DESIGN STUDY ON SMALL REACTOR FOR SILICON SEMICONDUCTOR PRODUCTION USING LWR FUEL

Byambajav Munkhbat

Department of Nuclear Engineering

Tokyo Institute of Technology

Toru Obara

Research Laboratory for Nuclear Reactors

Tokyo Institute of Technology

INTRODUCTION

• Nowadays, the use of electric vehicles such as hybrid cars and electric trains is increasing.

• These vehicles require a considerable amount of large-diameter power semiconductor devices.

• Ever-growing demand for such devices in the near future.

• It was confirmed that almost 1000 tons of NTD silicon will be needed in 2030. At the present, worldwide capacity is estimated to be 150-180 tons per annum.

• Mass production of semiconductors is becoming an important issue for many manufactures.

INTRODUCTION

• Neutron Transmutation Doping (NTD) is one of the promising methods for mass production.

• Basic idea is: 30Si(n,)31Si → 31P + - (T1/2=2.62 h)

30Si is 3.12% of natural silicon (rest - 28Si and 29Si) • NTD is carried out in the research reactors, but

their capability is becoming critical problem. • One of the solutions is to design a small reactor

for large-diameter NTD-Si using conventional PWR fuel assembly.

PREVIOUS WORK*

• A small reactor design concept for large-diameter NTD-Si is proposed.

• Calculation results showed such reactor design using PWR fuel is possible.

• But the core height is 100 cm

*Munkhbat Byambajav, Toru Obara, “Design study on a small reactor for silicon semiconductor production

using LWR fuel: (1) Reactor concept,” 2010 AESJ Annual Meeting, H01 (2010).

PURPOSE OF STUDY

• The purpose of study is to design a small nuclear reactor for NTD-Si using full-length conventional PWR fuel Assembly.

• Use of full length PWR assembly gives several advantages as : – Low cost for construction and operation

– Can be realized in short period of time

– Commercially available

– Large irradiation void

CORE DESIGN

Present work

Reactor thermal power 15 MWth

Core size 64.26 cm × 64.26 cm × 400 cm

Fuel assembly(FA) Conventional PWR-17x17 fuel assembly

Number of FA 9 (3x3)

Fuel and enrichment UO2, 4 wt%

Fuel pin pitch 1.26 cm

Cladding Zircalloy-4

Reflector Graphite

Coolant and moderator Light water

Burnable poison Gd2O3, Soluble boron

CRITICALITY AND BURN-UP ANALYSES

• Calculation method

– MVP/GMVP II: General Purpose Monte Carlo Codes with JENDL-4.0 data library.

– MVP-BURN: Burn-up Calculation Code Using A Continuous-energy Monte Carlo Code MVP.

CRITICALITY AND BURN-UP ANALYSES • Calculation condition

Reactor power 15 MWth

Core size 64.26 cm x 64.26 cm x 400 cm

Fuel UO2

Fuel enrichment 4 wt%

Cladding Zircalloy-4

Fuel assembly 17x17

Number of assembly 9 (3×3)

Burnable poison Gd2O3 (natural Gd)

Coolant and moderator Light water

Reflector Graphite

Soluble boron Boric acid (H3BO3)

OPTIMIZATION OF ASSEMBLY COMPOSITION AND BURNABLE POISON

• From previous work, reference core has a large excess reactivity at the beginning of operation.

• Gd2O3 was used, but it needs to be employed in an effective way.

• There are several variables in the effective use: – The number of fuel rods with burnable poison in the assembly

– The location of those rods in the assembly – uniform or heterogeneous positioning

– The concentration of burnable poison – it can vary within the assembly

– Uniform or heterogeneous employment – all assemblies contain the same or different configurations of burnable poison.

OPTIMIZATION OF ASSEMBLY COMPOSITION AND BURNABLE POISON

• The optimization of these variables was performed with the following basic criteria: – The reactor operation period cannot be shortened drastically

– Excess reactivity is kept as low as possible

– Power peaking must be within limits – the coolant outlet temperature must be less than 100oC.

– Power peaking is kept as low as possible.

• Soluble boron was used in addition to the burnable poison.

• The criterion for use of soluble boron was that its concentration must not exceed 2000 ppm.

CALCULATION RESULTS

Case Combination

BP – 1 All 9 assemblies each containing 16 fuel rods with 8 wt%-Gd2O3

BP – 2 All 9 assemblies each containing 16 fuel rods with 10 wt%-Gd2O3

BP – 3 All 9 assemblies each containing 16 fuel rods with 15 wt%-Gd2O3

BP – 4 All 9 assemblies each containing 25 fuel rods with 6 wt%-Gd2O3

BP – 5 All 9 assemblies each containing 25 fuel rods with 8 wt%-Gd2O3

BP – 6 All 9 assemblies each containing 25 fuel rods with 10 wt%-Gd2O3

BP – 7 All 8 outer assemblies, each containing 16 fuel rods with 2 wt%-Gd2O3, with the central assembly containing 128 fuel rods with 2 wt%-Gd2O3

BP – 8 All 8 outer assemblies, each containing 16 fuel rods with 15 wt%-Gd2O3, with the central assembly containing 64 fuel rods with 2 wt%-Gd2O3

CALCULATION RESULTS

CALCULATION RESULTS

CALCULATION RESULTS

CALCULATION RESULTS

CALCULATION RESULTS

CONCLUSIONS

• Small nuclear reactor for large-diameter NTD-Si can be designed by using full-length PWR fuel assembly.

• Reactor can be critical over 18 years and excess reactivity can be suppressed by burnable poison and soluble boron.

• Optimization result showed that all 9 assemblies, each containing 28 fuel rods with 7.0 wt%-Gd2O3, are the best option for this reactor concept.

• Up to 2000 ppm soluble boron is enough to suppress remaining excess reactivity.

THANK YOU

OUTLINE

• Introduction

• Previous work

• Purpose of study

• Core Design

• Criticality and Burn-up analyses

• Optimization of assembly composition and burnable poison

• Calculation results

• Conclusions