Out-of-pile ballooning and bursting tests on Zircaloy cladding rods with direct and indirect heating. Final report

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Commission of the European Communities
nuclear science
and technology
Out-of-pile ballooning
and bursting tests
on Zircaloy cladding rods
with direct and indirect heating Commission of the European Communities
nuclear science
and technology
Out-of-pile ballooning
and bursting tests
on Zircaloy cladding rods
with direct and indirect heating
R. Vesprini,1 L. Lombardi,1 P. Jones,2 F. Casadei2
1 TERM - ISP - Tecnologie dei componenti
ENEA - Centro studi Casaccia - Rome, Italy
2 CEC - Joint Research Centre
Ispra, Italy
Contract No SR-021-1
Final report
The work reported in this document was carried out as a jointly funded project with the
Commission of the European Communities by the Comitato nazionale per la ricerca e
ilo sviluppo dell'energia nucleare e delle energie alternative
Directorate-General
Science, Research and Development
1985 EUR 10073 EN Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Information Market and Innovation
Bâtiment Jean Monnet
LUXEMBOURG
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting on
behalf of then is responsible for the use which might be made of the
following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1985
ISBN 92-825-5622-0 Catalogue number:
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1985
Printed in Belgium CONTENTS
Page
ACKNOWLEDGMENTS V
1. INTRODUCTION AND BACKGROUND 1
2. EXPERIMENTAL 4
2.1. Range of test parameters
2.2. Rig description 5
2.3. Pre-operational tests 8
2.4. Test procedures 9
3. EXPERIMENTAL RESULTS 11
3.1. Test matrix
3.2. Post-test examination2
4. ANALYSIS AND DISCUSSION3
4.1. Group I tests
4.2. Rig heat-transfer characterisation 14
4.3. Results versus predictions5
4.4. Group II and III tests7
4.5. Axial distribution of strain 20
5. SUMMARY AND CONCLUSION1
REFERENCES 23
APPENDIX I 5
6. Test matrix experimental tables
APPENDIX II 167
7. Metallographie photographs
III ACKNOWLEDGMENTS
We would like to thank Mr. R. DEHON of FRAGEMA organization for his
contribution of the Zy4 rods and Mr. L. SBERZE of ENEA-IFEC for
cladding rods preparation.
Mr.A. MASPERONI, F. FORTUNATI of ENEA-TIB-MAT also gave us valuable
assistance by their metallographic analysis.
M. GHIDI and the design staff
A. PERNI and the engineering staff
R. CONTI and the instrumentation staff
F. LIMITI and the construction staff
of ENEA-TERM -ISP-TECOMP for their contribution in the const ruction of
CPT2 facility.
E. BACCHI
M. MONETTI
L. BASSI
for their contribution in performing the experiments
L. GIOIA
E. AMICO
for administrative assistance and text preparation of the semi-annual
progress reports and the final report.
In particular acknowledgment has to be given to:
F. IMPERIALI
E. CAMPANA
R. BONI
P. GIACOMETTI
D. ZORINI (NIRA)
G. POZZI
for their contribution in the early phase of the work. INTRODUCTION AND BACKGROUND
INTRODUCTION
This is the final report on work partially financed by a CEC
contract, and carried out both at ENEA-ROMA for the experimental
part and at JRC-ISPRA for the theoretical part.
This report summarizes the research programme which is inten­
ded to validate the R0DSWELL code recently developed by the "Fuel Mo­
delling Group" of JRC Ispra.
With present knowledge we can remark that the deformation pro­
cess and rupture behaviour of Zircaloy cladding tested at LOCA tran­
sient temperature and pressure conditions are strongly affected by
many factors such as: heating rate, external atmosphere (steam or
inert gas) and method of heating.
However it can be observed that the situation of "out of pile"
available experimental data can be subdivided in two areas: Tests
with direct heating of the cladding by J oule effect and tests with
indirect heating through an internal heater inserted in a pellet
stack simulating the effective geometry of LWR fuel rods.
The original objective of the study was to check if these two
different heating methods gave different results regarding ballooning
shape and extent. At the start of the contract a first test matrix
was proposed by S0PREN to perform a limited number of ballooning
(and eventually bursting) tests both with direct and indirect heating.
The experiments were to be performed in forced flow convection regime,
with controlled steam flow rate simulating conditions prevailing
at the beginning of the reflood phase. The experimental results were
to be analyzed with the calculation models derived by ENEA-SOPREN
research programme regarding fuel modelling.
Later, other authors such as: Hindle, Erbacher, Chapman ,et al.
[3,10,11,12,13] supplied sufficient answers explaining the influence
of the heating method on shape and extension of the ballooning. At
an "ad hoc" meeting held at ENEA-CASACCIA in February 1983, it was
decided, by all the interested people, to accept a proposal of the Fuel Modelling Group of Ispra for the reorientation of the research pro­
gramme .
The present objective of the research involves a differing
philosophy which is devoted to the confirmation of the current under­
standing of the various phenomena, the validation of Ispra's new
Rodswell code, and the checking of code predictions.
In the new experimental test matrix the total number of tests
was not changed.
However the tests are now almost all bursting tests and they
are divided into 3 groups, to check:
a) Heat transfer characterization and the effect on ballooning
failure strain
b) Basic data in the mixed alpha-beta phase
c) Oxidation and creep ductility in the beta phase
Moreover maximum temperature and maximum pressure were increased,
many tests were foreseen at constant temperature. Different values
of steam flow and some tests in inert gas were also included.
All this involved substantial modifications on test ring CPT2
concerning: internal heater design, hydraulic shroud diameter, tempe­
rature control system and steam flow availability.
No extension of CEC budget was requested.
The only request made and accepted was to extend the original
time limits for the project completion from December 1983 until June
1984.
BACKGROUND
The ballooning of Zircaloy clad LWR fuel rods during a hypothe­
tical loss of coolant accident has been investigated for some years.
The concern has been that emergency cooling of the fuel might be
inhibited if the coolant channels become appreciably blocked. In
a PWR adjacent rods will touch at about 30% strain of the cladding
and the sub-channels would be completely blocked if all the rods
strained in about 70% at the same axial level. Although such a situa­
tion is actually impossible, ballooning of this magnitude in many
rods might cause a problem.