148 research outputs found
Instrumenting Full scale Boron Injection Test Facility to support Atucha-2 NPP licensing
The Atucha-2 Pressurized Heavy Water Reactor is equipped with a back-up shutdown system based
on the fast injection of boron into the moderator tank. Such system had initially been designed to
cope with a 10%-area (0.1A) break Loss Of Coolant Accident (LOCA) scenario, but based on upgraded
licensing requirements the design had to be revised and possibly improved against a double-ended
guillotine (2A) break LOCA. In particular, the boron injection had to be proven fast enough to allow a
timely shutdown of the reactor, even in the case of a failure of the primary shutdown system
(control rods).
A full-scale test facility was built for such “design validation” purpose, in the framework of a
cooperation program between the University of Pisa – San Piero a Grado Nuclear Research Group
(GRNSPG) and the utility Nucleoeléctrica Argentina S.A. (NA-SA). A special instrumentation system,
based on conductivity probes designed on purpose by the Helmholtz Zentrum Dresden-Rossendorf
(HZDR), was adopted for the measurement of the injection delay, as well as for the monitoring of
pressure at several key locations. Care was taken to reproduce the relevant NPP conditions as closely
as possible to those expected on the basis of extensive safety analyses performed adopting a Best
Estimate Plus Uncertainty (BEPU) approach. In this respect, not only the test facility is full-scale, but
also the key components (such as the fast opening air valves, the boric acid tanks, the rupture
device, the injection lance) were directly borrowed from the Atucha-2 NPP.
The experimental campaign carried out by NA-SA on such test facility allowed to improve the design
of the boron injection system (especially as to some fluid-structure interaction issues) and finally to
achieve the main goal, i.e. the demonstration that the system’s performance is fast enough to assure
a timely and safe shutdown of the reactor. This was a key contribution to the successful completion
of the NPP licensing process
High discharge rate characteristics of nickel-cadmium batteries for pulse load filtering
Several tests of specially fabricated nickel-cadmium batteries having circular disk type electrodes were considered. These batteries were evaluated as filter elements between a constant current power supply and a five hertz pulsed load demanding approximately twice the power supply current during the load on portion of the cycle. Short tests lasting 10,000 cycles were conducted at up to a 21 C rate and an equivalent energy density of over 40 Joules per pound. In addition, two batteries were subjected to 10 to the 7 charge/discharge cycles, one at a 6.5 C rate and the other at a 13 C rate. Assuming an electrode to battery weight ratio of 0.5, these tests represent an energy density of about 7 and 14 Joules per pound respectively. Energy density, efficiency, capacitance, average voltage, and available capacity were tracked during these tests. After 10 to the 7 cycles, capacity degradation was negligible for one battery and about 20% for the other. Cadmium electrode failure may be the factor limiting lifetime at extremely low depth of discharge cycling. The output was examined and a simple equivalent circuit was proposed
CFD Code Validation against Stratified Air-Water Flow Experimental Data
Pressurized thermal shock (PTS) modelling has been identified as one of the most important industrial needs related to nuclear reactor safety. A severe PTS scenario limiting the reactor pressure vessel (RPV) lifetime is the cold water emergency core cooling (ECC) injection into the cold leg during a loss of coolant accident (LOCA). Since it represents a big challenge for numerical simulations, this scenario was selected within the European Platform for Nuclear Reactor Simulations (NURESIM) Integrated Project as a reference two-phase problem for computational fluid dynamics (CFDs) code validation. This paper presents a CFD analysis of a stratified air-water flow experimental investigation performed at the Institut de Mécanique des Fluides de Toulouse in 1985, which shares some common physical features with the ECC injection in PWR cold leg. Numerical simulations have been carried out with two commercial codes (Fluent and Ansys CFX), and a research code (NEPTUNE CFD). The aim of this work, carried out at the University of Pisa within the NURESIM IP, is to validate the free surface flow model implemented in the codes against experimental data, and to perform code-to-code benchmarking. Obtained results suggest the relevance of three-dimensional effects and stress the importance of a suitable interface drag modelling
Enhanced Nuclear Engineering Simulators
Engineering simulation is a sophisticated multi-purpose technology allowing the users of simulators to run a variety of engineering activities due to the possibility of modifying the simulated plant architecture and components, to adjust parameters, to test alternative solutions. Engineering Simulators (ES) have been built and used worldwide for a variety of purposes:
- Development and refinement of the plant design or plant modifications
- Safety analyses focused on the overall system behaviour
- Verification and Validation (V&V) of systems and components
- Development of Operational and Emergency Procedures
- Pre-Training of operators and supervisors
- High level education and Communication activities
- Human Factor Engineering Analysis
- Adaptive Control System training Engineering Simulators also play a role in developing and maintaining key nuclear skills, as knowledge repositories and tools for training at various levels of expertise
