Post-Test Examination 

Results from Integral, 

High-Burnup, Fueled 

LOCA Tests at Studsvik 

Nuclear Laboratory

Office of Nuclear Regulatory Research

NUREG-2160
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Post-Test Examination 

Results from Integral, 

High-Burnup, Fueled 

LOCA Tests at Studsvik 

Nuclear Laboratory

Manuscript Completed: April 2013 

Date Published: August 2013 

Michelle E. Flanagan

U.S. Nuclear Regulatory Commission

Peter Askeljung

Anders Puranen

Hot Cell Laboratory, Studsvik Nuclear AB, Sweden

Office of Nuclear Regulatory Research

NUREG-2160

iii NUREG-2160

ABSTRACT

This report presents and discusses the results of the U.S. Nuclear Regulatory Commission’s 

integral loss-of-coolant accident (LOCA) testing program conducted at Studsvik Nuclear AB in 

Sweden. In this program, refabricated, high burnup irradiated fuel rodlets were subjected to 

LOCA conditions. In total, six single-rod LOCA tests were conducted in the Hot Cell Laboratory 

at Studsvik Nuclear AB. This report documents the test conditions, rodlet response, and 

post-test examinations for all six tests. The purpose of this document is to make this 

information available for comparison to related or complementary experimental programs. 

The observations of fuel fragmentation, relocation, and dispersal in this experimental program 

may be of particular interest for comparison to related or complementary experimental 

programs.

v NUREG-2160

FOREWORD

The purpose of this document is to make available the results of the U.S. Nuclear Regulatory 

Commission’s integral loss-of-coolant accident (LOCA) testing program conducted at Studsvik 

Nuclear AB in Sweden for comparison to related or complementary experimental programs. 

Recently, discussion about the results of LOCA testing in the area of fuel fragmentation, 

relocation and dispersal has grown common and rigorous throughout the international 

community. Therefore, the observations of fuel fragmentation, relocation, and dispersal in this 

experimental program may be of particular interest for comparison to related or complementary 

experimental programs. 

vii NUREG-2160

CONTENTS

ABSTRACT ...................................................................................................................................................... III

FOREWORD .....................................................................................................................................................V

CONTENTS .....................................................................................................................................................VII

FIGURES...........................................................................................................................................................IX

TABLES............................................................................................................................................................XV

ABBREVIATIONS AND ACRONYMS....................................................................................................XVII

1. GENERAL INFORMATION ABOUT THE STUDSVIK LOCA TEST SERIES, 

EXPERIMENTAL PROCEDURES, AND EXAMINATIONS .......................................................... 1-1

2. SPECIFIC RESULTS OF EACH TEST............................................................................................... 2-1

2.1 TEST 189.................................................................................................................................................2-2

2.1.1 Initial State.........................................................................................................................................2-2

2.1.2 Transient Information .....................................................................................................................2-2

2.1.3 In-Cell Measurements....................................................................................................................2-4

2.1.4 Metallography and Hot-Vacuum Extraction.............................................................................2-6

2.1.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire 

Probe Measurements.....................................................................................................................2-6

2.2 TEST 191.................................................................................................................................................2-6

2.2.1 Initial State.........................................................................................................................................2-7

2.2.2 Transient Information .....................................................................................................................2-7

2.2.3 In-Cell Measurements....................................................................................................................2-8

2.2.4 Metallography and Hot-Vacuum Extraction...........................................................................2-11

2.2.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire 

Probe Measurements...................................................................................................................2-13

2.3 TEST 192...............................................................................................................................................2-15

2.3.1 Initial State.......................................................................................................................................2-15

2.3.2 Transient Information ...................................................................................................................2-15

2.3.3 In-Cell Measurements..................................................................................................................2-17

2.3.4 Metallography and Hot-Vacuum Extraction...........................................................................2-19

2.3.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire 

Probe Measurements...................................................................................................................2-23

2.4 TEST 193...............................................................................................................................................2-30

2.4.1 Initial State.......................................................................................................................................2-31

2.4.2 Transient Information ...................................................................................................................2-31

2.4.3 In-Cell Measurements..................................................................................................................2-32

2.4.4 Metallography and Hot-Vacuum Extraction...........................................................................2-35

2.4.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire 

Probe Measurements...................................................................................................................2-39

2.5 TEST 196...............................................................................................................................................2-40

2.5.1 Initial State.......................................................................................................................................2-41

2.5.2 Transient Information ...................................................................................................................2-41

2.5.3 In-Cell Measurements..................................................................................................................2-43
NUREG-2160 viii

2.5.4 Metallography and Hot-Vacuum Extraction...........................................................................2-45

2.5.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire 

Probe Measurements...................................................................................................................2-47

2.6 TEST 198...............................................................................................................................................2-50

2.6.1 Initial State.......................................................................................................................................2-51

2.6.2 Transient Information ...................................................................................................................2-51

2.6.3 In-Cell Measurements..................................................................................................................2-53

2.6.4 Metallography and Hot-Vacuum Extraction...........................................................................2-55

2.6.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire 

Probe Measurements...................................................................................................................2-58

3. REVIEW OF TEST RESULTS FOR SPECIFIC PARAMETER COMPARISONS .................... 3-1

3.1 INITIAL STATE .........................................................................................................................................3-1

3.2 TRANSIENT..............................................................................................................................................3-1

3.3 IN-CELL MEASUREMENTS....................................................................................................................3-2

4. CONCLUSIONS........................................................................................................................................ 4-1

5. REFERENCES.......................................................................................................................................... 5-1
ix NUREG-2160

FIGURES

Figure 1-1 Schematic of the apparatus used for the Studsvik LOCA tests.............................. 1-1

Figure 1-2 A detailed drawing of the rodlet components and dimensions............................... 1-2

Figure 2-1 Fill pressure adjustment at 300 °C for Test 189, which provides an 

indication of gas communication .......................................................................... 2-3

Figure 2-2 Temperature and pressure history for Test 189..................................................... 2-3

Figure 2-3 Rod segment from Test 189 (a) in test rig after transient and (b) a 

closeup of the rupture opening after the transient................................................. 2-4

Figure 2-4 A wire probe is inserted into the fuel rod to measure the voided 

cladding length..................................................................................................... 2-4

Figure 2-5 Rod segment from Test 189 showing no significant rod bending (a) in 

plane with the rupture or (b) out of plane with the rupture..................................... 2-5

Figure 2-6 Profilometry measurements of segment 189 post-transient. The rupture 

length is also indicated......................................................................................... 2-5

Figure 2-7 Images of fuel collected from Test 189.................................................................. 2-6

Figure 2-8 Fill pressure adjustment at 300 °C for Test 191, which provides an 

indication of gas communication .......................................................................... 2-8

Figure 2-9 Temperature and pressure history for Test 191..................................................... 2-8

Figure 2-10 Rod segment from Test 191 (a) in test rig after transient and (b) a 

closeup of the rupture opening after the transient............................................... 2-9

Figure 2-11 Rod segment from Test 191 showing (a) no significant rod bending out 

of plane with the rupture and (b) & (c) noticeable bending in plane with 

the rupture.......................................................................................................... 2-9

Figure 2-12 Profilometry measurements of segment 191 post-transient. The rupture 

length is also indicated..................................................................................... 2-10

Figure 2-13 Images of fuel collected from Test 191.............................................................. 2-10

Figure 2-14 Photo of test segment from Test 191, indicating the location of 

metallography and hydrogen measurements.................................................... 2-11

Figure 2-15 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 191 ................................................................................................ 2-12

Figure 2-16 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 191 at (a) 45° and (b) 225° ............................................................ 2-12

Figure 2-17 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 191 at (a) 0° and (b) 135° ............................................................. 2-13

Figure 2-18 Photo of test segment from Test 191, indicating the relative length of 

gamma scan results ......................................................................................... 2-13

Figure 2-19 Gamma scan results for Test 191 with comparison to profilometry and 

initial wire probe measurements....................................................................... 2-14

Figure 2-20 Fill pressure adjustment at 300 °C for Test 192, which provides an 

indication of gas communication ...................................................................... 2-16

Figure 2-21 Temperature and pressure history for Test 192................................................. 2-16

Figure 2-22 Rod segment from Test 192 (a) in test rig after transient and (b) a 

closeup of the rupture opening after the transient............................................. 2-17

Figure 2-23 Rod segment from Test 192 showing no significant rod bending (a) out 

of plane with the rupture or (b) in plane with the rupture................................... 2-17
NUREG-2160 x

Figure 2-24 Profilometry measurements of segment 192 post-transient. The 

rupture length is also indicated......................................................................... 2-18

Figure 2-25 Images of fuel collected from Test 192.............................................................. 2-18

Figure 2-26 Photo of test segment from Test 192, indicating the location of 

metallography and hydrogen measurements.................................................... 2-19

Figure 2-27 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 192 ................................................................................................ 2-20

Figure 2-28 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 192 at (a) 45° and (b) 135° ............................................................ 2-20

Figure 2-29 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 192 at (a) 0° and (b) 315° .............................................................. 2-21

Figure 2-30 Macrograph of cross section from 50 mm below the rupture region of 

rodlet tested in LOCA Test 192 ........................................................................ 2-22

Figure 2-31 Two high-resolution images of the cladding outer diameter from the 

metallography examination 50 mm below the rupture region of the 

rodlet tested in LOCA Test 192 at (a) 90° and (b) 315° .................................... 2-22

Figure 2-32 Two high-resolution images of the cladding inner diameter from the 

metallography examination 50 mm below the rupture region of the 

rodlet tested in LOCA Test 192 at (a) 45°and (b) 225° .................................... 2-23

Figure 2-33 Hydrogen measurements from 192 relative to segment strain profile and 

rupture length................................................................................................... 2-23

Figure 2-34 Photo of test segment from Test 192, indicating the relative length of 

gamma scan results and location of additional M/C examinations in the 

remaining fueled regions .................................................................................. 2-24

Figure 2-35 Gamma scan results for Test 192 with comparison to profilometry and 

initial wire probe measurements....................................................................... 2-25

Figure 2-36 Fuel fragments collected from the top end of rod 192 after gentle 

shaking just before gamma scan...................................................................... 2-26

Figure 2-37 Comparison of fuel fragment size distribution from two regions of 

segment 192 .................................................................................................... 2-27

Figure 2-38 Macrograph of transverse cross section 35 mm from the bottom of the 

rodlet tested in LOCA Test 192 ........................................................................ 2-28

Figure 2-39 A high-resolution image of the fuel cladding gap from the M/C 

examination 35 mm from the bottom of the rodlet tested in LOCA Test 

192................................................................................................................... 2-28

Figure 2-40 Macrograph of axial cross section covering a span approximately 50–

75 mm from the segment bottom of the rodlet tested in LOCA Test 192........... 2-29

Figure 2-41 High-resolution images of the cladding (a and b) inner and (c and d) 

outer diameter taken from the axial M/C shown above. These images 

were near the bottom (left) of the axial M/C, approximately 55 mm from 

the original segment bottom and approximately 100 mm below the 

rupture opening of the rodlet tested in LOCA Test 192..................................... 2-30

Figure 2-42 Fill pressure adjustment at 300 °C for Test 193, which provides an 

indication of gas communication ...................................................................... 2-31

Figure 2-43 Temperature and pressure history for Test 193................................................. 2-32

Figure 2-44 Rod segment from Test 193 (a) in test rig after transient and (b) a 

closeup of the rupture opening after the transient............................................. 2-33
xi NUREG-2160

Figure 2-45 Rod segment from Test 193 showing no significant rod bending (a) in 

plane with the rupture and (b) minor bending out of plane with the 

rupture.............................................................................................................. 2-33

Figure 2-46 Profilometry measurements of segment 193 post-transient. The 

rupture length is also indicated......................................................................... 2-34

Figure 2-47 Images of fuel collected from Test 193.............................................................. 2-34

Figure 2-48 Photo of test segment from Test 193, indicating the location 

of metallography............................................................................................... 2-35

Figure 2-49 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 193 ................................................................................................ 2-36

Figure 2-50 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 193 at (a) 90° and (b) 270° ............................................................ 2-36

Figure 2-51 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 193 at (a) 135° and (b) 270° .......................................................... 2-37

Figure 2-52 Macrograph of cross section from 35 mm above the rupture region of 

rodlet tested in LOCA Test 193 ........................................................................ 2-37

Figure 2-53 Two high-resolution images of the cladding outer diameter from the 

metallography examination 35 mm above the rupture region of the 

rodlet tested in LOCA Test 193 at (a) 45° and (b) 270° .................................... 2-38

Figure 2-54 Two high-resolution images of the cladding inner diameter from the 

metallography examination 35 mm above the rupture region of the 

rodlet tested in LOCA Test 193 at (a) 135° and (b) 270° .................................. 2-38

Figure 2-55 Etched cross section revealing hydrogen microstructure in the cladding 

in the rupture region of Test 193 ...................................................................... 2-39

