Study on Neutronics of plutonium and Minor Actinides Transmutation in Accelerator Driven System Reactor By Amer Ahmed Abdullah Al-Qaaod Ph.D student Physics Department, Faculty of Science, Ain Shams University, Cairo, Egypt

Outline Introduction Aim of the work Core Descriptions and Modeling Spent nuclear fuel Accelerator driven system Aim of the work Core Descriptions and Modeling Results Homogenous and heterogeneous distribution for Pu and MA Burnup calculations for Pu and MA Conclusion

Spent nuclear fuel is the source of nuclear waste

Partitioning and Transmutation (P&T) Spent fuel Reprocessing U、Pu Recycle Geological disposal (Glass waste form) FP、MA Conventional scheme P&T technology MA (Np, Am, Cm) Transmutation by ADS and/or FR Partitioning (Example) PGM (Ru, Rh, Pd) Utilization and/or disposal Geological disposal after cooling and/or utilization Heat generator (Sr, Cs) Geological disposal (high-density glass waste form) Remaining elements MA: Minor Actinides FP: Fission Products PGM: Platinum Group Metal FR: Fast Reactor ADS: Accelerator Driven System

Reduction of Radiological Toxicity by P&T Radiological Toxicity: Amount of radioactivity weighted by dose coefficient of each nuclide. Normalized by 1t of spent fuel. 9t of natural uranium (NU) is raw material of 1t of low-enriched uranium including daughter nuclides. Spent fuel (1t) High-level waste MA transmutation Natural uranium (9t) Radiological toxicity (Sv) Reduction Time period to decay below the NU level: Spent fuel 100,000y 　　↓ High-level waste 5,000y 　　↓ MA transmutation 300y　 Time after reprocessing (Year) 5

Short-lived or stable nuclides Long-lived nuclides (MA) Accelerator Driven System (ADS) for MA Transmutation Proton beam Max.30MW Super-conducting LINAC 100MW To accelerator 800MW 170MW Fission energy To grid Spallation target (LBE) MA: Minor Actinides LBE: Lead-Bismuth Eutectic 270MW Power generation Transmutation by ADS MA-fueled LBE-cooled subcritical core Utilizing chain reactions in subcritical state Proton Spallation target Fission neutrons Fast neutrons Characteristics of ADS: Chain reactions stop when the accelerator is turned off. LBE is chemically stable.  High safety can be expected. High MA-bearing fuel can be used. 　MA from 10 LWRs can be transmuted. Short-lived or stable nuclides Long-lived nuclides (MA)

Aim of the work Investigate the best distribution of a sample of Pu and MA inside the core, which maximize fission rate and efficiency. find a better distribution to burning the plutonium and minor actinides sample

Core Descriptions and Modeling The UT- TRIGA Mark II research reactor is licensed to at a nominal full power 1 MW construction completed in 1992 The hexagonal-spaced grid plates are surrounded by an aluminum-canned graphite reflector assembly with an effective inside diameter of 54.93 cm and a radial thickness of 25.91 cm The fully operational reactor core consists of up to 116 reactor fuel elements and four control rods for a total of 120 grid locations Klystron and power Supplies Power Supplies Covered Shield Area Not to Scale Fence - - - - -

TRIGA Fuel The nuclear fuel in TRIGA reactor is uranium zirconium hydride (U-ZrH) content (enriched to 19.7 % U-235) fuel length 38.1 cm, and 3.63 cm in diameter. clad in stainless steel, with graphite reflector above and below the fuel “meat” The U-ZrH provides the moderation for the core Fuel Zr AISI-304 Gr Air

Fig. 4.1: Effective multiplication factor versus control rod position Results and discussions Model validation Fig. 4.1: Effective multiplication factor versus control rod position

Homogenous and heterogeneous distribution for Pu and MA The present section aims to compare between two models core configuration by distributing the plutonium and minor actinides inside the core in two different ways (homogenous and heterogeneous). Neutron flux, neutron spectrum, fission rate (FR) and subcritical multiplication parameters are analyzed for two core configurations, proton and electron in energy range from 20 to 100 MeV are used also as an incident beam to produce the neutrons inside the reactor core. a) Heterogeneous b) Homogenous

1. Neutron flux Fig.4.5, shows the MCNPX calculated total flux distribution in the two core configurations with Pu and MA sample. The maximum flux, i.e, the peak is in the core center and the axial profile is generally symmetrical about this peak in both configuration, but there are disparity between them, where heterogeneous distribution has little peak than homogenous. Fig. 4.5: Neutron flux distribution in the core with two different configuration contents Pu and MA sample.

