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candice_84
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When designing a core lattice, which one of the thermal-hydraulics and neutronics consideration are important?
That's one parameter.candice_84 said:How about moderation-to-fuel ratio?
Yes, and that would harden the spectrum. In BWRs, one can reduce flow and increase voiding in an assembly and harden the spectrum. The harder spectrum produces more Pu-239 from conversion of U-238, which can increase fuel utilization. That operation is called spectral shift.candice_84 said:Is it true,If we increase the fuel, the fuel utilization increases? therefore moderation-to-fuel ratio decreases and the reactor becomes under moderated?
One can do both in-core and ex-core detectors. The problem with ex-core detectors is that the neutron flux is very low at the core periphery.candice_84 said:Where do they fit a flux detector in either pwr or vver? Is it inside the fuel rod? also does it conflict with absorber rods?
Neutron energy spectrum.candice_84 said:Where do they fit a flux detector in either pwr or vver? Is it inside the fuel rod? also does it conflict with absorber rods? Also when you mentioned about spectrum what spectrum exactly you are pointing on?
Astronuc said:Fast reactors generally use hexagonal lattices.[/url]
I believe that the tringular/hexagonal lattice is better from a neutronic standpoint. The neutron leakage is more before the mean free path of a fast neutron is much greater in a fast reactor than in a thermal reactor. In the latter, fast neutrons slow down relatively quickly.candice_84 said:Since there is no moderator involved in fast reactors, I assume hexagonal lattices perform better thermal-hydraulics than rectangular 17x17 in general. Is this a right assumption?
Probaby there is a decay heat removal system, but not an ECCS like that of an LWR. The liquid metal coolant has excellent thermal conductivity, and I suspect that in shutdown, there is an effective heat removal system and one does not have to be concerned of the core overheating or the coolant boiling as the case with an LWR. The problem for LWRs is that they have to operate under high pressure to maintain a liquid phase. Na systems operate at a few atmospheres. IIRC, a Na loop at 0.20 or 0.5 MPa (about 2 to 5 atm) provides much the same heat transfer coefficient as pressurized water at 2250 psia (15.5 MPa), 290 C (563 K).candice_84 said:In the pdf file for LMFR it says that LMFR don't need emergency cooling systems but I don't understand it.
It depends on the calculation.candice_84 said:How important is it, to get an accurate burnup calculation and couple it with thermal-hyraulics?
Is the question referring to core flow or upper head and by-pass flow?candice_84 said:What are the advantages and disadvantages of upward and Downward flow in PWR?
OK. I thought so, but there is also a use of the terminology of downflow and upflow for the bypass region which relates to baffle-jetting in some PWRs. Usually downflow plants have been converted to upflow in the bypass.candice_84 said:I mean core flow.
What if A and B are at the same elevation (h), or Δh=0, and water is pump (forced convection) from point A to B?candice_84 said:Pressure is higher at Point B, because P=[tex]\rho[/tex]gh. Since H is higher in point B, pressure is more at point B.
The primary cooling circuit or loop of a PWR is more or less a closed system, with the exeception of lines use to infuse or extract water for cooling pumps, boric acid, coolant sampling lines. The primary cooling system consists of the reactor core and pressure vessel (PV) internals, hot and cold legs, steam generators (headers and tubing), and cross over legs from the steam generator to reactor coolant pump on the cold leg. The pressurizer is attached to one of the hot legs and provides pressure to the system.candice_84 said:I think pressure at the horizontal line is the same.
I cannot picture the second question, therefore I don't know where the pressure is high in the tube.
candice_84 said:... But the actual flow in the pwr goes down in the downcomer and then flows upward which i don't think its a good design but there has to be a trade off that I am not aware of it.