The Phebus Fission Product (FP) program studies key phenomena and phenomenology of severe accidents in water-cooled nuclear reactors. In the framework of the Phebus program, five in-pile experiments were performed that cover fuel rod degradation and behavior of FPs released via the coolant circuit into the containment vessel. Analyses of FP behavior were performed using standard stand-alone versions of codes with input data mainly taken from measured boundary conditions.The FPT2 test used 33 GWd/t uranium dioxide fuel enriched to 4.5%, reirradiated in situ for 7 days to a burnup of 130 MWd/t. This test was designed to study low-pressure FP release and transport through a primary cooling system that included a noncondensing steam generator, with release into the containment vessel in steam-poor conditions. This test also investigated how diluted boric acid in the injected steam influenced FP speciation. In the containment vessel, the objective was to study iodine chemistry in an alkaline sump under evaporating conditions.The analytical approach consisted of progressive studies to explore and explain the main disagreements between base-case calculations and experimental results. Regarding releases in slightly degraded fuel zones, the fission gas behavior and characteristics are shown to be satisfactorily reproduced by the calculations. Electron microprobe analyses also validate the mechanisms for Mo and Ba releases, while the Cs mechanism requires further investigation. Concerning the transport of FPs, a strong connection is shown to exist between Cs, I, Mo, and Cd that substantially impacts vapor-phase chemistry in equilibrium and iodine volatility. Most of the cesium released from fuel is shown to rapidly convert into cesium borates and then into cesium molybdates when the molybdenum release becomes significant at the end of the hydrogen production phase. The main predicted iodine vapor species is cesium iodide. A low fraction of gaseous hydrogen iodide is also calculated at low temperature, but this fraction was found to be strongly dependent on the Cd release kinetics. Hydrogen iodide is the main candidate predicted by equilibrium chemistry calculations to explain the persistence at low temperatures of volatile iodine. Nevertheless, potential limitations on chemical kinetics in the primary circuit zones, characterized by a sharp decrease in temperature, could also be an explanation and are currently under investigation.In the containment, gas-phase reactions were found to predominate in governing iodine chemistry. As for the previous Phebus tests, the gaseous iodine fraction measured in the containment early in the test is thought to come from the primary circuit. However, this low gaseous iodine was hardly tractable by the few dedicated samplings mounted in the primary circuit cold leg upstream from the containment entrance. By favoring hydrolysis reactions of volatile iodine species, the alkaline sump is shown to act as an iodine trap despite the evaporating conditions that prevail during the long-term chemistry phase. However, during this latter phase, a persistent, low-level concentration of gaseous iodine was reached in the long term, as during the previous FPT0/1 tests, indicative of a competition in the containment between iodine traps and sources. Aside from the aerosol particles injected by the primary circuit, in situ iodine oxide particles were found to be continuously forming from the decomposition of I-2 and ICH3 by air radiolysis products. These particles are suspected to be fine, implying that they predominantly deposit by diffiusion on all the containment surfaces. Therefore, in the long term, both the persistence of gaseous iodine and the survival of iodine oxide particles are shown to exist in the containment.

The Phebus FP in-reactor integral experiments provided new insights into iodine transport through the primary circuit. Indeed, in these tests transported iodine was often found not associated with caesium as generally postulated up to now. Several iodine species were experimentally shown to have been transported in the hot leg at 700°C, while a fraction was also suspected to be in a gaseous form in the cold leg at 150°C. For a better estimate of the iodine source term to the containment, both in terms of speciation and quantity, it becomes thus necessary to reconsider iodine species behaviour along their pathway in the reactor coolant system (RCS).

Cette revue présente les périodes radioactives, les énergies de désintégration, et les principales raies γ et α de tous les isotopes radioactifs. Les tableaux ont été obtenus à partir d'une Banque de Données où se trouvent l'ensemble des raies γ et α.

L'évolution de la microstructure en fonction de la dose d'irradiation a été étudiée pour des lames épaisses de cuivre irradié par des ions cuivre de 500 keV. Une comparaison entre les résultats obtenus sur des échantillons dégazés et non dégazés nous a permis de montrer que les gaz dissous dans le matériau aidaient à la germination des boucles d'interstitiels. Les relations entre les boucles d'interstitiels et les cavités ont été étudiées et l'on en tire quelques conséquences en ce qui concerne la croissance des cavités et l'effet des surfaces libres.

Des lames minces de cuivre dégazées par recuit ont été implantées avec des doses variables d'oxygène, d'hélium, d'hydrogène et de carbone. Des cavités se forment dans les échantillons contenant de l'oxygène ou de l'hélium. Pour des teneurs inférieures à 30 ppm at. l'hélium est plus efficace que l'oxygène en ce qui concerne à la fois la germination des boucles d'interstitiels et des cavités. Pour les fortes teneurs en gaz, la densité de cavités obtenue, décroit pour l'hélium mais reste constante pour l'oxygène. Une interprétation de ce résultat basée sur les différences entre les solubilités de ces deux gaz dans le cuivre est donnée. L'effet d'une implantation de carbone dans des échantillons contenant déjà du gaz est également rapporté.

Calculational results are presented on the decay heat associated with the thermal fission of /sup 235/U and /sup 239/Pu. Calculations are based on the summation of the energies which are released by individual fission products. Two cases have been considered: the first corresponds to one instantaneous fission, the other to a 900 days irradiation time. In both cases the sensitivities of the afterheat to respectively independent yields, half-lives, average beta plus gamma energies of 512 instable fission products have been derived. This information has been used to calculate the afterheat uncertainties from experimental and evaluated nuclear data errors, when available. Results relating to the instantaneous fission of /sup 235/U and /sup 239/Pu are compared to calorimetric measurements between 100 and 10/sup 5/ second cooling time. Errors in the afterheat corresponding to a 900 days irradiation time have been estimated for cooling times ranging from 1 to 1000 seconds which are appropriate for Loss of Coolant Accident analyses in light water reactors. The computer programmes which have been developed can be applied to any irradiation and cooling time condition.

L'intérêt essentiel du bombardement par des ions lourds est de produire très rapidement, en quelques heures, un nombre important de déplacements d'atomes, que l'on n'obtient en pile qu'après une année d'irradiation au moins.Cette technique présente cependant des inconvénients : faible pénétration des ions lourds, production de défauts non homogène et implantation d'atomes étrangers dans l'échantillon ... Nous avons étudié la formation de cavités par agglomération de lacunes (gonflement) dans le nickel bombardé par des ions Ni+ de 500 keV.Le gonflement varie avec la température et passe par un maximum vers 620 OC.Un chargement préalable en hélium augmente le nombre de cavités mais diminue le gonflement.Le gonflement augmente avec la fluence de façon linéaire.Le nombre et la taille des cavités augmentent rapidement au début de l'irradiation.Nous avons étudié l'évolution de la densité de dislocations dans un acier austénitique bombardé par des ions Ni+.Nous avons observé une densité élevée de dislocations entre 400 et 700 OC.Cette densité est indépendante de l'état initial du matériau (hypertrempé ou écroui) et de la fluence dès que celle-ci atteint une valeur voisine de 10 déplacements par atome.Elle augmente avec le flux et diminue lorsque la température augmente.

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