Acoustic Saturation in Bubbly Cavitating Flow Adjacent to an Oscillating Wall

Bubbly cavitating flow generated by the normal oscillation of a wall bounding a semi-infinite domain of fluid is computed using a continuum two-phase flow model. Bubble dynamics are computed, on the microscale, using the Rayleigh-Plesset equation. A Lagrangian finite volume scheme and implicit adaptive time marching are employed to accurately resolve bubbly shock waves and other steep gradients in the flow. The one-dimensional, unsteady computations show that when the wall oscillation frequency is much smaller than the bubble natural frequency, the power radiated away from the wall is limited by an acoustic saturation effect (the radiated power becomes independent of the amplitude of vibration), which is similar to that found in a pure gas. That is, for large enough vibration amplitude, nonlinear steepening of the generated waves leads to shocking of the wave train, and the dissipation associated with the jump conditions across each shock limits the radiated power. In the model, damping of the bubble volume oscillations is restricted to a simple "effective" viscosity. For wall oscillation frequency less than the bubble natural frequency, the saturation amplitude of the radiated field is nearly independent of any specific damping mechanism. Finally, implications for noise radiation from cavitating flows are discussed

UNIPI STARTING REFERENCE DB

1) MOTIVATIONS FOR CONUSAF (at that time FONESYS-UG) given at related Meeting held on March 2, 2018 in College Station, Texas 2) IDEAS FOR THE CONDUCT OF CONUSAF ACTIVITIES also discussed in College Station 3) SAMPLE-STARTING TOPICS FROM UNIP

AN ADDITIONAL SAFETY BARRIER FOR EXISTING AND NEW NPP

content of slides MOTIVATION - BACKGROUND OBJECTIVE - THE ELEMENTS FOR THE PROPOSAL - ALARA - BEPU - E-SM - A - ERT - THE ADDITIONAL SAFETY BARRIER - FINAL REMARKS - APPENDICES (nuclear fuel & supporting references

Panel Session: Reliability of Passive Systems

Passive systems are embedded into the nuclear technology safety and design. In relation to safety, accumulators are one example of vital passive systems strictly needed to mitigate consequences of Large Break LOCA. In relation to design, the configurations of both PWR and BWR primary system is based on natural circulation: the mutual positions of core and steam generators in the case of PWR and the elevation of the feed water nozzle in the BWR vessel are determined to ensure (at least) removal of decay heat when active systems noticeably, centrifugal pumps are not available. Immediately after the Chernobyl accident in 1986, the passive systems received new attention by industry and scientists. Therefore, the importance of passive systems is well established in nuclear technology. Here one may add that passive systems include components like valves, pipes, heat exchangers and phenomena like draining of a tank, formation of incondensable gas bubbles, stratification and natural circulation. The discussion about reliability of passive systems shall include the components and the phenomena: a more detailed list of subjects can be found in the call for participation to the session. Special focus is given to the reliability of thermal-hydraulic phenomena expected during the operation of passive systems. The topic of reliability of phenomena occurring in passive systems was introduced before the year 2000, merging ideas from PSA and thermal-hydraulics

Passive systems and nuclear thermal-hydraulics

Passive systems are in use within nuclear technology, noticeably those systems which are capable of transferring thermal power from a heat source to a sink with the use of energy coming from gravity: Natural Circulation inside the vessel for Boiling Water Reactors (BWR) and between vessel and steam generators for Pressurized Water Reactor (PWR) constitutes noticeable example. A step-wise, somewhat fashion-type, renewed interest followed after the three major nuclear accidents in 1979, 1986 and 2011. The words thermal-hydraulic passive systems, design and safety, open to a myriad of research and application activities, which without surprise may appear contradictory and, at least, not converging into a common understanding. In the present paper an attempt is made to use the word reliability in order to select a space in the design and safety assessment and to derive agreeable outcomes for the technology of passive systems. The key conclusions are: (a) passive systems are not the panacea for protecting the core of nuclear reactors in each foreseeable accident condition; (b) specific licensing rules are strictly needed and not yet formulated; (c) reliability of operation, once a target mission is assigned, may reveal not unit; (d) systems implying the use of active components like pumps shall not be avoided in future designed/built nuclear reactors

Brief overview of past OECD/NEA/CSNI Specialists Meetings: Topics and selected Speakers

CSNI has been leading the development of nuclear thermal-hydraulics since the 70’s. A non-exhaustive list of cornerstone activities and related reports is: •ISP series: a couple of dozen in nuclear thermal-hydraulics including BWR, PWR and VVER simulators (e.g. [PWR]: LOFT, Semiscale, LOBI, LSTF, BETHSY, SPES, ATLAS; [BWR]: FIX-II, ROSA-III, PIPER-ONE; [VVER]: PACTEL). •SOAR series: TPCF; T-ECC; PWR-cont.; BWR-PSP; BWR-S; Scaling; Passive Systems (on-going). •“V” series of activity: ITF-CCVM; SETF-CCVM; VVER-CCVM, Cont.-CCVM + Accuracy quantification (FFTBM) •VARIOUS: Uncertainty (UMS, BEMUSE, PREMIUM, etc.); CT; PTS; Advanced Reactors; CFD; Projects; Training (THICKET). •SPEC. Meetings: TH, BEPU; coupled neutron physics / TH (see below)

