I will guess: By looking at a nuclide map, the neutron flux in seawater should activate the NaCl, and produce 36Cl, 38Cl with a half life of 3e5 years and 38 mi

I will guess: By looking at a nuclide map, the neutron flux in seawater should activate the NaCl, and produce 36Cl, 38Cl with a half life of 3e5 years and 38 minutes respectively. And 24Na with 15h half life. Additionally there may or may not be nasty reaction products, if we look at reactions of Oxygen with neutrons. ( I did not find any, but that does not mean there is none.)