Tuesday, September 28, 2010

Reactivity on Monday Lectures.....

A very good day to all.....
It is the summarize about what we have learns today(Monday 27th Sept 2010) with Mr Shamsul.
Lets check it out... 

Principles of Nuclear Power 

Atoms are constructed like miniature solar systems. At the center of the atom is the nucleus, and orbiting around it are electrons. The nucleus is composed of protons and neutrons, very densely packed together. Hydrogen, the lightest element, has one proton; uranium, the heaviest natural element has 92 protons.
      The main key of nuclear is Uranium. Nuclear power is generated using Uranium. Uranium can be found easily in any part of the world. In nuclear power plants (NPP), neutrons collide with uranium atoms, splitting them. This split releases neutrons from the uranium that in turn collide with other atoms, causing a chain reaction. This chain reaction is controlled with "control rods" that absorb neutrons.


Reactivity

Reactivity is a measure of the departure of a reactor from criticality. It is a useful concept to predict how the neutron population of the reactor will change over time
Nn = No(Keff)  ----> know number at particular time/generation

 
Accumulation = Production - Absorption - Leakage

 
If accumulation:
o = 0     critical           steady state       static
o >0      supercritical      increasing         kinetic/dynamic
o <0      subcritical        decreasing         kinetic/dynamic

k = 0 -----> neutron population steady


Criticality control
In order to keep an operating nuclear reactor critical must need to 'adjust' terms in the neutron balance

State of criticality:

Keff = 1       critical            p = 0
Keff > 1       supercritical       p > 0
Keff < 1       subcritical         p < 0



No reactor can be constantly critical :-
  • Fuel depletion
  • Fission product buildup
  • Temperature changes


K and Keff are used interchangeably.


Reactivity: dimensionless # (a ratio of two dimensionless quantities) the value is often a small decimal value               
      A parameter called reactivity is positive when a reactor is supercritical, zero at criticality, and negative when the reactor is subcritical. Reactivity can be controlled in various ways: by adding or removing fuel; by changing the fraction of neutrons that leaks from the system; or by changing the amount of an absorber that competes with thefuel for neutrons. Control is generally accomplished

      A nuclear chain reaction occurs when one nuclear reaction causes an average of one or more nuclear reactions, thus leading to a self-propagating number of these reactions. The specific nuclear reaction may be the fission of heavy isotopes (e.g. 235U) or the fusion of light isotopes (e.g. 2H and 3H). The nuclear chain reaction is unique since it releases several million times more energy per reaction than any chemical reaction.

        Reactivity can be controlled in various ways: by adding or removing fuel; by changing the fraction of neutrons that leaks from the system; or by changing the amount of an absorber that competes with the fuel for neutrons. Control is generally accomplished by varying absorbers, which are commonly in the form of movable elements control rods or sometimes by changing the concentration of the absorber in a reactor coolant. Leakage changes are usually automatic.

        Reactivity coefficient, the amount of change in eactivity per unit change in the parameter, to quantity the effect that a variation in parameter.Increasing in temperature, CR insertion, increase in neutron poison.

    


1 comment:

Mohd Syukri said...

It's not cool to copy and paste.