Despite the economic downturn, a radical change of plan and rumours of the project’s demise, the Russians appear to have been working steadily away on realising their vision of developing floating nuclear power plants based on the well established KLT-40 marine reactor, as widely used in icebreakers
Construction of the pilot power unit for the first such floating power plant started in 2007 at FSUE PO Sevmash in Severodvinsk. The power plant was originally intended to be located there after completion to provide power to the shipyard and for other consumers in Severodvinsk. But in 2008, the decision was taken to move the construction of the pilot floating power plant to the JSC Baltic Factory (in Saint-Petersburg). According to Atomenergoprom this was because of the large number of defence orders at Sevmash.
Transferring construction from Sevmash opened up the possibility of changing the location of the first installation. A thorough review of possible options resulted in the selection of Vilyuchinsk in Kamchatka as the new site of the pilot plant.
The contract for completion of the floating power unit was signed with JSC Baltic Factory in February 2009. According to the contract, factory testing is scheduled for the end of 2011, first criticality for 2012, delivery to the customer for the end of 2012, and final commissioning for 2013.
In fact, says Atomenergoprom, the world economic crisis has had practically no effect on the construction schedule. Rather, the main challenge facing project implementation has been organising the design of the integrated plant and enlisting and co-ordinating industry co-operation. The project involves over 180 “backbone” facilities and organisations across the nuclear, heavy engineering and ship-building sectors.
However the main difficulties have been resolved and the key task now is to complete and commission the pilot plant as soon as possible and prepare for deployment on a larger scale.
The Russians call the floating plant “PATES”, while the reactor plant model is the KLT-40S, which, as already noted, is based on the standardised KLT-40 icebreaker reactor, but with advanced features, aimed at increasing safety and reliability, with upgraded components and safety systems, including use of passive features.
Main data for the the KLT-40S reactor plant are presented in the table, right. Among the main features are:
• Use of vessel-type PWR, which is well established technology around the world, water-moderated and water-cooled with good self-protection properties.
• Layout of major components that excludes the possibility for large-scale primary circuit depressurisation.
• Four-loop configuration, with forced and natural primary coolant circulation in the steam generators.
• Use of direct-flow, coil-type steam generators.
• Location of all primary circuit auxiliary system nozzles in the upper part of the reactor block.
• Equipping of all primary circuit pipework with outflow limiters, preventing large and medium primary coolant leaks.
• Use of passive principles for operation of reactor scram, core cooling and reactor cooldown systems.
• Use of gas pressurisation system.
Reactor safety and core features
There are three independent emergency shutdown systems, including both absorber rods and liquid absorber. The shutdown reactor core is cooled by a multi-train emergency cooldown system (ECS): a double-train active system employing the steam generators and heat exchangers of circuits 1-3, with unlimited duration; and a double-train passive system providing reactor heat removal for 24 hours without operator intervention under full loss of power conditions.
In case of primary circuit depressurisation, emergency core cooling is provided by a multi-train emergency core cooling system (ECCS):
a double-train passive system using hydroaccumulators; a double-train active system with make-up pumps; and a double-train active system with recirculation pumps.
Additionally, reactor scram and heat removal systems can be initiated directly by self-activating systems based on a parameter such as reactor pressure.
Barriers to release of radioactive substances are increased to five (fuel matrix, fuel element cladding, primary circuit, containment, and reactor compartment protective enclosure), thanks to the use of low enrichment cermet fuel.
In the safety analysis, a wide spectrum of hypothetical, beyond-design-basis, accidents were considered, including safety system failures and/or personnel errors exacerbating initial events.
The beyond-design-basis accidents addressed include: complete loss of power at the plant with failure of safety control systems; primary circuit pipe break with full blackout or failure of active emergency core cooling systems; and transients involving safety control system failure.
The safety assessment of the?KLT-40S reactor showed that under hypothetical, beyond-design-basis, accidents, personnel have large time margins for accident control due to the application of passive safety systems.
In accidents involving loss of primary coolant and ECCS (emergency core cooling system) pump equipment failure, core preservation under water (in flooded condition) is provided for no less than 2 hours.
In the case of accidents involving full loss of power, reactor heat removal is maintained for
These margins, resulting from passive safety measures, are considerably better than those for the standard KLT-40 ship reactor.
In addition the KLT-40S reactor core has a number of useful features that derive from
its pedigree as a floating power source:
non-proliferation characteristics (uranium enrichment not higher than 19.7%); high manoeuvrability; high reliability; long service life and durability.
Main core data is summarised in the table, right.
Floating plant design
The floating plant itself is a smooth-deck, non-self-propelled, ship with a hull that is close to rectangular and a multi-tiered superstructure.
The hull is all-welded and equipped with special towage and securing systems for use at the chosen location. The underwater part of the hull has electrochemical corrosion protection and a paint-and-lacquer coating.
The reactor compartment and a nuclear fuel handling compartment are located at the mid-level of the ship. The turbogenerator and electrical compartments are located in the bow, while a compartment for auxiliaries, as well as living quarters are in the stern.
The floating plant has two reactors and two steam turbines.
Each of the reactors is enclosed in a leak-tight steel containment integrated with the hull and designed to cope with the maximum pressure possible in accident conditions.
The floating power plant is designed to withstand the following external loads: winds of 60 m/s; earthquake up to 9 on the MSK 64 scale; aircraft crash; lightning strike; explosions and fires. Systems are designed to remain operable in the case of an impact load of at least 3 g acting in any direction, under tilting or rolling conditions.
There will be a total of eight emergency diesel generators per floating plant.
The envisaged number of plant staff is 176 people, including two shift crews, plus auxiliary and management personnel. Preparations have begun for staff recruitment and training.
Electric power will be delivered to shore via a 10 kV cable network, with the option of a substation with step-up transformer (to 110 kV) for transmission to more distant consumers.
In addition the plant is designed to also supply heat, eg for district heating, via an intermediate circuit with water at 150-170 deg C.
As would be expected for a small plant, the per-MW capital cost of the 70 MW floating power plant is relatively high (compared with say a typical VVER-1000 project), about 240 million roubles (6 million euros).
But the target market of the floating plant is remote, difficult-to-reach and hostile locations (eg permafrost regions) where construction of large nuclear plants is not feasible (or would be prhibitively expensive) and where the low per demand would not justify it anyway.
The competitors to the PATES concept in such a region would generally be fossil-fuelled plants, which are cheaper to deploy but have higher operating expenses due to bigger fuel costs.
Overall, taking into account operating and fuel costs, the per-kWh costs for the PATES plant in such regions are estimated to be significantly lower than for fossil alternatives – despite the higher capital costs.