Natural production of radionuclides in geological formations

Abstract

Determination of underground production of radionuclides important in 'dating' groundwater and in problems related to underground disposal of high-level radioactive waste disposal is discussed. For estimation of natural production of radionuclides the neutron energy spectrum in the rock must be calculated based on the rock chemical composition and its physical parameters. Details on several interesting radionuclides produced in spontaneous fission of uranium and in reactions with underground neutrons are given.

Natural background radiation at Lab 2 of Callio Lab, Pyhäsalmi mine in Finland

“…As in the previous paper describing radiation environment at TU Bergakademie in Freiberg [18] the ratio of count rates under the peaks of 1460.8 keV and 1764.5 keV from 40 [25]; at Gran Sasso LNGS laboratory in dolomitic limestone covered by concrete it is 2 -6.2 depending on the season [31]; at LSC in Canfranc laboratory in calize rock, which is a calcium carbonate with traces of quartz, it is 5 [32]; in salt rock surrounded by anhydrite layer it is around 3.3 [22]. From this short overview, it seems that the combination of volcanic rock and shotcrete wall coverage is responsible for 40 K/ 214 Bi > 8 for depths greater than 1 km w.e.…”

“…The used shotcrete contains up to 30 % of furnace slag, a waste material of the iron industry. Depending on the source and patch the furnace slag concentrations for 40 as determined by the laboratory of Finnish Nuclear Safety Authority.…”

“…Complete characterization of the natural background radiation in an UL includes the estimation of the concentration of natural radioisotopes in rock and water, concentration of radon in air, and measurements of neutron and muon fluxes. The known main sources of background radiation are: cosmic ray (including muon) interactions, the decays of primordial radionuclides (mainly 40 K, 232 Th, and 238 U), the neutron interactions that originate from (α,n) reactions, the spontaneous fission of U and Th. The contribution from gaseous Rn coming from alpha decays of 226 Ra originating from the rock has to be taken into account as well.…”

Measurement of the Long-lived Radionuclide 81Kr in Pre-nuclear and Present-day Atmospheric Krypton

“…The "'Kr production is then obtained with the direct "'Kr fission yield of7X10-" [17]. Calculated from the total amount of "^Kr (t"2 = 10.8 y) released in nuclear fuel reprocessing estimated to be 260 Megacurie or 4.72 X W "'Kr atoms, and the fission yields of "'Kr (2.8 X 10"') and "'Kr (7 X 10").…”

“…The direct fission yield of is estimated to be 7X10"" [17]. By assuming a total atmospheric nuclear explosion yield of 500 Megaton TNT equivalent, one can estimate the total number of fissions and therefore the fission produced (see Table 2).…”