Transmutation of ¹²⁹I in a single-fluid double-zone Thorium Molten Salt Reactor

Transmutation of 129 I in a single-fluid double-zone Thorium Molten Salt Reactor 1 2 3 first-author https://orcid.org/0000-0002-3492-8742 1 2 https://orcid.org/0000-0002-5163-3903 1 2 3 https://orcid.org/0000-0002-7108-2344 1 2 corresp Corresponding author, zouchunyan@sinap.ac.cn Corresponding author, zouchunyan@sinap.ac.cn zouchunyan@sinap.ac.cn https://orcid.org/0000-0002-6564-4072 1 2 3 corresp Corresponding author, chenjg@sinap.ac.cn Corresponding author, chenjg@sinap.ac.cn chenjg@sinap.ac.cn https://orcid.org/0000-0002-7801-7895 Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201800, China CAS Innovative Academies in TMSR Energy System, Chinese Academy of Sciences, Shanghai 201800, China CAS Innovative Academies in TMSR Energy System, Chinese Academy of Sciences, Shanghai 201800, China University of Chinese Academy of Sciences, Beijing 100049, China University of Chinese Academy of Sciences, Beijing 100049, China Herein we assess the 129 I transmutation capability of a 2250-MWt single-fluid double-zone thorium molten salt reactor (SD-TMSR) by considering two methods. One is realized by loading an appropriate amount of 129 I before the startup of the reactor, and the amount of 129 I during operation is kept constant by online feeding 129 I. The other adopts only an initial loading of 129 I before startup, and no other 129 I is fed online during operation. The investigation first focuses on the effect of the loading of I on the Th- 233 U isobreeding performance. The results indicate that a 233 U isobreeding mode can be achieved for both scenarios for a 60-year operation when the initial molar proportion of LiI is maintained within 0.40% and 0.87%, respectively. Then, the transmutation performances for the two scenarios are compared by changing the amount of injected iodine into the core. It is found that the scenario that adopts an initial loading of 129 I shows a slightly better transmutation performance in comparison with the scenario that adopts online feeding of 129 I when the net 233 U productions for the two scenarios are kept equal. The initial loading of 129 I scenario with LiI = 0.87% molar proportion is recommended for 129 I transmutation in the SD-TMSR, and can transmute 1.88 t of 129 I in the 233 U isobreeding mode over 60 years. Key words: 129 I transmutation Thorium Molten Salt Reactor Th-U isobreeding 1. Introduction 1 Long-lived (over 10 5 years) fission products (LLFPs) are the primary contributors to the radioactive hazards of nuclear waste, which impede the sustainable development of nuclear energy. Because of its long half-life of 1.60 × 10 7 years, large radiotoxicity coefficient of 2.70 × 10 -1 Sv/g, and high geochemical mobility [ 1 1 ] , 129 I is one of the most important LLFPs. The annual production amount of 129 I is about 5 kg in a traditional 1000-MWe pressurized water reactor (PWR), which accounts for a mass fraction of about 80% in the iodine isotopes. The other 20% is provided by the stable isotope of 127 I [ 2 2 ] . Transmutation is an effective way to eliminate or minimize the radioactive hazard of 129 I [ 3 3 ] . When 129 I captures a neutron, it emits an electron and becomes stable 130 Xe. For the transmutation of 129 I, 127 I in the iodine isotopes must also be considered since the isotope separation of 129 I is very complex and costly. Thus, some 129 I will be produced from 127 I by two sequential neutron captures. Fortunately, both 127 I and its daughter product of 128 I have relatively small thermal neutron capture cross sections of 6.1 b and 3.7 b, respectively. In addition, 128 I with a half-life of 0.4 h will quickly decay to stable 128 Xe, which is also beneficial in reducing the production of 129 I from 127 I. The transmutation of 129 I has been extensively investigated in different types of reactors including the accelerator driven system (ADS) [ 4 4 , 5 5 ] , fast reactor [ 6 6 , 7 7 ] , and PWR [ 8 8 , 9 9 ] . For the 129 I transmutation in ADS, Song et al. performed a systematic study by loading