Prioritization of nuclear thermal-hydraulics researches

The difficulty in predicting locally and globally the transient evolution of two-phase or multiphase flows in complex systems is well recognized in nuclear thermal-hydraulics. Large efforts involving the expenditure of huge resources during the last three decades in previous century brought to the creation of giant databases (e.g. including experimental data and results of computer code calculations) and to the perception that the safety of nuclear reactors is guaranteed notwithstanding residual areas of unawareness. Nowadays, thousands of scientists continued to generate progress in the area having available much lower resources: more and more dead-ends for established research outcomes are experienced; the progress in knowledge resembles the slow expansion of a swamp rather than the fast moving of a river. In this paper a procedure is proposed to identify directions for research in nuclear thermal-hydraulics which are consistent with the needs in nuclear reactor safety. Two pillars for the procedure are constituted by the characterization of phenomena and by the application of qualified computational tools. Decision makers and scientists may prioritize research in areas where large impacts upon design and safety issues are identified in advance

OECD/NEA/CSNI – MADRID 2020 SM: The established CAPS

CSNI has a long-lasting history in nuclear thermal-hydraulics. This was established during the 70’s decade in previous century and testified by milestone type of reports and Specialists Meetings issued or held in the last 50 years . Namely, five groups of key reports can be distinguished: The SOAR: TPCF, TECC, BWRS, and, more recently, the Scaling (and the passive System) reports; The validation reports: a couple dozen ISP on thermal-hydraulics and the SET and the ITF related Validation matrices reports, including identification of phenomena. The uncertainty related reports: more details in the ‘justification’ row below. The CFD application & advancement activities, including synthesis views, conference documentation (noticeably CFD4NRS) and pioneering activities (e.g. the uncertainty in CFD prediction) Documentation of OECD project starting from LOFT: more details in the ‘justification’ row below. Specialists Meetings in the area of thermal-hydraulics are listed under the row ‘justification’ below. Furthermore, a specific activity has been started in 2004 dealing with transfer of competences. This is called THICKET. Thus one ‘indirect’ objective is to maintain the competence of CSNI in the area of thermal-hydraulics. The main ‘direct’ objective is to discuss the achievements and defining the needs of safety research in nuclear reactor accident thermal-hydraulics. In particular: •To report on the major achievements accomplished in recent years. •To discuss the maturity of nuclear thermal-hydraulics for evaluating safety of existing reactors, identifying strengths and drawbacks of the current analysis approaches. •To define the needs and priorities of research on safety-related thermal-hydraulics, particularly under accident conditions

Status report on thermal-hydraulic passive systems design and safety assessment

Passive systems noticeably those which are capable of transferring thermal power from a heat source to a sink without the use of energy which is not coming from gravity are in use of nuclear technology since the pioneering design of reactors. They received a step-wise, fashion-type, renewed interest following the three major nuclear accidents in 1979, 1986 and 2011. The words thermal-hydraulic passive systems, design and safety, open to a myriad of research and application activities, which without surprise may appear contradictory and, at least, not converging into a common understanding. In the present paper an attempt is made to use the word reliability in order to select a space in the design and safety assessment and to derive agreeable outcomes for the technology of passive systems. The key conclusions are: (a) passive systems are not the panacea for protecting the core of nuclear reactors in each foreseeable accident condition; (b) specific licensing rules are strictly needed and not yet formulated; (c) reliability of operation, once a target mission is assigned, may reveal not unit; (d) systems implying the use of active components like pumps shall not be avoided in future designed/built nuclear reactors

Nuclear Fission: from E. Fermi to Adm. Rickover, to industrial exploitation, to nowadays challenges

Nuclear fission energy reached a multiple bifurcation point: it may continue to decline in some countries, it may expand in other countries, large reactors may extinguish, small and/or micro reactors may exponentially grow in number, sodium fast reactors and innovative reactors may have a bright future or no future at all, thorium fuel might be used or might remain embedded into the terrestrial crust. Then, the purpose for the paper is to orient young generation of scientists. A historical excursus of nuclear era is given starting from the discovery of the nucleus and then moving to Einstein and Fermi, to Rickover and to the industry that led the exploitation of the nuclear fission energy for electricity production. The negative role of the web and the Global World Wide Market (GWWM) in creating cages for the thoughts of scientists is portrayed. The nowadays challenges for nuclear technology are discussed. Selected conclusions are: a) nuclear waste is not a technological problem; b) recently discovered nuclear fuel weakness and reactor complexity constitutes a potential threat for safety; c) regulatory framework needs innovation; d) small and micro reactors shall be deployed if large nuclear units survive; e) a new technological safety barrier appears necessary