Design Study of Innovative Simplified Small Pebble Bed Reactor

Dwi Irwanto1) and Toru OBARA2)

1)Department of Nuclear Engineering, Tokyo Institute of Technology2)Research Laboratory for Nuclear Reactor, Tokyo Institute of Technology

• Introduction• Current research purposes• Calculation procedures• Thermal hydraulic calculation of the

reference design• Conclusion

Outline

Page 2

Introduction

page 3

(Potential) Problem ?• The unloading machinery is a very complex

and high cost system

Pebble Bed Reactor

Introduction

• Peu a Peu fuel loading concept proposed by E.Teuchert et al (1992)

• Pebble bed reactor –based design with fuel unloading devices is removed

• Startup → lower layers filled → first criticality

• During operation → layer per layer filled →maintain criticality

• The end of the core → unloaded fuel

Peu a Peu Fuel Loading Scheme

Neutronic parameters for a reference design have been calculated in the previous study *

page 4* Design Study of Innovative Simplified Small Pebble Bed Reactor (1) Design concept and sample design analysis

Current Research Purposes

To calculate thermal hydraulic parameters of the reference design

page 5

Calculation Procedures

• From the calculation results of the neutronic analysis (MVP/MVP-Burn), power density and power distribution inside the reactor core were obtained.

• These parameters, then uses in the calculation which conducted by porous media flow and heat transfer modules in steady state condition.

• The analysis was performed by COMSOL Multiphysics code.

page 6

Reference Design

Design Specification

Reactor Power 20 MWth

Fuel TRISO

Core radius 125 cm

Core Height 500 cm

Reflector width 70 cm

Startup fuel layers 85 cm

Initial 235Uenrichment

12 %

Supply fuel 235Uenrichment

12 %

Packing Fraction 7.0 %Schematic view of reactor core

design

page 7

Uo = 1.06 m/s ;

P = 6 x 106 Pa

Axi

al s

ymet

ry

Tin = 550oC

Helium

Tout = ?

Pin = ?

Meshing

Q from MVP

ComsolHeat Transfer

module -> General Heat Transfer

Thermal Conductivity (k)

keffective (T) W/m K

Density (ρ) 3.7012 * kg/m3

Heat CapacityCp (comsollibrary)

J/kg K

Production/ absorption coef f (qs)

0W/m3

K

Heat source (Q) (MVP) W/m3

Velocity u = 0v = -1.06

m/s

Boundary condition

T 550 oC

ComsolChemical engineering module -> momentum transport -> porous media flow

Material Helium

Density (ρ) 3.7012 * kg/m3

Dynamic viscosity (η)

eta(T) (comsollibrary) Pa.s

Permeability (κ) 1.06 x 10-7 m2

Source term (F) 0 kg/m3 s

Boundary condition

P 6.0 x 106 Pa

*The Properties of Helium: Density, Specific Heats, Viscosity, and Thermal Conductivityat Pressures from 1 to 100 bar and from Room Temperature to about 1800 KHelge Petersen, Danish Atomic Energy Commision Research Establishmen Riso, September 1970

page 8

Calculation Results

Calculation Results

Temperature distribution

page 9

Pressure

Calculation Results

page 10

rho * 3.7021 kg/m^3D 0.06 mviscosity 3.86E-05 Pa.sporosity 0.39Cp 5163.499 J/kg Kkf * 0.304 W/MK

Pebble Ball radius 3.00E-02 mFuel zone radius 2.50E-02 msurface pebble 1.13E-02 m^2volume pebble 1.13E-04 m^3k ** 20 W/mK

** Improving Fuel Cycle Design and Safety Characteristics of a Gas Cooled Fast Reactor, Willem Fredick Geert van Rooijen

* The Properties of Helium: Density, Specific Heats, Viscosity, and Thermal Conductivity at Pressures from 1 to 100 bar and from Room Temperature to about 1800 K ; Helge Petersen, Danish Atomic Energy Commision Research Establishmen Riso, September 1970

Calculation Results

page 11

Q = 2.87 x 103 W/m3

Calculation Results

page 12

Q = 4.20 x 106 W/m3

Calculation Results

page 13

Conclusions

• Concept of innovative small high temperature gas cooled pebble bed reactor with possibility to simplify the reactor system by removing unloading devices has been performed

• Analysis of the maximum temperature inside the pebble ball at the end of the reactor life shown that the maximum temperature is 722oC which is still far below the safety limit of 1600oC.

• Optimization in term of the power distribution and burnup characteristic are the aspects will be performed in the future using method developed in this study.

page 14

THANK YOU

Parameter Surveys for Peu a Peu 20 MWt designReynolds Number(10,000); Helium velocity; Temperature

Parameter Surveys for Peu a Peu 20 MWt designReynolds Number(10,000); Helium velocity; Temperature

Parameter Surveys for Peu a Peu 20 MWt designReynolds Number(10,000); Helium velocity; Temperature