Design Study on Nuclear Reactor for Large Diameter NTD using PWR Fuel

Byambajav Munkhbat1 and Toru Obara2

1Department of Nuclear Engineering, Tokyo Institute of Technology2Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology

Outline• Introduction• Purpose of study• Design Concept• Core Design• Criticality and Burn-up analyses• Preliminary Thermal Hydraulic Analyses• Estimation of Production Rate by Few Group

Constant in Reflector• Conclusions

Introduction• Importance of large diameter semiconductor:

– power semiconductor devices – optimal approach of increasing mass production

efficiency• Use modern electric devices increasing• Rapidly increasing demand of large diameter

semiconductor • Many preparation methods – conventional

methods and neutron transmutation doping (NTD) using nuclear reactor

Introduction

• 30Si(n,γ)31Si → 31P + β- (T1/2=2.62 h)30Si is 3.12% of natural silicon (rest - 28Si and 29Si)• NTD process is basically carried out in the

research reactors • Their low cost mass production capability for

large diameter semiconductor is becoming critical problem

• One of the solutions is to design small reactor for large diameter NTD

Purpose of study

• In order to employ in short time without large construction cost and operation cost, well proven technology must be used.

• The purpose of study is to design small nuclear reactor for NTD using conventional PWR fuel elements.

Design Concept

• To employ the conventional PWR fuel elements order to achieve low construction cost and short time deployment.

• To keep the reactor size which was previously determined as optimum size by other researchers* from view point of core performance and semiconductor production rate.

*Toru Obara, Liem Peng Hong, Naoyuki Takaki, Basic Concept of Water Moderated Small Reactor for Neutron Transmutation Doping, Trans. American Nuclear Society, 99, 745 (2008)

Design ConceptPrevious work Present work

Reactor thermal power

15 MW 15 MW

Core size 60 cm x 60 cm x 100 cm 64.26 cm x 64.26 cm x 100 cmFuel assembly (FA)

8x8 fuel pins (10cm x 10cm x 100cm)

17x17 fuel pins (21.42cm x 21.42cm x 100cm)

Number of FA 36 9Fuel UO2, 3% UO2, 4%Fuel pin pitch 1.25 cm 1.26 cmReflector Heavy water, Beryllium,

GraphiteGraphite

Burnable poison

--- Gd2O3

Criticality and Burn-up analyses

Calculation method

• SRAC2006: A Comprehensive NeutronicsCalculation Code System with JENDL-3.3 data library

• Auxiliary code COREBN - multi-dimensional core burn-up code

Calculation Condition

Reactor power 15 MWth (tentative value) Core size 64.26 cm x 64.26 cm x 100 cmFuel UO2

Fuel enrichment 4%Cladding Zircalloy-4Fuel assembly 17x17Number of assembly 9Burnable poison Gd2O3 (2%, 8%, 10% 15%, 17%, 20% natural Gd)Reflector GraphiteControl rod B4C (10B 91% enriched, total boron 77.92 wt %)

Case 2 (Suitable combinations)Case Combination

BP-1Center assembly contains 64 rods with 2% Gd

Outer 8 assemblies contain 16 rods with 15% Gd

BP-2Center assembly contains 128 rods with 2% Gd

Outer 8 assemblies contain 16 rods with 2% Gd

BP-3Center assembly contains 64 rods with 2% Gd

Outer 8 assemblies contain 16 rods with 17% Gd

BP-4Center assembly contains 64 rods with 2% Gd

Outer 8 assemblies contain 16 rods with 20% Gd

BP-5 All assemblies contain 25 rods with 8% Gd

BP-6 All assemblies contain 25 rods with 10% Gd

Core burn-up

Core power peaking

Two the most suitable combinationsCombination 2Combination 1

Preliminary Thermal Hydraulic Analyses

Calculation method

• Using COMSOL multiphysics 3.4 code• Steady-state single channel analysis• Axial symmetry (2D, r-z) geometry • The simulation is the solid-fluid interaction in

the turbulence flow • k-ε turbulence model • Convection and conduction model

Calculation condition

Cladding and Coolant temperature profile

Estimation of Production Rate by Few Group Constant in

Reflector

Calculation method

• Empirical formula (obtained by JAEA )

• ρt - target resistivity (Ω cm)• Np - number of phosphorus nuclei after the

irradiation in the unit volume (cm-3)

Calculation method

• Np - can be determined from thermal neutron capture reaction:

• V - volume of the ingot (cm3)• NSi-30 - initial number of 30Si nuclei in the ingot• σSi-30 - capture cross section for thermal

neutron (barn)• φ - thermal neutron flux (n/(cm2s))• tI - irradiation time (s)

Location of silicon ingot

Neutron flux distribution

Production rate

Conclusions

• Simple and small size nuclear reactor for large diameter NTD process can be designed by using conventional PWR fuel elements.

• Excess reactivity and power peaking during core life time were analyzed and they can be reduced using combination different concentration of burnable poison Gd2O3.

• It will insert just enough negative reactivity if four-side assemblies have control rods.

Conclusions

• Coolant bulk temperature is less than 500C, so the heat removal from core is possible in 1 atmof coolant pressure.

• Production rate of semiconductor is estimated and reactor production rate is 80 kg/hour if target resistivity is required as 50 Ωcm.

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