Technology Base for the ACR Fuel Channels

8/13/2019 Technology Base for the ACR Fuel Channels

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Technology Base for the ACR:

FUEL CHANNELS

By Doug Rodgers, Director, Fuel Channels

Presented to US Nuclear Regulatory Commission

Office of Nuclear Reactor Regulation

September 26, 2002


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ACR FUEL CHANNEL DESIGN


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FUEL CHANNEL COMPONENTS


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NPD

cold-worked

Zircaloy-2

Pickering 1 & 2

cold-worked

Zircaloy-2

Pickering, Bruce, Darlington,

and early CANDU 6

cold-worked Zr-2.5Nb

Current CANDU 6cold-worked

Zr-2.5Nb

with low H & Cl

KANUPP

heat treated

Zr-2.5Nb

ACR

cold-worked

Zr-2.5Nb

with low H & ClPLUS

PRESSURE TUBE EVOLUTION


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FUEL CHANNEL PERFORMANCE

31 CANDU reactors in 6 countries

208 to 480 pressure tubes per reactor

More than 150,000 pressure tube years of

equivalent full-power operation Only 2 pressure tube ruptures

Less than 1 rupture per 75 thousand tubeyears of operation


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PERFORMANCE STATISTICS

0

10

20

30

40

50

60

1960 1970 1980 1990 2000

CrackedPress

ureTubes


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FUEL CHANNEL TECHNOLOGY

Aging Mechanisms Reactor Experience

R&D and Engineering


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AGING MECHANISMS

Delayed Hydride Cracking

Corrosion and Hydrogen Ingress

Dimensional Changes

Mechanical Properties


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DELAYED HYDRIDE CRACKING

Zirconium alloys can be susceptible

Sufficient hydrogen in the metal must be

available

Need a driving force for diffusion, e.g. a stressgradient

Anisotropic behavior

When conditions are met, there is the potential

for Delayed Hydride Cracking (DHC)


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IN-REACTOR EXPERIENCE

1974 & 1982


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FABRICATION STRESSES


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LEAK-BEFORE-BREAKDEMONSTRATED

High residual stresses from over-rolling

Delayed Hydride Cracking during reactor

shutdowns only

Leakage and detection

Safe shutdown

Replacement of pressure tubes


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SOLUTIONS

Replace cracked pressure tubes

Stress relieve other reactors with over-rolled

pressure tube joints

Development of zero-clearance rolled jointwith lower residual stresses

Implemented in subsequent reactor

constructions, e.g. all CANDU 6 reactors


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LEAK-BEFORE-BREAK

t = (CCL - Leak L)/(2xVaxial)

CCL

LeakL


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LEAKAGE EXPERIMENTS


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CORROSION & HYDROGEN INGRESS

Interaction of hot coolant with zirconium

Limited corrosion and hydrogen ingress

Solubility limit for hydrogen in zirconium When the solubility limited is exceeded, there is

the possibility of Delayed Hydride Cracking and

changes in material properties


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CORROSION & HYDROGEN INGRESS

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16

Time (hot years)

Deute

riumC

oncentration(p

pm)

Zircaloy-2

Zr-2.5Nb [CANDU 6]


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BLISTERS

1983


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BLISTER FRACTURE


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BLISTERS


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CONTACT

Without support from spacers, the pressure tube can

sag into contact with the calandria tube


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PRESSURE TUBE CONTACT

Spacer movement (2 spacers)

High deuterium pick-up in Zircaloy-2

Pressure tube sagged into contact with the

calandria tube creating local cold spots

Hydrogen diffusion and hydride blister formation

Cracking of several brittle blisters

Rupture of the pressure tube

Shutdown and replacement of the pressure tube


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SOLUTIONS

High Hydrogen:

Re-tube Zircaloy-2 reactors with Zr-2.5Nb

Spacer Movement:

In-reactor inspections for spacer locations andhydride blisters

Reposition spacers in operating reactors

Assessment methodologies

Install 4 tight-fitting spacers in new reactors


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DIMENSIONAL CHANGES

Response of fuel channel to:

Temperature

Stress

Neutron Flux/fluence

Change in shape:

Length Diameter

Sag


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ELONGATION

0

20

40

60

80

100

0 2 4 6 8 10

Fluence, n/m2x1025

mm


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FUEL CHANNEL REPLACEMENTS

Long history for Single Fuel Channel

Replacements (SFCR): Early 1960s at Douglas Point

1967 at NPD

Motivations

Single fuel channel issue

Material Surveillance

PLIM / PLEX


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LARGE-SCALE FUEL CHANNELREPLACEMENTS