Figure 2-56 Photo of test segment from Test 193, indicating the relative length of 

gamma scan results ......................................................................................... 2-39

Figure 2-57 Gamma scan results for Test 193 with comparison to profilometry and 

initial wire probe measurements....................................................................... 2-40

Figure 2-58 Fill pressure adjustment at 300 °C for Test 196, which provides an 

indication of gas communication ...................................................................... 2-42

Figure 2-59 Temperature and pressure history for Test 196................................................. 2-42

Figure 2-60 Rod segment from Test 196 (a) in test rig after transient and (b) a 

closeup of the rupture opening after the transient............................................. 2-43

Figure 2-61 Rod segment from Test 196 showing no significant rod bending....................... 2-43

Figure 2-62 Profilometry measurements of segment 196 post-transient. The rupture 

length is also indicated..................................................................................... 2-44

Figure 2-63 Images of fuel collected from Test 196.............................................................. 2-44

Figure 2-64 Photo of test segment from Test 196, indicating the location of 

metallography and hydrogen measurements.................................................... 2-45

Figure 2-65 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 196 ................................................................................................ 2-46

Figure 2-66 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 196 at (a) 90° and (b) 270° ............................................................ 2-46

Figure 2-67 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 196 at (a) 45° and (b) 270° ............................................................ 2-47
NUREG-2160 xii

Figure 2-68 Hydrogen measurements from 196 relative to segment strain profile 

and rupture length ............................................................................................ 2-47

Figure 2-69 Photo of test segment from Test 196, indicating the relative length of 

gamma scan results ......................................................................................... 2-48

Figure 2-70 Gamma scan results for Test 196 with comparison to profilometry and 

initial wire probe measurements....................................................................... 2-48

Figure 2-71 Fuel fragments collected from the bottom of rod 196 after gentle shaking 

just before gamma scan ................................................................................... 2-49

Figure 2-72 Comparison of fuel fragment size distribution from two regions 

of segment 196 ................................................................................................ 2-50

Figure 2-73 Fill pressure adjustment at 300 °C for Test 198, which provides an 

indication of gas communication ...................................................................... 2-52

Figure 2-74 Temperature and pressure history for Test 198................................................. 2-52

Figure 2-75 Rupture opening after the transient simulation for Test 198 .............................. 2-53

Figure 2-76 Rod segment from Test 198 showing no significant rod bending....................... 2-53

Figure 2-77 Profilometry measurements of segment 198 post-transient. The rupture 

length is also indicated..................................................................................... 2-54

Figure 2-78 Images of fuel collected from Test 198.............................................................. 2-54

Figure 2-79 Photo of test segment from Test 198, indicating the location of 

metallography and hydrogen measurements.................................................... 2-55

Figure 2-80 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 198 ................................................................................................ 2-55

Figure 2-81 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 198 at (a) 90° and (b) 270° ............................................................ 2-56

Figure 2-82 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 198 at (a) 90° and (b) 225° ............................................................ 2-56

Figure 2-83 Macrograph of cross section from 50 mm below the rupture region of 

rodlet tested in LOCA test 198 ......................................................................... 2-57

Figure 2-84 Two high-resolution images of the cladding outer diameter from the 

metallography examination 50 mm below the rupture region of the 

rodlet tested in LOCA Test 198 at (a) 90° and (b) 180° .................................... 2-57

Figure 2-85 Two high-resolution images of the cladding inner diameter from the 

metallography examination 50 mm below the rupture region of the 

rodlet tested in LOCA Test 198 at (a) 90° and (b) 225° .................................... 2-57

Figure 2-86 Hydrogen measurements from Test 198 relative to segment strain 

profile and rupture length ................................................................................. 2-58

Figure 2-87 Photo of test segment from Test 198, indicating the relative length of 

gamma scan results and location of an additional M/C examination in 

the remaining fueled region.............................................................................. 2-59

Figure 2-88 Gamma scan results for Test 198 with comparison to profilometry and 

initial wire probe measurements....................................................................... 2-60

Figure 2-89 Macrograph of axial cross section covering a span approximately 80–

105 mm from the segment bottom of the rodlet tested in LOCA Test 

198................................................................................................................... 2-61

Figure 2-90 High-resolution images of the cladding (a and b) inner and (c and d) 

outer diameter taken from the axial M/C shown above. These images 
xiii NUREG-2160

were near the bottom (left) of the axial M/C, approximately 85 mm from 

the original segment bottom of the rodlet tested in LOCA Test 198.................. 2-62

Figure 3-1 Pressure drop after rupture in the top plenum, plotted as a function of 

time, for all six tests.............................................................................................. 3-2

Figure 3-2 Approximate percentage of fuel loss during each test, color-coded by 

when fuel loss occurred. Note: Measured mass loss was compared to 

an estimated initial fuel mass of 150 g for the 300-mm segment. ......................... 3-3

Figure 3-3 Fragment size distribution for each test................................................................. 3-4

xv NUREG-2160

TABLES

Table 2-1 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of the Six LOCA Tests Run at Studsvik in the 

NRC’s LOCA Research Program.......................................................................... 2-1

Table 2-2 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of Test 189 .................................................................. 2-2

Table 2-3 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of Test 191 .................................................................. 2-7

Table 2-4 Fragment Size Distribution Results from Test 191................................................ 2-11

Table 2-5 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of Test 192 ................................................................ 2-15

Table 2-6 Fragment Size Distribution Results from Test 192................................................ 2-19

Table 2-7 Hydrogen Measurements for Test 192 ................................................................. 2-23

Table 2-8 Fragment Size Distribution Results for Fuel Fragments Collected from the 

Top End of Rod 192 after Gentle Shaking Just before Gamma Scan .................. 2-26

Table 2-9 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of Test 193 ................................................................ 2-30

Table 2-10 Fragment Size Distribution Results from Test 193.............................................. 2-35

Table 2-11 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of Test 196 .............................................................. 2-41

Table 2-12 Fragment Size Distribution Results from Test 196.............................................. 2-45

Table 2-13 Hydrogen Measurements for Test 196 ............................................................... 2-47

Table 2-14 Fragment Size Distribution Results for Fuel Fragments Collected from 

the Bottom End of Rod 196 after Gentle Shaking Just before Gamma 

Scan .................................................................................................................. 2-50

Table 2-15 Measurements and Values That Characterize the Initial State, Transient, 

and In-Cell Measurements of Test 198 .............................................................. 2-51

Table 2-16 Fragment Size Distribution Results from Test 198.............................................. 2-54

Table 2-17 Hydrogen Measurements from Test 198 ............................................................ 2-58

Table 3-1 Summary of All “Initial State” Information from the Six LOCA Tests ....................... 3-1

Table 3-2 Summary of All “Transient” Information from the Six LOCA Tests .......................... 3-2

Table 3-3 Summary of All “In-Cell Measurement” Information from the Six LOCA 

Tests...................................................................................................................... 3-3

xvii NUREG-2160

ABBREVIATIONS AND ACRONYMS

C Celsius

cm centimeter

CP-ECR Equivalent cladding reacted, as calculated by the Cathcart-Pawel Oxidation 

equation

F Fahrenheit

GWd/MTU gigawatt days per metric ton uranium

IR infrared radiation

kW/m kilowatt per meter

LHGR linear heat generation rate

LOCA loss-of-coolant accident

M/C metallography and ceramography

PIE postirradiation examination

PWR pressurized-water reactor

wppm weight parts per million

1-1 NUREG-2160

1. GENERAL INFORMATION ABOUT THE STUDSVIK LOCA TEST 

SERIES, EXPERIMENTAL PROCEDURES, AND EXAMINATIONS

The U.S. Nuclear Regulatory Commission (NRC) commissioned six single-rod, out-of-pile, 

integral loss-of-coolant accident (LOCA) tests at the Hot Cell Laboratory of Studsvik Nuclear AB 

to assess the mechanical performance of ballooned and ruptured high-burnup fuel rods. 

In each of these tests, a pressurized, high-burnup, fueled rod segment was subjected to a 

temperature transient in a steam environment to induce ballooning, rupture, and 

high-temperature steam oxidation. The apparatus used for the Studsvik LOCA tests is shown 

below in Figure 1-1.

Figure 1-1 Schematic of the apparatus used for the Studsvik LOCA tests

The LOCA apparatus was designed to externally heat a 30 centimeters (cm) long, pressurized, 

irradiated fuel rodlet up to 1,200 degrees Celsius (C) (2192 degrees Fahrenheit (F)) by infrared 

(IR) radiation. The fuel rodlets are heated in a flowing steam environment from 300 degrees C 

(572 degrees F) to a target temperature of about 1,200 degrees C at a rate of 5 degrees 

C/second (s) (41 degrees F/s). The rodlet temperature is measured with a thermocouple 

attached by a metal clamp 50 millimeters above the axial mid plane. The test segment is 

pressurized with helium. Internal pressures were consistent with typical end of life rod internal 

pressure, although likely on the high end, and were chosen to induce ballooning and rupture 

with rupture strains in the range of 30 percent-50 percent. Rodlet temperatures were held at 

1,200 degrees C for either 0, 5, 25, or 85 seconds to achieve various oxidation levels.

Identical pressure transducers were used at the bottom and at the top of the rodlet, measuring

the internal pressure throughout the preparation and testing phases. The void volumes of the 
NUREG-2160 1-2

rodlet were: 7.3 cm3 above the rod (approximately 6.1 cm3 in the upper pressure line and 

approximately 1.2 cm3 in the upper rod plenum) and 3.1 cm3 below the rod (approximately

2.4 cm3 in the lower pressure line and approximately 0.7 cm3 in the lower rod plenum). Thus, 

the total void volume was approximately 10.4 cm3

. A drawing showing the main parts of the 

rodlet is shown in Figure 1-2. Additional information about the LOCA apparatus and test train 

design can be found in reference [1].

Figure 1-2 A detailed drawing of the rodlet components and dimensions

The LOCA tests performed at Studsvik used segments taken from pressurized-water reactor 

(PWR) rods. For the first four tests (189, 191-193) the segments were taken from rods with a 

rod average burnup level between 68-69 gigawatt days per metric ton uranium (GWd/MTU). 
1-3 NUREG-2160

For the last two, 196 and 198, the segments were taken from rods with a rod average burnup 

level of 55 GWd/MTU, respectively. Two of the tests (189, 196) were terminated just after 

rupture, while the four other tests each experienced some degree of high-temperature steam 

oxidation, followed by quench.

Following the LOCA simulation, four-point bend tests were conducted to measure the residual 

mechanical behaviour of the ballooned and ruptured region. The results of the four-point bend 

tests on the first four LOCA tests have been reported elsewhere [2]. After the four-point bend 

test, a shake test was performed to determine the mobility of fuel fragments that remained in the 

fuel rod. The shake test consisted of an inversion of the two halves of the broken fuel rod,

followed by minor shaking to dislodge any loose fuel fragments. The shake test was conducted 

approximately 2 days after the LOCA simulation.

During these tests, significant fuel loss was observed at various stages of the experimental 

procedures and multiple measurements and observations were made to characterize the fuel 

loss. Wire probe measurements were performed to measure the length of cladding that was 

“empty” of fuel for each segment. Mass measurements were made before and after the LOCA 

simulation, after the four-point bend test and after the shake test to determine the fuel loss at 

each stage by comparison to the mass at the previous step (the exception is Test 189, which 

did not have an initial rodlet mass and therefore fuel mass loss was determined by weighing the 

collected fuel). Photos were taken to document the appearance of the fuel and cladding at all 

stages. Fragment size measurements were completed by processing fuel fragments through a 

series of six sieves to determine the distribution of the fuel fragments by size (the exception is 

Test 189, which was sent for disposal before sieving analysis). Some of the observations of fuel 

relocation and loss have been reported in previous conference papers and reports [3-4].

Axial locations of interest were identified for each test segment, and multiple metallography 

samples were prepared, along with measurement of the hydrogen content by hot vacuum 

extraction.

Almost 1 year after the last LOCA tests were completed, emerging questions prompted

additional postirradiation examination (PIE) investigations. The wire probe measurements 

performed after the shaking test indicated a long length of empty cladding, but also a significant 

amount of residual fuel material in some test segments. To investigate the length and condition 

of the remaining fueled segments, gamma scans were performed on many of the remaining 

fueled portions of each test segment. This report documents the test condition, rodlet response,

and post-test examinations for all six LOCA tests. 

2-1 NUREG-2160

2. SPECIFIC RESULTS OF EACH TEST

In this section, specific information about each test will be presented and discussed. Table 2-1

summarizes basic information for all six loss-of-coolant (LOCA) tests run in the U.S. Nuclear 

Regulatory Commission’s (NRC’s) LOCA program at Studsvik. In the following subsections, the 

initial state, transient information and in-cell measurements will be discussed for each test.

