NUREG/CR-1344, Embrittlement Criteria for Zircaloy Fuel Cladding Applicable to Accident

168 Pages·2012·8.81 MB·English

NUREG/CR-1 344 NUREG/CR-1 344
ANL-79-48 ANL-79-48
EMBRITTLEMENT CRITERIA
FOR ZIRCALOY FUEL CLADDING
APPLICABLE TO ACCIDENT SITUATIONS
IN LIGHT-WATER REACTORS:
SUMMARY REPORT
by
H. M. Chung and T. F. Kassner
ARGONNE NATIONAL LABORATORY, ARGONNE, ILLINOIS
Prepared for the U. S. NUCLEAR REGULATORY COMMISSION
under Interagency Agreement DOE 40-550-75
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ANL-79 -48
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EMBRITTLEMENT CRITERIA FOR ZIRCALOY FUEL CLADDING
APPLICABLE TO ACCIDENT SITUATIONS
IN LIGHT-WATER REACTORS:
SUMMARY REPORT
by
H. M. Chung and T. F. Kassner
Materials Science Division
January 19 8 0
Prepared for the Division of Reactor Safety Research
Office of Nuclear Regulatory Research
U. S. Nuclear Regulatory Commission
Washington, D.C. 20555
Under Interagency Agreement DOE 40-550-75
NRC FIN No. A2017
EMBRITTLEMENT CRITERIA FOR ZIRCALOY FUEL CLADDING
APPLICABLE TO ACCIDENT SITUATIONS
IN LIGHT-WATER REACTORS:
SUMMARY REPORT
by
H. M. Chung and T. F. Kassner
ABSTRACT
The capability of Zircaloy cladding to withstand thermal-
shock loads during the reflood stage of a loss-of-coolant-accident
(LOCA) transient as well as anticipated loads during handling
and transport of heavily oxidizedfuel assemblies has been evalu-
ated. Although the type and magnitude of the forces on the clad-
ding under the latter situations have not been quantified, the
critical fracture loads under conditions of impact, tension, and
diametral compression have been determined as functions of
the degree of oxidation of the material and microstructure pro-
duced by cooling through the temperature range of the P - '
phase transformation at different rates. The effects of balloon-
ing and rupture (i.e., wall thinning) and hydrogen uptake by the
cladding during oxidation in steam on the deformation charac-
teristics at room temperature have also been evaluated. The
best correlation of the thermal-shock failure characteristics,
the failure-impact energy, and the diametral-compression prop-
erties with an oxidation-related parameter was obtained rela-
tive to the thickness of the transformed P-phase layer, with a
maximum oxygen content, for cladding that was oxidized at tem-
peratures between 1200 and 1700 K for various times. Em-
brittlement criteria, which encompass the mechanical response
of the cladding under different loading modes, have beenformu-
lated relative to the thermal-shockand 0.3-J impact resistance
of the material.
NRC
FIN No. Title
A2017 Mechanical Properties of Zircaloy
ii
TABLE OF CONTENTS
Page
EXECUTIVE SUMMARY .............. .. 1...............
I. INTRODUCTION ................................ . 4
II. BACKGROUND INFORMATION RELATIVE TO ZIRCALOY-
EMBRITTLEMENT CRITERIA AND EMERGENCY CORE-
COOLING SYSTEMS ............................... 4
III. DATA BASE FOR ZIRCALOY EMBRITTLEMENT RELATIVE TO
THE 1973 ACCEPTANCE CRITERIA FOR ECCS's ... ........ 7
IV. ZIRCALOY-4 CLADDING MATERIAL ... ............ 9
A. Specimen Geometry and Chemical Composition ........... 9
B. Texture ...................................... 9
C. Zircaloy-Oxygen Phase Diagram .................... 9
D. Zirconium-Hydrogen Phase Diagram ................. 12
E. Effect of Cooling Rate and Oxygen Content on the Morphology
of Transformed -phase Zircaloy .................... 13
V. EXPERIMENTAL AND ANALYTICAL PROCEDURES .......... 14
A. Fuel-rod Simulation ............................. 14
B. Cladding Deformation and Rupture ................... 14
C. Time-Temperature Transient ...................... 15
D. Effect of Maximum Temperature at Flooding on Wetting
Temperature .................................. 18
E. Analysis of Local Oxygen Content and Distribution in
Oxidized Cladding .............................. 18
F. Determination of Hydrogen Uptake by Zircaloy Cladding
during Transient Heating and Rupture in Steam ........... 20
VI. THERMAL-SHOCK-FAILURE PROPERTIES OF RUPTURED
ZIRCALOY-4 CLADDING .............................. 21
A. Oxidation Time-Temperature Limit for Survival of Thermal
Shock ......................................... 21
B. Thermal-shock Failure Mode ....................... 22
C. Correlation of Thermal-shock Failure Data with Oxidation
Parameters ................................... 23
