Study on SiC Components to Improve the Neutron Economy in HTGR - PowerPoint PPT Presentation

Study on SiC Components to Improve the Neutron Economy in HTGR Piyatida TRINURUK and Assoc.Prof.Dr. Toru OBARA Department of Nuclear Engineering Research Laboratory for Nuclear Reactors Tokyo Institute of Technology, Japan

Contents  Introduction  Objectives of this study  Computer code and Parametric survey  Results and discussions  Conclusions

Introduction  HTGR : High Temperature Gas-cooled Reactor  A graphite-moderator and helium gas-cooled reactor.  HTTR (High Temperature Test Reactor): Prismatic block type HTGR.  Japan Atomic Energy Research Institute (JAERI) in 1996.  Thermal output 30 MW.  Fuel blocks, control rod blocks, reflector blocks and irradiation blocks.  Uranium enrichments: 3.4 - 9.9%wt - U 235 Fuel compact Coated Fuel Particle Fuel block & Fuel rod

Introduction Convention way to compensate Pros. the excess reactivity in HTTR  High output temperature  Inherent safety reactor Cons.  Once-through fuel cycle.  High excess reactivity.  Unavailable in commercial technique for fuel reprocessing. (Source: N.Fujimoto and et.al., Nuclear design, Nuclear Eng. and design 233 , 2004)

Properties of SiC  SiC is a compound of silicon and carbon.  Silicon (Si):  Higher absorption cross section Poor moderating material  Smaller scattering cross section compared to graphite  Higher mass number Carbon Si-28 Source: http://wwwndc.jaea.go.jp  Disadvantage of SiC:  SiC decomposes at lower temperature as compared to IG-110 graphite.  SiC corrodes by Palladium (Pd).

Objectives  To evaluate the use of SiC in various parts of fuel block assembly instead of graphite to take the benefit of transmutation under the concept of neutron spectrum shifting. Shifting the neutron spectrum Increase the conversion of fertile into fissile material More fission product by without increasing the U-235 enrichment Compensate reactivity and prolong fuel cycle The neutron economy

Computer code and Parametric survey  MVP-2.0 : Continuous energy neutron transport Monte Carlo method  JENDL- 4.0 : Nuclear data library I. One fuel block assembly II. Several fuel block assemblies Number of fuel rods / block 33 Burnable poison No 5% wt of U 235 Enrichment of fuel Packing fraction 30% History / batch 30,000 Batch (Skips + tallies) 50+150 Boundary condition Periodic boundary Number of energy groups 176

Parametric survey 4 3 1 2 Combination between Fuel pin Fuel compact Fuel block SiC block & GP block Case Conditions Specification Graphite  SiC 1. Fuel compact material Graphite  SiC 2. Fuel sleeve material Graphite  SiC 3. Fuel block material 4. Combination between SiC block and GP block Based on 3 fuel blocks

Results and Discussions

I. Effects of SiC on the neutron spectrum Conditions:  One fuel block assembly.  33 Fuel pins with 30% of packing fraction.  Enrichment : Natural Uranium, 5%, 10%, 20%.  SiC material : fuel compact / fuel sleeve / fuel block.  No burnable poison.

I. Effects of SiC on the neutron spectrum 1.6E-03 5.0E-03 Nat. U En.5% Ref. case Ref. case 1.4E-03 (n/s/cm3/Lethargy/sourc) SiC fuel compact 4.0E-03 (n/s/cm3/Lethargy/sourc) SiC fuel compact Neutrom spectrum 1.2E-03 Neutrom spectrum SiC sleeve SiC sleeve 1.0E-03 3.0E-03 8.0E-04 2.0E-03 SiC fuel block 6.0E-04 SiC fuel block 4.0E-04 1.0E-03 2.0E-04 0.0E+00 0.0E+00 1.0E-04 1.0E-01 1.0E+02 1.0E+05 1.0E-04 1.0E-01 1.0E+02 1.0E+05 Energy (eV) Energy (eV) 8.0E-04 8.0E-04 Ref. case En.10% En.20% 7.0E-04 7.0E-04 SiC fuel compact (n/s/cm3/Lethargy/sourc) (n/s/cm3/Lethargy/sourc) 6.0E-04 6.0E-04 SiC sleeve Neutrom spectrum Neutrom spectrum SiC fuel block 5.0E-04 5.0E-04 SiC fuel block 4.0E-04 4.0E-04 3.0E-04 3.0E-04 2.0E-04 2.0E-04 1.0E-04 1.0E-04 0.0E+00 0.0E+00 1.0E-04 1.0E-01 1.0E+02 1.0E+05 1.0E-04 1.0E-01 1.0E+02 1.0E+05 Energy (eV) Energy (eV)