Table 2-1 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of the Six LOCA Tests Run at Studsvik in the NRC’s 

LOCA Research Program

Test Adjacent H (wppm) Average Oxide 

(μm)

189 176 20

191 187, 271 20-30

192 176, 288 25-30

193 187 20

196 149 20

198 225 20

Test Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture Pressure 

(bar)

Time (s) to 50% of rupture 

P for top/bottom gauges

CP-ECR 

(%) Quench

189 950 700 109 35 / 7 0 No

191 1185 680 104 21 / 10 13 Yes

192 1185 700 81 13 / 15 11 Yes

193 1185 728 81 45 / 8 17 Yes

196 950 686 81 5 / 2 0 No

198 1185 693 81 3 / 2 15 Yes

Test Max Strain (%) Length >10% 

Strain (mm)

189 48 105

191 50 70

192 56 85

193 50 100

196 25 95

198 25 115

Initial State

Transient

In-cell 

Measurements

Rod Internal Pressure 

at 300°C (bar)

110

110

82

82

82

82

Rupture Dimensions 

(mm) (Width/Length)

10.5 / 23.9

17.5 / 21.6

9 / 22.7

13.8 / 17.8

Rod Average Burn Up (GWd/MTU)

68.2

69.3

68.2

69.3

55.2

55.2

Wire Probe Measurement (mm) 

(Top/Bottom)

82 / 66

0.2 / 1.5

1.6 / 11

70 / 55

85 / 73

113 / 91 

90 / 66

55 / 76
NUREG-2160 2-2

2.1 Test 189

Table 2-2 summarizes measurements and values that characterize the initial state, transient, 

and in-cell measurements of Test 189. The initial state, transient information, and in-cell 

measurements will be described further in the following sections. 

Table 2-2 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of Test 189

2.1.1 Initial State

For Test 189, a segment of high burnup Westinghouse ZIRLOTM was used. The segment was 

taken from a rod that was irradiated at a U.S. pressurized-water reactor (PWR) power plant and 

had a rod average burnup of 68.2 gigawatt days per metric ton uranium (GWd/MTU). The 

particular father rods used in Tests 189-193 had a unique operating history characterized by an 

end-of-life power that is greater than typical operating practice, namely a mean linear heat 

generation rate (LHGR) of approximately 24 kilowatts per meter (kW/m) for cycle one, 23 kW/m 

for cycle two, 5 kW/m for cycle three, and 15 kW/m for cycle four. The 300-millimeter segment 

was taken from the middle section of the fuel rod, approximately 1,400 millimeters from the 

bottom of the full length rod. A hydrogen content of 176 weight parts per million (wppm) was 

measured just above the segment. The eddy current measurements indicate that the oxide 

layer thickness was relatively constant over the length of this segment, and average about 

20 micrometers.

2.1.2 Transient Information

To begin the transient, the rodlet was heated and maintained at 300 degrees Celsius (C)

(572 degrees Fahrenheit (F)) for approximately 15 minutes to achieve thermal equilibrium. 

Before initiating the temperature ramp, the desired fill pressure was established at 

300 degrees C. For Test 189, the rodlet was pressurized to 110 bar (at 300 degrees C). The 

pressure adjustment procedure provides an indication of gas communication by observing the 

response time of the lower pressure transducer, as shown in Figure 2-1. Recall that while the 

gas line is open, the top pressure transducer indicates the gas line pressure and the bottom 

should reflect the ability of gas to move the 300 millimeter segment length to equilibrate 

pressure. Once the desired fill pressure was established, the gas line was closed and the rodlet 

Adjacent H (wppm) Average Oxide 

(μm)

176 20

Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture 

Pressure (bar)

Time (s) to reach 50% of rupture 

P for top/bottom gauges CP-ECR (%) Quench

950 700 109 35 / 7 0 No

Max Strain (%) Length >10% 

Strain (mm)

48 105

Rod Internal Pressure at 

300°C (bar)

110

Rupture Dimensions 

(mm) (Width/Length)

10.5 / 23.9

Rod Average Burn Up (GWd/MTU)

68.2

Wire Probe Measurement (mm) (Top/Bottom)

82 / 66

Initial State

Transient

In-Cell 

Measurements
2-3 NUREG-2160

was heated at 5 degrees C/second (s) (41 degrees F/s) through ballooning and rupture. This 

was a “ramp-to-rupture” test and therefore the furnace was shut off to terminate the test at 

950 degrees C (1,742 degrees F) and there was no quench. Rupture is estimated to have 

taken place when the rod internal pressure reached 109 bar and the cladding temperature 

reached 700 degrees C (1,292 degrees F). The depressurization rate was relatively slow for 

Test 189; the top pressure gauge recorded a 50 percent reduction in pressure (relative to 

109 bar) after 35 seconds and the bottom pressure gauge recorded a 50 percent reduction in 

pressure after 7 seconds. No significant oxidation was accumulated during this test. The 

temperature and pressure history for Test 189 is shown in Figure 2-2.

Figure 2-1 Fill pressure adjustment at 300 °C for Test 189, which provides an indication 

of gas communication

Figure 2-2 Temperature and pressure history for Test 189
NUREG-2160 2-4

2.1.3 In-Cell Measurements

After the simulated LOCA transient was complete, the fuel rod was examined. Figure 2-3

provides two photos of the fuel rod after the transient. The rupture opening was measured to be 

10.5 millimeters wide and 23.9 millimeters in length. It is significant to note that when the 

rupture opening was examined after the transient, no fuel could be seen in the region. In fact, a 

wire probe was used to measure the length of voided cladding after all experimental steps 

(LOCA transient, bending, and shaking) and the probe traveled unobstructed approximately 

66 millimeter above and approximately 82 millimeter below the rupture center. The technique to 

measure the voided cladding is illustrated below in Figure 2-4.

 (a) (b)

Figure 2-3 Rod segment from Test 189 (a) in test rig after transient and (b) a closeup of 

the rupture opening after the transient

Figure 2-4 A wire probe is inserted into the fuel rod to measure the voided 

cladding length
2-5 NUREG-2160

The rod did not experience distortion or bending during the LOCA transient, which can be seen 

in Figure 2-5. Profilometry measurements were made, and they are shown in Figure 2-6. In 

Figure 2-6, the initial diameter and rupture length are also indicated. The mid-wall rupture strain 

value for Test 189 was calculated to be 48 percent.

(a)

(b)

Figure 2-5 Rod segment from Test 189 showing no significant rod bending (a) in plane 

with the rupture or (b) out of plane with the rupture

Figure 2-6 Profilometry measurements of segment 189 post-transient. 

The rupture length is also indicated.

Following the simulated LOCA transient of Test 189, a large amount of fuel was collected from 

the LOCA test train. Additional fuel fragments were collected during the four-point bend test 

and after minor shaking of the bent segment. The pre-test rod mass was not measured, so it is 

possible that the total fuel loss was not accounted for by weighing and totalling the mass of 

collected fuel fragments. All of the readily collected fuel was weighed, but it is likely some 

additional fuel fragments remained within the test train, quench tank, or in the hot-cell itself.
NUREG-2160 2-6

In total, it appears that about half of the fuel fell out of this rod during the simulated LOCA 

transient test and during shaking. The collected fuel in LOCA test chamber totalled 41 grams. 

Fuel which was lost during the four-point bend test and after minor shaking was also collected 

and weighed. The mass of fuel that was collected after the bend test and after shaking was 

20 grams. In total, 61 grams of fuel were collected. Figure 2-7 provides an image of the 

collected fuel fragments.

Figure 2-7 Images of fuel collected from Test 189

The fuel dispersed and collected from Test 189 was sent to disposal before sieve analysis; 

therefore, there is no quantitative information regarding fragment size distribution for this rodlet.

2.1.4 Metallography and Hot-Vacuum Extraction

No metallography or hot-vacuum extraction measurements were made of the rodlet from 

Test 189.

2.1.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire Probe 

Measurements 

No gamma scans were performed on the rodlet from Test 189 because it was sent for disposal 

before the decision to conduct gamma scanning.

2.2 Test 191

Table 2-3 summarizes measurements and values that characterize the initial state, transient, 

and in-cell measurements of Test 191. The initial state, transient information, and in-cell 

measurements will be described further in the following sections. Metallography, hydrogen 

measurements, and gamma scan results will also be provided.
2-7 NUREG-2160

Table 2-3 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of Test 191

2.2.1 Initial State

For Test 191, a segment of high burnup Westinghouse ZIRLOTM was used. The segment was 

taken from a rod which was irradiated at a U.S. PWR power plant and had a rod average 

burnup of 69.3 GWd/MTU. Again, the operating history for this rod was non-typical and defined 

by a mean LHGR of approximately 24 kW/m for cycle one, 23 kW/m for cycle two, 5 kW/m for 

cycle three, and 15 kW/m for cycle four. The 300-millimeter segment was taken from the middle 

section of the fuel rod, approximately 1,800 millimeters from the bottom of the full length rod. 

The measured hydrogen content just below and above the segment was 187 and 271 weight 

parts per million (wppm), respectively. The eddy current measurements indicate that the oxide 

layer thickness increased slightly over the length of this segment, and range from about 

20 micrometers to 30 micrometers.

2.2.2 Transient Information

To begin the transient, the rodlet was heated and maintained at 300 degrees C for 

approximately 15 minutes to achieve thermal equilibrium. Before initiating the temperature 

ramp, the desired fill pressure was established at 300 degrees C. For Test 191, the rodlet was 

pressurized to 110 bar (at 300 degrees C). The pressure adjustment procedure provides an 

indication of gas communication by observing the response time of the lower pressure 

transducer, as shown in Figure 2-8. Recall that while the gas line is open, the top pressure 

transducer is indicating the gas line pressure and the bottom should reflect the ability of gas to 

move the 300 millimeters to equilibrate pressure.

The rodlet was then heated at 5 degrees C/s until the rodlet temperature reached 

1,160 degrees C (2120 degrees F) (previous benchmarks [1] indicated that the control 

thermocouple location is a relatively cold location and that a majority of the cladding 

circumference sees a slightly higher temperature. The set point of 1,160 degrees C was 

selected, based on prior measurements, to provide cladding temperature in the range of 1185

plus or minus 20 degrees C). The rodlet was held at 1,160 degrees C for 25 seconds. The 

calculated Cathcart-Pawel equivalent cladding reacted (CP-ECR) (based on measured rupture 

strain reported below) was approximately 13 percent.

Adjacent H (wppm) Average Oxide 

(μm)

187, 271 20-30

Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture 

Pressure (bar)

Time (s) to reach 50% of rupture 

P for top/bottom gauges CP-ECR (%) Quench

1185 680 104 21 / 10 13 Yes

Max Strain (%) Length >10% 

Strain (mm)

50 70

69.3

Wire Probe Measurement (mm) (Top/Bottom)

70 / 55

Rupture Dimensions 

(mm) (Width/Length)

17.5 / 21.6

Rod Internal Pressure at 

300°C (bar) Rod Average Burn Up (GWd/MTU)

110

Initial State

Transient

In-Cell 

Measurements
NUREG-2160 2-8

Figure 2-8 Fill pressure adjustment at 300 °C for Test 191, which provides an indication 

of gas communication

Rupture is estimated to have taken place when the rod internal pressure reached 104 bar and 

the cladding temperature reached 680 degrees C. The depressurization rate was relatively slow 

for Test 191; the top pressure gauge recorded a 50 percent reduction in pressure (relative to 

104 bar) after 21 seconds and the bottom pressure gauge recorded a 50 percent reduction in 

pressure after 10 seconds. The temperature and pressure history for Test 191 is shown in

Figure 2-9.

Figure 2-9 Temperature and pressure history for Test 191

2.2.3 In-Cell Measurements

After the simulated LOCA transient was complete, the fuel rod was examined. Figure 2-10

provides two photos of the fuel rod after the test. The rupture opening was measured to be 

17.5 millimeters wide and 21.6 millimeters in length along the axial direction. In Figure 2-10 (b), 

inside the rupture opening, it appears that the pellet-pellet interfaces can be seen on the inside 

cladding wall.
2-9 NUREG-2160

(a) (b)

Figure 2-10 Rod segment from Test 191 (a) in test rig after transient and (b) a closeup of 

the rupture opening after the transient

The rod experienced distortion (or bending) during the LOCA transient, which can be seen in 

Figure 2-11. The bending was in plane with the rupture (Figure 2-11 b & c) and the segment 

remained straight out of plane with the rupture (Figure 2-11 a). The distortion of this fuel rod 

was addressed with a small modification to the test train; the modification proved effective as 

later test segments did not experience significant bending.

(a)

 (b) (c)

Figure 2-11 Rod segment from Test 191 showing (a) no significant rod bending out of 

plane with the rupture and (b) & (c) noticeable bending in plane with the 

rupture
NUREG-2160 2-10

Profilometry measurements were made and they are shown in Figure 2-12. In Figure 2-12, the 

initial diameter and rupture length are also indicated. The mid-wall rupture strain value for 

Test 191 was calculated to be 56 percent.