double-annular LLFP target assemblies with CaI 2 in the reflector region of an ADS [ 4 4 ] . Afterward, Ismailov et al. improved the 129 I transmutation rate by loading the sodium iodide assembly in both the core and the surrounding core region, and a transmutation rate of 129 I up to 46 kg/y was achieved in an 800-MWt ADS [ 5 5 ] . Regarding the 129 I transmutation in a fast reactor, Wakabayshi investigated the 129 I transmutation performance by loading NaI in the blanket region of a 1600-MWt fast reactor, and about 18 kg/y of 129 I was transmuted [ 7 7 ] . The 129 I transmutation in a thermal reactor is also recognized as a promising method owing to the large thermal neutron capture cross section of 129 I and the mature operation technology of PWR. Recently, Liu et al. studied the 129 I transmutation capability in a 1000-MWe PWR by loading the MgI 2 target in the guide tube and discrete pins [ 9 9 ] . The discrete pin loading scenario provided an excellent 129 I transmutation capability of 20.25 kg/y. Recently, a liquid-fueled reactor concept of a molten salt reactor (MSR) was investigated for the 129 I transmutation [ 10 10 ] . MSR has many fascinating characteristics including inherent safety, excellent neutron economy, no fuel fabrication, online refueling, and reprocessing [ 11 11 ] . Different from the 129 I transmutation in a solid-fuel reactor where only a small portion of 129 I can be loaded in the irradiation targets, MSR allows for a large amount of iodine to be initially loaded and/or continuously added to the fuel salt during the reactor operation, implying an attractive potential of 129 I transmutation in an MSR. The 129 I transmutation capacity for a 2500-MWt Thorium Molten Salt Reactor (TMSR) was evaluated. The inventory of 129 I was kept constant (290 kg) by online feeding 129 I into the fuel salt during the reactor operation based on the 233 U isobreeding mode. The transmutation capacity of 129 I in the TMSR was 10.2 kg/y [ 10 10 ] . Nevertheless, the 129 I transmutation weakened the Th-U breeding or conversion capacity of the reactor because a considerable number of neutrons in the core can be absorbed by 129 I instead of 232 Th. This means that an MSR with a higher Th-U breeding/conversion capacity may offer a remarkably higher 129 I transmutation capability. A single-fluid double-zone thorium molten reactor (SD-TMSR) was proposed by optimizing the ratios of molten salt and graphite in both the inner and the outer fuel assemblies [ 12 12 ] . The Th-U breeding ratio of SD-TMSR was about 1.08, which is significantly larger than that of the above TMSR. Hence, we focus on evaluating the 129 I transmutation based on the SD-TMSR under the 233 U isobreeding condition. The initial and online loading of 129 I are analyzed to compare their 129 I transmutation performances as well as their influences on reactor operation. Section 2 describes the SD-TMSR and the calculation tool. Results and discussions are presented in Sect. 3. Section 4 gives the conclusions. 2. Description of SD-TMSR and calculation tool 1 2.1 Core description 2 The SD-TMSR is a 2250-MWt reactor with a thermal neutron spectrum. Figure 1 Figure 1 shows a quarter vertical geometry model of the SD-TMSR including the fuel salt, graphite moderator and reflectors, B 4 C neutron protection layer, and Hastelloy N alloy vessel. The main parameters of the SD-TMSR are listed in Table 1 Table 1 . The total fuel salt volume is 52.9 m³, which is distributed in the inner and outer zones in the core, top plenum, bottom plenum, and heat exchanger. Fuel salt with a composition of 70 LiF-17.5 BeF 2 -12.5 HNF 4 (mol%) is adopted in the SD-TMSR, where the 7 Li enrichment and the fuel salt density are 99.995% and 3.33 g/cm 3 , respectively. The B 4 C layer and Hastelloy N alloy vessel have an identical thickness of 10 cm. 1 1 Parameters 1 1 Value 1 1 Thermal power (MWt) 1 1 2250 1 1 Fuel volume (m 3 ) 1 1 52.9 1 1 Core diameter and height (cm) 1 1 460/460 1 1 Inscribed radius of graphite hexagonal prism (cm) 1 1 6.495 1 1 Inner fuel salt channel radius (cm)Outer fuel salt channel radius (cm) 1 1 3.55 1 1 Thickness above and below salt plena (cm) 1 1 30 1 1 Thickness above, below, and side graphite (cm) 1 1 130/130/50 1 1 Thickness of B 4 C (cm) 1 1 10 1 1 Fuel salt composition (mol%) 1 1 70 LiF-17.5 BeF 2 -12.5 HNF 4 1 1 Fuel salt temperature (K) 1 1 900 1 1 Density of fuel salt at 900 K (g/cm 3 ) 1 1 3.3 1 1 Dilatation coefficient of fuel salt (g/cm³/K) 1 1 -6.7 × 10 -4 1 1 Enrichment of 7 Li (mol%) 1 1 99.995 1 1 Density of graphite (g/cm 3 ) 1 1 2.3 1 1 Density of B 4 C (g/cm 3 ) 1 1 2.52 1 1 Enrichment of 10 B (mol%) 1 1 18.4 2.2 Calculation tool 2 The MSR reprocessing sequence (MSR-RS) [ 13 13 - 15 15 13-15 ] is adopted in this work to simulate the iodine transmutation, which is coupled with the criticality analysis module (CSAS6), problem-dependent cross-section processing module (TRITON), and depletion and decay calculation module (ORIGEN-S) in the SCALE6.1 program. A flowchart of the MSR-RS is displayed in Fig. 2 Fig. 2 . First, the core geometry and molten salt compositions are initialized. Then, a criticality calculation is performed by CSAS6 based on the entire core, and a 238-group ENDF/B-VII cross-section database is used. A one-group cross-section library is generated by the TRITON calculation, which performs problem-dependent cross-section processing followed by a multigroup neutron transport calculation. The burnup calculation is performed by ORIGEN-S with online reprocessing and refueling. During each burnup time step, the molten salt compositions are modified following a reprocessing scheme set by the user and are followed by another CSAS6 calculation step to obtain a new neutron flux and a new k eff determined by both depletion and refueling. Then, a new TRITON input file is produced for the next-step burnup calculation. The cycle calculation is performed iteratively until the cycle time reaches the value set by the user. The MSR-RS was verified in our previous work [ 12 12 - 16 16 12-16 ] . In this MSR-RS, the gaseous and noble metallic FPs in the fuel salts are removed online through a helium bubbling system with a constant separation time of 30 s and separation efficiency of 100%. The other soluble FPs are continuously removed, and Pa is extracted online by chemical reprocessing at a reprocessing rate of 5 m 3 /d and separation efficiency of 100% [ 12 12 ] . In addition, 232 Th and 233 U are injected online into the fuel salt to maintain the reactor criticality and the total actinide inventory constant for the stability of the molten salt. 3. Results and discussions 1 The online feeding and initial loading of 129 I scenarios are introduced in this section. Then, the net 233 U production of the SD-TMSR for the above scenarios is analyzed by varying the LiI loading to obtain a Th- 233 U isobreeding. Finally, the 129 I transmutation performances for the above scenarios with different LiI loadings are compared. 3.1 129 I transmutation scenarios 2 It is essential to select a proper chemical compound of iodine to minimize its effects on the fuel salt component of SD-TMSR. Several iodide forms such as ThI 4 , UI 4 , BeI 2 , and LiI have been investigated during the past several decades. Compared with ThI 4 , UI 4 , and BeI 2 , LiI is more appropriate for 129 I transmutation because it has excellent stability in air and can be dissolved into the molten salt at a large amount [ 17 17 ] . Hence, LiI is chosen as sample form and is loaded into the fuel salt to substitute for some LiF in the FLiBe carrier salt. For instance, the fuel salt composition becomes 69 LiF-1 LiI-17.5 BeF 2 -12.5 HNF 4 (mol%) if 1.0 mol% of LiI is loaded into the fuel salt. An analysis of the 129 I transmutation scenario (named scenario 1) is performed by online feeding 129 I into the fuel salt to keep the 129 I amount in the core constant during the SD-TMSR operation. Nevertheless, the online feeding of 129 I is relatively complex for the SD-TMSR operation because it requires an accurate monitoring of the 129 I inventory both in the core and online feed during the entire operation. Considering the disadvantages in scenario 1, we