iii
TABLE OF CONTENTS
Page
D. Effect of Cooling Rate through the aa ' Phase-
transformation Range on the Thermal-shock Failure
Characteristics ............................... 25
E. Influence of Cooling Rate through the ca ' Phase-
-
transformation Range on the Microstructure and Oxygen
Distribution of Transformed Layer ............... . 29
F. Tabulation of Thermal-shock Data with Various Oxidation-
related Parameters for Zircaloy-4 Cladding .... . . . . . . . 38
VII. IMPACT AND DIAMETRAL-RING-COMPRESSION PROPERTIES
OF UNDEFORMED ZIRCALOY-4 CLADDING AFTER OXIDA-
TION IN STEAM ................................ . 44
A. Experimental Methods for Impact and Diametral Ring-
compression Tests on Undeformed Cladding after Oxidation
in Steam ....... . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
B. Impact Properties of Zircaloy Cladding at Room Tempera-
ture after Oxidation in Steam and Cooling through the
0 - a' Phase Transformation at 5 K/s ............... 45
C. Diametral Ring-compression Properties of Oxidized
Cladding at Room Temperature .................... 47
D. Correlation of Impact and Diametral Ring-compression
Properties of Undeformed Zircaloy Cladding after
Oxidation in Steam ............................. 50
E. Effect of Wall Thickness on the Capability of Zircaloy
Cladding to Withstand Thermal Shock and Impact Loads
after Oxidation in Steam ......................... 51
F. Effect of Cooling Rate through the - a' Phase Trans-
formation on the Impact and Diametral Compression
Properties of Oxidized Zircaloy Cladding ............. 55
G. Tabulation of Impact and Diametral Ring-compression Data
for Undeformed Zircaloy-4 Cladding ................. 59
VIII. IMPACT, DIAMETRAL TUBE-COMPRESSION, AND AXIAL
TENSILE PROPERTIES OF DEFORMED AND RUPTURED
ZIRCALOY-4 CLADDING AFTER OXIDATION IN STEAM.. 63
A. Impact Properties of Ruptured Zircaloy-4 Cladding That
Survived Thermal Shock ......................... 63
iv
TABLE OF CONTENTS
Page
B. Metallurgical Interpretation of the Impact-failure
Characteristics ...... . 67
'7 . . . . .. . .
C. Diametral Tube-compression Properties of Ruptured
Zircaloy-4 Cladding. . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
D. Tensile Properties of Zircaloy-4 Cladding after Rupture and
Oxidation in Steam ............................ . 77
IX. OXIDATION AND HYDROGEN UPTAKE CHARACTERISTICS OF
DEFORMED AND RUPTURED ZIRCALOY-4 CLADDING ...... . 83
A. Effect of Alumina-pellet Eccentricity on Normal Inner-
surface Oxidation .............................. 83
B. Morphology of Anomalous Oxide Layers at the Inner and
Outer Surfaces of Zircaloy-4 Cladding ................. 84
C. Factors That Influence Porous-oxide Formation .......... 89
D. Correlation of Hydrogen Uptake and Inner-surface Oxidation
of Cladding from Integral Tube-burst/Thermal-shock Tests. 94
X. RECOMMENDED ZIRCALOY EMBRITTLEMENT CRITERIA
BASED UPON THE RESULTS OF THIS INVESTIGATION ....... 101
XI. SUMMARY AND CONCLUSIONS ....................... 10Z
APPENDIXES
A. Computation of Oxidation Parameters for Zircaloy Cladding. . 105
1. Oxidation Model for Zircaloy ........ ............ 105
2. Computer Programs .......................... 110
B. Analysis of Uncertainties in the Experimental Data........ 129
1. Random Error in Measured Quantities ............. 129
2. Estimated Uncertainty Limits Associated with the
Thermal-shock and Impact Results Used to Formulate the
Embrittlement Criteria ........................ 133
C. Correlation of Circumferential Strain due to Ballooning
Deformation with Average Wall-thickness Ratio Determined
from Cladding Cross Sections ...................... 135
v
TABLE OF CONTENTS
Page
D. Experimental Test Method for Zircaloy Embrittlement .... . 140
1. Evaluation of Cladding Embrittlement by Metallographic
Measurements ...... . . . . . . . . . . . . . . . . . . . . . . . . 140
2. Evaluation of Cladding Embrittlement by Impact Measure-
ments at Temperatures of 400 K ..... . . . . . . . . . . . . 140
ACKNOWLEDGMENTS ...... . . . . . . . . . . . . . . . . . . . . . . . . . . 142
REFERENCES ..................................... . 142
vi
LIST OF FIGURES
No. Title Page
1. Microstructure of As-received Stress-relieved Zircaloy-4
Cladding. ...... ...... ................ . .. ... . .. . . . 11
2. Schematic Illustration of Preferred Crystallographic Orientation