Figure 2-12 Profilometry measurements of segment 191 post-transient. The rupture 

length is also indicated.

In total, it appears that about half of the fuel fell out of this rod during the simulated LOCA 

transient test and during shaking. During the wire probe measurement, completed after all 

experimental steps (LOCA transient, bending and shaking), the probe traveled unobstructed 

approximately 55 millimeters above and approximately 70 millimeters below the rupture center. 

The mass loss measured following the LOCA test was 52 grams. The mass loss measured 

following the bend test and after shaking was 7 grams. In total, 59 grams of fuel was lost. 

Figure 2-13 provides an image of the collected fuel fragments.

Figure 2-13 Images of fuel collected from Test 191

The fragment size distribution of the fuel dispersed and collected from Test 191 was 

investigated using sieve analysis. The measured mass of each sieve group is provided in 

Table 2-4, along with the mass percentage of each group relative to the total fuel analyzed.
2-11 NUREG-2160

Table 2-4 Fragment Size Distribution Results from Test 191

2.2.4 Metallography and Hot-Vacuum Extraction

One metallography examination was made of the rodlet used in Test 191. The metallography 

sample shown in Figure 2-15 was taken from the rupture opening as indicated in Figure 2-14. 

Select, high-resolution images from the outer cladding diameter and inner cladding diameter are 

included in Figure 2-16 and Figure 2-17, respectively.

Figure 2-14 Photo of test segment from Test 191, indicating the location of 

metallography and hydrogen measurements

Size Weight fuel (g) % of total

< 0.125 mm 9.2 18%

0.125 - 0.25 6.3 12%

0.25 - 0.5 mm 8.2 16%

0.5 - 1 mm 10.9 21%

1 - 2 mm 9.9 19%

2 - 4 mm 6.3 12%

> 4 mm 0 0%

Sum: 50.8 100%

Metallography #1:

rupture opening
NUREG-2160 2-12

Figure 2-15 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 191

 (a) (b)

Figure 2-16 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 191 at (a) 45° and (b) 225°

Here, it is useful to recall that the calculated CP-ECR was 13 percent, with a hold time at 

1,185 degrees C (2,165 degrees Fahrenheit) of 25 seconds. In Figure 2-16, the initial oxide 

thickness can be seen to have cracked and separated in this high strain (56 percent) area, and 

the transient oxidation layer is seen beneath the damaged initial oxide layer. In Figure 2-17, it 

appears that some fuel fragments remain on the inner diameter and that the initial fuel-cladding 

bonding layer has also cracked and separated. An inner diameter transient oxidation layer is 

seen, which appears to approximately the same thickness at the outer transient oxidation layer. 

These observations are expected at this location because it is in the rupture node and exposed 

to a steam environment after rupture.
2-13 NUREG-2160

 (a) (b)

Figure 2-17 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 191 at (a) 0° and (b) 135°

No hydrogen measurements were made of the rodlet used in Test 191.

2.2.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire Probe 

Measurements

Almost 1 year after the last LOCA tests were completed, emerging questions prompted new 

postirradiation examination (PIE) investigations. The wire probe measurements performed just 

after the LOCA tests indicated a long length of empty cladding, but also a significant amount of 

residual fuel material in some test segments. To investigate the length and condition of the 

remaining fueled segments, gamma scans were performed. Recall that the rodlet used in 

Test 191 fractured in the rupture node during the four-point bend test. The two halves of the 

rodlet were gamma scanned separately and the scans in combination covered almost the entire 

length of the rodlet, as shown in Figure 2-18. 

Figure 2-18 Photo of test segment from Test 191, indicating the relative length of 

gamma scan results

In Figure 2-19, the gamma scan results were plotted together with the profilometry results and 

the wire probe measurements performed just after the LOCA test (indicated as “post-LOCA” in 

the figure below) and just after the shaking test (indicated as “final wire probe measurement” in 

the figure below).

Gamma scan of both top and 

bottom ends
NUREG-2160 2-14

Figure 2-19 Gamma scan results for Test 191 with comparison to profilometry and 

initial wire probe measurements

As indicated earlier, theses gamma scan results were obtained over 1 year after the LOCA test 

was performed. In the time between the LOCA test and these gamma scans, the rodlet portions 

were stored in metal cans in the hot-cell. It is important to note that the gamma scan was 

performed with the balloon end down and that the bottom end of the rodlet portion was filled 

with epoxy because of the preparation work for making the metallography sample in the balloon 

node. The gamma scan indicates fuel material in the 110-120 millimeter range and a gradual 

decline of the fuel column in the 75-90 millimeter range in Figure 2-19. The fuel material in the 

110-120 millimeter range is probably loose material that is trapped by the epoxy filling. 

However, the balloon end of the top rodlet portion was open during storage and some fuel 

material was found in the metal can once this rodlet portion was removed for gamma scanning. 

The mass of fuel material found in the can was 16.7 grams. It is important to note that this fuel 

had fallen out of the rod before the gamma scan. This additional fuel loss during storage 

approximately accounts for the difference between the final wire probe measurement and the 

indication on the gamma scan results of the start of the remaining fuel column on the top rodlet 

portion.
2-15 NUREG-2160

2.3 Test 192

Table 2-5 summarizes measurements and values that characterize the initial state, transient, 

and in-cell measurements of Test 192. The initial state, transient information and in-cell 

measurements will be described further in the following sections. Metallography, hydrogen 

measurements, and gamma scan results will also be provided.

Table 2-5 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of Test 192

2.3.1 Initial State

For Test 192, a segment of high burnup Westinghouse ZIRLOTM was used. The segment was 

taken from a rod that was irradiated at a U.S. power plant and had a rod average burnup of 

68.2 GWd/MTU. Again, the operating history for this rod was defined by a mean LHGR of 

approximately 24 kW/m for cycle one, 23 kW/m for cycle two, 5 kW/m for cycle three, and 

15 kW/m for cycle four. The 300-millimeter segment was taken from the middle section of the 

fuel rod, approximately 1800 millimeters from the bottom of the full length rod. The hydrogen 

content was measured just below and above the segment and was determined to be 176 and 

288 wppm, respectively. The eddy current measurements indicate that the oxide layer 

thickness increased slightly over the length of this segment, and ranged from about 25 

micrometers to 30 micrometers.

2.3.2 Transient Information

To begin the transient, the rodlet was heated and maintained at 300 degrees C for 

approximately 15 minutes to achieve thermal equilibrium. Before initiating the temperature 

ramp, the desired fill pressure was established at 300 degrees C. The pressure adjustment 

procedure provides an indication of gas communication by observing the response time of the 

lower pressure transducer, as shown in Figure 2-20. Recall that while the gas line is open, the 

top pressure transducer indicates the gas line pressure and the bottom should reflect the ability 

of gas to move the 300 millimeters to equilibrate pressure. Once the desired fill pressure was 

established, the gas line was closed and the rodlet was heated at 5 degrees C/s until the rodlet 

temperature reached 1,160°C. The rodlet was held at 1,160°C for 5 seconds. The calculated 

CP-ECR (based on measured rupture strain reported below) was approximately 11 percent.

Adjacent H (wppm) Average Oxide 

(μm)

176, 288 25-30

Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture 

Pressure (bar)

Time (s) to reach 50% of rupture 

P for top/bottom gauges CP-ECR (%) Quench

1185 700 81 13 / 15 11 Yes

Max Strain (%) Length >10% 

Strain (mm)

56 85

68.2

Wire Probe Measurement (mm) (Top/Bottom)

85 / 73

Rupture Dimensions 

(mm) (Width/Length)

9 / 22.7

Rod Internal Pressure at 

300°C (bar)

82

Rod Average Burn Up (GWd/MTU)

Initial State

Transient

In-Cell 

Measurements
NUREG-2160 2-16

Figure 2-20 Fill pressure adjustment at 300 °C for Test 192, which provides 

an indication of gas communication

Rupture is estimated to have taken place when the rod internal pressure reached 81 bar and the 

cladding temperature reached 700 °C. The depressurization rate was relatively slow for 

Test 192; the top pressure gauge recorded a 50 percent reduction in pressure (relative to 

81 bar) after 13 seconds and the bottom pressure gauge recorded a 50 percent reduction in 

pressure after 15 seconds. The temperature and pressure history for Test 192 is shown in 

Figure 2-21.

Figure 2-21 Temperature and pressure history for Test 192
2-17 NUREG-2160

2.3.3 In-Cell Measurements

After the simulated LOCA transient was complete, the fuel rod was examined. Figure 2-22

provides two photos of the fuel rod after the test. The rupture opening was measured to be 

9.0 millimeters wide and 22.7 millimeters in length along the axial direction.

 (a) (b)

Figure 2-22 Rod segment from Test 192 (a) in test rig after transient and (b) a closeup of 

the rupture opening after the transient

The rod did not experience significant distortion (or bending) during the LOCA transient, which 

can be seen in Figure 2-23. Profilometry measurements were made and they are shown in 

Figure 2-24. In Figure 2-24, the initial diameter and rupture length are also indicated. The 

mid-wall rupture strain value for Test 192 was calculated to be 56 percent.

(a)

(b)

Figure 2-23 Rod segment from Test 192 showing no significant rod bending (a) out of 

plane with the rupture or (b) in plane with the rupture
NUREG-2160 2-18

Figure 2-24 Profilometry measurements of segment 192 post-transient. 

The rupture length is also indicated.

In total, it appears that about half of the fuel fell out of this rod during the simulated LOCA 

transient test and during shaking. During the wire probe measurement, completed after all 

experimental steps (LOCA transient, bending and shaking), the probe traveled unobstructed 

approximately 73 millimeters above and approximately 85 millimeters below the rupture center. 

The mass loss measured following the LOCA test was 68 grams. The mass loss measured 

following the bend test and after shaking was16 grams. In total, 84 grams of fuel was lost. 

Figure 2-25 provides an image of the collected fuel fragments.

Figure 2-25 Images of fuel collected from Test 192

The fragment size distribution of the fuel dispersed and collected from Test 192 was 

investigated using sieve analysis. The measured mass of each sieve group is provided in 

Table 2-6, along with the mass percentage of each group relative to the total fuel analyzed.
2-19 NUREG-2160

Table 2-6 Fragment Size Distribution Results from Test 192

2.3.4 Metallography and Hot-Vacuum Extraction

Two metallography examinations and seven hydrogen measurements were made of the rodlet 

used in Test 192. The locations of metallography and hydrogen measurements are shown in 

Figure 2-26.

Figure 2-26 Photo of test segment from Test 192, indicating the location of 

metallography and hydrogen measurements

The metallography sample shown in Figure 2-27 was taken from the rupture opening. Select, 

high-resolution images from the outer cladding diameter and inner cladding diameter are 

included in Figure 2-28 and Figure 2-29, respectively.

Size Weight fuel (g) % of total

< 0.125 mm 22.6 32%

0.125 - 0.25 8.0 11%

0.25 - 0.5 mm 9.1 13%

0.5 - 1 mm 10.2 14%

1 - 2 mm 13.3 19%

2 - 4 mm 8.2 11%

> 4 mm 0 0%

Sum: 71.4 100%

Metallography #1:

Metallography #2: rupture opening

50 mm below rupture opening

Hydrogen @ 0, 15, 25, 30, 40, 50, 60

mm above rupture opening
NUREG-2160 2-20

Figure 2-27 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 192

 (a) (b)

Figure 2-28 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 192 at (a) 45° and (b) 135°
2-21 NUREG-2160

 (a) (b)

Figure 2-29 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 192 at (a) 0° and (b) 315°

Here, it is useful to recall that the calculated CP-ECR was 11 percent, with a hold time at 

1,185 degrees C of 5 seconds. In Figure 2-28, the initial oxide thickness can be seen to have 

cracked and separated in this high strain (56 percent) area, and the transient oxidation layer is 

seen beneath this damaged initial oxide layer. The noticeable scalloping of the oxide layer was 

often seen in the outer diameter of the LOCA test samples. In Figure 2-29, it appears that some 

fuel fragments remain on the inner diameter and that the initial fuel-cladding bonding layer has 

also cracked and separated. An inner diameter transient oxidation layer is seen, which appears 

to be approximately the same thickness at the outer transient oxidation layer. These 

observations are expected at this location because it is in the rupture node and therefore 

exposed to a steam environment after rupture.

The metallography sample shown in Figure 2-30 was taken from a section 50 millimeters below 

the rupture opening. Select, high-resolution images from the outer cladding diameter and inner 

cladding diameter are included in Figure 2-31 and Figure 2-32, respectively.

