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The OSCAR-FP V1.4 code simulation of fission product and alpha emitter contamination in PWR circuits

Abstract : Understanding the PWR primary circuit contamination is a crucial issue for reactor operation and design, as well as in the perspective of decommissioning. For this purpose, the CEA has developed, in cooperation with EDF and Framatome, the OSCAR code package, a unique tool to simulate PWR contamination by corrosion products, fission products (FP), and actinides.This paper presents a general overview of OSCAR-FP V1.4, the latest version of OSCAR computation scheme dealing with fission product and actinide contamination. The source term calculation for these nuclides and the behavior considered in the primary circuit are described in detail, as well as the validation process against primary activity measurements. Fission products are released in the primary circuit in case of a fuel cladding defect, depending on the nuclear fuel characteristics composition, temperature, and burn-up. Therefore, the CEA fuel code ALCYONE is included in OSCAR-FP and allows calculating the source term for these nuclides. However, fission product release into rod free volumes is increased due to fuel oxidation in case of a clad defect. The fuel code ALCYONE has then been adapted to defective fuel situation through the adjustment of different parameters enhanced diffusion in the fuel grain, enhanced grain boundary fracturing, and reduced fuel thermal conductivity. In addition, in the event of significant cladding damage, fuel oxide particles may disseminate in the primary circuit. These particles solubilize very slowly and are still present in the primary circuit several cycles after the dissemination. They include long life fission products as well as heavy nuclides among which alpha emitters and fissile nuclides. They are mainly deposited on the primary surfaces and are subject to further erosion and deposition mechanisms. As their behavior is linked to the one of corrosion product particles, a specific OSCAR computation scheme is used, allowing coupled simulation between corrosion products and actinides. Calculated primary activities are compared to measured fission product and alpha activities, obtained from primary gamma activity monitoring as well as from sampling and analysis campaigns of primary coolant or surface deposits. Code qualification is obtained for different types of nuclides i) gaseous and volatile gamma emitters Xe, K, I, Cs whatever the isotope half-life, ii) alpha emitters, which are mainly insoluble, iii) long life beta emitter $^{90}$Sr, which undergoes adsorption/desorption mechanism and is sensitive to pH. The paper shows that the OSCAR-FP V1.4 code is a powerful tool to study fission product and alpha contamination in PWR primary circuits, and is helpful for fuel and waste management as well as for the alpha risk assessment. Moreover, new results obtained with the V1.4 version are highlighted mechanistic erosion and deposition models have been calibrated for corrosion products and applied to actinides. This provides a good simulation of actinides with very few adjusted parameters, and confirms the coupled behavior of corrosion products and actinides in the primary circuit.
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Submitted on : Wednesday, December 4, 2019 - 2:56:58 PM
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  • HAL Id : cea-02328973, version 1

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Jb. Genin, T. Jobert, N. Engler. The OSCAR-FP V1.4 code simulation of fission product and alpha emitter contamination in PWR circuits. The 21st international conference on water chemistry in nuclear reactor systems (NPC 2018), Sep 2018, San Francisco, United States. ⟨cea-02328973⟩

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