propose an alternative 129 I transmutation (scenario 2) in which 129 I is initially loaded into fuel salt before the startup of the reactor, and no other 129 I is fed into the fuel salt during the reactor operation. A large loading of 129 I may improve the transmutation capacity of 129 I. However, the physicochemical properties of the fuel salt may be changed when a large amount of LiI is loaded. In addition, more 233 U is loaded into the fuel salt to maintain the reactor criticality, which is disadvantageous from the standpoint of Th-U fuel breeding. Hence, a proportion of 1% LiI is adopted as the upper limit to minimize the change in the fuel salt component. 3.2 Th- 233 U isobreeding performance 2 Owing to the larger thermal neutron absorption cross section of 129 I compared with 19 F, more thermal neutrons in the core are absorbed when 19 F is replaced by 129 I in the fuel salt, which hardens the neutron spectrum of the SD-TMSR (see Fig. 3 Fig. 3 ). Therefore, more 233 U loading is required to maintain the reactor criticality when a large amount of iodine is loaded into the fuel salt. Fig. 4 Fig. 4 shows the initial 129 I inventory and the required initial 233 U loading as a function of the LiI molar proportion under the critical condition ( k eff ≈ 1). When the LiI proportion increases from 0 to 1.0 mol%, the increment of initial 129 I loading is about 2.7 t, and the corresponding 233 U mass increases almost linearly by about 0.35 t. The burnups for the above two 129 I transmutation scenarios with different LiI loading proportions are simulated by the MSR-RS for up to 60 years. The Th-U breeding performance can be evaluated by the net 233 U production, which is defined as [ 18 18 , 19 19 ] <math display="block" id="M1"><mrow><msup><mrow/><mrow><mn>233</mn></mrow></msup><mtext>U </mtext><mrow><mo>(</mo><mrow><mtext>production</mtext></mrow><mo>)</mo></mrow><mtext> </mtext><msup><mo>=</mo><mrow><mn>233</mn></mrow></msup><mtext>U </mtext><mrow><mo>(</mo><mrow><mtext>residue</mtext></mrow><mo>)</mo></mrow><mtext> </mtext><msup><mo>+</mo><mrow><mn>233</mn></mrow></msup><mtext>Pa </mtext><mrow><mo>(</mo><mrow><mtext>extract</mtext></mrow><mo>)</mo></mrow><mtext> </mtext><msup><mo>−</mo><mrow><mn>233</mn></mrow></msup><mtext>U </mtext><mrow><mo>(</mo><mrow><mtext>inject</mtext></mrow><mo>)</mo></mrow><mo>,</mo></mrow></math> where 233 U (inject) is the total injected 233 U amount into the core, which includes the initially loaded and online-fed 233 U masses; 233 Pa (extract) is the extracted mass of 233 Pa from the core; and 233 U (residue) is the residual mass of 233 U in the core. A positive value of the net 233 U production means that more 233 U can be bred than consumed in the core, while a negative value indicates that the produced 233 U in the core is insufficient to compensate for the consumed 233 U, and additional 233 U from other reactors should be fed into the core to maintain the reactor criticality. The evolutions of the net 233 U production and inventories of key nuclides for both scenarios with LiI = 1.0% are presented in Fig. 5 Fig. 5 . For scenario 1, the net 233 U production monotonically decreases during the 60 years of operation, while the 233 U inventory in the core increases gradually with the operation time. In particular, some actinides generated from 233 U, including nonfissile isotopes (e.g., 234 U) and fissile isotopes (e.g., 235 U), also keep accumulating in the reactor. The generation of new fissile isotopes is insufficient to compensate for the negative reactivity inserted by the accumulation of new nonfissile isotopes during the operation. Hence, additional 233 U has to be injected into the core to maintain the reactor criticality, which makes the 233 U amount in the core increase gradually from 1.63 t at startup to 1.81 t at the end of life, as shown in Fig. 5(b) Fig. 5(b) . During the first two years, the slight increase of 233 U amount in the core is primarily caused by the accumulated FPs since no considerably heavier actinides are produced in the core for such a short operation time. To maintain the critical