Assessment of radioactive contamination in primary circuit of WWER-440 type reactors by computer code OSCAR for the decommissioning case

International audienceThe article presents the results of modeling of the contamination of primary circuit of WWER-440 type reactor.The modeling has been performed using the OSCAR computer code (Nuclear research Centre in Cadarache, CEA,France), version V1.3 for decommissioning of nuclear power plants, taking into account the peculiarities of theWWER-440 reactor primary circuit, such as geometry, volumes, operational regime, materials. The results havebeen analyzed in the light of the scaling factor approach with the aim to demonstrate the modeling capabilitiesto identify the possibility of scaling factor application and to reproduce the activity correlation between difficultto measure and key nuclides. Calculated scaling factors for corrosion products are comparable with the ones ofother nuclear power plants. Calculation results of surface activity contamination confirmed the applicability of $^{60}$Co as a key radionuclid

Simulations of corrosion product transfer with the OSCAR v1.2 code

International audienceActivated Corrosion Products (ACPs) generate a radiation field in PWRs, which is the major contributor to the dose absorbed by nuclear power plant staff working during shutdown operations and maintenance. Therefore, a thorough understanding of the mechanisms that control the corrosion product transfer is of the highest importance. Since the 1970's, the R&D strategy in France has been based on experiments in test loops representative of PWR conditions, on in-situ gamma spectrometry measurements of the PWR primary system contamination and on simulation code development. The simulation of corrosion product transfers in PWR primary circuits is a major challenge since it involves many physical and chemical phenomena including: corrosion, dissolution, precipitation, erosion, deposition, convection, activation… In addition to the intrinsic difficulty of multi-physics modelling, the primary systems present severe operating conditions (300 °C, 150 bar, neutron flux, fluid velocity up to 15 m.s-1 and very low corrosion product concentrations). The purpose of the OSCAR code, developed by the CEA in cooperation with EDF and AREVA NP, is to predict the PWR primary system contamination by corrosion and fission products. The OSCAR code is considered to be not only a tool for numerical simulations and predictions (operational practices improvements and new-built PWRs design) but also one that might combine and organise all new knowledge useful to progress on contamination. The OSCAR code for Products of Corrosion, OSCAR PC, allows researchers to analyse the corrosion product behaviour and to calculate the ACP volume and surface activities of the primary and auxiliary systems. In the new version, OSCAR PC V1.2, the corrosion product transfer in the particulate form is enhanced and a new feature is the possibility to simulate cold shutdowns. In order to validate this version, the contamination transfer has been simulated in 5 French PWRs with different operating and design characteristics. After a description of the models of the main transfer mechanisms, the paper presents the calculated ACP surface and volume activities, the calculated concentrations of metallic elements and their comparisons with on-site measurements for one of the 5 validation cases. The simulations of a steam generator replacement and a cold shutdown are also presented. There is a good agreement between the OSCAR PC V1.2 results and the measured values during power operation and cold shutdown as well. Furthermore, the variations with operating cycle of the surface activities are correctly reproduced. Compared to the previous versions, these improvements are mainly due to the improvement of the thermodynamic database of the OSCAR chemistry module, PHREEQCEA, and to the enhancement of the corrosion product transfer in the particulate form

The OSCAR code: a simulation tool to assess the PWR contamination for decommissioning

International audienceKnowing the contamination state of the end-of-life nuclear reactor systems by Long-Lived RadioNu-clides (LLRNs) is a key stage for the decommissioning process. Indeed, the initial state is necessary to optimize the decommissioning works and to manage the radioactive waste as well. To address this issue, the contamination state is usually characterized using different types of techniques: in-situ gamma spectrometry, gamma camera scanning, dose rate measurements, , , measurements of samples obtained by smears or scrapings and then chemical separation processes, scaling factor approach… To reduce the amount of these measurements and thus the Occupational Radiation Ex-posure (ORE) and the decommissioning costs, a method is to assess the level of contamination by simulation. Furthermore, at the design stage of a new reactor, its decommissioning has to be taken into account and a simulation tool, such as the OSCAR code, can predict the radioactive source term at the end of life of a future reactor.The OSCAR code (Outil de Simulation de la ContAmination en Réacteur - tOol of Simulation of Con-tAmination in Reactor) has been developed by the CEA in collaboration with EDF and Framatome since the 1970s. The OSCAR code simulates the production and transfer of Activated Corrosion Products (ACPs) and Actinides and Fission Products and (AFPs) in the reactor systems and thus calculates the masses and activities of radionuclides deposited inside piping and heat exchangers of different circuits. As the OSCAR code has been originally devoted to mainly an industrial objective, which is the reduction of the Occupational Radiation Exposure (ORE) for operating PWRs, it deals with the main ACPs, 60Co, 58Co, 54Mn…, which are short-lived radionuclides. Nevertheless, it also cal-culates LLRNs of interest for decommissioning, such as 55Fe, 63Ni, 90Sr, 239Pu…, most of which are difficult to measure. The OSCAR code is validated through on-site measurements, including the EMECC campaigns, an operational experience feedback unique in the world, that consist of measur-ing the gamma surface activities mainly of the PWR primary system but also of auxiliary systems.After a presentation of the features and modeling of the OSCAR code, the paper will present some OSCAR simulation results of long-lived ACPs and AFPs deposited inside PWR circuits and their comparison with measurements. Perspectives of the OSCAR code on the decommissioning pro-grams will also be discussed

The OSCAR code package : A unique tool for simulating PWR contamination

International audienceUnderstanding the PWR primary circuit contamination by corrosion products, fission productsand actinides is a crucial issue for reactor operation and design. The main challenges aredecreasing the impact on personnel exposure to radiation, optimizing the plant operation,limiting the activity of the wastes produced during the reactor lifetime and preparingdecommissioning.In cooperation with EDF and AREVA NP, CEA has developed the OSCAR code package, aunique tool for simulating PWR contamination. The OSCAR package results from the mergingof two codes, which simulate PWR contamination by fission products and actinides (PROFIPcode) and by activated corrosion products (PACTOLE code).These two codes have been validated separately against an extensive set of data obtained over 40years from in-situ gamma spectrometry measurements, sampling and analysing campaigns ofprimary coolant, as well as experiments in test loops or experimental reactors, which arerepresentative of PWR conditions.In this paper, a new step is presented with the OSCAR code package, combining the features ofthe two codes and motivated by the fact that, wherever they originate from, the contaminationproducts are subject to the same severe conditions (300 °C, 150 bar, neutron flux, water velocityup to 15 m.s-1) and follow the same transport mechanisms in the primary circuit. The main processes involved are erosion/deposition, dissolution/precipitation, adsorption/desorption,convection, purification, neutron activation, radioactive decrease.The V1.1 version of the OSCAR package is qualified for fission products (Xe, Kr, I, Sr),actinides (U, Np, Pu, Am, Cm) and corrosion products (Ni, Fe, Co, Cr).This paper presents the different release modes (defective fuel rod release, fissile materialdissemination, material corrosion and release), then the processes which govern contaminationtransfer, and finally, we give examples of the comparison of the OSCAR package results withmeasurements in French PWR primary circuit obtained for representative radioisotopes : $^{133}$Xe,$^{90}$Sr, $^{58}$Co, $^{60}$Co. In particular, we focus on the main upgrades in the OSCAR simulations compared to thePROFIP and PACTOLE codes : adaptation of the MARGARET module to assess fission productrelease out of fuel pellets in a defective rod, adsorption/desorption model development forstrontium behaviour, multi-criteria calibration of input data which are not well known forcorrosion product simulation