What is Boron 10 Depletion – Definition

by
Since the isotope 10B has a significantly higher neutron cross-section, the 10B depletes in a reactor core much more faster than 11B. Boron 10 Depletion. Periodic Table
Natural boron consists primarily of two stable isotopes, 11B (80.1%) and  10B (19.9%). In nuclear industry boron is commonly used as a neutron absorber due to the high neutron cross-section of isotope  10B. Its (n,alpha) reaction cross-section for thermal neutrons is about 3840 barns (for 0.025 eV neutron). Isotope  11B has absorption cross-section for thermal neutrons about 0.005 barns (for 0.025 eV neutron). Most of (n,alpha) reactions of thermal neutrons are 10B(n,alpha)7Li reactions accompanied by 0.48 MeV gamma emission.

(n,alpha) reactions of 10B

Since the isotope 10B has a significantly higher neutron cross-section, the 10B depletes much more faster than 11B. Without the addition of fresh boron (19,9% of 10B) into the primary coolant system the enrichment of 10B in boric acid continuously decreases. In the result the enrichment of 10B at the end of the fuel cycle can be for example below 18% of 10B. This phenomenon must be considered in all the criticality calculations (e.g. shutdown margin calculations, estimated critical conditions or general core depletion calculations).

Boron 10. Comparison of total cross-section and cross-section for (n,alpha) reactions.
Source: JANIS (Java-based Nuclear Data Information Software); The JEFF-3.1.1 Nuclear Data Library
Boron letdown curve (chemical shim) and boron 10 depletion
Boron letdown curve (chemical shim) and boron 10 depletion during a 12-month fuel cycle. At the beginning of specific fuel cycle concentration of boric acid is highest. At the end of this cycle concentration of boric acid is almost zero and a reactor must be refueled, because there is no positive reactivity that can be inserted to compensate negative reactivity of fuel burnup (increase in reactor slagging).

See also:

Boric Acid – Chemical Shim

See also:

Boron 10

See also:

H3BO3 Converter

We hope, this article, Boron 10 Depletion, helps you. If so, give us a like in the sidebar. Main purpose of this website is to help the public to learn some interesting and important information about radiation and dosimeters.

Related Posts