Radiation Effects in Chloride Molten Salt Compositions
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cooling intervals of 1, 10, 100 hours, 1 month and 1 year. For thermal neutron irradiation the following nuclides are of major importance just after irradiation ends: CI-36 (1.5-10 5Bq/cm3), Na-24 (8.3"109 Bq/cm 3), S-35 (2.1"109 Bq/cm 3), P-32 (1.1.106 Bq/cm3 ), K-42 (0.9.106 Bq/cm3),
Cu-64
(1.9.105
Bq /em3), As-76 (2.4.10' Bq/em3), Ag-ll0m
(4.1.103
Bq/em3), Sb-122 (1.1-105
3
3
3
Bq/cm ), Sb-124 (2.0"104 Bq/cm ), Hg-197 (1.8.104 Bq/cm ) and Pb-209 (9.7-108 Bq/cmr). After a 1 year cooling interval the target activity was determined mainly by S-35 (1.15.108 Bq/cm 3), CI-36 (1.5.105 Bq/cm3), Ca-45 (2.4.102 Bq/cm3), Fe-55 (6.9.102 Bq/cm3), Zn-65 (1.4.103 Bq/cm3), Ag-ll0m (1.5-103 Bq/cm 3), Sb-124 (3-102 Bq/cmr3) and Tl-204 (1.6-102 Bq/cm 3). For irradiation by the fission neutron spectrum, among the major radioactivity contributors just after irradiation are Na-24 (3.6.106 Bq/cm3 ), K-42 (3.7.10' Bq/cm3 ), Ar-41 (1.3.103 Bq/cm3), Ar-37 (1.1.104 Bq/cm3 ), Mn-54 (5.4.102 Bq/cm3), Mn-56 (1.7.103 Bq/cm 3), Co-58 (7.4.10' Bq/cm3), Cu-64 (3.8-102 Bq/cm3 ), Sb-122 (2-103 Bq/cm ), Sb-124 (3-7-102 Bq/cm 3), Pb-203 (1.5"105 Bq/cm3), Pb-209 (3.3-106 Bq/cm 3), and Po-210 (10 Bq/cm3). The Ar-39 (2.1.102 Bq/cm), Mn-54 (2.4.102 Bq/cm3), and Co-58 (2.1.102 Bq/cm3) were dominant after one year of cooling. INFLUENCE OF SECONDARY NEUTRONS The secondary neutron flux densities generated by the primary proton beam in the target in question were also calculated for the conditions of the LANSCE accelerator (proton energy Ep=800 MeV, current Ip=l mA, Gaussian radial distribution of the proton current with sigma -1.60 cm) using the MARS-10 code. These densities (in n.cm 2E.s-1 ), averaged on the radius cR>o versus the target length cZ>ยป(in cm), are Z 10=1.56"10 13, Z 20=1.8"10 13, Z50=1.25.10 13 , Z 70=9.3.1012, Z4o=5.6-1012, Z11o=2.5.10 12, Z.3o=3.1.10 11, Z15o=1.0.10n, Z17o=4.0"10' 0, and Z 19o=2.0.10 10. The proton flux density was -40 times less than the neutron density. The spectra for secondary neutrons and protons leaking through the lateral surface of the target, as well as in the target center, in a cell with AZ-100-110 cm and AR=0-2.5 cm were also calculated. The results are presented in Tables I and II. The total number of neutrons leaking through the target lateral surface was -8.1 per primary proton, or -5.0_1016 n/s, while the leakage through the total target surface and planes was as much as -8.6 neutrons per proton. The total number of leaking protons per primary proton was -0.2.
1 2 3 4 5 6 7
Table I. Proton spectrum in the target Neutron fraction, % Energy interval, MeV Target center Leakage 0.1 10-20 0.1 2.6 20-30 0.8 6.2 30-50 38.0 20.0 50-100 37.0 30.0 100-200 23.0 40.0 200-400 1.2 1.0 400-600
500
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Table II. Neutron spectrum in the target Neutron fraction, % Energy interval, MeV Leakage Target center S.0.001 0.003 -0 0.025 0.03 0.001-0.01 0.92 0.80 0.01-0.1 2.20 1.70 0.1-0.2 3.60 2.60 0.2-0.4 6.50 6.60 0.4-0.8 0.8-1.4 13.8 13.8 16.5 1.4-2.5 16.8 13.2 2.5-4.0
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