Fig. 4.6: Comparison between cross-sections of the 235U(n,γ), 241Am(n,γ), 239Pu(n,γ) and 244Cm(n,γ) reactions 90

Subcritical multiplication parameters Neutron multiplication M Subcritical multiplication factor ks External source efficiency

Table 4.4: Fission rate FR, neutron multiplication M, Subcritical multiplication factor ks and source efficiency j* for heterogeneous and homogenous cores. Core Configuration   keff = 0.92 FRa FRa for MA ks b Mc j* d Heterogeneous 0.261 0.046 0.983 57.28 4.87 Homogenous 0.336 0.045 0.986 72.66 6.18 a Statistical error in FR is less than 2.25E-7 b Statistical error in Ks is less than 6.8E-6 c Statistical error in M is less than 0.036 d Statistical error in j* is less than 0.04 The results shown that the fission rate for Pu and MA in heterogeneous distributions is slightly higher than homogenous this due to the most neutrons emitting from the source are fast, hence the presence of the Pu and MA sample near the source gives a greater opportunity to benefit from them, especially as the most isotopes in the minor actinides sample fission by the fast neutrons.

2. Beam type and energy Table 4 : Neutron multiplication M Subcritical multiplication factor ks and source efficiency φ* for proton and electron beam at varying incident energies in homogenous distribution. a Statistical error in Ks is less than 6.8E-6 b Statistical error in M is less than 0.04 c Statistical error in ϕ*is less than 0.043  

Plutonium and minor actinides burnup The burnup of plutonium and minor actinides is calculated by MCNPX for heterogeneous and homogenous distribution based on electron-driven ADS. The core is simulated with keff as 0.93 in the two configuration types. The burnup time was set at 720 days, in the first 650 days, the time interval of 50 days was chosen, and from 650 days to 720 days, a time interval of 70 days was chosen. Fig. 4.10: Burnup of Plutonium and minor actinide material in heterogeneous and homogenous distribution

Fig. 4.11: variation of mass of 239Pu in two years operation cycle in heterogeneous and homogenous distribution.

Fig. 4.12: variation of mass of 240Pu with two years operation cycle in heterogeneous and homogenous distribution.

Fig. 4.14: variation of mass of 241Am in two years operation cycle in heterogeneous and homogenous distribution.

Fig. 4.15: variation of mass of 243Am with two years operation cycle in heterogeneous and homogenous distribution.

Fig. 4.16: variation of mass of 244Cm in two years operation cycle in heterogeneous and homogenous distribution.

Fig. 4.18: variation of mass of 245Cm in two years operation cycle in heterogeneous and homogenous distribution

Conclusion The heterogeneous distributions achieve slightly more fission rate for the Pu and MA due to the fast neutrons contribution. The external source efficiency is found to be clearly higher for electron beam at energy range from 20 to 60 MeV than proton beam at the same incident energy. The 239Pu mass is decreased significantly during operation time . At the same time there is no significant deference between the two core configuration, this due to that the 239Pu can be split by both thermal and fast neutrons. The heterogeneous distributions give a good results for transmuted of both isotopes 241Am and 243Am with decreases in mass ratio by ~ 21% and 17%, respectively. Whereas the homogenous distributions are considered better suited to 245Cm transmutation.

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What is the minor actinides ? The minor actinides are the actinide elements in used nuclear fuel other than uranium  and plutonium, which are termed the major actinides. The minor actinides include neptunium, americium, curium, berkelium, californium, einsteinium, and fermium.

Computational Tools MCNP5 can be used for neutron, photon, electron, or coupled neutron/ photon/ electron transport, including the capability to calculate eigenvalues for critical systems. For neutrons, all reactions given in a particular cross-section evaluation (such as ENDF/B-VI) are accounted for. MCNPX is a Fortran 90 (f90) Monte Carlo radiation transport computer code that transports 34 particle types, including four light ions, at nearly all energies. MCNPX stands for MCNP eXtended Newer capabilities and enhancements of MCNPX include the depletion/burnup capability which based on CINDER90.

Fig. 4.7: Comparison between calculated neutron spectra in the two configuration, heterogeneous and homogenous.

Fig. 4.17: Probability of fission per neutron absorbed in actinides isotopes for thermal and fast spectra (IAEA, 2010)

Fig. 4.13: Actinides formation scheme in neutronic simulations (KIT)91