Lecture_2008_3

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Nuclear Fission

Thermal neutron fission of 235U forms compound,

yielding over 80 primary fission fragments (products).

92 0 37 55 0

235 U + 1 n 87 Br + 146 La + 31 n

23592U +

10n

7230Zn +

16062Sm + 4

10n

The fission yield is defined as the proportion(percentage) of the total nuclear fissions that form

1Nuclear Reactors, BAU, 1st Semester, 2007-2008Saed Dababneh .

.for fast.


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Nuclear Fission

emem er neu ron excess. (A,Z) (A,Z+1) or (A-1,Z).

Only leftside of the

mass

Nuclear Reactors, BAU, 1st Semester, 2008-2009Saed Dababneh .

2

parabola.

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Nuclear Fission

235U+ n 93Rb + 141Cs + 2n

=

165 MeVaverage kinetic

What if other fragments? Different number of neutrons.

energy carriedby fission

a e e as a represen a ve va ue.

fission.

e e

Heavyfragments

Lightfragments

3

miscalibratedNuclear Reactors, BAU, 1st Semester, 2008-2009

Saed Dababneh .

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Nuclear Fission

neutronsemitted er

fission. depends

nuclide and

on neutronenergyinducingfission.


4

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Nuclear Fission

Mean neutron energy 2MeV.

2.4 neutrons per fission(average) 5 MeV

carried by prompt neutrons

per fission.

Show that the average momentum carried by a neutron is only

. a carr e y a ragmen . Thus neglecting neutron momenta, show that the ratio betweenkinetic energies of the two fragments is the inverse of the ratio of

5

their masses.

1

2

2

1

m

m

E

E

14095

98

66Nuclear Reactors, BAU, 1st Semester, 2008-2009

Saed Dababneh .

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Nuclear Fission

Distribution of fission energyEnge

Kranesums

them up

as decays.

Lost !


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Nuclear Fission

Segr Distribution of fission energy

Lost !

a

bc

How much is recoverable?How much is recoverable? What about capture gammas?What about capture gammas? (produced by(produced by --1 neutrons1 neutrons))

7

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Nuclear Fission

and emissions fromradioactive fissionproducts carry part

energy, even after

shut down. ,and half-life increases. Long-lived isotopes constitute the mainhazard.

an nter ere w t ss on process n t e ue . Example?Example? (poisoning).(poisoning). Important for research.

-deca favors hi h ener ~20 MeV com ared to ~6 MeV for .


Only ~ 8 MeV from -decay appears as heat. Why?Why?

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Nuclear Fission

-f

, Z

i

A, Z-1

k

A-1, Z

j

-

n,

A, Z+1A+1, Z

,

dNi/dt = Formation Rate - Destruction rate - Decay Rate

iiiikkjjffii NNNNN

dt ++=


i sa ura es an s g er w g er neu ron ux, arger ss on y e an

longer half-live.


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Nuclear Fission

HW 7HW 7

Investigate the activity, decay and gammaenergies of fission products as a function of time.

idN

Comment on consequences (e.g. rod cooling).

iikkdt

=

HW 8HW 8

giving full description for the buildup and decay ofiikk iikk



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Nuclear Fission

sMeVTttxtP /)(101.4)( 2.02.011 +=.

T= time of operation.

Fission

productac v yafter

shutdown?



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Nuclear Fission

The fission gamma radiation.

energy of 0.9 MeV. dela ed ammas.

Investigate how promptInvestigate how prompt

HW 9HW 9

gammas interact withgammas interact withwater, uranium and lead.water, uranium and lead.



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Nuclear Fission

EeEE 29.2sinh453.0)( 036.1=HW 10HW 10

The experimental

neutrons is fitted by

the above equation.Calculate the meanand the most

pro a e neu ronenergies.


13

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Nuclear Fission

Recoverable energy release 200 MeV per 235Ufission. Fission rate = 2.7x1021P fissions er da .P in MW.

3.12x1016

fissions per second per MW, or 1.2x10-5

gram of235

Uper second per MW (thermal). . . .

The fissioning of 1.05 g of 235Uyields 1 MWd of energy.

Specific BurnupSpecific Burnup = 1 MWd / 1.05 g 950000 MWd/t (pure(pure 235235U !!).U !!).Fractiona BurnupFractiona Burnup = Thermal reactor loaded with 98 metric tons of UO2, 3% enriched,o erates at 3300 MWt for 750 da s.

c ua y muc ess.c ua y muc ess.

86.4 t U. Specific burnup 28650 MWd/t. Not all fissions from 235U. 238


. 238Uconverted to plutonium more fission.

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Nuclear Fission

)(EE

= Ca ture-to-fission ratio:

)(Ef

Consumption rateConsumption rate: 1.05(1+) P g/day.

Read all relevant material in LamarshRead all relevant material in LamarshCh. 4. We will come back to this later.Ch. 4. We will come back to this later.

Two neutrinos are expected immediately from thedecay of the two fission products, what is the minimum


15

ux o neutr nos expecte at 1 m rom t e reactor.

4.8x1012 m-2s-1

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Nuclear Fission

3.1x1010 fissions per second per W.

In thermal reactor, majority of fissions occur inthermal energy region, and are maximum. v u

V Thermal reactor powerThermal reactor power (quick calculation)(quick calculation)

Pf

th =


. x16Nuclear Reactors, BAU, 1st Semester, 2008-2009

Saed Dababneh .

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Lecture_2008_3

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