Page 316 - 00. Complete Version - Progress Report IPEN 2014-2016

316 Materials and Nanotechnology | Progress Report

cold-compacted in uniaxial press with 450 for hydride to form at the flaw tip and the lo-
MPa pressure and sintered in an EDG furnace cal tensile stress must be sufficiently large to
under 10-3 torr of mechanical vacuum and crack the hydride. A crack will not extend if the
650°C in 6 h. The samples were prepared me- threshold in stress intensity factor, KIH, is not
tallographically and observed in an optical mi- exceeded. Hence, the threshold stress intensi-
croscope, the micrographs indicated coalesc- ty factor KIH at 227 °C and 250 °C of zircaloy-4
ing of the copper particles and other metallic tubes charged with 125 ppm of hydrogen was
elements and formation of porosity. determined. This study, carried out in CCTM,
was part of a global round-robin test involv-
Optical micrographs indicated presence of po- ing 10 countries with PWR reactors and coordi-
rosity inside the structure and partial homo- nated by the IAEA. The objective was to deter-
geneity, due to the non-dissolution of the ele- mine whether zircaloy-4 clad spent in nuclear
ments involved in the metal alloy (Figure 39). fuel is immune from Delayed Hydride Crack-
ing during Dry Storage. The overall results of
Control rod plates for the IEA-R1 reactor this Coordinated Research Project suggested
that unirradiated Zircaloy-4 fuel cladding is im-
An innovative program to develop new control mune from DHC above about 320°C and this
rods for the IEA-R1 Research Reactor at IPEN temperature increases to 360°C by irradiation.
was undertaken. Four rectangular Ag-In-Cd
plates were inserted and sealed in stainless Options for the Back-End of the Nuclear
steel envelopes using a laser welding process Fuel Cycle of research reactors
(Figure 40). The sealed steel envelopes were
then laser welded to stainless steel plates to Research reactors (RR) are used worldwide for
form one of two forks of a control rod. education of nuclear scientist and engineers,
to produce medical and industrial radioiso-
topes, for Silicon doping, to perform advanced
fuel and material testing to support life ex-
tension of operating nuclear power plants, to
qualify new fuels (including studies on fuel
behaviour in incidental and accidental con-
ditions), etc. Presently, there are over 400 RRs
Figure 40: IEA-R1 reactor’s control rod plate as- worldwide and of these 230 are operating and
sembled for laser welding.
the rest are either in a stand by situation, de-
commissioned or under decommissioning. A
Hydrogen induced degradation common problem related to all RR is manage-
of zircaloy-4 ment of the Back End of the Nuclear Fuel Cy-

cle. To help address this problem, the IAEA ini-
Delayed Hydride Cracking (DHC) has been re- tiated in 2015 a Coordinated Research Project
sponsible for cracking in zirconium alloy pres- (CRP) to develop a comprehensive set of op-
sure tubes and fuel cladding and is a concern tions for the back end of the fuel cycle. The
for spent fuel storage. A flaw in a loaded com- options included the means and methods for
ponent may extend by DHC because hydrogen storage, transport, security, and disposal. In
diffuses up the tensile stress gradient at the addition, the CRP is creating a tool to analyse
flaw tip. Sufficient hydrogen must be present scenarios comprised of these options with a

Instituto de Pesquisas Energéticas e Nucleares