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WWER Fuel with accident tolerant cladding


Study of Accident-Tolerant Claddings for WWER Type Fuel

Tech Area / Field

  • FIR-ENG/Reactor Engineering and NPP/Fission Reactors
  • FIR-MOD/Modelling/Fission Reactors
  • FIR-NSS/Nuclear Safety and Safeguarding/Fission Reactors

3 Approved without Funding

Registration date

Leading Institute
Nuclear and Radiation Safety Center of Armenian Nuclear Regulatory Authority, Armenia, Yerevan

Supporting institutes

  • Institute of Nuclear Physics, Kazakstan, Astana


  • Brookhaven National Laboratory, USA, NY, Upton\nBrno University of Technology, Czechoslovakia, Brno

Project summary

The current status in the area of study
In 2011, the accident in the Fukushima Daiichi nuclear power plant, due to earthquake and consequential tsunami, raised conceptual concerns about zirconium based claddings behavior in steam environment. Fukushima accident revealed unwanted performance of the zirconium based fuel rods during severe accidents, particularly, unacceptable oxidation and accelerated hydrogen production under LOCA conditions. Therefore, new concept of accident tolerant fuel, that should exclude or substantially diminish oxidation and hydrogen production potential of fuel rods under design-basis accident and severe-accident conditions, became the primary focus for the next generation LWR fuels.
Based on comprehensive analysis of above-mentioned desirable accident tolerant features as well as existing constraints, like manufacturability, backward compatibility with current fuel fabrication facilities, fuel handling equipment, and LWR (WWER) designs and economics lead to several cladding technologies that could be pided in 3 main groups: Zr-alloy coatings, hybrid materials, completely new materials.

One of the key aspects contributing on economics of accident tolerant fuel is neutronics analysis. The low parasitic absorption cross-section of thermal neutrons of Zr-based alloys resulted in on favorable neuron balance for LWR (WWER) reactors that enables low enriched fuel. Unfortunately, almost all proposed new cladding materials have higher absorption cross-section of thermal neutrons than Zr-based alloys, therefore reactivity penalty is expected for the new candidate materials.
The main research towards to accident tolerant fuels with regard of neutronics is focused for western square lattice type fuel assemblies with silicon carbide and FeCrAl coatings as well as stainless steel. Proposed research targets WWER type hexagonal lattice fuels with ZrN coating since it’s not systematically investigated as the cladding for fuel rods and because of its high thermal conductivity, low neutron capture cross-section and chemical compatibility with existing fuel cycle technology.
The main objective of this project are:
    · Study and quantify the impact of the major accident tolerant claddings including ZrN in the WWER fuel in terms of safety and economics;
    · Manufacturing of ZrN coatings and experimental investigation of ZrN claddings before and after the corrosion tests in water vapor environment
    Expected results and their application

The main result of the project will be selected optimum accident-tolerant fuel for WWER reactors from neutronics point of view. Implementation of the project will deliver:
    · Optimized WWER type fuel design with accident-tolerant cladding;
    · Reference core designs for WWER-440 reactor loaded with accident-tolerant fuel;
    · Optimized core loading patterns for WWER-440 reactor loaded with accident-tolerant fuel;
    · State-of-the-art data on properties of ZrN accident tolerant claddings;
    · Assessment of economic feasibility of accident-tolerant fuel with ZrN coating for WWER type reactors.
    Scope of Activities. The following activities will be carried out in the framework of the Project:
      · Development of WWER-440 fuel assembly models with major accident tolerant claddings including ZrN by MCNP6/KENO-VI codes;
      · Calculation of reactivity change of fuel assembly with accident tolerant cladding in course of its depletion in the WWER-440 reactor core;
      · Fuel Assembly lattice level design optimization studies;
      · Development of WWER-440 reactor core 3D model by PARCS-PATHS;
      · Calculation of reactivity feedback coefficients;
      · Three-dimensional core design study at steady state ;
      · Development of neutron-nucleus cross-section library; Development of optimal core loading patterns;
      · Fuel Cycle Analysis and Core Design Optimization;
      · Fuel cycle economic analysis;
      · Development of methods of coating Zr claddings with ZrN;
      · Coating of Zr claddings with ZrN;
      · Investigation of structure and phase composition of developed coatings and stability of coatings in the steam environment;
      · Investigation of structure and phase composition of developed coatings after corrosion tests;
      · Electron-microscopic investigation of developed coatings after corrosion tests;
      · Investigation of ZrN claddings before and after the corrosion test in water vapor at T = 700 °C.
    Research will be conducted in accordance with the recommendations of the IAEA and the relevant international safety standards .


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