Pickering Units 1 and 2

Replace Zircaloy-2 with

Zr-2.5Nb

Install 4 spacers

Avoid high hydrogen pickup,

pressure tube contact with

calandria tube, andpossibility of blisters

Pickering Units 3 and 4

Replace Zr-2.5Nb with

Zr-2.5Nb

Install 4 spacers

Avoid pressure tube contact

with calandria tube and

possibility of blisters Allow for greater pressure

tube elongation


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MANUFACTURING FLAW1985


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DELAYED HYDRIDE CRACKING


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LEAK-BEFORE-BREAKDEMONSTRATED

Residual stresses from over-rolling

Manufacturing Flaw

Delayed Hydride Cracking with multipleinitiation sites

Leakage and detection

Safe shutdown


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SOLUTIONS

Replace cracked pressure tube and rupturedcalandria tube

Inspect archive material for similar

manufacturing flaws Inspect selected tubes in operating reactors

Adjusted manufacturing process for all

subsequent reactor constructions


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IN-REACTOR INSPECTION

Non-destructive Volumetric inspections required by

CSA Standard

Flaw detection

Spacer locations

Dimensional inspection diameterand sag


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INSPECTION TOOLING


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MOCK-UP TESTING


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MATERIAL PROPERTIES

Changes in response to:

Operating temperature

Flux/Fluence Hydrogen Ingress

Time


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MATERIAL PROPERTIES


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KEYS TO HIGH PEFORMANCE

High-Quality Manufacturing Material Surveillance

In-Depth Knowledge and Understanding

In-Reactor Inspections

Assessment Methodologies


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PERFORMANCE STATISTICS

0

10

20

30

40

50

60

1960 1970 1980 1990 2000

Cr

ackedPressureTubes

NO FAILURES SINCE 1986

NO FAILURES IN

ANY CANDU 6


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ACR-Specific R&D

Anticipatory R&D


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ACR Design

OPERATING CONDITIONS

Slightly higher temperature

Slightly higher internal

pressure

Slightly higher neutron flux

than CANDU 6 reactors

FUEL CHANNEL DESIGN

Thicker pressure tube

and

Thicker calandria tube


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ACR-SPECIFIC ANTICIPATORY R&D

Fracture and Leak-Before-Break

Deformation

Corrosion and Hydrogen Ingress

Calandria Tubes Core Integrity

Confirmation of expected behavior


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ACR R&D FRACTURE & LBB

Material Property data:

KIH Crack velocity

Penetration length

Leak rates

Critical crack length

Strength

Extension of Databases: Temperature

Irradiation

ACR specification


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TYPICAL LBB ASSESSMENT

0

50

100

150

200

0 1 2 3 4 5

Time from Start of Leakage (hr)

CrackLength(mm)

CCL

CRACK


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ACR R&D - DEFORMATION


Creep and growth

Microstructure

Extension of databases: Temperature

Irradiation

ACR specification

0 1 2 3 4 5 6

0

Clea

rance

Axial Distance (m)

SPACER LOCATIONS


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ACR R&D - CORROSION


Oxidation

Hydrogen pick-up

Hydrogen vs.

Deuterium

Extension of Databases:

Temperature

Irradiation

Microstructure

ACR specification500 1000 1500 2000 2500 3000

Fe concentration (ppm (wt))

0.2

0.3

0.4

0.5

0.6

Deuterium Pickup (mg/dm2)

decreasing [C]


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CTL-1

ROLLED

JOINTTESTING


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ACR R&D CALANDRIA TUBES

Confirmation for:

Manufacturing of thicker

calandria tubes

Mechanical properties ofACR calandria tubes

Postulated accident

performance properties


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ACR FUEL CHANNELAssessments for 30 years:

Based on: Extrapolations of current knowledge

Conservative estimates of improvement benefits

All behaviors will be acceptable: DHC & Leak-Before-Break

Deformation, and

Corrosion and Hydrogen Ingress.

ANTICIPATORY R&D TO CONFIRM EXPECTATIONS


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FUEL CHANNEL SUMMARY

Well-Established R&D Program

Established for over 40 years more than 2000 person-years Cooperation between AECL, CANDU utilities, and others

Proven Excellent Fuel Channel Performance 2 ruptures in >150,000 pressure tube years

No fractures since 1986

Extension of Existing R&D Programs for ACR Temperature and pressure

ACR specification


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Technology Base for the ACR Fuel Channels