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Pebble Bed Modular Reactor

Design and Operation

Pebble Bed Modular Reactor Basics

• High Temperature

• Graphite Moderated

• Graphite Core and Graphite Core Support Structures

* Helium Coolant

• Brayton Cycle

• Gas Turbines in Power Conversion System

* Spherical Ceramic Fuel Elements

* Continuous On-line Refueling

* Passive Response to Design Basis Accidents

PBMR Plant Specifications

Maximum Rated Power

Continuous Stable Power Range

Ramp Rate

Step Change

Load Reject w/o Trip

General Overhauls

Emergency Planning Zone

Plant Operating Life

120 MWe

0-100%

10%/o/min

10% Power

100%

30days/6Yrs

<400 Meters

40 Yrs

High Pressu'eTurbine LowP ressureT urbi ne

Pov~erTurbineRecupea~tor

High P reswire LowP resare I Compressor Compressor

iLHeium irjeclion and Heium hnjeciion frum HlCS remwxo tomn HI CS

- - -

PBMR Helium Flow Process Diagram

Generator

Irter~o~oer PrL-cooler

I

2 BMR Thermal CycleP B M R

Sea water 121-C OUT

400C 10

U) 0)

U w

1.48 m3/sec" 180C Sea water

IN

- em r

C

P Q M

EZ�ZJ

L�J

-KzJ

11(S

Power System Helium Flow

Eý c

I~~ I

Reactor Vessel

HPT __ LFT

Core Conditioning System

PBMR MPS

GeneratDr

I

IF-

Pre-Cooler-

Recuperator----

PTG

Start-Up Blower System

PBMR Main Power System

)

*1*rA

AW II I

Reactor Pressure vessel conditioning Sytem

Reactivity Control System Drives Reserve Shutdown System

w (A 2. 0. - 4 0

4 4 n R

4

2 I

1 4

-46

-13

-'I U, (A 'C -U -' C a

I a. a

3 S 0

'I

(D

0

CO)

(D

CL

(D

900

-01 1800 E) -- 0• o -0 0 \ 0

Graphite0

GraphiteCoeRfetrBokLyu

(Side and Bottom)

PBMR "Pebble" Fuel Elements

PBMR Annular Core With Center Graphite Pebbles

Spent Fuel Tank

Fuel Handling and Storage System

5mm Graphite layeir

Coated; pa rticles Imbedded 7in' Graphite Matrix

Dia. 60mm fuel Sphere.

-- APyryt'cCtabofl4oi01 o~mm Slli~n d bldariirdod g ýsrvoo

I•~diz aCubffei§9511 000mm

Dia; 0,92mm

Coated Particle. Urani~um'Dioxid'e Fuel. Kernel

PBMR Fuel Element and (TRISO) Coated Fuel Particle

TRISO Coated Particle and Pebble Fuel Element Design

TRISO Coated Particle Design

Uranium Dioxide Kernel

Low Density Pyrocarbon Buffer Layer: Porous plenum volume for fission gas Accommodate irradiation-induced kernel swelling

Inner High Density Pyrocarbon Layer: Retains most of the fission products; Protects the next (SiC) layer from chemical attack from

Silicon Carbide Layer: Main barrier to the escape of gaseous and solid fission

Largest contributor to particle mechanical strength

Functions as a pressure vessel 110mAg readily diffuses through layer

fuel fission products

products

Outer High Density Pyrocarbon Layer: Protect SiC layer from chemical attack outside the particle Adds strength to the SiC layer.

Pebble Fuel Element:

TRISO particles in spherical graphite matrix fueled zone

KERNELMATRIX

F' IBUFFER LAYER

lb, I

FUEL-FREE

FUELED ZONESHELL

INNER

SiC-LAYER

PyC-LAYER

OUTER PyC LAYER

Pebble Fuel Element and TRISO Particle

Kernel

Buffer

PyC

Fission Product Concentration in Intact TRISO Particles

I I I. I 4*

,

1200. 140.0. 16..00 l80.0 2000.

IE+00

1E-O1

1 E-,2,

IE4-3

1E"64

1E-05

1E-0.6-"24.00.

Fuel Temperatures [°C]

TRISO Particle Failure Fraction Vs Temperature

0

0

22001000 2600

'I 3k - * 0 0.r

f

-r

U) 1 -3 --

.0 10-4.-_,j - -17000C_ ,-,40.-0o co ---/-/ -- "3VR82/20

I o,--°" I.-°-K Iv3/,2

._ 10-5 i• -,- o

°HFR'K3I1

•" o •o--.oFRJ2-K13/4 o

o0.A-I 1,.. 7 0..0" 0 A.R74/11

10-6 ... ~~2'V822

10-7

10-80 100 200 300 400 500

Heating time (h)

Cesium Release in Isothermal Heating Tests

(German TRISO Coated Pebble Fuel)

/

I

Reactor Cavity Cooling System Surrounding Reactor Pressure Vessel

MAIN CRANE

HICs Helium Inventoy Control System •

NEW FUEL CASKS

HMS Helium Make-Up System If"

