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Fig. 4. (A) Neutron fluence at different concrete depths without neutron absorbing materials, (B) integrated neutron fluence (E,<0.4 eV) as a function of concrete thickness in the front wall indicated as position 2 in Fig. 1. The proton beam current is 60 YA. Horizontal and vertical dashed lines correspond to the thermal neutron flux of 10° n-crv?-s' and 64 cm concrete to be radioactive waste, respectively. coming into the concrete interact with the hydrogens in a Fig. 3. Neutron spectrum in the forward direction respect to the proton beam indicated as position 1 in Fig. 1 at 40 cm before the concrete. The spectrum contains 20% thermal neutrons and 80% epithermal and fast neutrons. The vertical dashed line indicates the thermal neutron energy of 0.4 eV.

Figure 4 (A) Neutron fluence at different concrete depths without neutron absorbing materials, (B) integrated neutron fluence (E,<0.4 eV) as a function of concrete thickness in the front wall indicated as position 2 in Fig. 1. The proton beam current is 60 YA. Horizontal and vertical dashed lines correspond to the thermal neutron flux of 10° n-crv?-s' and 64 cm concrete to be radioactive waste, respectively. coming into the concrete interact with the hydrogens in a Fig. 3. Neutron spectrum in the forward direction respect to the proton beam indicated as position 1 in Fig. 1 at 40 cm before the concrete. The spectrum contains 20% thermal neutrons and 80% epithermal and fast neutrons. The vertical dashed line indicates the thermal neutron energy of 0.4 eV.

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Table 1. Major Radionuclides in Concrete and Corresponding Char- acteristics trons that are already installed and are in operation.
Table 1. Major Radionuclides in Concrete and Corresponding Char- acteristics trons that are already installed and are in operation.
Fig. 2. Neutron absorption cross sections for “Gd, ""B, and ""H taken from JENDL-4.0 [17]. The vertical dashed line indicates the thermal neutron energy of 0.4 eV. 1, 2, 3, and 4 are shown in this work. In this simulation, the concrete wall was divided into layers with the dimensions of 30 x 30 cm? and the thickness of 3 cm. Neutrons were scored at each layer using the [T-Track] tally in the PHITS code. The scored neutron fluence was folded with the cross sections taken from JENDL-4.0 to consider the impact of the thermal, epithermal and fast neutrons on the radionuclides produc- tion. The thickness of the H2'*O target was 1.04 cm with a di- ameter of 1.4 cm. The target is bombarded with 16.5-MeV protons. The radioactivity is due to trace element in the con- crete such as Eu and Co. The magnitude of activation will highly depend on the concrete composition. In this calcula- tions, concrete compositions are taken from PAL-XFEL-2017 Pohang Accelerator Laboratory X-ray Free Electron Laser) 18] with the densitv of 2.337 g:cm”.
Fig. 2. Neutron absorption cross sections for “Gd, ""B, and ""H taken from JENDL-4.0 [17]. The vertical dashed line indicates the thermal neutron energy of 0.4 eV. 1, 2, 3, and 4 are shown in this work. In this simulation, the concrete wall was divided into layers with the dimensions of 30 x 30 cm? and the thickness of 3 cm. Neutrons were scored at each layer using the [T-Track] tally in the PHITS code. The scored neutron fluence was folded with the cross sections taken from JENDL-4.0 to consider the impact of the thermal, epithermal and fast neutrons on the radionuclides produc- tion. The thickness of the H2'*O target was 1.04 cm with a di- ameter of 1.4 cm. The target is bombarded with 16.5-MeV protons. The radioactivity is due to trace element in the con- crete such as Eu and Co. The magnitude of activation will highly depend on the concrete composition. In this calcula- tions, concrete compositions are taken from PAL-XFEL-2017 Pohang Accelerator Laboratory X-ray Free Electron Laser) 18] with the densitv of 2.337 g:cm”.
to be the radioactive waste were determined. terials so as the effects of each material could be investigated separately. In the calculations, Gd2Os (7.407 g-cm*), BuC (2.52 g-cm®), BPE (1.01 g-cm*), and PE (0.94 g-cm*), with thicknesses of 5, 10, and 15 cm were considered for each ma- terial. In addition, a combination of PE+Gd.2O3, and PE+B.C were studied as well. Optimum material was determined by considering the thermal neutron absorption capability, the material cost and availability. Finally, the concrete thickness to be the radioactive waste were determined.
to be the radioactive waste were determined. terials so as the effects of each material could be investigated separately. In the calculations, Gd2Os (7.407 g-cm*), BuC (2.52 g-cm®), BPE (1.01 g-cm*), and PE (0.94 g-cm*), with thicknesses of 5, 10, and 15 cm were considered for each ma- terial. In addition, a combination of PE+Gd.2O3, and PE+B.C were studied as well. Optimum material was determined by considering the thermal neutron absorption capability, the material cost and availability. Finally, the concrete thickness to be the radioactive waste were determined.
PE, polyethylene; BPE, borated polyethylene. Table 2. Neutron Absorbing Materials and Thicknesses Used in the Calculations and Corresponding Transmitted Thermal Neutrons at Depth of 64 cm in Concrete
PE, polyethylene; BPE, borated polyethylene. Table 2. Neutron Absorbing Materials and Thicknesses Used in the Calculations and Corresponding Transmitted Thermal Neutrons at Depth of 64 cm in Concrete
Fig. 5. Thermal neutron fluences for different neutron absorbing materials and corresponding ratios, (yi sniet/ Pro shied) AS function of concret thickness in the front wall indicated as position 2 in Fig. 1. (A, B) for GdzOs, (C, D) for BG, (E, F) for PE, and (G, H) for BPE. Horizontal dashe lines correspond to thermal neutron flux of 10° n-crv?s". PE, polyethylene; BPE, borated polyethylene.