of Textured Zircaloy Tubing Used in Present Investigation .... . 11
3. Basal Pole Figure for Lot 7FD12 Zircaloy-4 Tube .......... . 11
4. Pseudobinary Zircaloy-Oxygen Phase Diagram Determined from
Metallographic Measurements on Oil-quenched Specimens .... . 12
5. Zirconium-Hydrogen Phase Diagram . 12
6. Schematic Diagram of Cladding Tube Used in the Embrittlement
Study .. 14
7. Temperature-vs-Time Curves from a Tube-burst/Thermal-shock
Test That Show an Abrupt Change in Cooling Rate at Tempera-
tures between 650 and 790 K ........................ . 15
8. Temperature-vs-Time Curves from a Tube-burst/Thermal-shock
Test That Show an Abrupt Change in the Cooling Rate at Tempera-
tures between -750 and.840 K ........................ . 15
9. Zircaloy-4 Cladding after Thermal-shock Failure Showing Loca-
tion of Thermocouples That Produced the Temperature-vs-
Time Curves in Fig. 7.. ................. 16
10. Zircaloy-4 Cladding after Thermal-shock Failure Showing Loca-
tion of Thermocouples That Produced the Temperature-vs-
Time Curves in Fig. 8 ...... . . . . . . . . . . . . . . . . . . . . . . . 16
11. Temperature-vs-Time Curves from a Tube-burst/Thermal-
shock Test in Which the Tube Was Quenched from 1273 K by
Bottom-flooding with Water at a Rise Rate of 50 mm/s ....... . 17
12. Wetting Temperature of Heavily Oxidized Zircaloy-4 Cladding as
a Function of Temperature at Which Flooding of the Tube Was
Initiated . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
13. Schematic for Sectioning of Oxidized Zircaloy Cladding for
Metallographic and Chemical Analyses ....... . . . . . . . . . . . 19
14. Microstructures of Cross Section of Oxidized Zircaloy-4
Cladding from Integral Tube-burst/Thermal-shock/
Impact Tests .......... 19
15. Schematic of Oxygen Distribution in Tube Wall and Definitions of
Oxygen Concentrations in Oxide, , and Phases at the Layer
Interfaces ..................................... . 20
vii
LIST OF FIGURES
No. Title Page
16. Capability of Zircaloy-4 Cladding to Withstand Thermal Shock
by Bottom-flooding with Water after Rupture, Isothermal
Oxidation in Steam for Various Times at Temperatures between
1140 and 1770 K, and Slow Cooling through the P - att Trans-
formation at a Rate of 5 K/s ..... . . . . . . . . . . . . . . . . . . . . 21
17. Representation of Thermal-shock Fracture Relative to the Time
and Temperature of Isothermal Oxidation after Rupture in Steam
under Transient-heating Conditions .................... . 22
18. Failure Map for Zircaloy-4 Cladding by Thermal Shock or
Normal Handling Relative to the Equivalent-cladding-reacted
Parameter and Maximum Isothermal Oxidation Temperature
after Rupture in Steam .Z..... . . . . . . . . . . . . . . . . . . . . . . . 23
19. Failure Map for Zircaloy-4 Cladding by Thermal Shock Relative
to the Fractional Thickness of Previous P-phase Layer and
Oxidation Temperature after Rupture in Steam .... . . . . . . . . . 24
20. Failure Map for Zircaloy-4 Cladding by Thermal Shock Relative
to Fractional Saturation of Phase and Oxidation Temperature
after Rupture in Steam ...... . . . . . . . . . . . . . . . . . . . . . . . 24
21. Failure Map for Zircaloy-4 Cladding by Thermal Shock Relative
to Wall Thickness with 1.0 wt % Oxygen after Isothermal
Oxidation ..................................... . 25
22. Capability of Zircaloy-4 Cladding Tubes to Withstand Thermal
Shock after Rupture, Isothermal Oxidation, and Bottom-flooding
from Isothermal Oxidation Temperature ..... . . . . . . . . . . . . 26
23. Thermal-shock Failure Map for Zircaloy-4 Cladding Relative to
the Equivalent-cladding-reacted Parameter and Maximum
Oxidation Temperature after Rupture in Steam .... . . . . . . . . . 26
24. Failure Map for Zircaloy-4 Cladding by Thermal Shock Relative
to Fractional Thickness of Previous P-phase Layer and Oxidation
Temperature after Rupture in Steam and Flooding with Water at
Oxidation Temperature ............................ . 27
25. Failure Map for Zircaloy-4 Cladding by Thermal Shock Relative
to Fractional Saturation of Phase and Oxidation Temperature
after Rupture in Steam and Flooding with Water at Oxidation
Temperature ................................... . 27
26. Failure Map for Zircaloy-4 Cladding by Thermal Shock Relative
to the Wall Thickness with 0.9 wt % Oxygen after Isothermal
Oxidation and Flooding with Water at the Oxidation Temperature . 28
viii