Regional Basic Professional Training Course in Korea

Neutron activation of other materials
❙ 177 ❙
3. Basic Principles Of Nuclear Safety
Neutrons may be absorbed in various other materials to produce radionuclides of interest
in safety. Among these sources are:
Tritium production from neutron absorption in deuterium‐‐particularly important in
heavy water reactors.
Formation of nitrogen‐16 from oxygen in the water‐‐a shielding concern because of
the high‐energy gamma emitted as nitrogen‐16 decays.
Formation of argon‐41 from argon‐40 in air dissolved in the coolant‐‐also a
shielding concern because of a high‐energy gamma.
Neutron absorption in fertile material
Most present day power reactors use low‐enriched uranium fuel, containing a high
proportion of uranium‐238. While U‐238 is not fissionable in a thermal neutron spectrum, it
will capture neutrons, and plutonium‐239 will be produced. Some of the Pu‐239 will be
fissioned, but some will absorb neutrons, and Pu‐240 will be produced, and so forth.
Generally, these “higher actinides” or “transuranic” elements are radioactive alpha‐emitters,
with very long half‐lives (thousands of years). Due to the short range of alpha particles, the
principal hazard from the transuranic elements is through inhalation. The higher actinides
are important contributors to the radiotoxicity of spent fuel in the long term, but their
contribution to the radiological hazard in the operating reactor is limited.
3.4.3. Summary
3.4.3.1. Sources of radionuclides
The inventory of radionuclide in the reactor core is the primary hazard against which the