In Figure 2-30, the interior of the cladding contains a large feature in the middle of the cross 

section. This feature is an artifact of the epoxy casting. This rod was cast with epoxy in two 

stages and the features in the interior of the cladding reveal the boundary between the two 

stages of epoxy casting.
NUREG-2160 2-22

Figure 2-30 Macrograph of cross section from 50 mm below the rupture region of rodlet 

tested in LOCA Test 192

 (a) (b)

Figure 2-31 Two high-resolution images of the cladding outer diameter from the 

metallography examination 50 mm below the rupture region of the rodlet 

tested in LOCA Test 192 at (a) 90° and (b) 315°

In Figure 2-31, the initial oxide thickness can be seen to have slightly cracked and separated in 

this area, although much less than in the images taken from the rupture node. The strain in this 

region was approximately 5-7 percent. As in the rupture node, the transient oxidation layer is 

seen beneath this damaged initial oxide layer. In Figure 2-32, it appears that some fuel 

fragments remain on the inner diameter and that the initial fuel-cladding bonding layer has also 

cracked and separated. An inner diameter transient oxidation layer is seen, which appears to 

approximately the same thickness at the outer transient oxidation layer. 
2-23 NUREG-2160

 (a) (b)

Figure 2-32 Two high-resolution images of the cladding inner diameter from the 

metallography examination 50 mm below the rupture region of the rodlet 

tested in LOCA Test 192 at (a) 45°and (b) 225°

The location and values of hydrogen content, measured by hot vacuum extraction, are provided 

in Table 2-7 and illustrated, relative to the segment post-LOCA strain profile and rupture length 

measurements, in 

Figure 2-33.

Table 2-7 Hydrogen Measurements for Test 192

Distance above rupture 

opening (mm) 0 15 25 30 40 50 60

Hydrogen Content 

(wppm) 212 781 963 938 738 635 453

Figure 2-33 Hydrogen measurements from 192 relative to segment strain profile and 

rupture length

2.3.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire Probe 

Measurements

Almost 1 year after the last LOCA tests were completed, emerging questions prompted new PIE 

investigations. The wire probe measurements performed just after the LOCA tests indicated a 

long length of empty cladding, but also a significant amount of residual fuel material in the end 
NUREG-2160 2-24

regions of the test segments. To investigate the length and condition of the remaining fueled

regions, gamma scans and additional metallography and ceramography (M/C) examinations 

were performed. Recall that the rodlet used in Test 192 fractured in the rupture node during the 

four-point bend test, and multiple cladding segments were removed for metallography and 

hydrogen analysis. The remaining portions of the rodlet were gamma scanned separately and 

the scans in combination covered about two-thirds of length of the rodlet, as shown in

Figure 2-34. The locations of additional M/C examinations are also shown in Figure 2-34.

Figure 2-34 Photo of test segment from Test 192, indicating the relative length of gamma 

scan results and location of additional M/C examinations in the remaining 

fueled regions

In Figure 2-35, the gamma scan results were plotted together with the profilometry results and 

the wire probe measurements performed just after the LOCA test (indicated as “post-LOCA” in 

the figure below) and just after the shaking test (indicated as “final wire probe measurement” in 

the figure below).

Gamma scan of portions of 

both top and bottom ends

Axial M/C at the boundary of 

remaining fuel

Transverse M/C approximately 35 

mm from segment bottom
2-25 NUREG-2160

Figure 2-35 Gamma scan results for Test 192 with comparison to profilometry and initial 

wire probe measurements

As indicated earlier, theses gamma scan results were obtained over 1 year after the LOCA test 

was performed. In the time between the LOCA test and these gamma scans, the rodlet portions 

were stored in metal cans in the hot-cell. Some fuel material was found in the metal cans once 

the rodlet portions were removed for gamma scanning and some additional material fell out after 

minor shaking. The mass of fuel material found in the can storing the top portion of the rodlet 

was 5.4 grams (no additional fuel loss was noticed in the can storing the bottom portion of the 

rodlet). It is important to note that this fuel had fallen out of the rod before the gamma scan.

This additional fuel loss during storage approximately accounts for the difference between the 

final wire probe measurement and the indication on the gamma scan results of the start of the 

remaining fuel column on the top rodlet portion. An image of the fuel material collected from the 

top end of rodlet 192 is shown in Figure 2-36.
NUREG-2160 2-26

Figure 2-36 Fuel fragments collected from the top end of rod 192 after gentle shaking 

just before gamma scan

Considering the initial wire probe measurements, the fuel fragments collected after the LOCA 

test and initial shake test (shown in Figure 2-25 and quantified in Table 2-6) likely originated 

from the middle 150 millimeter region of the fuel rod that was measured to be empty following 

the LOCA test. However, the fuel fragments shown in Figure 2-36 collected 1 year later, after 

gentle shaking just before the gamma scan, likely originated from some span beyond the middle 

150 millimeters, possibly in the axial length between the wire probe measurement and the 

indication of fuel in the gamma scan (approximately 230-255 millimeters in Figure 2-35). 

Additional sieve analysis was performed to characterize the fragment size distribution of the 

fragments shown in Figure 2-36. The measured mass of each sieve group is provided in 

Table 2-8, along with the mass percentage of each group relative to the total fuel analyzed. 

Figure 2-37 provides a comparison of the fuel fragment size distribution from these two regions 

of segment 192. The comparison suggests that fragmentation may be less pronounced in 

regions near the rodlet ends and further from rupture.

Table 2-8 Fragment Size Distribution Results for Fuel Fragments Collected from the Top 

End of Rod 192 after Gentle Shaking Just before Gamma Scan

Size Weight fuel (g) % of total

< 0.125 mm 0.4 7%

0.125 - 0.25 0.2 4%

0.25 - 0.5 mm 0.3 6%

0.5 - 1 mm 0.3 6%

1 - 2 mm 0.9 17%

2 - 4 mm 3.3 61%

> 4 mm 0 0%

Sum: 5.4 100%
2-27 NUREG-2160

Figure 2-37 Comparison of fuel fragment size distribution from two regions 

of segment 192

Additional M/C examinations provide an even more detailed characterization of the remaining 

fueled region than the gamma scan results. The transverse M/C sample shown in Figure 2-38

was taken approximately 35 millimeters from the segment bottom. The image reveals a largely 

intact pellet cross section. A high-resolution image, shown in Figure 2-39, reveals that some 

amount of fuel remains attached to the inner cladding wall. Many small fuel fragments can be 

seen in the space between the cladding and the relatively intact remaining fuel material.
NUREG-2160 2-28

Figure 2-38 Macrograph of transverse cross section 35 mm from the bottom of the rodlet 

tested in LOCA Test 192

Figure 2-39 A high-resolution image of the fuel cladding gap from the M/C examination

35 mm from the bottom of the rodlet tested in LOCA Test 192

The axial M/C sample shown in Figure 2-40 was taken at the boundary of remaining fuel and 

empty cladding, covering a span approximately 50-75 millimeters from the segment bottom. 
2-29 NUREG-2160

The image reveals that the boundary between fueled an empty cladding is abrupt, and that the 

fueled region contains cracked, but largely complete, pellet cross sections.

Figure 2-40 Macrograph of axial cross section covering a span approximately 50–75 mm

from the segment bottom of the rodlet tested in LOCA Test 192

Select, high-resolution images are included in Figure 2-41 from the inner (a and b) and outer (c 

and d) cladding diameter. These images were near the bottom (left) of the axial M/C, 

approximately 55 millimeters from the original segment bottom of the rodlet tested in LOCA 

Test 192. Again, here it is useful to recall that for Test 192 the calculated CP-ECR was 

11 percent, with a hold time at 1,185 degrees C of 5 seconds.

In Figure 2-41 (a and b), fuel fragments remain on the inner diameter and the fuel-clad bond 

layer appears more intact than in the M/C images in Figure 2-29 and Figure 2-32 taken within 

and 50 millimeter below the rupture node, respectively. Also, an alpha layer microstructure can 

be seen on the inner diameter. This region of the test segment remained fueled and was far 

(approximately 100 millimeters) from the rupture location; therefore, the inner diameter was not 

exposed to a steam environment during the transient. The oxygen necessary for the inner 

diameter alpha layer is proposed to have originated from the fuel-cladding bond layer. In 

Figure 2-41 (c and d), the initial oxide layer, transient oxide layer, and an alpha layer can be 

seen.
NUREG-2160 2-30

 (a) (b)

 (c) (d)

Figure 2-41 High-resolution images of the cladding (a and b) inner and (c and d) outer 

diameter taken from the axial M/C shown above. These images were near 

the bottom (left) of the axial M/C, approximately 55 mm from the original 

segment bottom and approximately 100 mm below the rupture opening of 

the rodlet tested in LOCA Test 192.

2.4 Test 193

Table 2-9 summarizes measurements and values that characterize the initial state, transient, 

and in-cell measurements of Test 193. The initial state, transient information and in-cell 

measurements will be described further in the following sections. Metallography, hydrogen 

measurements, and gamma scan results will also be provided.

Table 2-9 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of Test 193

Adjacent H (wppm) Average Oxide 

(μm)

187 20

Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture 

Pressure (bar)

Time (s) to reach 50% of rupture 

P for top/bottom gauges CP-ECR (%) Quench

1185 728 81 45 / 8 17 Yes

Max Strain (%) Length >10% 

Strain (mm)

50 100 113 / 91 

Wire Probe Measurement (mm) (Top/Bottom) Rupture Dimensions 

(mm) (Width/Length)

13.8 / 17.8

Initial State

Transient

In-Cell 

Measurements

Rod Internal Pressure at 

300°C (bar)

82

Rod Average Burn Up (GWd/MTU)

69.3
2-31 NUREG-2160

2.4.1 Initial State

For Test 193, a segment of high burnup Westinghouse ZIRLOTM was used. The segment was 

taken from a rod that was irradiated at a U.S. PWR power plant and had a rod average burnup

of 69.3 GWd/MTU. Again, the operating history for this rod was non-typical and defined by a 

mean LHGR of approximately 24 kW/m for cycle one, 23 kW/m for cycle two, 5 kW/m for cycle 

three, and 15 kW/m for cycle four. The 300-millimeter segment was taken from the middle 

section of the fuel rod, approximately 1400 millimeters from the bottom of the full length rod. A 

hydrogen content of 187 wppm was measured just above the segment. The eddy current 

measurements indicate that the oxide layer thickness is relatively constant over the length of 

this segment, averaging about 20 micrometers thick.

2.4.2 Transient Information

To begin the transient, the rodlet was heated and maintained at 300 degrees C for 

approximately 15 minutes to achieve thermal equilibrium. Before initiating the temperature 

ramp, the desired fill pressure was established at 300 degrees C. For Test 193, the rodlet was 

pressurized to 82 bar (at 300 degrees C). The pressure adjustment procedure provides an 

indication of gas communication by observing the response time of the lower pressure 

transducer, as shown in Figure 2-42. Recall that while the gas line is open, the top pressure 

transducer indicates the gas line pressure and the bottom should reflect the ability of gas to 

move the 300 millimeter to equilibrate pressure. Once the desired fill pressure was established, 

the gas line was closed and the rodlet was heated at 5 degrees C/s until the rodlet temperature 

reached 1,160 degrees C. The rodlet was held at 1,160°C for 85 seconds. The calculated 

CP-ECR (based on measured rupture strain reported below) was approximately 17 percent.

Figure 2-42 Fill pressure adjustment at 300 °C for Test 193, which provides 

an indication of gas communication

Rupture is estimated to have taken place when the rod internal pressure reached 81 bar and the 

cladding temperature reached 728 degrees C. The depressurization rate was relatively slow for 

Test 193; the top pressure gauge recorded a 50 percent reduction in pressure (relative to 
NUREG-2160 2-32

81 bar) after 45 seconds and the bottom pressure gauge recorded a 50 percent reduction in 

pressure after 8 seconds. The temperature and pressure history for Test 193 is shown in 

Figure 2-43.

Figure 2-43 Temperature and pressure history for Test 193

2.4.3 In-Cell Measurements

After the simulated LOCA transient was complete, the fuel rod was examined. Figure 2-44

provides two photos of the fuel rod after the transient. The rupture opening was measured to be 

13.8 millimeters wide and 17.8 millimeters in length.
2-33 NUREG-2160

 (a) (b)

Figure 2-44 Rod segment from Test 193 (a) in test rig after transient and (b) a closeup of 

the rupture opening after the transient

The rod experienced minor distortion (or bending) during the LOCA transient, which can be 

seen in Figure 2-45. Profilometry measurements were made and they are shown in 

Figure 2-46. In Figure 2-46, the initial diameter and rupture length are also indicated. The 

mid-wall rupture strain value for Test 193 was calculated to be 50 percent.

(a)

(b)

Figure 2-45 Rod segment from Test 193 showing no significant rod bending (a) in plane 

with the rupture and (b) minor bending out of plane with the rupture
NUREG-2160 2-34

Figure 2-46 Profilometry measurements of segment 193 post-transient. 

The rupture length is also indicated.

In total, it appears that about half of the fuel fell out of this rod during the simulated LOCA 

transient test and during shaking. During the wire probe measurement, completed after all 

experimental steps (LOCA transient, bending and shaking), the probe traveled unobstructed 

approximately 92 millimeters above and approximately113 millimeters below the rupture center. 

