Information Notice No. 97-02: Cracks Found in Jet Pump Riser Assembly Elbows at Boiling Water Reactors
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555-0001
February 6, 1997
NRC INFORMATION NOTICE 97-02: CRACKS FOUND IN JET PUMP RISER ASSEMBLY
ELBOWS AT BOILING WATER REACTORS
All holders of operating licenses or construction permits for boiling water
nuclear power reactors (BWR) models 3, 4, 5 and 6 (BWR/3-6), except those
licenses that have been amended to possession-only status.
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information
notice to alert addressees that cracking has been detected in a jet pump riser
assembly at a location not previously known to have cracks. It is expected
that recipients will review the information for applicability to their
facilities and consider actions, as appropriate, to detect or avoid similar
problems. However, suggestions contained in this information notice are not
NRC requirements; therefore, no specific action or written response is
Description of Circumstances
On November 26, 1996, General Electric Nuclear Energy (GENE) notified the NRC
staff about cracking recently discovered in jet pump riser assembly elbows at
a foreign BWR plant. The plant is approximately 25 years old. Cracks were
discovered in 2 of the 10 jet pump riser assembly elbows while plant personnel
were performing a visual examination (VT-1) using a remote underwater camera.
The cracks were circumferential cracks in the 10-inch piping and were
approximately 83 mm [3.27 in] and 112 mm [4.41 in] in length. No depth
measurements were obtained because techniques for volumetric examination of
this location do not currently exist.
As a result of the cracking found in the foreign BWR, GENE issued Service
Information Letter (SIL) 605, "Jet Pump Riser Pipe Cracking," dated
December 6, 1996, that provides recommendations for inspection and detection
of jet pump riser pipe cracking [Accession No. 9612190076].
On January 15, 1997, the licensee for LaSalle Unit 2 notified the NRC staff
about cracking found during its inspection of jet pump riser assembly elbows.
The licensee, in performing visual inspections (enhanced VT-1) as recommended
in GENE's SIL 605, found three
9702050049. IN 97-02
February 6, 1997
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indications in 2 of the 10 jet pump riser assembly elbows. Preliminary
information provided to the NRC staff suggests that the indications ranged in
length from approximately 20 mm to
150 mm [0.75 to 6 inches]. No depth measurements were taken. The smallest
indication had an axial orientation; the other two indications were
Jet pumps are part of the reactor coolant recirculation system in BWR/3-6
plants. They are installed in the annulus between the core shroud and the
reactor pressure vessel (RPV), and each vessel contains between 12 and 24 jet
pumps. Most BWRs have 20 jet pumps. There are several BWR jet pump designs;
however, the basic jet pump configuration is the same for all plants. Figure
1 is a schematic that shows the configuration of a typical jet pump and
identifies the major components.
Each jet pump consists of a riser assembly, two inlet-mixer assemblies, two
diffuser assemblies, and a riser brace. The riser assembly elbow is a 10-
inch, 90 degree short radius elbow, fabricated from Type 304 stainless steel.
It is welded to the recirculation inlet nozzle thermal sleeve. The riser
assembly is supported near the top by the riser brace, which is welded to the
riser pipe and to pads on the RPV wall (some plants have two riser braces for
each riser). Lateral support is also provided by the jet pump restrainer
brackets which attach the adjacent jet pump inlet mixers to the riser. The
entrance end of each inlet-mixer assembly is clamped to the top of the riser
transition piece by the beam-bolt assembly. The exit end of the inlet-mixer
forms a slip joint with the entrance end of the diffuser. This interface
between the inlet mixers and the diffusers provides some additional lateral
support to the riser. The top of the slip joint is located near the bottom of
the fuel; the exact elevation of the slip joint is plant specific.
The cracking in both the foreign BWR and the LaSalle Unit 2 occurred in the
heat-affected zone of the weld connecting the jet pump riser elbow to a
thermal sleeve. The characteristics of the cracking are indicative of
intergranular stress corrosion cracking (IGSCC).
Separation of the jet pump riser piping could have a potential safety impact
on some BWR plants under certain accident conditions. If the jet pump riser
piping were to separate under normal operating conditions, there does not
appear to be a safety concern in that the loss of a jet pump assembly would
not cause a plant to lose its capability to safely shut down. According to
GENE, a loss of one jet pump assembly would be detected by plant operators.
The BWR Owners Group Vessel and Internals Project (BWRVIP) is working closely
with GENE and has provided a safety assessment, "Assessment of BWR Jet Pump
Riser Elbow to . IN 97-02
February 6, 1997
Page 3 of 3
Thermal Sleeve Weld Cracking (BWRVIP-28)," dated December 1996, to the NRC
staff [Accession No. 9701030009].
This information notice requires no specific action or written response. If
you have any questions about the information in this notice, please contact
one of the technical contacts listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
signed by D.B. Matthews
Thomas T. Martin, Director
Division of Reactor Program Management
Office of Nuclear Reactor Regulation
Technical contacts: C. E. Carpenter, Jr., NRR
Kerri A. Kavanagh, NRR
1. Jet Pump Assembly Schematic (See File IN97002.WP1 for figure)
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