Design Study of Innovative Simplified Small

Pebble Bed Reactor

Dwi IRWANTO1), Toru OBARA2)

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

Introduction Research Purposes Calculation Procedures Parametric Survey Reference Design Conclusions

Outline

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Introduction

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

and high cost system

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

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

• The reactor core subdivided into several fuelling zones

• 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

Research Purposes

• To find a means of carrying out the exact calculations needed to analyze the Peu à Peu fuel-loading scheme

• Optimize the fuel design by perfoming parametric survey in the infinite geometry

• Calculate a whole core design by using the optimized fuel design

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Development of a Code for Automate Process of Peu a Peu

Fuel Loading Scheme

Calculation Procedures

• Some studies have been performed previously, they have used a diffusion-based method but the large empty cavity region in the core, makes accurate calculations is difficult to performed

• The Monte Carlo method is used to perform calculations with high accuracy at the top region of the core near the large cavity

• Unfortunately, the calculation procedures for the Peu à Peu modus using the Monte Carlo method require lot of steps

• Therefore, a computer code to automate the process of the Peu à Peu fuel load scheme has been developed using Fortran-77 and based on the Monte Carlo MVP/MVP-BURN code

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Development of a Code for Automate Process of Peu a Peu Fuel Loading Scheme

• Time needed to prepare the input files, calculate it and sequentially do all the process is very huge

• Huge number of nuclear materials data to edit and/or add to the input files

• In order to avoid mistakes in preparing the input

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Motivation

This code significantly reduce time needed to perform the calculation process of the Peu a Peu fuel load scheme

Parametric Survey

Parametric Survey

Parametric Survey235U enrichment 1 – 20 %

Packing Fraction 1 – 20 %

ParametersBurn-Up MWD/Ton

Energy per Ball MWD

235U and 238U used in the core %

Consumed mass of 235U and 238U gram

Critical periods month

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Parametric Survey

Parametric survey of the burn-up (MWD/Ton 235U)

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12 %wt 235U7% packing fraction

of CFP

Reference Design

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

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Reference Design

Fuel BallDiameter of the ball 6.0 cmDiameter of fuel zone 5.0 cmPacking fraction of Coated FuelParticle (CFP)

7.0 %

Enrichment of 235U 12 %Equivalent natural boron content ofimpurities in uranium

4.0 ppm

Percentages of fuel balls in the core 57 %Packing fraction of fuel and dummyballs in the core

61 %

Fuel Kernel Radius of the kernel 0.250 mm UO2 density 10.4 g/cm3

Boron impurities 4 ppm

Coatings First Buffer Layer (PyC) Thickness 0.09 mm Density 1.1 g/cm3

Boron impurities 1.3 ppm Second Layer (PyC) Thickness 0.04 mm Density 1.9 g/cm3

Boron impurities 1.3 ppm Third Layer (SiC) Thickness 0.035 mm Density 3.18 g/cm3

Boron impurities 1.3 ppm Forth Layer (PyC) Thickness 0.04 mm Density 1.9 g/cm3

Boron impurities 1.3 ppm page 10 of 13

Reference Design

keff for each fuel-loading step

* The average burnup value of this design is 9.44 x 104 MWD/T-U page 11 of 13

Conclusions

Conclusions• Concept of innovative small high temperature gas cooled

pebble bed reactor with possibility to simplify the reactor system by removing the unloading devices has been performed

• A code for criticality analysis of automates Peu a Peufuel load scheme process has been developed and tested

• From the parametric survey in the infinite geometry, the maximum burnup value can be expected if the inserted fuel element is 12 wt% U-235 enrichment with 7% packing fraction

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• A whole-core calculation for the small 20 MWth reactor was performed. This reactor design can maintain its criticality for up to 12 years, with the average burnup is 9.44 x 104 MWD/T-U, which is comparable to that of the conventional PBRs design

• Further analysis such as reduction of the power peak near the top of the reactor core is necessary to performed in order to optimize this design

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Conclusions

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