Study on SiC Components to Improve the Neutron Economy in HTGR

Transcription

1 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

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

3 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 Thermal output 30 MW. Fuel blocks, control rod blocks, reflector blocks and irradiation blocks. Uranium enrichments: %wt - U 235 Fuel block & Fuel rod Fuel compact Coated Fuel Particle

4 Introduction Pros. High output temperature Inherent safety reactor Convention way to compensate the excess reactivity in HTTR 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)

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

6 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

7 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 Enrichment of fuel 5% wt of U 235 Packing fraction 30% History / batch 30,000 Batch (Skips + tallies) Boundary condition Periodic boundary Number of energy groups 176

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

9 Results and Discussions

10 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.

11 Neutrom spectrum (n/s/cm3/lethargy/sourc) Neutrom spectrum (n/s/cm3/lethargy/sourc) Neutrom spectrum (n/s/cm3/lethargy/sourc) Neutrom spectrum (n/s/cm3/lethargy/sourc) I. Effects of SiC on the neutron spectrum 5.0E E E-03 Ref. case SiC fuel compact SiC sleeve Nat. U 1.6E E E E-03 Ref. case SiC fuel compact SiC sleeve En.5% 8.0E E-03 SiC fuel block 6.0E-04 SiC fuel block 1.0E E E E E E E E+05 Energy (ev) 8.0E-04 Ref. case 7.0E-04 SiC fuel compact 6.0E-04 SiC sleeve 5.0E-04 SiC fuel block 4.0E E E E E E E E E+05 Energy (ev) En.10% 0.0E E E E E+05 Energy (ev) 8.0E E E E-04 SiC fuel block 4.0E E E E E E E E E+05 Energy (ev) En.20%

12 Infinite multiplication factor Infinite multiplication factor Infinite multiplication factor Infinite multiplication factor II. Effects of SiC on the reactivity SiC fuel block Nat. U ,000 10,000 15,000 20,000 25,000 30, En.5% 0 5,000 10,000 15,000 20,000 25,000 30, En.10% 0.20 En.20% ,000 10,000 15,000 20,000 25,000 30, ,000 10,000 15,000 20,000 25,000 30,000

13 III. Effects on the change of nuclide density 1.8E E E-04 U E E-02 Enrichment : Natural Uranium U E E-04 Pu E E E-05 Pu E E E E E E E E E E E E E E E E E E E E E E+00 Enrichment : 5% 1.4E E E E-04 U E E E E-02 U E E E-04 Pu E E E E E-05 Pu E E E E E E E E E E E E E E E E+00

14 III. Effects on the change of nuclide density 5.0E E E-03 U E E E E-02 Enrichment : 20% (HEU) U E E E-04 Pu E E E-06 Pu E E E E E E E E E E E E E E E E+00

15 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% 17.85% 14.22% 64.30% Fuel block Fuel compact Fuel Sleeve Coating layer

16 Infinite multiplication factor IV. Combination of SiC blocks & graphite blocks ,000 50,000 60,000 70,000 Condition: 5 % enriched uranium 3 fuel blocks All graphite blocks GP : SiC blocks = 2 : 1 GP : SiC blocks = 1 : 2 All SiC blocks 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.

17 Infinite multiplication factor V. Improvement of reactivity in SiC block ,000 50,000 60,000 Increase the fuel enrichment in SiC block can success to improve the reactivity and make the reactor operate at the criticality.

18 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.

19 Thank you for your kind attention