10 research outputs found
A Note on the Generalized Friedmann Equations for a Thick Brane
Within our thick brane approach previously used to obtain the cosmological
evolution equations on a thick brane embedded in a five-dimensional
Schwarzschild Anti-de Sitter spacetime it is explicitly shown that the
consistency of these equations with the energy conservation equation requires
that, in general, the thickness of the brane evolves in time. This varying
brane thickness entails the possibility that both Newton's gravitational
constant and the effective cosmological constant are time
dependent.Comment: 6 pages,To appear in GR
On matching LTB and Vaidya spacetimes through a null hypersurface
In this work the matching of a LTB interior solution representing dust matter
to the Vaidya exterior solution describing null fluid through a null
hypersurface is studied. Different cases in which one is able to smoothly match
these two solutions to Einstein equations along a null hypesurface are
discussed.Comment: 5 pages, to appear in GR
A pragmatic approach towards designing a second shutdown system for Tehran research reactor
One second shutdown system is proposed for the Tehran Research Reactor to
achieve the goal of higher safety in compliance with current operational
requirements and regulations and improve the overall reliability of the
reactor shutdown system. The proposed second shutdown system is a diverse,
independent shutdown system compared to the existing rod based one that
intends to achieve and maintain sub-criticality condition with an enough
shutdown margin in many of abnormal situations. It is designed as much as
practical based on neutron absorber solution injection into the existing core
while the changes and interferences with the existing core structure are kept
to a minimum. Core neutronic calculations were performed using MCNPX 2.6.0
and MTR_PC package for the current operational core equipped with the second
shutdown system, and one experiment was conducted in the Tehran Research
Reactor to test the neutronic calculations. A good agreement was seen between
theoretical results and experimental ones. In addition, capability of the
second shutdown system in the case of occurrence of design basis accident in
the Tehran Research Reactor is demonstrated using PARET program
Development and Experimental Validation of a Correlation Monitor Tool Based on the Endogenous Pulsed Neutron Source Technique
A correlation measuring tool for an endogenous pulsed neutron source experiment is developed in this work. Paroxysmal pulses generated by a bursts of neutron chains are detected by a 10-kbit embedded shift register with a time resolution of 100 ns. The system is implemented on a single reprogrammable device making it a compact, cost-effective instrument, easily adaptable for any case study. The system was verified experimentally in the Esfahan heavy-water zero power reactor (EHWZPR). The results obtained by the measuring tool are validated by the Feynman-α experiment, and a good agreement is seen within the boundaries of statistical uncertainties. The theory of the methods is briefly initiated in the text. Also, the system structure is described, the experimental results and their uncertainties are discussed, and neutron statistics in EHWZPR is examined experimentally