Fig. 5. Thermal neutron fluences for different neutron absorbing materials and corresponding ratios, (yi sniet/ Pro shied) AS function of concret thickness in the front wall indicated as position 2 in Fig. 1. (A, B) for GdzOs, (C, D) for BG, (E, F) for PE, and (G, H) for BPE. Horizontal dashe lines correspond to thermal neutron flux of 10° n-crv?s". PE, polyethylene; BPE, borated polyethylene.
Fig. 6. Thermal neutron fluences for different neutron absorbing materials and corresponding ratios, (Pwin snieti/ Pro snietd) AS function of concrete thickness in the front wall indicated as position 2 in Fig. 1. (A, B) for PE+BsC and (C, D) for PE+Gd2Os. The layers of BaC and Gd2Os are placed between the wall and PE. Horizontal dashed lines correspond to thermal neutron flux of 10° n-cm?:s". PE, polyethylene.
Fig. 6. Thermal neutron fluences for different neutron absorbing materials and corresponding ratios, (Pwin snieti/ Pro snietd) AS function of concrete thickness in the front wall indicated as position 2 in Fig. 1. (A, B) for PE+BsC and (C, D) for PE+Gd2Os. The layers of BaC and Gd2Os are placed between the wall and PE. Horizontal dashed lines correspond to thermal neutron flux of 10° n-cm?:s". PE, polyethylene.
Fig. 7. Thermal neutron fluences for PE and PE+B.C combinations as function of concrete thickness. (A) In the backward wall indicated a: position 3 in Fig. 1 and (B) in the left side wall indicated as position 4 in Fig. 1. Horizontal dashed lines correspond to thermal neutron flux o 10°n-cm*-s". PE, polyethylene.
Fig. 7. Thermal neutron fluences for PE and PE+B.C combinations as function of concrete thickness. (A) In the backward wall indicated a: position 3 in Fig. 1 and (B) in the left side wall indicated as position 4 in Fig. 1. Horizontal dashed lines correspond to thermal neutron flux o 10°n-cm*-s". PE, polyethylene.
Fig. 8. Distributions of thermal neutron flux (E,<0.4 eV) inside the cyclotron room and the concrete walls in vertical (left column) and to views (right column) (A, B) without neutron absorbing materials, (C, D) with 10 cm-thick PE, and (E, F) with 10 cm-thick PE+0.1 cm-thic B,C. The thin layer of BaC is placed between the wall and PE. The numbers indicate the depths at which thermal neutron flux exceeds 1( n-cm?-s" and concrete is radioactive waste. PE, polyethylene.
Fig. 8. Distributions of thermal neutron flux (E,<0.4 eV) inside the cyclotron room and the concrete walls in vertical (left column) and to views (right column) (A, B) without neutron absorbing materials, (C, D) with 10 cm-thick PE, and (E, F) with 10 cm-thick PE+0.1 cm-thic B,C. The thin layer of BaC is placed between the wall and PE. The numbers indicate the depths at which thermal neutron flux exceeds 1( n-cm?-s" and concrete is radioactive waste. PE, polyethylene.
Fig. 9. (A) Fast neutron fluence (E,>1 MeV) against the concrete depth without and with the 10 cm-thick PE+0.1 cm-thick B.C shielding, (B transmitted fast neutrons, (yi sriet/Pro shied) AS A function of concrete thickness in the front wall indicated as position 2 in Fig. 1. PE, polyethyl: ene. Structural concrete is often reinforced with steel bars that become activated via *Fe(n,y)*Fe, “Fe(n,p)*Mn, and °Co(n,y)Co reactions. The reinforcing bars contribution to the activation can be significant [21]. However, the number of fast and thermal neutrons significantly decrease by using 10 cm-thick PE+0.1 cm-thick B.C as the shielding material and the activation of the reinforcing bars are also decreased proportionally. It is noticed that the activated bars are local- ized and could be separated from the concrete during the tion decreased exponentially with the concrete depth and proportionally. It is noticed that the activated bars are local- and “Co at the concrete surface. The “Mn and ”Na produc-
Fig. 9. (A) Fast neutron fluence (E,>1 MeV) against the concrete depth without and with the 10 cm-thick PE+0.1 cm-thick B.C shielding, (B transmitted fast neutrons, (yi sriet/Pro shied) AS A function of concrete thickness in the front wall indicated as position 2 in Fig. 1. PE, polyethyl: ene. Structural concrete is often reinforced with steel bars that become activated via *Fe(n,y)*Fe, “Fe(n,p)*Mn, and °Co(n,y)Co reactions. The reinforcing bars contribution to the activation can be significant [21]. However, the number of fast and thermal neutrons significantly decrease by using 10 cm-thick PE+0.1 cm-thick B.C as the shielding material and the activation of the reinforcing bars are also decreased proportionally. It is noticed that the activated bars are local- ized and could be separated from the concrete during the tion decreased exponentially with the concrete depth and proportionally. It is noticed that the activated bars are local- and “Co at the concrete surface. The “Mn and ”Na produc-
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