Planning and preparation approaches for non-nuclear waste disposal Lucia Sarchiapone Laboratori Nazionali di Legnaro (Pd) Istituto Nazionale di Fisica Nucleare INFN Lucia.Sarchiapone@lnl.infn.it +39 049 8068 394
Outline Laboratori Nazionali di Legnaro The SPES Project Expected levels of radioactivity, studies: The irradiation target The shielding structure Approach for the disposal NEA Workshop on the Management of Non-nuclear Radioactive Waste 2
NEA Workshop on the Management of Non-nuclear Radioactive Waste New building area hosting the cyclotron and the irradiation bunkers Existing acceleration line Linear accelerator ALPI 3
The SPES Project (Selective Production of Exotic Species) Radioactive Cyclotron ALPI beams: 90 Rb, 135 I, 137 Te, 138 Xe, 94 Kr, 132 Sn, 134 Sn PIAVE TANDEM RIB: Sn-132 +n, I-135 +n, 9 MeV/amu RIB: Sn-132 +n, I-135 +n, up to 40 kv RIB: Sn-132 +1, I-135 +1, up to 40 kv according to mass Protons, 40 MeV 200 ma NEA Workshop on the Management of Non-nuclear Radioactive Waste 4
The Cyclotron name: p70 made by: Best Cyclotron energy: 40-70 MeV maximum current: 750 ua particles: H- special remarks: dual port NEA Workshop on the Management of Non-nuclear Radioactive Waste 5
The fissionable target Graphite holder 7 UC 2 disks 1 mm thick Graphite dump Developed by the SPES target group, www.lnl.infn.it/~spes_target/ NEA Workshop on the Management of Non-nuclear Radioactive Waste 6
Target ISOL technique beam effusion at work Ionization of the radioactive beam The type of source is related to the final beam NEA Workshop on the Management of Non-nuclear Radioactive Waste A. Andrighetto 7
Fluka geometry The target: irradiation cycle and inventory The SPES target is made of 7 UCx disks, 4 cm diameter, 1 mm thickness (about 30 g uranium-238 content) Graphite box Proton beam window UC x disk dumper The irradiation cycle lasts 14 days, a total of 10 21 protons on target and a total of 10 19 fissions are induced on the target NEA Workshop on the Management of Non-nuclear Radioactive Waste 8
Atomic abundances (atoms per 200 ua) atomic abundance (atoms per 200uA) Atomic number Z Z Atoms atoms per per proton proton Production in production target at in target 40 at MeV 40 proton energy 100 The target: irradiation cycle and inventory 90 10-1 10-2 80 10-3 Direct fission from 40 MeV protons on UC 2 70 60 50 40 10-4 10-5 10-6 10-7 10 12 30 20 10-8 10-9 10 10-10 10 11 0 0 20 40 60 80 100 120 140 N Number of neutrons N 10-11 FLUKA simulation 10 10 10 13 fissions/sec 10 9 60 80 100 120 140 160 180 mass number (A) Mass number A Total target activity after 2 weeks irradiation 3.7 10 13 Bq NEA Workshop on the Management of Non-nuclear Radioactive Waste 9
The target: irradiation cycle and inventory 14 days 10 21 protons on target 10 19 fissions/cycle About 1 kci totally produced in 1 cycle 10% 1% 2% T 1/2 < 1 hour 1 hour < T 1/2 < 1 day 1 day < T 1/2 < 1 month 1 month < T 1/2 < 1 year 1 year < T 1/2 < 10 years T 1/2 > 10 years 17% 70% NEA Workshop on the Management of Non-nuclear Radioactive Waste 10
The target: induced radioactivity Bq NEA Workshop on the Management of Non-nuclear Radioactive Waste 11
The temporary storage design Small area to store the irradiated targets before their final destination as waste NEA Workshop on the Management of Non-nuclear Radioactive Waste 12
Simulation set up Lead and steel box, as designed and realized by the target group at LNL NEA Workshop on the Management of Non-nuclear Radioactive Waste 13
Y (cm) RP consideration on temporary storage 800 700 600 500 400 300 200 100 0 Gamma dose rate from exhausted targets Ceiling floor -100 2800 3200 3600 4000 4400 X (cm) < 50 msv/h Once filled the rack, targets will shield each other: dose rate below 50 usv/h A concrete wall 50 cm thick will reduce the dose rate by a factor 100 msv/h 10 7 10 6 10 5 10 4 10 3 10 2 10 1 10-1 10-2 NEA Workshop on the Management of Non-nuclear Radioactive Waste 14
