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WP 2 : Screening irradiation of novel Inert Matrix Fuels in LWR conditions

The objective of WP2 “Screening irradiation of novel Inert Matrix Fuels in LWR conditions” is the fabrication, irradiation and post-irradiation examination of CERMET Inert Matrix Fuels loaded with PuO2.

  • T2.1: Fuel design will be performed by SCK•CEN in cooperation with NRG. The design preparation should from the beginning interact with the fabrication laboratories. Design preparation includes neutronic and fuel performance assessment, burnup evolution, etc. taking into account the specific irradiation conditions of the PWR loop of the BR-2 Materials Test Reactor. The design report sets the fabrication parameters (enrichment, dimensions, end-pellet composition) of the fuel pellets. The fabrication and control documents are drafted on the basis of the design document by the fabrication facility (ITU and NRG) and submitted for approval to the reactor operator.
  • T2.2: Fuel fabrication will be done by ITU and NRG. One matrix is Mo (NRG production), the other is Fe-Cr (ITU production). For each matrix, two fuels will be produced, one with a micro-dispersion (< 60 µm) of sol-gel PuO2 beads and a second one with a macro-dispersion (>60 µm) of these beads. Fabrication, fabrication control and detailed characterisation include the manufacturing of the nuclear fuel, the assembly of these fuels in small rodlets. Fuel and cladding dimensions are dictated by the experimental facility and the objective of rapid accumulation of burnup. Fuel dimensions are anticipated to be 6 mm diameter and a fuel column of 150 mm for each fuel pin. Cladding will be zircaloy. Fabrication control includes assessment of geometry, surface finish, isotopic composition, impurity analysis, thermal stability check, humidity and total H2 content controls, total density and open porosity, ceramographic observation (grain size, porosity)… SCK•CEN will perform the analysis of impurities in the Mo-CERMET fuel. Centreless grinding of the pellets and roughness determination will be performed by ITU prior to fabrication of the rodlets at ITU. NRG will organize transport of the Mo- CERMET pellets to ITU.
  • T2.3: Irradiation will be performed in the Pressurised Water Loop CALLISTO of the BR-2 reactor. This loop simulates the irradiation conditions of a commercial PWR and offers high flexibility for intermittent unloading and loading of the individual fuel pins for hot-cell investigations of the experimental fuel pins. The loop is furthermore highly instrumented such that the power of the fuel pins can be monitored on-line. The intermittent out-of-pile non-destructive tests will include gamma spectrometric analysis to calibrate the on-line power measurements. Furthermore, the mechanical stability of the pins and the cladding integrity will be checked at regular intervals.

This WP will start at T0 with fuel design. The design should be completed by T0+3 such that the fuel fabrication can be completed by T0+15. Transport, inspection, loading will take 3 months, and irradiation will start at T0+18 and ideally be completed by T0+30 with a first intermittent NDT campaign at T0+22. The final NDT campaign can start at T0+30 and should be completed by T0+36.

The irradiation is anticipated to be performed in the same in-pile section of the PWR loop CALLISTO that is hosting other irradiation experiments. Failure risks of the accompanying experiments will have their impact on the other projects, but apart from possible delays in execution, the continuation of each experiment can be guaranteed to be independent from each other.

One should furthermore analyse the fuel fabrication capacities with regard to requested fabrication specifications and controls (reactor operation and safety authorities). Transport problems might have their impact on the overall timing of the work package, but not make the experiment impossible.