1,721,034 research outputs found
Valutazione del rateo di esposizione gamma dovuto ad un autocarro contenente NORM
No full textLa presente relazione tecnica riguarda la determinazione con codice di tipo Monte Carlo del rateo di esposizione gamma all’esterno di un autocarro contenente NORM, avente le dimensioni di un container da 20 ft o 40 ft, alle distanze di 1 e 2 m dal punto centrale della sua superficie laterale
Innovative engineering safeguards to cope with corium relocation: Identification of loads and failure modes
No full textThe proposed study deals with the assessment of passive systems, implemented in reactor designs to extend the coping period in the event of adverse situations, involving the melting of the core, such as occurred at the Fukushima Daiichi plant. To the aim, the feasibility of a new in-vessel core melt retention (IVCR) strategy is investigated. This strategy is based on an original design of a core catcher made of batch of ceramic multi-layered pebble that, by profiting of the low thermal conductivity, is capable to retard the heat-up of the lower head of the vessel during the relocation of the corium (recognized as the “Achilles-heel” of the Gen. II or earlier PWR designs). The arrest of heat-up and eventual quenching is indeed the key to the survival of the RPV as the significant thermal and pressure loadings may cause a reduction of mechanical strength of the vessel, and even its failure. In doing that, issues evolving and caused by the corium relocation are investigated both analytically and numerically. Thermo-mechanical analyses are performed by means of FEM code, assuming firstly homogeneous pool condition. The heat transport to the hemispherical boundary is simulated through conduction, and, then, through a boundary layer created by the downward flow along the curved wall from the upper part of the pool. Results show that the heat-up of the vessel wall, in the long time period, may cause a thermal degradation of the vessel strength. Nevertheless, the adoption of the proposed core catcher solution extends the coping period: after 1 hr from the event initiating the maximum temperature reached by the vessel wall is below the allowed limit for which localized failure may appea
Analysis of feasibility of a new core catcher for the in-vessel core melt retention strategy
Full text linkThis study deals with the feasibility study of a new in-vessel core melt retention (IVCMR) strategy capable to extend the coping period in the event of adverse situations, involving the melting of the core. Since Fukushima accident, many studies have been carried out to resolve the severe accident mitigation issues related to the corium stabilization inside and outside the reactor vessel. This is in fact one of the most relevant safety issues to secure LWRs from the point of view of severe accident mitigation and containment integrity. As for the corium stabilization inside the reactor vessel, in this study it is proposed a new IVCMR concept, developed at the University of Pisa, based on the adoption of an original core catcher design made of batches of ceramic material. By profiting of its low thermal conductivity, this core catcher is capable to retard the heat-up of the lower head of the vessel during the phase of relocation of the corium. To support the feasibility of its design analytical and numerical analyses have been performed assuming homogeneous pool condition. Results show that the adoption of the proposed core catcher solution extends the severe accident coping period: after 1 h from the initiating event, the maximum temperature of the vessel wall is below the limit for which localized failure may appear
A new sensitization technique combining CO2 and UV treatments for improved neutron dosimetry of CR-39 track detectors
No full textA new sensitization technique combining carbon dioxide and UV treatments was investigated for improved neutron dosimetry of CR-39 track detectors. The detectors were irradiated with an 241Am–Be neutron source in a low-scatter laboratory facility, delivering a personal dose equivalent Hp(10)of 1 mSv. Prior to their chemical etching, the detectors were treated in carbon dioxide at a pressure of 0.6 MPa for 6 days followed by a UV (254 nm)treatment at a distance of 5 cm from the lamp, for 20 h. The opposite, UV followed by carbon dioxide treatment, was also investigated. The qualitative impact of these treatments on the background noise of the detectors, and their track size distributions compared to only carbon dioxide, only UV treated detectors, and untreated ones was analysed. Overall, the technique combining CO2 and UV treatments, independently of their order, increased the sensitivity by about 40% and 120% compared to the UV treatment alone and the untreated detectors, respectively, and reduced approximately 15% compared to the CO2 treatment alone. It also significantly enhanced the average diameter of the tracks compared to both treatments separated, allowing a better distinction between real tracks and the noisy background
Innovative engineering safeguards to cope with corium relocation: Identification of loads and failure modes
No full textThe proposed study deals with the assessment of passive systems, implemented in reactor designs to extend the coping period in the event of adverse situations, involving the melting of the core, such as occurred at the Fukushima Daiichi plant. To the aim, the feasibility of a new in-vessel core melt retention (IVCR) strategy is investigated. This strategy is based on an original design of a core catcher made of batch of ceramic multi-layered pebble that, by profiting of the low thermal conductivity, is capable to retard the heat-up of the lower head of the vessel during the relocation of the corium (recognized as the “Achilles-heel” of the Gen. II or earlier PWR designs). The arrest of heat-up and eventual quenching is indeed the key to the survival of the RPV as the significant thermal and pressure loadings may cause a reduction of mechanical strength of the vessel, and even its failure. In doing that, issues evolving and caused by the corium relocation are investigated both analytically and numerically. Thermo-mechanical analyses are performed by means of FEM code, assuming firstly homogeneous pool condition. The heat transport to the hemispherical boundary is simulated through conduction, and, then, through a boundary layer created by the downward flow along the curved wall from the upper part of the pool. Results show that the heat-up of the vessel wall, in the long time period, may cause a thermal degradation of the vessel strength. Nevertheless, the adoption of the proposed core catcher solution extends the coping period: after 1 hr from the event initiating the maximum temperature reached by the vessel wall is below the allowed limit for which localized failure may appear
A SENSORISED LORA-BASED NETWORK FOR THE MONITORING AND IDENTIFICATION OF RADIOACTIVE WASTE DRUMS
No full textA monitoring and surveillance system is a mandatory element to ensure that a radioactive waste disposal facility provides and meets the required level of safety during both its operational and closure periods. Thanks to the technological advancement that has taken place in recent years, it has become possible to implement distributed wireless networks of low-power and low-cost sensors to monitor parameters of interest in different scenarios that relate to sectors such as the civil, environmental, and industrial ones. In this study an innovative approach for the identification and monitoring of the structural integrity of stored radioactive drums is presented. It consists of a network of radio frequency nodes equipped with solid-state gamma-ray and thermal neutrons detectors developed at the University of Pisa within the European project PREDIS. The nodes provide a unique identifier to the waste drums, and at the same time they allow cyclic measurements of the emitted radioactivity with a frequency and duration established by the user. Since nodes must be battery powered, a high level of hardware and software optimization has been performed to guarantee several years of battery lifetime minimizing human operators' interaction. Data collected by the nodes are automatically transferred to radio gateways through LoRa technology for visualization, processing, and storage purposes. The proposed solution demonstrates the possibility of collecting data automatically and passively from radioactive waste drums at a great distance without the use of mobile and/or mechanical scanning systems, enabling a much greater storage capability compared to common identification solutions based on radio frequency identification or near field communication tags
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