8/9/2019 Boron Worth

1/17

Neutron X-section

8/9/2019 Boron Worth

2/17

Boron

Boron used as chemical shim

Reactivity control due

Power transients

Fuel B/U Fission Fragments Poisoning etc

Shutdown margin during shutdown and

refueling

Dissolved in coolant uniformly Constant flux profile

Avg. power density increase

Better b/u

8/9/2019 Boron Worth

3/17

Boron

Stable

Weak acid hence less pH variation

Remains dissolved if < 5%w/w at room temp

B is 17.7% of H3BO3,B19.8% B10, 80.2 B11

B10 Wa=3837 b; forBWa=3837.198=760b

B10 is 1/v absorber

eLiBnB 24273*11

5

1

0

10

5 pp E

eHn 42 3142*11

5

1

0

10

5 pp E

8/9/2019 Boron Worth

4/17

Concentration =

Concentration measured in ppm

ppm | parts per million

Boron

610vsolventofmass

soluteofmass

610vsolventofass

soluteofass

8/9/2019 Boron Worth

5/17

Neutron Moderation

Collision with Nuclei

\=2/(A+2/3)

N = ln(Eh/El)/\

\ = 0.948 for water

8/9/2019 Boron Worth

6/17

8/9/2019 Boron Worth

7/17

Nuclear Stability

8/9/2019 Boron Worth

8/17

Nuclear Stability

8/9/2019 Boron Worth

9/17

Binding Energy

Let us analyze Fe-56, Z=26

Atomic Mass = 55.934930 amu

26 P, 30 N, 30 e

! 26(1.00727647)+30(1.00866501)

+26(5.485803E-04)

! 56.463402

! 56.46340255.934930=0.528472 amu

Interesting!!!!

8/9/2019 Boron Worth

10/17

Binding Energy

1 amu = 1.660566E-27 kg=931.502 Mev/c2

0.528472 931.502 =492.272725 Mev/c2

8.79 MeV/neucleon

8/9/2019 Boron Worth

11/17

8/9/2019 Boron Worth

12/17

Nuclear Fission

Splitting of a heavy nucleus to 2 or

more light nuclei

Release of Energy

Fission is initiated by absorption of a

neutron by fissionable material

2 to 3 neutrons on the average are

released in each fission. The fission fragments are radioactive

8/9/2019 Boron Worth

13/17

Nuclear Fission

Nucleus contains P & N

Electric Coulomb forces of repulsion

between Ps short range strong nuclear forces which

bind the particles of a nucleus together

Normally a certain ratio of N/P is stable

N/P ~ 1 is stable for smaller values

8/9/2019 Boron Worth

14/17

Nuclear Fission

N/P > 1 is required for largernuclei

For very large nuclei, (Zaround 90) no completestability Nuclei with large half lives are

considered almost stable

Nuclei tend to become stable

by emitting radiations (E, F, p,n, positron)

Many isotopes of larger nucleicould be almost stable

8/9/2019 Boron Worth

15/17

Nuclear Fission

Binding energy is to be supplied to break a

nucleus

B

E is eqt. to the mass deficit If energy is supplied to a nucleus by a K,

the result may emission of any radiation to

obtain naturally stable form.

The stable form may be isotope of the same

element or radioactive nucleus of another

atom still changing to some stable nucleus.

8/9/2019 Boron Worth

16/17

Further Topics of Discussion

Nuclear chain Reaction

Uses of Fission

Non fissionable absorption, escape

k, criticality, critical mass/size

Moderator

Reduction in non fissionable capture by isotope

separation (enrichment) Purification of materials(Fuel, moderator)

Control of chain reaction, weapon or power

8/9/2019 Boron Worth

17/17