Irradiation process the shielding UC 2 target (30 g) in the form of 7 thin disks. Energy: 40 MeV Current: 200 ma Irradiation period: 20 years Working load: 5000 hours/year target 2 m distant from the wall surface; shielding wall 360 cm wide; UC 2 cylindrical activation sample cut in the wall, radius 3 cm, zero degree parallel to the beam direction p 40MeV 200 ma NEA Workshop on the Management of Non-nuclear Radioactive Waste 15
Shielding Material Elemental composition of concrete (r=2.3 g/cm 3 ) used for the shielding of the target hall: Hydrogen underestimated (conservative assumption neutron slowing down effect); Eu and Co important because of their long half lives; Iron percentage does not include that due to the reinforcement rods. Element Atomic Fraction Weight Fraction Hydrogen 0.1047 0.55% Oxygen 0.584 48.91% Magnesium 0.0157 2.0% Aluminum 0.0317 4.48% Silicon 0.2115 31.1% Calcium 0.0479 10.05% Iron 0.01 2.92% Europium 3.7 10-8 0.294 ppm Cobalt 0.826 10-6 2.55 ppm Reinforcement is obtained with a stainless steel grid, with rods of radius 1 cm, spaced by 10 cm. NEA Workshop on the Management of Non-nuclear Radioactive Waste 16
cm -2 per proton Neutron fluence p 40MeV 200 ma UC 2 NEA Workshop on the Management of Non-nuclear Radioactive Waste 17
Neutron energy Reactions of neutrons with nuclei in the shielding: Thermal neutrons (E < 1 ev) High energy neutrons (E > 20 MeV) NEA Workshop on the Management of Non-nuclear Radioactive Waste 18
Neutron energy and radioactive species Some long lived radionuclides are produced by high energy neutrons ( 54 Mn, 22 Na) 54 Mn 54 Fe (n,p) 55 Mn (n,2n) 22 Na 23 Na (n,2n) NEA Workshop on the Management of Non-nuclear Radioactive Waste 19
Neutron energy and radioactive species Some radionuclides produced by thermal neutrons: the activity concentration as a function of the depth in concrete resembles that of thermal flux. 46 Sc 45 Sc (n,g) 59 Fe 58 Fe (n,g) 60 Co 59 Co (n,g) 152 Eu 151 Eu (n,g) NEA Workshop on the Management of Non-nuclear Radioactive Waste 20
Radioactive species in concrete Following the irradiation of the concrete structure by secondary neutrons, nuclei de-excite by the emission of energetic g-rays; Nuclide Half life 152 Eu 13.5 y 60 Co 5.27 y 59 Fe 44.5 d 56 Co 77.27 d g-ray energy (kev) 121.78 1408.01 1173.24 1332.5 1099.22 1291.56 846.7 1238.0 Table: Radionuclides with T 1/2 > 1 month. The more energetic g emitters have been included. 54 Mn 312.12 d 834.83 46 Sc 83.79 d 26 Al 7.4 10 5 y 889.25 1120.51 1808.0 1129.0 22 Na 2.602 y 1274.54 NEA Workshop on the Management of Non-nuclear Radioactive Waste 21
Radioactive species in concrete Long lived radionuclides in a sample 20 cm deep from the surface, at the end of the irradiation period (20 years). Nuclide Half life 152 Eu 13.5 y 60 Co 5.27 y Activity (Bq/g) 232.7 172.7 6% of the overall activity is due to nuclides with half life longer than 1 year. The nuclides specified in the table are found in the concrete sample. In the rods some of these nuclides can be found (species produced by irradiation of iron, 60 Co, 59 Fe, 55 Fe, 54 Mn) with higher concentrations. 59 Fe 44.5 d 137.8 55 Fe 2.73 y 1.2 10 4 54 Mn 312.12 d 1.5 10 3 45 Ca 162.61 d 1.0 10 4 26 Al 7.4 10 5 y 216.0 22 Na 2.602 y 223.0 3 H 12.33 y 1.4 10 3 NEA Workshop on the Management of Non-nuclear Radioactive Waste 22
Activation and cooling Activity concentration rapidly decays as the depth increases in the first 20-30 cm. Symbols represent the activity concentration in the rods, while lines represent the same quantity in concrete. As a representative value, 1Bq/g is obtained after 20 years of cooling time in the outer part 185 cm thick. NEA Workshop on the Management of Non-nuclear Radioactive Waste 23
Conclusions LNL host particles accelerators for research in nuclear physics New projects and high power involved push for consideration of waste production and planning for disposal Necessary to start the study before civil construction starts, in order to plan places and techniques for future disposal. NEA Workshop on the Management of Non-nuclear Radioactive Waste 24
Thank you for your attention L. Sarchiapone Laboratori Nazionali di Legnaro (Pd) Istituto Nazionale di Fisica Nucleare INFN Lucia.Sarchiapone@lnl.infn.it NEA Workshop on the Management of Non-nuclear Radioactive Waste 25 +39 049 8068 394