Studies of and production in and Pb collisions
The production of and mesons is studied in proton-proton and
proton-lead collisions collected with the LHCb detector. Proton-proton
collisions are studied at center-of-mass energies of and ,
and proton-lead collisions are studied at a center-of-mass energy per nucleon
of . The studies are performed in center-of-mass rapidity
regions (forward rapidity) and
(backward rapidity) defined relative to the proton beam direction. The
and production cross sections are measured differentially as a function
of transverse momentum for and , respectively. The differential cross sections are used to
calculate nuclear modification factors. The nuclear modification factors for
and mesons agree at both forward and backward rapidity, showing
no significant evidence of mass dependence. The differential cross sections of
mesons are also used to calculate cross section ratios,
which show evidence of a deviation from the world average. These studies offer
new constraints on mass-dependent nuclear effects in heavy-ion collisions, as
well as and meson fragmentation.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://lhcbproject.web.cern.ch/Publications/p/LHCb-PAPER-2023-030.html (LHCb
public pages
Fraction of decays in prompt production measured in pPb collisions at TeV
The fraction of and decays in the prompt
yield, , is measured by
the LHCb detector in pPb collisions at TeV. The study
covers the forward () and backward () rapidity
regions, where is the rapidity in the nucleon-nucleon
center-of-mass system. Forward and backward rapidity samples correspond to
integrated luminosities of 13.6 0.3 nb and 20.8 0.5
nb, respectively. The result is presented as a function of the
transverse momentum in the range 1 GeV/.
The fraction at forward rapidity is compatible with the LHCb
measurement performed in collisions at TeV, whereas the
result at backward rapidity is 2.4 larger than in the forward region
for GeV/. The increase of at low at backward rapidity is compatible with the suppression of the
(2S) contribution to the prompt yield. The lack of in-medium
dissociation of states observed in this study sets an upper limit of
180 MeV on the free energy available in these pPb collisions to dissociate or
inhibit charmonium state formation.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-028.html (LHCb
public pages
Observation of strangeness enhancement with charmed mesons in high-multiplicity collisions at TeV
The production of prompt and mesons is measured by the LHCb
experiment in proton-lead () collisions in both the forward
() and backward () rapidity regions at a
nucleon-nucleon center-of-mass energy of TeV.
The nuclear modification factors of both and mesons are
determined as a function of transverse momentum, , and
rapidity. In addition, the to cross-section ratio is measured
as a function of the charged particle multiplicity in the event. An enhanced
to production in high-multiplicity events is observed for the
whole measured range, in particular at low
and backward rapidity, where the significance exceeds six standard deviations.
This constitutes the first observation of strangeness enhancement in charm
quark hadronization in high-multiplicity collisions. The results
are also qualitatively consistent with the presence of quark coalescence as an
additional charm quark hadronization mechanism in high-multiplicity proton-lead
collisions.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-021.html (LHCb
public pages
Search for violation in the phase space of decays with the energy test
A search for violation in and decays is reported.
The search is performed using an unbinned model-independent method known as the
energy test that probes local violation in the phase space of the
decays. The data analysed correspond to an integrated luminosity of
fb collected in proton-proton collisions by the LHCb experiment at
a centre-of-mass energy of ~TeV, amounting to approximately 950000
and 620000 signal candidates for the and modes, respectively. The
method is validated using
and decays, where
-violating effects are expected to be negligible, and using
background-enhanced regions of the signal decays. The results are consistent
with symmetry in both the and the decays, with
-values for the hypothesis of no violation of 70% and 66%,
respectively.Comment: All figures and tables, along with any supplementary material and
additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-019.html (LHCb
public pages
Enhanced production of baryons in high-multiplicity collisions at TeV
The production rate of baryons relative to mesons
in collisions at a center-of-mass energy TeV is measured
by the LHCb experiment. The ratio of to production
cross-sections shows a significant dependence on both the transverse momentum
and the measured charged-particle multiplicity. At low multiplicity, the ratio
measured at LHCb is consistent with the value measured in
collisions, and increases by a factor of with increasing multiplicity.
At relatively low transverse momentum, the ratio of to
cross-sections is higher than what is measured in
collisions, but converges with the ratio as the momentum
increases. These results imply that the evolution of heavy quarks into
final-state hadrons is influenced by the density of the hadronic environment
produced in the collision. Comparisons with a statistical hadronization model
and implications for the mechanisms enforcing quark confinement are discussed.Comment: All figures and tables, along with machine-readable versions and any
supplementary material and additional information, are available at
https://cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2023-027.html (LHCb
public pages
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