operation of the SD-TMSR for 60 years, the total fed mass of 233 U is about 42.69 t. Meanwhile, the total extracted mass of 233 Pa is about 37.89 t, which is 4.80 t smaller than the total fed mass of 233 U. Hence, according to Eq. (1), the net 233 U production for scenario 1 is about -4.62 t at the end of life (LiI = 1.0%). By contrast, the 129 I inventory in the core for scenario 2 decreases from 2.73 t at startup to 0.59 t at the end of life since no 129 I is fed online into the core during operation. The decrease of 129 I inventory in the core induces a positive reactivity that exceeds the total negative reactivity caused by the neutron absorption of accumulated FPs and heavier actinides during the entire operation. Therefore, the 233 U inventory in the core decreases from 1.63 t at startup to 1.53 t at the end of life. However, the initially loaded 233 U is insufficient to maintain the critical operation of the core in the depletion process owing to its fission depletion and the accumulation of FPs and heavier actinides. Therefore, 233 U should be continuously fed into the fuel salt to maintain the reactor criticality during the entire operation. For the 60-year operation, k eff of the core is kept at ~1.0 by the online feeding of 233 U and Th. In addition, with a lower total 129 I inventory in the core, the transmutation rate of 129 I for scenario 2 in the depletion process is much smaller than that for scenario 1, which indicates that scenario 2 requires less 233 U to compensate for the negative reactivity by 129 I than scenario 1. In other words, 233 U is fueled online into the core to primarily compensate for its fission consumption for scenario 2, which leads to a much smaller amount of externally fed 233 U fuel than scenario 1. The net 233 U production for scenario 2 is -0.43 t at the end of life, which is 4.19 t greater than that for scenario 1, as shown in Fig. 5(a) Fig. 5(a) . One can also find from Fig. 5 Fig. 5 that the net 233 U production for both scenarios has significantly different evolution trends and always changes with the operation time. Considering the negative net 233 U production for both scenarios (LiI = 1.0%) at the end of life, the dependence of net 233 U production on varying LiI loading is presented in Fig. 6 Fig. 6 . The loss rate of the net 233 U production for scenario 2 is much smaller than that for scenario 1 because the total 129 I loading amount of the core for the former is much smaller than that for the latter. For instance, the total 129 I loading amount of the core for scenario 2 (LiI = 1.0%) is 2.73 t, which is 3.67 t smaller than that for scenario 1 (LiI = 1.0%) because no 129 I is fed online into the core for scenario 2 (LiI = 1.0%). It is found that when the initial molar proportions of LiI for both scenarios are maintained within ~0.40% and 0.87%, respectively, the net 233 U production is equal to 0 t, indicating that a 233 U isobreeding mode for both scenarios can be achieved for a 60-year operation in the SD-TMSR, as shown in Fig. 6 Fig. 6 . 3.3. Transmutation capability of 129 I 2 The 129 I transmutation capability of the SD-TMSR can be evaluated by two important parameters: transmuted mass and fraction. The transmuted fraction is defined as <math display="block" id="M2"><mrow><mtext>TF</mtext><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow><mtext> </mtext><mo>=</mo><mtext> </mtext><mfrac><mrow><mtext>Δ</mtext><mi>M</mi><mo> </mo><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow><mrow><msub><mi>M</mi><mn>0</mn></msub><mo> </mo><mrow><mo>(</mo><mi>t</mi><mo>)</mo></mrow></mrow></mfrac><mo>,</mo></mrow></math> where M 0 ( t ) is the injected mass of 129 I into the core, which includes the initially loaded and online-fed 129 I masses at operating time t . Δ M ( t ) is the transmuted mass of 129 I, which is equal to the difference between the injected mass and the residual mass of 129 I in the core at operating time t . Fig. 7 Fig. 7 presents the evolutions of the transmuted mass, injected mass, and transmuted fraction of 129 I for both scenarios (LiI = 1.0%). It is found