Modelling of Zry-4 cladding oxidation by air, under severe accident conditions using the MAAP4 code

International audienceIn a nuclear power plant, a potential risk in some low probability situations in severe accidents is air ingress into the vessel. Air is a highly oxidizing atmosphere that can lead to an enhanced core oxidation and degradation affecting the release of Fission Products (FP), especially increasing that of ruthenium. This FP is of particular importance because of its high radio-toxicity and its ability to form highly volatile oxides. Oxygen affinity is decreasing between Zircaloy cladding, fuel and ruthenium inclusions in the fuel. It is consequently of great need to understand the phenomena governing cladding oxidation by air as a prerequisite for the source term issues. A review of existing data in the field of Zircaloy-4 oxidation in air-containing atmosphere shows that this phenomenon is quantitatively well understood. The cladding oxidation process can be divided into two kinetic regimes separated by a breakaway transition. Before transition, a protective dense zirconia scale grows following a solid state diffusion-limited regime for which experimental data are well fitted by a parabolic time dependence. For a given thickness, which depends mainly on temperature and the extent of pre-oxidation in steam, the dense scale can potentially breakdown. In case of breakaway combined with oxygen starvation, cladding oxidation can then be much faster because of the combined action of oxygen and nitrogen through a complex self sustaining nitriding-oxidation process. A review of the pre-existing correlations used to simulate zirconia scale growth under air atmospheres shows a high degree of variation from parabolic to accelerated time dependence. Variations also exist in the choice of the breakaway parameter based on zirconia phase change or oxide thickness. Several correlations and breakaway parameters found in the literature were implemented in the MAAP4.07 Severe Accident code. They were assessed by simulation of the QUENCH-10 test, which is a semi-integral test designed to study fuel bundle exposure to steam first and then to air. This paper deals with the main results obtained with MAAP4.07 when simulating QUENCH-10

Dysexecutive disorders and their diagnosis: A position paper.

Although executive function disorders are among the most prevalent cognitive impairments a consensus on diagnostic criteria has yet to be reached. With a view to harmonizing these criteria, the present position paper (i) focuses on the main dysexecutive disorders, (ii) examines recent approaches in both the behavioral and cognitive domains, (iii) defines diagnostic boundaries for frontal syndrome, (iv) reports on the frequency and profile of the executive function disorders observed in the main brain diseases, and (v) proposes an operationalization of diagnostic criteria. Future work must define the executive processes involved in human adaptive behavior, characterize their impairment in brain diseases, and improve the management of these conditions (including remediation strategies and rehabilitation)

New outlook on the diagnosis, treatment and follow-up of childhood-onset craniopharyngioma

Childhood-onset craniopharyngiomas are rare embryonic tumours of low-grade histological malignancy. Novel insights into the molecular pathogenesis of human adamantinomatous craniopharyngioma have started to unveil the possibility of testing novel treatments targeting pathogenic pathways. Hypothalamic involvement and/or treatment-related lesions result in impaired physical and social functionality and in severe neuroendocrine sequelae. Quality of survival in patients with craniopharyngioma with hypothalamic involvement is impaired by severe obesity, physical fatigue and non-optimal psychosocial development. Patients with craniopharyngioma involving hypothalamic structures have reduced 20-year overall survival, but overall and progression-free survival are not related to the degree of surgical resection. Irradiation is effective in the prevention of tumour progression and recurrence. For favourably localized craniopharyngiomas, the preferred treatment of choice is to attempt complete resection with preservation of visual, hypothalamic and pituitary function. For unfavourably localized tumours in close proximity to optic and/or hypothalamic structures, a radical neurosurgical strategy attempting complete resection is not recommended owing to potential severe sequelae. As expertise has been shown to have an impact on post-treatment morbidity, medical societies should establish criteria for adequate professional expertise for the treatment of craniopharyngioma. On the basis of these criteria, health authorities should organize the certification of centres of excellence that are authorized to treat and care for patients with this chronic disease