The mass loss measured following the LOCA test was 105 grams. The mass loss measured 

following the bend test and after shaking was 41 grams. In total, 146 grams of fuel was lost. 

Figure 2-47 provides an image of the collected fuel fragments.

Figure 2-47 Images of fuel collected from Test 193

The fragment size distribution of the fuel dispersed and collected from Test 193 was 

investigated using sieve analysis. The measured mass of each sieve group is provided in 

Table 2-10, along with the mass percentage of each group relative to the total fuel analyzed.
2-35 NUREG-2160

Table 2-10 Fragment Size Distribution Results from Test 193

2.4.4 Metallography and Hot-Vacuum Extraction

Two metallography examinations were made of the rodlet used in Test 193. The locations of 

metallography samples are shown in Figure 2-48.

Figure 2-48 Photo of test segment from Test 193, indicating the location 

of metallography

The metallography sample shown in Figure 2-49 was taken from the rupture opening. Select, 

high-resolution images from the outer cladding diameter and inner cladding diameter are 

included in Figure 2-50 and Figure 2-51, respectively.

Size Weight fuel (g) % of total

< 0.125 mm 18.6 18%

0.125 - 0.25 10.7 10%

0.25 - 0.5 mm 13.7 13%

0.5 - 1 mm 17.4 17%

1 - 2 mm 19.6 19%

2 - 4 mm 20.2 20%

> 4 mm 2.1 2%

Sum: 102.3 100%

Metallography #1:

rupture opening

Metallography #2:

35 mm above rupture opening
NUREG-2160 2-36

Figure 2-49 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 193

 (a) (b)

Figure 2-50 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 193 at (a) 90° and (b) 270°

Here, it is useful to recall that for Test 193 the calculated CP-ECR was 17 percent, with a hold 

time at 1,185°C of 85 seconds. In Figure 2-50, the initial oxide thickness can be seen to have 

cracked and separated in this high strain (50 percent) area, and the transient oxidation layer is 

seen beneath this damaged initial oxide layer. In Figure 2-51, it appears that some fuel 

fragments remain on the inner diameter and that the initial fuel-cladding bonding layer has also 

cracked and separated. An inner diameter transient oxidation layer is not apparent in these 

images, although the micrographs indicate some unique microstructure layer that may be an 

alpha zirconium layer. The absence of an inner diameter transient oxidation layer is somewhat 

surprising at this location because it is in the rupture node and was held for 85 seconds at high 

temperature.
2-37 NUREG-2160

 (a) (b)

Figure 2-51 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 193 at (a) 135° and (b) 270°

The metallography sample shown in Figure 2-52 was taken from a section 35 millimeters above 

the rupture opening. Select, high-resolution images from the outer cladding diameter and inner 

cladding diameter are included in Figure 2-53 and Figure 2-54, respectively.

Figure 2-52 Macrograph of cross section from 35 mm above the rupture region of rodlet 

tested in LOCA Test 193
NUREG-2160 2-38

 (a) (b)

Figure 2-53 Two high-resolution images of the cladding outer diameter from the 

metallography examination 35 mm above the rupture region of the rodlet 

tested in LOCA Test 193 at (a) 45° and (b) 270°

 (a) (b)

Figure 2-54 Two high-resolution images of the cladding inner diameter from the 

metallography examination 35 mm above the rupture region of the rodlet 

tested in LOCA Test 193 at (a) 135° and (b) 270°

In Figure 2-53, the initial oxide thickness can be seen to have cracked and separated at this 

location 35 millimeters above the rupture node, and the transient oxidation layer is seen 

beneath this damaged initial oxide layer. The local strain in this region is approximately 

15 to 20 percent. In Figure 2-54, it appears that some fuel fragments remain on the inner 

diameter and that the initial fuel-cladding bonding layer has also cracked and separated. An 

inner diameter transient oxidation layer is not apparent in these images, although the

micrographs indicate some unique microstructure layer that may be an alpha zirconium layer. 

No hydrogen measurements were ordered for this sample; however, metallography was 

completed on etched samples, which reveals the microstructure and hydrogen features across 

the cross section. One example is shown in Figure 2-55, which is taken from the M/C sample at 

the rupture mid-plane.
2-39 NUREG-2160

Figure 2-55 Etched cross section revealing hydrogen microstructure in the cladding in 

the rupture region of Test 193

2.4.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire Probe 

Measurements

Almost 1 year after the last LOCA tests were completed, emerging questions prompted new PIE 

investigations. The wire probe measurements performed just after the LOCA tests indicated a 

long length of empty cladding, but also a significant amount of residual fuel material in some test 

segments. To investigate the length and condition of the remaining fueled segments, gamma 

scans were performed. Recall that the rodlet used in Test 193 fractured in the rupture node 

during the four-point bend test. The two halves of the rodlet were gamma scanned separately 

and the scans in combination covered almost the entire length of the rodlet, as shown in 

Figure 2-56.

Figure 2-56 Photo of test segment from Test 193, indicating the relative length of gamma 

scan results

In Figure 2-57, the gamma scan results were plotted together with the profilometry results and 

the wire probe measurements performed just after the LOCA test (indicated as “post-LOCA” in 

the figure below) and just after the shaking test (indicated as “final wire probe measurement” in 

the figure below).

Gamma scan of both top and 

bottom ends
NUREG-2160 2-40

Figure 2-57 Gamma scan results for Test 193 with comparison to profilometry and initial 

wire probe measurements

As indicated earlier, theses gamma scan results were obtained over 1 year after the LOCA test 

was performed. In the time between the LOCA test and these gamma scans, the rodlet portions 

were stored in metal cans in the hot-cell. Some fuel material was found in the metal cans once 

the rodlet portions were removed for gamma scanning and some addition material fell out after 

minor shaking. The mass of fuel material found in the can storing the bottom portion of the 

rodlet was 6.6 grams. A small amount of fuel material was also found in the can storing the top 

portion of the rodlet. It is important to note that this fuel had fallen out of the rod before the 

gamma scan. This additional fuel loss during storage is slight less than what would be expected 

from the difference between the final wire probe measurement and the indication on the gamma 

scan results of the start of the remaining fuel column on the top rodlet portion.

2.5 Test 196

Table 2-11 summarizes measurements and values that characterize the initial state, transient, 

and in-cell measurements of Test 196. The initial state, transient information and in-cell 

measurements will be described further in the following sections. Metallography, hydrogen 

measurements, and gamma scan results will also be provided.
2-41 NUREG-2160

Table 2-11 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of Test 196

2.5.1 Initial State

For test 196, a segment of high burnup Westinghouse ZIRLOTM with a Zirconium Diboride 

Integral Fuel Burnable Absorber (IFBA) coating was used. The segment was taken from a rod 

that was irradiated at a U.S. PWR power plant and had a rod average burnup of 

55.2 GWd/MTU. The operating history for this rod was typical of U.S. power plant operation to 

this burnup. The pellet enrichment was 4.94 weight percent (wt%) U235. The 300-millimeter 

segment was taken from the middle section of the fuel rod, approximately 1300 millimeters from 

the bottom of the full length rod. A hydrogen content of 149 wppm was measured at a location 

adjacent to the segment. The eddy current measurements indicate that the oxide layer 

thickness is relatively constant over the length of this segment, averaging about 20 micrometers 

in thickness.

2.5.2 Transient Information

To begin the transient, the rodlet was heated and maintained at 300 degrees C for 

approximately 15 minutes to achieve thermal equilibrium. Before initiating the temperature 

ramp, the desired fill pressure was established at 300 degrees C. For test 196, the rodlet was 

pressurized to 82 bar (at 300 degrees C). The pressure adjustment procedure provides an 

indication of gas communication by observing the response time of the lower pressure 

transducer, as shown in Figure 2-58. While the gas line is open, the top pressure transducer 

indicates the gas line pressure and the bottom should reflect the ability of gas to move the 

300 millimeter segment length to equilibrate pressure. Once the desired fill pressure was 

established, the gas line was closed and the rodlet was heated at 5 degrees C/s through 

ballooning and rupture. This was a “ramp-to-rupture” test and therefore the furnace was shut off 

to terminate the test at 950 degrees C and there was no quench. No significant oxidation was 

accumulated during this test.

Adjacent H (wppm) Average Oxide 

(μm)

149 20

Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture 

Pressure (bar)

Time (s) to reach 50% of rupture 

P for top/bottom gauges CP-ECR (%) Quench

950 686 81 5 / 2 0 Yes

Max Strain (%) Length >10% 

Strain (mm)

25 95

Wire Probe Measurement (mm) (Top/Bottom)

Rod Average Burn Up (GWd/MTU)

55.2

90 / 66

Rod Internal Pressure at 

300°C (bar)

82

Rupture Dimensions 

(mm) (Width/Length)

0.2 / 1.5

Initial State

Transient

In-Cell 

Measurements
NUREG-2160 2-42

Figure 2-58 Fill pressure adjustment at 300 °C for Test 196, which provides an indication 

of gas communication

Rupture is estimated to have taken place when the rod internal pressure reached 81 bar and the 

cladding temperature reached 686 °C (1267 degrees F). The depressurization rate was 

relatively fast for test 196; the top pressure gauge recorded a 50 percent reduction in pressure 

(relative to 81 bar) after 5 seconds and the bottom pressure gauge recorded a 50 percent

reduction in pressure after 2 seconds. The temperature and pressure history for Test 196 is 

shown in Figure 2-59.

Figure 2-59 Temperature and pressure history for Test 196
2-43 NUREG-2160

2.5.3 In-Cell Measurements

After the simulated LOCA transient was complete, the fuel rod was examined. Figure 2-60

provides two photos of the fuel rod after the transient. The rupture opening was measured to be 

0.2 millimeter wide and 1.5 millimeters in length.

 (a) (b)

Figure 2-60 Rod segment from Test 196 (a) in test rig after transient and (b) a closeup of 

the rupture opening after the transient

The rod did not experience distortion (or bending) during the LOCA transient, which can be 

seen in Figure 2-61. Profilometry measurements were made and they are shown in 

Figure 2-62. In Figure 2-62, the initial diameter and rupture length are also indicated. The 

mid-wall rupture strain value for Test 196 was calculated to be 25 percent.

Figure 2-61 Rod segment from Test 196 showing no significant rod bending
NUREG-2160 2-44

Figure 2-62 Profilometry measurements of segment 196 post-transient. The rupture 

length is also indicated.

Because this rodlet did not experience significant oxidation and therefore was expected to be 

highly ductile, there was no bend test performed on this rod. Instead, the rod was manually cut 

into two pieces, through the rupture node. The two pieces were then shaken and fuel loss was 

observed. There was no fuel loss measured following the LOCA test; however, it appears that 

about half of the fuel fell out of this rod during shaking. During the wire probe measurement, 

completed after shaking, the probe traveled unobstructed approximately 90 millimeters above 

and approximately 66 millimeters below the rupture center. The mass loss measured following 

the bend test and after shaking was 77 grams. Figure 2-63 provides an image of the collected 

fuel fragments.

Figure 2-63 Images of fuel collected from Test 196

The fragment size distribution of the fuel dispersed and collected from Test 196 was 

investigated using sieve analysis. The measured mass of each sieve group is provided in 

Table 2-12, along with the mass percentage of each group relative to the total fuel analyzed.
2-45 NUREG-2160

Table 2-12 Fragment Size Distribution Results from Test 196

2.5.4 Metallography and Hot-Vacuum Extraction

One metallography examination and four hydrogen measurements were made of the rodlet 

used in Test 196. The locations of metallography and hydrogen measurements are shown in 

Figure 2-64.

Figure 2-64 Photo of test segment from Test 196, indicating the location of 

metallography and hydrogen measurements

The metallography sample shown in Figure 2-65 was taken from the rupture opening. Select, 

high-resolution images from the outer cladding diameter and inner cladding diameter are 

included in Figure 2-66 and Figure 2-67, respectively.

Size Weight fuel (g) % of total

< 0.125 mm 0.4 1%

0.125 - 0.25 0.4 1%

0.25 - 0.5 mm 0.3 0%

0.5 - 1 mm 0.3 0%

1 - 2 mm 0.6 1%

2 - 4 mm 9.4 12%

> 4 mm 65.9 85%

Sum: 77.3 100%

Hydrogen at 0, 20, 30, 60 mm above 

rupture opening

Metallography #1:

rupture opening
NUREG-2160 2-46

Figure 2-65 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 196

In Figure 2-66, the initial oxide thickness can be seen to have cracked and separated with the 

strain of the cladding. The strain at this location was approximately 25 percent. No transient 

oxidation layer can be observed in these images, which is expected for this test because it was 

a “ramp-to-rupture” test and did not accumulate significant oxidation. In Figure 2-67, some 

remnants of a fuel-clad bonding layer can be observed. This layer can be seen to have cracked 

and separated with the strain of the cladding. Again, this is expected because the test was 

terminated just after rupture and before significant transient oxidation could accumulate.