that the transmuted mass of 129 I for scenario 2 increases with the operation time, but the transmutation rate decreases with the operation time compared to scenario 1 because of the decrease of 129 I inventory in the core [see Fig. 5(b) Fig. 5(b) ]. Therefore, the transmuted mass of 129 I for scenario 2 is about 2.14 t at the end of life, which is 1.53 t smaller than that for scenario 1. However, the transmuted fraction of 129 I for the former is 78.34% at the end of life, which is 20.83% greater than that for the latter. To investigate the relationship between the transmutation capability of 129 I and net 233 U production, the transmuted mass and fraction of 129 I at the end of life as a function of the net 233 U production for both scenarios are presented in Fig. 8 Fig. 8 . The transmuted mass of 129 I for scenario 2 is slightly larger than that for scenario 1 under an identical net 233 U production condition, indicating that scenario 2 is superior to scenario 1. When the SD-TMSR achieves a 233 U isobreeding mode, the transmuted mass of 129 I for scenario 2 is about 1.88 t, which is 0.16 t greater than that for scenario 1. In addition, the transmuted fraction for the former is 78.96%, which is also significantly larger than that for the latter (65.50%). The transmuted mass and fraction of 129 I and the net 233 U production for both scenarios with different LiI loadings are listed in Table 2 Table 2 and Table 3 Table 3 , respectively. 1 1 Initial molar proportion 1 1 0% 1 1 0.30% 1 1 0.40% 1 1 0.50% 1 1 0.70% 1 1 0.90% 1 1 1.00% 1 1 Initially loaded 129 I (t) 1 1 0 1 1 0.83 1 1 1.10 1 1 1.38 1 1 1.92 1 1 2.46 1 1 2.73 1 1 Fed 129 I (t) 1 1 0 1 1 1.37 1 1 1.74 1 1 2.13 1 1 2.81 1 1 3.45 1 1 3.67 1 1 Residual 129 I at the end of life (kg) 1 1 1.86 1 1 862.48 1 1 1124.96 1 1 1404.61 1 1 1943.66 1 1 2498.98 1 1 2718.29 1 1 Transmuted mass of 129 I (kg) 1 1 -1.86 1 1 1337.30 1 1 1722.66 1 1 2102.56 1 1 2778.36 1 1 3412.77 1 1 3668.97 1 1 Transmuted fraction of 129 I (%) 1 1 - 1 1 60.79 1 1 60.50 1 1 59.95 1 1 58.73 1 1 57.73 1 1 57.51 1 1 Net 233 U production (t) 1 1 4.46 1 1 1.04 1 1 0.12 1 1 -0.83 1 1 -2.48 1 1 -4.05 1 1 -4.62 1 1 Initial molar proportion 1 1 0% 1 1 0.30% 1 1 0.50% 1 1 0.70% 1 1 0.87% 1 1 0.90% 1 1 1.00% 1 1 Initially loaded 129 I (t) 1 1 0 1 1 0.83 1 1 1.38 1 1 1.92 1 1 2.38 1 1 2.46 1 1 2.73 1 1 Residual 129 I at the end of life (kg) 1 1 1.86 1 1 156.61 1 1 270.28 1 1 392.42 1 1 500.61 1 1 521.05 1 1 589.82 1 1 Transmuted mass of 129 I (kg) 1 1 -1.86 1 1 671.62 1 1 1105.48 1 1 1527.21 1 1 1878.47 1 1 1938.83 1 1 2138.84 1 1 Transmuted fraction of 129 I (%) 1 1 - 1 1 81.09 1 1 80.35 1 1 79.56 1 1 78.96 1 1 78.82 1 1 78.34 1 1 Net 233 U production (t) 1 1 4.46 1 1 2.91 1 1 1.88 1 1 0.89 1 1 0.18 1 1 -0.01 1 1 -0.43 In order to investigate the difference in 129 I transmutation performance under the 233 U isobreeding mode between the above two scenarios, the evolutions of the transmuted mass and inventory of 129 I are displayed in Fig. 9 Fig. 9 . For scenario 1, the transmuted mass of 129 I increases linearly with the operation time, which is about 1.72 t at the end of life owing to the constant inventory of 129 I in the core. This indicates that the transmutation rate of 129 I can stay almost constant at about 28.67 kg/y. By contrast, the transmuted mass of 129 I for scenario 2 is about 1.88 t at the end of life, while the transmutation rate declines with the operation time owing to the decrease of 129 I inventory in the core. Hence, the transmuted mass of 129 I for scenario 2 is larger than that for scenario 1 during the 60 years of operation. However, most of the 129 I for scenario 2 is transmuted during the first 30 years and is about 1.28 t, which is much greater than that during the remaining 30 years at 0.6 t. Considering its higher transmutation performance and simpler operation of the reactor, scenario 2 with an initial molar proportion of LiI = 0.87% is recommended for the 129 I transmutation in the SD-TMSR. The transmutation capability of 129 I in the SD-TMSR is also compared with other reactors in Table 4 