Turbi[no FH5S Fuel Handling &- r u

Storage System Turbne Spent fuel contan VT

P oaverTurblne

FHSS Fresh Fuel Loading Machine

FHSS Recuperator

Fuel lHandling Storage System Gas Cmponents

PEBBLE BED MODULAR-REACTOR1 RCCS ____ ___ ____ ___ ____ ___Reactor Cavty

MAIN POWER SYSTEM Cooing System WITH

SUPPORT SYSTEMS

PBMR Main Power System with Support Systems

PBMR Module Elevation Relative to Grade Level

- .---

Layout for 10 PBMR Modules

Pebble Bed Modular Reactor

Safety Objectives and Characteristics

Safety Objectives and Characteristics

Retain Fission Products

o Manufacture PBMR fuel with very low TRISO particle defect rate

matching German quality standards

Qualify (Test) PBMR fuel for PBMR operating and accident

conditions with performance equivalent to German pebble fuel

Ensure that core operating and DBA conditions do not exceed fuel

qualification envelop (e.g., 80,000 MWd/t, 12500C max operating

temperature, 160000)

Support high temperature performance with ceramic fuel materials

Control graphite chemical attack (e.g., oxidation from air, moisture)

Safety Objectives and Characteristics

Ensure Core Shutdown

or Provide diverse active scram systems (i.e RCS, RSS) for

anticipated transients

e, Provide passive reactor shutdown mechanisms (i.e., low excess

reactivity with strong negative temperature feedback) for potential

core heat-up accidents

Safety Objectives and Characteristics

Ensre deqateCore Heat Removal%

Operate at low core power density and core with large

thermal heat capacity (i.e., for slow accident response times

and limited core temperature rise)

Utilize coolant which does not change phase (i.e. no abrupt

reduction in Helium heat transfer coefficient)

Provide for passive decay heat removal processes and

equipment for transients and accidents (i.e., no active core

cooling systems or components)

Decay heat removal does not rely on He coolant

Safety Objectives and Characteristics

LiitPoetialfr rahieChemclAtk

Use Helium coolant (i.e., He is chemically inert)

Operate He/water heat exchangers with He-side pressure

above water-side pressure (i.e., He leaks into water side)

Locate HXs below elevation of the bottom of the core and

minimize the water volume on the water side

Use RPB and PCSPB specifications for low failure potential

Use confinement building to limit available air volume for

graphite oxidation following a pipe break

Safety Objectives and Characteristics

Limit Need for Operator Actions_

Utilize passive safety functions that do not rely on near-term

operator actions

Minimize the adverse effects of operator errors

Pebble Bed Modular Reactor

Accident and Transient Analyses

PBMR Accidents and Transients

"* Loss of Forced Cooling Transients - Depressurized (LOCA) - Pressurized

"* Reactivity Transients - Failure to Scram - Over Cooling - Rod Withdrawal - Rod Ejection - Moisture Ingress - Pebble Bed Compaction

"* Chemical Attack - Air Ingress - Moisture Ingress

S (4)) LUj

Oat 001. 08 09 Oz 0 I II0

II I

II I

axainjedadwej AdU LunwOAV I

I -I. . . . .. . . . .

I . . . . . . . . . . . . . -00

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- --I- - - - - - -0 8 -I

I I

InI -e

" I 1 - I I L ------ ------

o3070 a uJnp uojlnqJJJSIa anjejadwa.lB :aool "ad &Ngd Mk 99

N UOA^ i 4UeIOOO o sso-l 9 "6!

Arom ýq VR -,.2 0 i,-la 6 "

8e--fri'e-,b, "' VVI- Bericli-le 1,2clo VDr Verlay (/13y)

Obere Schmelztemperatur 1280*C

so I

40

OAuBencore

llinnencoreý Anzahl Kugein

20 1

10

0900 1000 1100 1200 1300

Maximaltemperatur (*C)

Abb. 6: TemperaturmeBkugeln (oben) mit 20 Schmelzdrahten (Aussc

aus R6ntgenaufnahme, Mitte) zeigten teilweise unerwarte

hohe Temperaturen (unten).

Pebble Bed Modular Reactor

Pre-Application Review Objectives and Activities

PBMR Pre-Application Review Objectives

To develop guidance on the regulatory process, regulations framework and

the technology-basis expectations for licensing a PBMR, including identifying

significant technology, design, safety, licensing and policy issues that would

need to be addressed in licensing a PBMR.

* To develop a core infrastructure of analytical tools, contractor support, staff

training and NRC staff expertise needed for NRC to fully achieve the

capacity and the capability to review a modular HTGR license application.

PBMR Pre-Application Review Scope

Selected Design, Technology and Regulatory Review Areas:

Performance

• Nuclear Design

* Thermal-Fluid Design

Hi-Temp Materials Performance

° Severe Accident Source Term

Containment Design

° PBMR Regulatory Framework

• Human Performance and Digital I&C

0 Prototype Testing Program

0 Probabilistic Risk Assessment

0 Postulated Licensing-Basis Events

0 Fuel Cycle Safety

a Emergency Planning

0 SSC Safety Classifications

0 Fuel Design and

PBMR Safety Significant Review Issues

• Fuel Performance and Qualification

0 Passive Design and Safety Characteristics

0 Accident Source Term and Basis*

0 Postulated Licensing Basis Events*

0 Prototype Testing Scope and Regulatory Credit

• Containment Functional Design Basis*

• Emergency Planning Basis*

0 Risk-Informed Regulatory Framework*

• Probabilistic Risk Assessment

Commission Policy Decision is Likely Involved