 (a) (b)

Figure 2-66 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 196 at (a) 90° and (b) 270°
2-47 NUREG-2160

 (a) (b)

Figure 2-67 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 196 at (a) 45° and (b) 270°

The location and values of hydrogen content, measured by hot vacuum extraction, are provided 

in Table 2-13, and illustrated, relative to the segment post-LOCA strain profile and rupture

length measurements, in Figure 2-68.

Table 2-13 Hydrogen Measurements for Test 196

Distance above rupture opening (mm) 0 20 30 60

Hydrogen Content (wppm) 137 110 144 131

Figure 2-68 Hydrogen measurements from 196 relative to segment strain profile 

and rupture length

2.5.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire Probe 

Measurements

Almost 1 year after the last LOCA tests were completed, emerging questions prompted new PIE 

investigations. The wire probe measurements performed after the shaking test indicated a long 

length of empty cladding, but also a significant amount of residual fuel material in some test 

segments. To investigate the length and condition of the remaining fueled segments, gamma 

scans were performed. Recall that the rodlet used in Test 196 was cut into two pieces and that 

multiple portions of cladding material were removed for metallography and hydrogen analysis. 

The remaining portions of the upper and lower portions were gamma scanned separately and 
NUREG-2160 2-48

the scans in combination covered a little over half of the length of the rodlet, as shown in 

Figure 2-69.

Figure 2-69 Photo of test segment from Test 196, indicating the relative length of 

gamma scan results

In Figure 2-70, the gamma scan results were plotted together with the profilometry results and 

the wire probe measurements performed after the shake test (indicated as “final wire probe 

measurement” in the figure below).

Figure 2-70 Gamma scan results for Test 196 with comparison to profilometry and initial 

wire probe measurements

Gamma scan of portions of 

both top and bottom ends
2-49 NUREG-2160

As indicated earlier, theses gamma scan results were obtained over 1 year after the LOCA test 

was performed. In the time between the LOCA test and these gamma scans, the rodlet portions 

were stored in metal cans in the hot-cell. Some fuel material was found in the metal cans once 

the rodlet portions were removed for gamma scanning and some addition material fell out after 

minor shaking. The mass of fuel material found in the can storing the bottom portion of the 

rodlet was 8.3 grams. A few milligrams of fuel material was found in the can storing the top 

portion of the rodlet. An image of the fuel material collected from the bottom end of rodlet 196 is 

shown in Figure 2-71. It is important to note that this fuel had fallen out of the rod before the 

gamma scan. This additional fuel loss during storage approximately accounts for the difference 

between the final wire probe measurement and the indication on the gamma scan results of the 

start of the remaining fuel column on the top rodlet portion.

Figure 2-71 Fuel fragments collected from the bottom of rod 196 after gentle shaking just 

before gamma scan

Considering the initial wire probe measurements, the fuel fragments collected after the LOCA 

test and initial shake test (shown in Figure 2-63 and quantified in Table 2-12) likely originated 

from the middle 150 millimeter region of the fuel rod that was measured to be empty following 

the LOCA test. However, the fuel fragments shown in Figure 2-71 collected 1 year later after 

gentle shaking just before the gamma scan likely originated from some span beyond the middle 

150 millimeter, possibly in the axial length between the wire probe measurement and the 

indication of fuel in the gamma scan (approximately 70 to 75 millimeter in Figure 2-70). 

Additional sieve analysis was performed to characterize the fragment size distribution of the 

fragments collected and shown in Figure 2-71. The measured mass of each sieve group is 

provided in Table 2-14, along with the mass percentage of each group relative to the total fuel 

analyzed. Figure 2-72 provides a comparison of the fuel fragment size distribution from these 

two regions of segment 196. The comparison suggests that fragmentation size distribution is 

comparable in these two regions.
NUREG-2160 2-50

Table 2-14 Fragment Size Distribution Results for Fuel Fragments Collected from the 

Bottom End of Rod 196 after Gentle Shaking Just before Gamma Scan

Figure 2-72 Comparison of fuel fragment size distribution from two regions 

of segment 196

2.6 Test 198

Table 2-15 summarizes measurements and values that characterize the initial state, transient, 

and in-cell measurements of Test 198. The initial state, transient information and in-cell 

measurements will be described further in the following sections. Metallography, hydrogen 

measurements, and gamma scan results will also be provided.

Size Weight fuel (g) % of total

< 0.125 mm 0.01 0%

0.125 - 0.25 0.01 0%

0.25 - 0.5 mm 0.03 0%

0.5 - 1 mm 0.07 1%

1 - 2 mm 0.50 8%

2 - 4 mm 1.77 27%

> 4 mm 4.27 64%

Sum: 6.66 100%
2-51 NUREG-2160

Table 2-15 Measurements and Values That Characterize the Initial State, Transient, and 

In-Cell Measurements of Test 198

2.6.1 Initial State

For Test 198, a segment of high burnup Westinghouse ZIRLOTM fuel with a Zirconium Diboride 

Integral Fuel Burnable Absorber (IFBA) coating was used. The segment was taken from a rod 

which was irradiated at a U.S. PWR power plant and had a rod average burnup of 

55.2 GWd/MTU. The operating history for this rod was typical of U.S. power plant operation to 

this burnup. The pellet enrichment was 4.94 wt% U235.

 The 300-millimeter segment was taken 

from the middle section of the fuel rod, approximately 2200 millimeters from the bottom of the 

full length rod. A hydrogen content of 225 wppm was measured below the segment. The eddy 

current measurements indicate that the oxide layer thickness is relatively constant over the 

length of this segment, and average about 20 micrometers.

2.6.2 Transient Information

To begin the transient, the rodlet was heated and maintained at 300 degrees C for 

approximately 15 minutes to achieve thermal equilibrium. Before initiating the temperature 

ramp, the desired fill pressure was established at 300 degrees C. For Test 198, the rodlet was 

pressurized to 82 bar (at 300 degrees C). The pressure adjustment procedure provides an 

indication of gas communication by observing the response time of the lower pressure 

transducer, as shown in Figure 2-73. Recall that while the gas line is open, the top pressure 

transducer indicates the gas line pressure and the bottom should reflect the ability of gas to 

move the 300 millimeter segment length to equilibrate pressure. Once the desired fill pressure 

was established, the gas line was closed and the rodlet was heated at 5 degrees C/s until the 

rodlet temperature reached 1,185 degrees C. The rodlet was held at 1,185 degrees C for 

85 seconds. The calculated CP-ECR (based on measured rupture strain reported below) was 

approximately 15 percent.

Adjacent H (wppm) Average Oxide 

(μm)

225 20

Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture 

Pressure (bar)

Time (s) to reach 50% of rupture 

P for top/bottom gauges CP-ECR (%) Quench

1185 693 81 3 / 2 15 Yes

Max Strain (%) Length >10% 

Strain (mm)

25 115

Wire Probe Measurement (mm) (Top/Bottom)

55 / 76

Rod Average Burn Up (GWd/MTU)

55.2 82

Rupture Dimensions 

(mm) (Width/Length)

1.6 / 11

Rod Internal Pressure at 

300°C (bar) Initial State

Transient

In-Cell 

Measurements
NUREG-2160 2-52

Figure 2-73 Fill pressure adjustment at 300 °C for Test 198, which provides an indication 

of gas communication

Rupture is estimated to have taken place when the rod internal pressure reached 81 bar and the 

cladding temperature reached 693 degrees C (1279 degrees F). The depressurization rate was 

relatively fast for Test 198; the top pressure gauge recorded a 50 percent reduction in pressure 

(relative to 81 bar) after 3 seconds and the bottom pressure gauge recorded a 50 percent 

reduction in pressure after 2 seconds. The temperature and pressure history for Test 198 is 

shown in Figure 2-74.

Figure 2-74 Temperature and pressure history for Test 198
2-53 NUREG-2160

2.6.3 In-Cell Measurements

After the simulated LOCA transient was complete, the fuel rod was examined. Figure 2-75

provides a photo of the fuel rod after the transient. The rupture opening was measured to be 

1.6 millimeters wide and 11 millimeters in length.

Figure 2-75 Rupture opening after the transient simulation for Test 198

The rod did not experience distortion (or bending) during the LOCA transient, which can be 

seen in Figure 2-76. Profilometry measurements were made and they are shown in 

Figure 2-77. In Figure 2-77, the initial diameter and rupture length are also indicated. The 

mid-wall rupture strain value for Test 198 was calculated to be 25 percent.

Figure 2-76 Rod segment from Test 198 showing no significant rod bending
NUREG-2160 2-54

Figure 2-77 Profilometry measurements of segment 198 post-transient. The rupture 

length is also indicated.

There was no fuel loss measured following the LOCA test, however, it appears that about half of 

the fuel fell out of this rod during shaking. During the wire probe measurement, completed after 

shaking, the probe traveled unobstructed approximately 55 millimeters above and approximately 

76 millimeters below the rupture center. There was no measured mass loss following the LOCA 

test. The mass loss measured after shaking was 62 grams. Figure 2-78 provides an image of 

the collected fuel fragments.

Figure 2-78 Images of fuel collected from Test 198

The fragment size distribution of the fuel dispersed and collected from Test 198 was 

investigated using sieve analysis. The measured mass of each sieve group is provided in 

Table 2-16, along with the mass percentage of each group relative to the total fuel analyzed.

Table 2-16 Fragment Size Distribution Results from Test 198

Size Weight fuel (g) % of total

< 0.125 mm 0.50 1%

0.125 - 0.25 0.50 1%

0.25 - 0.5 mm 0.50 1%

0.5 - 1 mm 0.40 1%

1 - 2 mm 0.80 1%

2 - 4 mm 17.50 28%

> 4 mm 42.10 68%

Sum: 62.3 100%
2-55 NUREG-2160

2.6.4 Metallography and Hot-Vacuum Extraction

Two metallography examinations and ten hydrogen measurements were made of the rodlet 

used in Test 198. The locations of metallography and hydrogen measurements are shown in 

Figure 2-79.

Figure 2-79 Photo of test segment from Test 198, indicating the location of 

metallography and hydrogen measurements

The metallography sample shown in Figure 2-80 was taken in the rupture opening. Select, 

high-resolution images from the outer cladding diameter and inner cladding diameter are 

included in Figure 2-81 and Figure 2-82, respectively.

Figure 2-80 Macrograph of cross section from the rupture region of rodlet tested in 

LOCA Test 198

Metallography #1:

rupture opening Metallography #2:

50 mm below rupture opening

Hydrogen at 0, 10, 20, 30, 35, 40, 50, 60, 

80 and 100 mm above rupture opening
NUREG-2160 2-56

 (a) (b)

Figure 2-81 Two high-resolution images of the cladding outer diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 198 at (a) 90° and (b) 270°

 (a) (b)

Figure 2-82 Two high-resolution images of the cladding inner diameter from the 

metallography examination in the rupture region of the rodlet tested in 

LOCA Test 198 at (a) 90° and (b) 225°

Here, it is useful to recall that for Test 198 the calculated CP-ECR was 15 percent, with a hold 

time at 1,185 degrees C of 85 seconds. In Figure 2-81, the initial oxide thickness can be seen 

to have cracked and separated, and the transient oxidation layer is seen beneath this damaged 

initial oxide layer. In Figure 2-82, it appears that some fuel fragments remain on the inner 

diameter and that the initial fuel-cladding bonding layer is somewhat cracked and separated. 

An inner diameter transient oxidation layer is seen, which appears to be approximately the 

same thickness at the outer transient oxidation layer. These observations are expected at this 

location because it is in the rupture node.

The metallography sample shown in Figure 2-83 was taken from a section 50 millimeters below 

the rupture opening. Select, high-resolution images from the outer cladding diameter and inner 

cladding diameter are included in Figure 2-84 and Figure 2-85, respectively.
2-57 NUREG-2160

Figure 2-83 Macrograph of cross section from 50 mm below the rupture region of rodlet 

tested in LOCA test 198

 (a) (b)

Figure 2-84 Two high-resolution images of the cladding outer diameter from the 

metallography examination 50 mm below the rupture region of the rodlet 

tested in LOCA Test 198 at (a) 90° and (b) 180°

 (a) (b)

Figure 2-85 Two high-resolution images of the cladding inner diameter from the 

metallography examination 50 mm below the rupture region of the rodlet 

tested in LOCA Test 198 at (a) 90° and (b) 225°
NUREG-2160 2-58

In Figure 2-84, the initial oxide thickness can be seen to have cracked and separated, and the 

transient oxidation layer is seen beneath this damaged initial oxide layer. In Figure 2-85, a few 

small fuel fragments remain on the inner diameter. An inner diameter transient oxidation layer 

is not observed at this location 50 millimeters below the rupture opening. These observations 

are interesting because they suggest this region, 50 millimeters below the rupture node, was not 

exposed to a steam environment during the transient. The metallography samples were not 

prepared in such a way to reveal the presence and thickness of an alpha layer and the extent of 

fuel cladding bonding on this sample has not been characterized.

