Hot cell examination results of hafnium control rods from Maanshan-1 PWR

Technical Report · Thu Jan 31 23:00:00 EST 1991

OSTI ID:6127709

Lin, L F ^[1]

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1. Institute of Nuclear Energy Research, Lung-Tan (Taiwan)

Hydriding and swelling of absorber material have been determined as the causes of cracks and bulges in PWR control rods that use hafnium in stainless steel cladding as the control material. The objective of this effort was to determine the root causes of cracks and bulges in PWR control rods consisting of a hafnium absorber within stainless steel cladding. Researchers used underwater cameras to examine the Maanshan-1 stuck control assembly poolside. Segments from rodlets found to contain cracks were sent to a hot cell for visual inspection, profilometric measurements, metallographic examination, and fractography. Some segments from rodlets thought to be sound were also included for comparison. All bulges and cracks in the stainless cladding, including the circumferential cracks that resulted in end cap separation, were attributed to the hydriding of the hafnium absorber and the resultant swelling. The swelling of the absorber resulted in bulging in areas where the cladding was sufficiently ductile and in cracks where the cladding was embrittled because of irradiation. Circumferential cracks are thought to be caused by stress induced by hydriding of the end faces of hafnium slugs, combined with the jamming of the slug against the cladding due to blisters and swelling in the radial direction. Cracks initiated on the external surface of the cladding, in locations where the hafnium absorber contained a single large hydride blister, and on the internal surface of locations containing many small blisters. In addition to the cracks observed on segments known to be defective, the hot cell examination revealed that almost half of the segments thought to be sound contained cracks. 1 ref., 67 figs., 5 tabs.

• Research Organization: Electric Power Research Inst., Palo Alto, CA (USA); Institute of Nuclear Energy Research, Lung-Tan (Taiwan)
• Sponsoring Organization: EPRI; Electric Power Research Inst., Palo Alto, CA (USA)
• OSTI ID: 6127709
• Report Number(s): EPRI-NP-7143
• Country of Publication: United States
• Language: English

Related Subjects

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS
210200* -- Power Reactors
Nonbreeding
Light-Water Moderated
Nonboiling Water Cooled
ALLOYS
CHEMICAL REACTIONS
CLADDING
CONTROL ELEMENTS
CRACKS
DEFORMATION
DEPOSITION
DOCUMENT TYPES
DUCTILITY
ELEMENTS
EQUIPMENT
HAFNIUM
HIGH ALLOY STEELS
HOT CELLS
HYDRIDATION
IRON ALLOYS
IRON BASE ALLOYS
LABORATORY EQUIPMENT
MECHANICAL PROPERTIES
METALS
NEUTRON ABSORBERS
PHYSICAL RADIATION EFFECTS
POST-IRRADIATION EXAMINATION
PROGRESS REPORT
PWR TYPE REACTORS
RADIATION EFFECTS
REACTOR COMPONENTS
REACTORS
REMOTE VIEWING EQUIPMENT
STAINLESS STEELS
STEELS
STRESSES
SURFACE COATING
SWELLING
TENSILE PROPERTIES
TRANSITION ELEMENTS
WATER COOLED REACTORS
WATER MODERATED REACTORS