II. Effects of SiC on the reactivity 1.60 1.60 1.40 1.40 Infinite multiplication factor Infinite multiplication factor 1.20 1.20 1.00 1.00 0.80 0.80 0.60 0.60 SiC fuel block 0.40 0.40 0.20 0.20 Nat. U En.5% 0.00 0.00 0 5,000 10,000 15,000 20,000 25,000 30,000 0 5,000 10,000 15,000 20,000 25,000 30,000 MWD/Ton MWD/Ton 1.60 1.60 1.40 1.40 Infinite multiplication factor Infinite multiplication factor 1.20 1.20 1.00 1.00 0.80 0.80 0.60 0.60 0.40 0.40 0.20 0.20 En.10% En.20% 0.00 0.00 0 5,000 10,000 15,000 20,000 25,000 30,000 0 5,000 10,000 15,000 20,000 25,000 30,000 MWD/Ton MWD/Ton

III. Effects on the change of nuclide density Enrichment : Natural Uranium 1.8E-04 2.32E-02 2.50E-04 8.00E-05 U235 U238 Pu239 Pu241 1.6E-04 7.00E-05 2.30E-02 2.00E-04 1.4E-04 6.00E-05 Nuclide density 1.2E-04 2.28E-02 Nuclide density Nuclide density Nuclide density 5.00E-05 1.50E-04 1.0E-04 2.26E-02 4.00E-05 8.0E-05 1.00E-04 3.00E-05 6.0E-05 2.24E-02 2.00E-05 4.0E-05 5.00E-05 2.22E-02 1.00E-05 2.0E-05 0.00E+00 0.00E+00 0.0E+00 2.20E-02 0 10,000 20,000 30,000 0 10,000 20,000 30,000 0 10,000 20,000 30,000 0 10,000 20,000 30,000 MWD/Ton MWD/Ton MWD/Ton MWD/Ton Enrichment : 5% 1.4E-03 2.21E-02 2.50E-04 4.50E-05 U235 U238 Pu239 Pu241 4.00E-05 2.20E-02 1.2E-03 2.00E-04 3.50E-05 1.0E-03 2.19E-02 Nuclide density Nuclide density Nuclide density Nuclide density 3.00E-05 1.50E-04 8.0E-04 2.18E-02 2.50E-05 2.00E-05 6.0E-04 2.17E-02 1.00E-04 1.50E-05 4.0E-04 2.16E-02 1.00E-05 5.00E-05 2.0E-04 2.15E-02 5.00E-06 0.00E+00 0.0E+00 2.14E-02 0.00E+00 0 10,000 20,000 30,000 0 10,000 20,000 30,000 0 10,000 20,000 30,000 0 10,000 20,000 30,000 MWD/Ton MWD/Ton MWD/Ton MWD/Ton

III. Effects on the change of nuclide density Enrichment : 20% (HEU) 5.0E-03 2.50E-04 1.20E-05 1.86E-02 U235 U238 Pu239 Pu241 1.86E-02 4.5E-03 1.00E-05 2.00E-04 1.85E-02 Nuclide density 4.0E-03 Nuclide density Nuclide density Nuclide density 8.00E-06 1.85E-02 1.50E-04 3.5E-03 1.84E-02 6.00E-06 1.00E-04 1.84E-02 3.0E-03 4.00E-06 1.83E-02 5.00E-05 2.5E-03 2.00E-06 1.83E-02 1.82E-02 0.00E+00 2.0E-03 0.00E+00 0 10,000 20,000 30,000 0 10,000 20,000 30,000 0 10,000 20,000 30,000 0 10,000 20,000 30,000 MWD/Ton MWD/Ton MWD/Ton MWD/Ton

Effects of SiC in each component  Using SiC in HTTR instead of graphite can make the spectrum harden.  The benefit of transmutation by the shift of neutron spectrum is more effective for LEU because SiC can slow down the depletion of fissile nuclide as U-235 and increase the utilization of fertile nuclide U-238.  The magnitude of the spectrum shifting depends on the ratio of graphite which is replaced with SiC. The percent of graphite volume of each component in a fuel block 3.63% Fuel block 17.85% Fuel compact Fuel Sleeve 14.22% 64.30% Coating layer

IV. Combination of SiC blocks & graphite blocks 1.50 Condition: 1.40 1.30  5 % enriched uranium Infinite multiplication factor 1.20  3 fuel blocks 1.10 1.00 All graphite blocks 0.90 GP : SiC blocks = 2 : 1 0.80 0.70 GP : SiC blocks = 1 : 2 0.60 All SiC blocks 0.50 0.40 0.30 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 MWD/Ton  Increase the ratio of SiC blocks in the core can compensate the excess reactivity and flatten the reactivity.  SiC block results into the reactor operated under the criticality.

V. Improvement of reactivity in SiC block 1.6 1.4 1.2 Infinite multiplication factor 1.0 0.8 0.6 0.4 0.2 0.0 0 10,000 20,000 30,000 40,000 50,000 60,000 MWD/Ton  Increase the fuel enrichment in SiC block can success to improve the reactivity and make the reactor operate at the criticality.

Conclusions  SiC has a potential to make the neutron spectrum harden and increase the fissile material by the transmutation.  The magnitude of spectrum shifting depends on the ratio of SiC replacement : more SiC, more effective to harden spectrum.  LEU and HEU under the harden spectrum can perform as burnable poison to compensate the excess reactivity, but it will lead the reactor operated under the critical.  The optimization between the ratio of SiC replacement and the fuel enrichment is need to pay attention in order to achieve the neutron economy.

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