artis said:
And I thought Xe is only produced (also burned) during neutron flux in an active core and some time after stopping of neutron flux/chain reaction.
Xe (i.e., isotopes of Xe) is a fission product (which decays to Cs) and a decay product of another fission product (I). During fission, two atoms are produced, one has atomic number Z and the other 92-Z. The first has atomic mass A, and the other atomic mass 234-A, or 233-A, based on an excited nucleus from n +
235U =>
236U, and the 234 assumes 2 neutrons released, while 233 assumes 3 neutrons released. Complicating the picture is fast fission of
238U, which shifts the A-distributions up by 1 or 2 units for each f.p., as well as thermal fission of
236Np,
238Np,
239Pu and
241Pu, and fast fission of other transuranics.
So, there is distribution of population of fission products with a dual peak, one based around A = 89-90 and the other about A=145. In reality, fission produces an amount of every radionuclide from Cu (Z=29) to Eu (Z=63), or Z = 46 +/- 17 (46 from 92/2). The since most fission products have half-lives on the order of seconds, minutes, hours, days, months, the main concern are those that decay slowly over years; all the short-lived radionuclides decay into long-lived fission products or stable nuclides.
There is a lot of concern about radioactive I and Cs, because I is taken up by the thyroid gland, and Cs behaves like Na and K in the body, so could migrate to nerves, and Ba (Cs-decay product) behaves like Ca, so goes to the bones. Of course, any fission product, or dust covered in fission product could settle onto clothing or skin, or inhaled into nose, throat or lungs, or swallowed into the alimentary system. So lots of opportunity for external and internal exposure. External exposure is primarily from gamma radiation, which penetrates cms to 100s of cms. Internally, but gamma and beta radiation are a concern, along with rate and energies of the beta and gamma radiation.
For the heavy f.p., the main ones would be
129I,
134Cs,
137Cs and
133Ba, and possibly decay products from transuranics and other species. It depends on what and how much was released and deposited, and it is nearly 36 years since the accident.
Looking at Xe, those radioisotopes and their precursors should have decayed away by now.