it has low Neutron Absorption & Moderation properties. This facilitates high-velocity, high concentration of Neutrons in the Reactor, vital for Breeding. From a safety perspective, it's high Thermal Inertia would give Operators sufficient time to execute a safe shutdown, in case of a Loss Of Coolant Accident [LOCA].

Early efforts to source Pumps from the German Company KSB & the European Consortium of SERENA-FASTEC were dropped in favour of homegrown options, owing to sanction vulnerabilities. The first experimental, indigenous, Sodium-flowing Centrifugal Pump, developed in the 80s, could discharge 50 m³/hr, at a speed of 2,900 rpm.

The Primary Sodium Pump [PSP], developed for the PFBR is amongst the largest such pumps in the world. It's Single-Stage Top Suction [SSTS] design would discharge 15,500 m³/hr of fluid, operating at a speed of 590 rpm. IGCAR has Water-tested the Pump to designed ratings on the specially purposed Rig.

The PFBR houses 2 PSP to circulate Sodium through the Main Vessel. Only the Pumps proposed for the stillborn European Fast Reactor [EFR], discharging 29,650 m³/hr at 531 rpm and the French Superphénix which operated at 500 rpm, discharging slightly more 16,000 m³/hr, were bigger. However, while the former was a vapourware, the latter France already decommissioned. The Russian BN-800 reactor, utilises a lesser capacity Pump.

One interesting concept implementation is a Single Point Tilting Pump Rotor. Owing to Thermal expansion, the Pump, subjected to progressively increasing temperature, before attaining stable operating parameter, would experience Mechanical displacement. To compensate for this, designers decided to position the Pump Shaft with a slight tilt of 0.4 degrees w.r.t. vertical, in it's static condition. As it begins operation, thermal expansion due to rising temperature would re-position it, such that it is aligned vertically at operating condition. At the top, the Pump shaft is guided by a spherical bearing in an inert Argon Gas environment, while hydrostatic Sodium-lubricated bearing supports it from the bottom.

At the SSMC, it uses a vertical shaft type, Single-Stage Bottom Suction [SSBS], centrifugal SSC Pump. It was this Pump, during whose load-trial, Operators observed deviations. A paper titled, 'Design, Manufacturing And Testing Of Secondary Sodium Pump', elaborates on it's development programme undertaken at IGCAR.

The challenges of reliably operating a Pump to handle the volatile Sodium, at high temperatures close to 400^o C, in a Radioactive environment, can not be overstressed. During Commissioning, officials observed excessive wear & vibration in the Electromagnetic [EM] Pumps & the Main Sodium Pump [MSP]. Any failure in coolant operation, would lead to unacceptably high Reactor Temperature, triggering a combination of Boron Poison injection to halt the Chain Reaction, as well as initiating passive safety features to come online, all of which could render such a Reactor unusable for subsequent use.

The highly volatile nature of Sodium, with high oxygen & water affinity, further compound challenges. Therefore, it is imperative that Sodium, heated to liquid form, flows only through an inert non-oxygen-based environment. Following the decision to develop an indigenous solution, an IGCAR-spearheaded effort lead to the development of the Coolant Pumps for the PFBR. The 2018 issue of the Current Science Journal chronicles vital details including design-iterations, performance parameter considerations, Metallurgy & testing methodology adopted towards realisation of this goal, achieved through a Public-Private effort in the country.

 

The PFBR programme has seen technology spin-off & development of fabrication techniques. One of this is the Explosive Welding process, developed in conjunction with DRDO's Terminal Ballistic Research Laboratory [TBRL]. Using this, operators can plug those Water Tubes, measuring 12.7 mm in diameter, which have suffered degradation through prolonged operation. Plastic deformation resulting from the impact of large energy the explosive releases, would fuse the plug to the walls of the SG, forming the desired joint weld.

As mentioned earlier, the Rotatable Plugs enable Operators to feed & remove Fuel Sub-Assembly Rods from the Reactor Core. It would help align the Transfer Arm over the PFBR's Fuel Channels. Proper operation would require it to function with a 0.5 mm positional accuracy.

Design of India's Prototype Fast Breeder Reactor integrates safe operation as a pre-eminent driver. Features such as Core Catcher, multiple gravity-activated Shutdown Systems for the Reactor - CSRDM & DSRDM, utilisation of Natural phenomenon to remove Decay Heat [SGDHR], in-Service Robotic Inspection of Main Vessel,  use of multiple, independently-operating Sensors that working on diverse phenomenon, to monitor the a given parameter, ensure that Reactor's safety features are in the category of the State Of The Art. Significant considerations have been brought to bear on Beyond Design Basis Events [BDBE], while designing the PFBR.

Unfortunate event of the older-generation of the Fukushima NPP Reactor prompted seeking a re-affirmation of the soundness of the PFBR. Resulting from the Task Force undertaken Study to further bolster safety, IGCAR has evolved further SOP & incorporated additional safety features such as increasing Bund Height by more than 70% [from 5.4 m to 9.4 m], incorporating additional redundancies to already existing redundancies, among others. Globally, the PFBR would rank amongst the safest Reactors to operationalise.

Thanks to the 1 2 3 Agreement, India can now source, both, Nuclear Reactor & Fuel from overseas OEM & Mines respectively. It has been pursuing matters in these fronts, with middling success. In light of this windfall, coupled with perceived delays encountered with India's 3-Stage Nuclear programme, one could be vulnerable to entertain thoughts of ending the programme, pursuing the import route, instead.

Already murmurs in some corners have begun suggesting so. A trial balloon, of sorts, to gauge perception, before scaling up rhetoric. India's Atomic Energy Programme has, justifiably, enjoyed the backing of successive Governments, cutting across political affiliations. It is unlikely that support would waiver anytime in future. However, one must be on guard to avoid being seduced by such ideas from creeping into popular narrative. The 3-Stage Nuclear Programme is an endeavour of National self-reliance & development, that ought not to be deviated from.

Godspeed

Also Read: How A Chinese Transfer Helped India Power It's Reactors - A One-Off Instance