Table 4 . The supportive factor is defined as the ratio of the transmuted mass of 129 I in the different reactors to the yield of 129 I in a traditional 1000-MWe PWR under normalized thermal output and operation time [ 20 20 ] . The transmutation rate, supportive factor, and transmuted fraction of the SD-TMSR are 13.92 g/(MWt·y), 8.19, and 78.96%, respectively, which are significantly larger than those of the TMSR. The SD-TMSR also exhibits an excellent 129 I transmutation performance compared with the PWR and the fast reactor. Although the transmutation rate and supportive factor of the SD-TMSR are much smaller than those of the ADS, the transmuted fraction of the former is significantly larger than that of the latter since the solid 129 I target in a solid-fuel reactor cannot undergo long-term operation owing to its mechanism and irradiation performance. 1 1 Type 1 1 Fast reactor 1 1 ADS 1 1 PWR 1 1 TMSR 1 1 SD-TMSR 1 1 Power (MWt) 1 1 1600 1 1 800 1 1 2941 1 1 2500 1 1 2250 1 1 Transmutation rate (g/MWt·y) 1 1 11.25 1 1 57.50 1 1 6.88 1 1 4.08 1 1 13.92 1 1 Supportive factor 1 1 6.62 1 1 33.82 1 1 4.05 1 1 2.40 1 1 8.19 1 1 Transmuted fraction (%) 1 1 5.20 1 1 5.58 1 1 7.00 1 1 67.48 1 1 78.96 4. Conclusion 1 A systematic study of the 129 I transmutation in the SD-TMSR was performed. First, the initial 233 U loading as a function of 129 I loading was analyzed. Then, both the online feeding (scenario 1) and initial loading (scenario 2) of 129 I were analyzed to compare their transmutations and Th-U breeding capabilities. Conclusions drawn from the above analyses are as follows: The initial 233 U loading was first analyzed for different LiI loadings from 0 to 1.0 mol%. When the initial loading proportion of LiI increased from 0 to 1%, the initial 233 U loading mass increased by 0.35 t to maintain the reactor criticality since the neutron spectrum of the core became harder. Then, the Th-U breeding performance and 129 I transmutation capability for both scenarios were investigated with different LiI molar proportions in the fuel salt. A large loading of 129 I is a disadvantage to the Th-U breeding or conversion of the reactor. When the loading proportion of LiI increased from 0 to 1 mol%, the net 233 U production for scenario 1 at the end of life decreased from 4.46 t to -4.62 t, while that for scenario 2 at the end of life decreased from 4.46 t to -0.43 t. To achieve 233 U isobreeding for the two scenarios, the initial molar proportion of LiI had to be kept within 0.40% for scenario 1 and 0.87% for scenario 2. Under the 233 U isobreeding mode, the transmuted mass and fraction of 129 I for scenario 2 were about 1.88 t and 78.96%, respectively, which are larger than those for scenario 1. Accordingly, an initial loading of 129 I scenario with LiI = 0.87% is recommended for the 129 I transmutation in the SD-TMSR. The transmutation rate, supportive factor, and transmuted fraction of SD-TMSR were 14.36 g/(MWt·y), 8.45, and 78.96%, respectively, which are significantly larger than those of the PWR and fast reactor. 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Des . 241 , 395 - 401 ( 2011 ). https://doi.org/10.1016/j.nucengdes.2010.10.019 https://doi.org/10.1016/j.nucengdes.2010.10.019 Study on the LLFPs transmutation in a super-critical water-cooled fast reactor 10.1007/s41365-019-0720-1 This work was supported by the Chinese TMSR Strategic Pioneer Science and Technology Project (No. XDA02010000) and the Frontier Science Key Program of the Chinese Academy of Sciences (No. QYZDY-SSW-JSC016). 2019-09-29 2019-11-11 2019-11-12 2020-01-03 2020-01-01 2021-04-10 © China Science Publishing & Media Ltd. (Science Press), Shanghai Institute of Applied Physics, the Chinese Academy of Sciences, ChineseNuclear Society and Springer Nature Singapore Pte Ltd. 2020 This is a post-peer-review, pre-copyedit version of an article published in Nuclear Science and Techniques. The final authenticated version is available online at: http://dx.doi.org/10.1007/s41365-019-0720-1 http://dx.doi.org/10.1007/s41365-019-0720-1 . 2020 Nuclear Science and Techniques 1 31