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Session Overview
3.02-2: Fast Neutron Reactors – Sodium Fast Reactors - II
Tuesday, 17/Mar/2020:
1:45pm - 3:15pm

Session Chair: David SETTIMO, Electricite de France (EDF), France
Location: L-1011

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Additional considerations on the design of small modular sodium-cooled fast reactor

Timothée Kooyman, Pierre Sciora, Christine Coquelet-Pascal

CEA Cadarache

Small modular reactors have attracted significant attention in the past years, due to potentially more favorable economics and enhanced safety. Numerous designs have been proposed considering either the use of a thermal or a fast spectrum. This paper investigates in more details the specificities of the design of a small modular sodium-cooled fast reactor. Indeed, by leveraging the advantages of a fast neutron spectrum and the high output temperature of the primary coolant, such a reactor could be used for multiple purposes (heat, desalinization, H2 production) while reducing the plutonium stockpiles. Such reactors are expected to be deployed in a grid-independent in potentially isolated areas and thus would benefit from a very long cycle length, in order to maximize their capacity factor.

However, the size of such a core combined with the fast spectrum physics leads to a strenuous constraints on the reactivity management system and thus on the cycle length. Indeed, three conflicting behaviors are determining for the core design: the number of control rods should be minimized to maximize the fuel volume fraction; the cycle length should be maximized for economic reasons; the reactivity loss of the core should be minimized to reduce the reactivity control requirements. Combined with manufacturing limits on the plutonium content in the fuel and operating limits in the core, these three guidelines are sufficient to entirely characterize the design space of potential sodium-cooled fast reactors. It is thus shown in this paper that the geometrical design of control rod mechanisms is a key parameter limiting the cycle length of small fast reactor and that it is not possible to achieve significantly longer cycle length using current technologies.

Fuel cycle closure for high power fast neutron reactor

Alexander Egorov, Valerii Rachkov, Elena Rodina, Iurii Khomiakov

Innovative and Technology Center by "PRORYV" Project

The Russian Federation is developing a number of technologies within the «Proryv» project for closing the nuclear fuel cycle utilizing mixed (U-Pu-MA) nitride fuel. Key objectives of the project include improving fast reactor nuclear safety by minimizing reactivity changes during fuel operating period and improving radiological and environmental fuel cycle safety through Pu multi-recycling and MA transmutation.

This advanced technology is expected to allow operating the reactor in an equilibrium cycle with a breeding ratio equaling approximately 1 with stable reactivity and fuel isotopic composition. Nevertheless, to reach this state the reactor must still operate in an initial transient state for a lengthy period (over 10 years) of time, which requires implementing special measures concerning reactivity control.

The results obtained from calculations show the possibility of achieving a synergetic effect from combining two objectives. To sustain the required reactivity margin on burnup the initial fuel loading includes MA from thermal reactor spent fuel. This should be combined with using reactivity compensators in the first fuel micro-campaigns.

The work presents the findings obtained from modeling the entire lifecycle of a 1200 MWe fast reactor, the transition to an equilibrium state and the changes occurring in spent nuclear fuel nuclide and isotopic composition. The work also demonstrates the possibility of completely utilizing MA from thermal and fast reactor spent fuel in next generation FRs without the need of special actinide burners.

Manufacturability of SFR core materials for fuel assemblies - Status of industrial prospection and research on manufacturing processes

Fabrice Mazaudier, Patrick Olier, Pierre-François Giroux, A. Jankowiakb, Hicham Maskrot, Philippe Dubuisson

Commissariat à l'Energie Atomique

Among the technical challenges we face for the SFR, the manufacturability of core materials, following the conception, specifications and controls are pregnant. The conception and specifications have been pushed forward while the industrial manufacturing routes for producing specific SFR components are gradually disappearing.

The SFR core includes a few hundred of fuel sub-assemblies. Each of them is made up of a few hundred of pins which contain plugged 15-15-Ti stainless steel cladding, filled with fuel pellets and surrounded by a space wire. Pins form a bundle mounted on a hanging grid and then inserted in a martensitic wrapper (hexagonal tube). In the upper end of the 4-meter wrapper, specific pre-form part is docked e.g. neutron shielding filled with boron carbide. The core architecture also consists in several rows of reflector sub-assemblies with magnesium oxide.

We present a few examples of manufacturing routes investigated for each materials or specific components or devices such as fuel cladding, space wire, hexagonal wrapper, B4C and MgO sintered pellets. We also study the manufacturability of more specific devices i.e. support grids for fuel clad, upper neutron shielding, flow devices, by additive manufacturing. For illustrative purposes, we map out the results of our investigations on the classical TRL scale to compare objects or components for which industrial tools and routes are potentially available to the supply and those for which developments are needed.

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