The location and values of hydrogen content, measured by hot vacuum extraction, are provided 

in Table 2-17, and illustrated, relative to the segment post-LOCA strain profile and rupture

length measurements, in Figure 2-86.

Table 2-17 Hydrogen Measurements from Test 198

Distance 

above 

rupture 

opening

(mm)

0 10 20 30 35 40 50 60 80 100

Hydrogen 

Content 

(wppm)

733 1531 1155 641 636 442 294 367 247 201

Figure 2-86 Hydrogen measurements from Test 198 relative to segment strain profile and 

rupture length

2.6.5 Gamma Scan Results with Comparison to Profilometry and Initial Wire Probe 

Measurements

Almost 1 year after the last LOCA tests were completed, emerging questions prompted new PIE 

investigations. The wire probe measurements performed after the shaking test indicated a long 

length of empty cladding, but also a significant amount of residual fuel material in the end 

regions of the test segments. To investigate the length and condition of the remaining fueled

segments, gamma scans and additional M/C examination were performed. Recall that the 

rodlet used in Test 198 broke into two halves during the four-point bend test and that multiple 
2-59 NUREG-2160

portions of cladding material were removed for metallography and hydrogen analysis. The 

remaining length of the lower portion was gamma scanned, as shown in Figure 2-87. The 

location of the additional M/C examination is also shown in Figure 2-87.

Figure 2-87 Photo of test segment from Test 198, indicating the relative length of gamma 

scan results and location of an additional M/C examination in the remaining 

fueled region

In Figure 2-88, the gamma scan results were plotted together with the profilometry results and 

the wire probe measurements performed after the shaking test (indicated as “final wire probe 

measurement” in the figure below).

Gamma scan of bottom end

Axial M/C at the boundary of 

remaining fuel
NUREG-2160 2-60

Figure 2-88 Gamma scan results for Test 198 with comparison to profilometry and 

initial wire probe measurements

As indicated earlier, theses gamma scan results were obtained over 1 year after the LOCA test 

was performed. In the time between the LOCA test and these gamma scans, the rodlet portions 

were stored in metal cans in the hot-cell. Some fuel material was found in the metal cans once 

the rodlet portions were removed for gamma scanning. The mass of fuel material found in the 

can storing the bottom portion of the rodlet was 6.6 grams. It is important to note that this fuel 

had fallen out of the rod before the gamma scan. This additional fuel loss during storage 

approximately accounts for the difference between the final wire probe measurement and the 

indication on the gamma scan results of the start of the remaining fuel column on the bottom

rodlet portion.

An additional M/C examination provides an even more detailed characterization of the 

remaining fueled region than the gamma scan results. The axial M/C sample shown in 

Figure 2-89 was taken at the boundary of remaining fuel and empty cladding, covering a span 

approximately 80-105 millimeters from the segment bottom. The image reveals that the 

boundary between fueled an empty cladding is rather abrupt, and that the residual fuel is 

relatively intact. The fuel-clad gap in this image appears rather large and it is somewhat 

surprising that these fuel pellets did not relocate even after the agitation of the shake test.
2-61 NUREG-2160

Figure 2-89 Macrograph of axial cross section covering a span approximately 

80–105 mm from the segment bottom of the rodlet tested in LOCA Test 198

Select, high-resolution images are included in Figure 2-90 from the inner (a) and outer (b) 

cladding diameter. These images were near the bottom (left) of the axial M/C, approximately 

84 millimeters from the original segment bottom of the rodlet tested in LOCA Test 198.

In Figure 2-90 (a), a thin fuel-clad bond layer and an alpha layer microstructure can be seen on 

the inner diameter. This region of the test segment remained fueled and was far (more than

100 millimeters) from the rupture location. In Figure 2-90 (c and d), the initial oxide layer and 

transient oxide layer can be seen. Again, it is useful to recall that for Test 198 the calculated 

CP-ECR was 15 percent, with a hold time at 1185 degrees C of 85 seconds.
NUREG-2160 2-62

 (a) (b)

 (c) (d)

Figure 2-90 High-resolution images of the cladding (a and b) inner and (c and d) outer 

diameter taken from the axial M/C shown above. These images were near 

the bottom (left) of the axial M/C, approximately 85 mm from the original 

segment bottom of the rodlet tested in LOCA Test 198.
3-1 NUREG-2160

3. REVIEW OF TEST RESULTS FOR SPECIFIC PARAMETER 

COMPARISONS

In this section, the test results presented above will be revisited and grouped for specific 

parameter comparisons. In addition, new figures will be presented which facilitate the 

comparison of important parameters between tests. Previous papers have discussed 

postulated explanations for the observations of each test [4] and future reports are planned to 

utilize results from this program and others to support a mechanistic understanding of fuel 

fragmentation, relocation, and dispersal phenomenon [5, 6]. For the purpose of this report 

however, the test results provided above are simply being revisited to facilitate comparison by 

the reader.

3.1 Initial State

Table 3-1 provides the burnup value of the segment from each LOCA test, as well as the values 

of initial hydrogen, oxide thickness, and rod internal pressure. The rod segments for Tests 189

and 191-193 are very similar, as are the rod segments for Tests 196 and 198. The pre-test 

hydrogen and oxide layers are similar for all six rod segments.

Table 3-1 Summary of All “Initial State” Information from the Six LOCA Tests

3.2 Transient

Table 3-2 provides the value of peak cladding temperature, rupture temperature and pressure,

and depressurization rate (time in seconds for top/bottom pressure gauge to reach 50 percent of 

rupture pressure) for each test. The pressure response after rupture in the top plenum as a 

function of time for all six tests is plotted in Figure 3-1. The rupture conditions for all six tests 

are relatively similar; however, the depressurization rates for Tests 196 and 198 were notably 

faster than for Tests 189 and 191-192. The depressurization behavior in Test 193 is unique, 

with a hold up near 40 bar even after 90 seconds. This is assumed to be attributed to fuel 

fragments clogging the pressure gauge, thus interfering with the accuracy of the measurement. 

The relatively slow depressurization rates, particularly the rates for 189, 191-192, suggest that 

the fuel remaining at the rodlet ends induces some gas flow restriction between the gas plenum 

at the top and bottom of the rods and the rupture opening.

Test Adjacent H (wppm) Average Oxide 

(μm)

189 176 20

191 187, 271 20-30

192 176, 288 25-30

193 187 20

196 149 20

198 225 20

68.2

69.3

68.2

69.3

55.2

55.2

Rod Internal Pressure 

at 300°C (bar)

110

110

82

82

82

82

Rod Average Burn Up (GWd/MTU)
NUREG-2160 3-2

Table 3-2 Summary of All “Transient” Information from the Six LOCA Tests

Figure 3-1 Pressure drop after rupture in the top plenum, plotted as a function of time, 

for all six tests

3.3 In-Cell Measurements

Table 3-3 provides the value of maximum circumferential strain, rupture dimensions and wire 

probe measurements for each test. In addition, the length of circumferential strain greater than 

10 percent was identified for each test and is provided in Table 3-3. Figure 3-2 provides the 

approximate percentage of fuel loss during each test. In this case, the values provided in the 

previous section for total mass lost during the LOCA transient and total mass lost during 

bending and shaking were used to depict mass loss relative to the total segment fuel mass 

(approximated to be 150 grams).

Test Peak Cladding 

Temperature (°C)

Rupture Temp 

(°C)

Rupture Pressure 

(bar)

Time (s) to 50% of rupture 

P for top/bottom gauges

CP-ECR 

(%) Quench

189 950 700 109 35 / 7 0 No

191 1185 680 104 21 / 10 13 Yes

192 1185 700 81 13 / 15 11 Yes

193 1185 728 81 45 / 8 17 Yes

196 950 686 81 5 / 2 0 No

198 1185 693 81 3 / 2 15 Yes
3-3 NUREG-2160

Table 3-3 Summary of All “In-Cell Measurement” Information from the Six LOCA Tests

Figure 3-2 Approximate percentage of fuel loss during each test, color-coded by when 

fuel loss occurred. Note: Measured mass loss was compared to an 

estimated initial fuel mass of 150 g for the 300-mm segment.

Fuel fragment size measurements were made for the total mass of fuel material found outside of 

the fuel rod for five of the LOCA tests (the exception is Test 189, which was sent to disposal 

before fragmentation analysis) and have been tabulated in the previous sections. Figure 3-3

provides the results of the fuel fragment size measurements using a bar chart to more easily 

depict the distribution of fragments in each test and the comparison of results between tests.

One of the first observations that are apparent is a significant difference in distribution between 

Tests 191-193 and Tests 196 and 198. In Tests 191-193, the fuel was finely fragmented and all 

fragments measured less than 4 millimeters (except a small amount from Test 193). The mass 

Test Max Strain (%) Length >10% 

Strain (mm)

189 48 105

191 50 70

192 56 85

193 50 100

196 25 95

198 25 115

0.2 / 1.5

1.6 / 11

Wire Probe Measurement (mm) 

(Top/Bottom)

82 / 66

70 / 55

85 / 73

113 / 91 

90 / 66

55 / 76

Rupture Dimensions 

(mm) (Width/Length)

10.5 / 23.9

17.5 / 21.6

9 / 22.7

13.8 / 17.8

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

189 191 192 193 196 198

Approximate percentage of fuel release

Approximate 

percentage of 

fuel release 

during the 

bending and 

shaking tests

Approximate 

percentage of 

fuel release 

during LOCA 

simulation
NUREG-2160 3-4

of fuel fragments from these tests was approximately evenly distributed between the size 

groups separated by the six sieves used. In contrast, the fuel in Tests 196 and 198 was not 

finely fragmented and the fragments measured predominately larger than 4 millimeters.

Figure 3-3 Fragment size distribution for each test

0.00

10.00

20.00

30.00

40.00

50.00

60.00

70.00

80.00

90.00

191 192 193 196 198

Mass Percentage of Fragments in Size Range

< 0,125 mm 0,125 - 0,25 mm

0,25 - 0,5 mm 0,5 - 1 mm

1 - 2 mm 2 - 4 mm

> 4 mm
4-1 NUREG-2160

4. CONCLUSIONS

This report presented and discussed the results of the U.S. Nuclear Regulatory Commission’s 

(NRC’s) integral loss-of-coolant accident (LOCA) testing program conducted at Studsvik 

Nuclear AB in Sweden, including the test conditions, rodlet response, and post-test 

examinations for each test. Recently, discussion about the results of LOCA testing in the area 

of fuel fragmentation, relocation, and dispersal has grown common and rigorous throughout the 

international community. Therefore, the observations of fuel fragmentation, relocation, and 

dispersal in this experimental program are likely to be of particular interest for comparison to 

related or complimentary experimental programs. Previous papers have discussed postulated 

explanations for the observations of each test [4] and future reports are planned to utilize results 

from this program and others to support a mechanistic understanding of fuel fragmentation, 

relocation, and dispersal phenomenon [5, 6].

5-1 NUREG-2160

5. REFERENCES

1. M. Helin, J. Flygare, STUDSVIK/N-11/130, “NRC LOCA Tests at Studsvik, Design and 

Construction of Test Train Device and Tests with Unirradiated Cladding Material,” 

Available in USNRC’s ADAMS Public Document Collection, Agencywide Documents 

Access and Management System Accession No. ML12215A431.

2. M. Flanagan, “NUREG-2119: Mechanical Behavior of Ballooned and Ruptured 

Cladding,” February 2012.

3. P. Raynaud, “NUREG-2121: Fuel Fragmentation, Relocation, and Dispersal during the 

Loss-of-Coolant Accident,” March 2012.

4. M. Flanagan, P. Askeljung, “Observations of Fuel Fragmentation, Mobility and Release 

in Integral, High-Burnup, Fueled LOCA Tests,” Presented at the LOCA workshop of the 

May 2012 Halden Program Group Meeting in Lyon, France.

5. M. Flanagan, B.C. Oberländer, A. Puranen “Research Efforts in the Area of Fuel 

Fragmentation, Relocation and Dispersal under LOCA Conditions” Presented at the 

Enlarged Halden Program Group Meeting, Storefjell, Norway, March 10–15, 2013.

6. M. Flanagan, B.C. Oberländer, A. Puranen “Fuel Fragmentation, Relocation and 

Dispersal under LOCA Conditions: Experimental Observations” Manuscript prepared for 

TOPFUEL Conference, Charlotte, NC, September 2013.




UNITED STATES 

NUCLEAR REGULATORY COMMISSION

WASHINGTON, DC 20555-0001

--------------------

OFFICIAL BUSINESS
NUREG

-2160 Post Test Examination Results from Integral, High-Burnup, 

Fueled LOCA Tests at Studsvik Nuclear Laboratory