Nuclear Reactor Instrumentation

8/6/2019 Nuclear Reactor Instrumentation

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Nuclear Reactor

Instrumentation

Prepared by

S.AvinashE&I 2011


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2

.Moderator

1.Fuel

3.Control

rod

5.Stea

m

gen

era

tor

4. Coolant

6.

8.

7.


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1. Fuel2. Moderator3. Control Rods

4. Coolant5. Steam Generator6. Turbine/Generato

r7. Pumps8. Heat Exchanger


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Definitions

Nuclear fuel is a material that can be 'consumed' by fission orfusion to derive nuclear energy, by analogy to chemical fuel thatis burned for energy. Nuclear fuels are the most dense sources ofenergy available.

moderatoris a medium that reduces the speed of fast neutrons,thereby turning them into thermal neutrons capable of sustaininga nuclear chain reaction.

A control rod is a rod made of chemical elements capable ofabsorbing many neutrons without fissioning themselves. They areused in nuclear reactors to control the rate of fissionof uranium and plutonium.


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Nuclear reactor coolant is used to remove heat from

the nuclear reactor core and transfer it to electrical

generators .

Steam generators are heat exchangers used to convertwater into steam from heat produced in a nuclear reactor

core. They are used in pressurized water reactors between

the primary and secondary coolant loops.

Turbine generatoris a device that converts mechanicalenergy to electrical energy.

Pumps are used to circulate the water through the primary

and secondary loops .

Heat exchangerat the secondary loop removes the heat of

the super saturated steam. So that it can further be used in

the reactor.


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Neutron Flux Neutron flux is a term referring to the number

of neutrons passing through an area over a span of time. It is

most commonly measured in neutrons/(cms).[1 This is drawn

from the mathematical definition of flux. The neutron

influence is defined as the neutron flux integrated over acertain time period and represents the number of neutrons per

unit area that passed during this time.

Both within natural processes and in the experimental

laboratory, neutron flux may be applied to atomic nuclei, in

which nuclei are bombarded with neutrons at a steady rate.This can be used to produce different isotopes, including

unstable, radioactive ones, of a given chemical element.


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Control rod calliberation

The reactivity of nuclear reactors may change during operation due

to various causes. The operating reactor has always to be kept in

critical condition (in this case its reactivity is zero) mostly using

neutron absorbing rods, usually called control rods.

There are several methods for determining the characteristic curve

of control rods. The applied method depends on the reactor type,

the individual rod values, the available instrument and time. The

basic problem consists essentially in determining the reactivity for

different control rod positions.


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The current methods are:

a) Determination of reactivity based on the reactor periodmeasurement

b) Rod calibration in a sub-critical system.

c) Intercalibration method.

d) Rod oscillation method.

e) Rod drop method.

Of them, the first & third ones are currently applied.


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Rod curve determined by the reactor period

method

The reactor period T method fits low worth rods as a rule. The shortest

reactor period usually permissible during this measurement is 10 s. It is

an absolute method, permitting to dir

With the rod in different withdrawn positions, the reactor isoperating at low power and the reactor period isdetermined. Only the rod to be calibrated is in fully downposition.

If P(t) is the reactor power at time t and P(0) is the powerat time 0 when starting the experiment

P(t) = P(0) T ... reactor period in [s]


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If P(t) = 1.5.P(0), then 1.5 P(0) = P(0) and

T = t/ln1.5 = 2.47.t t .... time in seconds for a

1.5 times power increase

To carry out this experiment stop watches are used to measure

the time during which the reactor power increases for a factor of

1.5. This time is multiplied by the factor 2.47 (see above) and the

reactor period is obtained. The inhour equation relates thereactor period to the reactivity, therefore, from available tables

the reactivity can be determined. Continuing this procedure

stepwise the total length of the control rod can be calibrated .

One of the drawback of this method is that it takes a long time

for complete calibration of the rod


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Intercalibration method. in this method, the characteristic curve of the control rod of unknown

efficiency is recorded by means of another, already determined rod.

The measurement is rapid, although of a limited accuracy, since duringmeasurement, flux distribution in the active zone is always changingbecause of the varying shading effect of neighbouring rods, affecting alsothe reactivity worth value.

The measurement is done with the reactor operated"automatically" at low power. The tested control rod (e.g. the

"manual" rod) is pushed in. The known control rod (now the"automatic" rod) is somewhat pulled out and its exact positionmarked. Now the tested rod is pulled out by 10% of its length fromthe active zone. To keep criticality at a constant power, theautomatic control system inserts the other (automatic) control rodin such a way that the thereby engaged reactivity is just equal tothe reactivity disengaged upon with drawing the tested rod. When

its condition is fulfilled, positions of both rods are measured, andthe reactivity difference corresponding to the displacementdetermined on the characteristic curve of the known rod. Thisvalue will be the reactivity difference for 10% displacement of thetested rod. The measurement is continued stepwise in thedescribed manner until the tested rod is fully pulled out.


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References

http://en.wikipedia.org/

http://www.reak.bme.hu

C.B.S.E 12th

physics N.C.E.R.T book
http://en.wikipedia.org/http://www.reak.bme.hu/http://www.reak.bme.hu/http://en.wikipedia.org/

Documents

Nuclear Reactor Instrumentation