Information Notice 1990-10, Primary Water Stress Corrosion Cracking of Inconel 600
| ML053070392 | |
| Person / Time | |
|---|---|
| Site: | Davis Besse  |
| Issue date: | 02/23/1990 |
| From: | Rossi C Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| IN-90-010, NUDOCS 9002160093 | |
| Download: ML053070392 (4) | |
0 Q 0 0 0 9 0 3 h&@h.
/-3!37 REG I V E D
EXP-90i01536 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D,C.
20555 MAR 05 1990
Dl-M
February 23, 1990
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NRC INFORMATION NOTICE NO. 90-10: PRIMARY WATER STRESS CORROSION CRACKING
(PWSCC) OF INCONEL 600
Addressees
All holders o f operating licenses or construction permits for pressur
reactors (PWRs) .
zed water
Purpose
This information notice is intended to alert addressees to potential problems
related to primary water stress corrosion cracking (PWSCC) of Inconel 600 that
has occurred in pressurizer heater thermal sleeves and instrument nozzles at
It i s expected that recipients will
review the information for applicability to their facilities and consider
actions, as appropriate, to avoid similar problems. However, suggestions
contained in this information notice do not constitute NRC requirements;
therefore, no specific action or written response is required.
-several domestic and foreign PWR plants,
Description of Circumstances
During the 1989 refueling outage at Calvert Cliffs Unit 2 (CC-2), visual
examination detected leakage in 20 pressurizer heater penetrations and 1 upper-level/pressure tap instrument nozzle. Leakage was indicated by the
presence of boric acid crystals at the penetrations and on the nozzle. Non- destructive examinations (liquid penetrant and eddy current examinations)
were performed on 28 thermal sleeves and 3 instrument nozzles. Crack indi- cations were reported in 24 thermal sleeves, including the 20 originally
identified to be leaking as well as the leaking nozzle.
No crack indications
were found in the two lower instrument nozzles. The examinations showed that
all cracks in the sleeves and the nozzle were axially oriented with a maximum
length not greater than 1.5 inches.
was identified as PWSCC.
The mode of failure for the thermal sleeves
The heater sleeves and the instrumentation nozzles were made of Inconel 600
tubing and bar materials, respectively, supplied by INCO. All thermal sleeves
were made in a high strength heat (NX8878) with a reported yield strength of
63.5 ksi. No chemical contaminants were found on the sleeve fracture surfaces.
A review of the fabrication records showed that all 120 thermal sleeves in CC-2 were reamed 3.5 inches from the top before welding and all but two were also
IrJ 90-10
9002 160093 Y
February 23, 1990
Page 2 of.4, , ,
reamed after welding to facilitate the insertion of the heater rods. All
cracks in the sleeves were reported to be located inside the reamed :r&g,ioflI,,
either above or below the J-groove weld.
All instrument nozzles were made from heat no, NX8297 and its yield strength
was reported to be 36 ksi, The licensee indicated that four upper instrument
nozzles, including the leaking one, had been extensively reworked when the
faulty J-groove welds were repaired. Based on the results of the investiga- tions, the licensee, Baltimore Gas and Electric (BG&E), postulated that the
leaking in the pressurizer thermal sleeves and the instrumentation nozzle
was due to PWSCC,
samp?e from the leaking instrument nozzle for failure analysis to identify
the mode of failure.
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The licensee is in the process o f removing a metallurgical
On February 27, 1986, a small leak (about 0.15 gpm) was observed on a
3/4-inch-diameter upper pressurizer level instrument nozzle at San Onofre
Nuclear Generating Station (SONGS) Unit 3 while the plant was in hot standby.
An axial flaw about 5/8 inch in length was identified on the inside diameter
surface o f the nozzle.
nozzle inside the pressurizer and extended beyond the attachment weld (1/2 inch
in depth) approximately 1/8 inch into the annulus area of the nozzle assembly.
results of the metallurgical examination performed on the flawed nozzle
assembly indicated that the cracking was PWSCC.
In spring 1989, leakage from instrument nozzles was observed in two foreign
PWRs (one from each 1300-MW plant) when the hydrostatic pressure testing o f
the primary system was performed durlng the first refueling outage. The
instrument nozzles were made of Inconel 600 material. The installation
of the nozzles included mechanically rolling a portion of the nozzle into
the pressurizer she1 1.
Nondestructive examinations (NDEs) were performed
on the leaking nozzles and found the cracks to be principally axial in
orientation; however, some circumferential cracking was observed. Destructive
examlnation o f these two leaking nozzles to identify the root causes has not
been completed. Additional NDEs were performed on all the instrument nozzles
of five 1300-MW PWRs.
Crack indications were found in 12 instrument nozzles.
The flaw appeared to originate from the end of the
'The flawed nozzle was cut out, including the entire attachment weld, The
Discussion:
Extensive laboratory testing has shown that intergranular stress corrosion
cracking (IGSCC) requires the presence of the following three key elements:
an aggressive environment, susceptible material, and 'sufficient tensile
stresses for crack initiation and propagation. PWSCC refers to IGSCC in
the primary water environment of PWRs. The laboratory demonstration of
PWSCC in Inconel 600 was first reported by Coriou almost 30 years ago.
The studies of PWSCC in Inconel 600 have been documented in numerous
published reports.
is still not well understood.
In PWRs, PWSCC o f Inconel 600 was first
reported in steam generator tubing.
However, the mechanism for PWSCC in Inconel 600
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February 23, 1990 !
The cracking to date in the thermal sleeves and the instrument nozzles of the
domestic PWRs has been reported as being only axially oriented. The safety
implication of an axial crack is not considered a significant threat to the
leak.
nozzles of several foreign PWRs.
been attributed to the different type of mechanical working (rolling vs. reaming)
being performed on these nozzles and thermal sleeves.
crack in the rolled instrument nozzle is consistent with that observed in the
roll-expanded region of steam generator tubing, Circumferential cracking
poses a more serious safety concern because if it were to go undetected it
could lead to a structural failure of a component rather than to a limited
leak.
The reported cracking of the pressurizer thermal sleeves and the instrument
nozzle at Calvert Cliffs Unit 2 and the instrument nozzle at SONGS Unit 3 are the most current PWSCC events for Inconel 600 in domestic PWRs besides
the cracking problem associated with the steam generator tubin and plugs.
.The pressurizer thermal sleeves in Calvert Cliffs Unit 1 (CC-1 7 were also
made of the same heat of susceptible material, but the recent inspection
of the CC-1 pressurizer did not reveal any leaking or cracking of the thermal
sleeves. The licensee indicated that the major difference in the fabrication
of thermal sleeves between CC-1 and CC-2 is that the pre-installation reaming
operation was not performed on CC-1 sleeves. The Combustion Engineering Owners
Group (CEOG) performed an evaluation of pressurizer heater sleeve susceptibility
to PWSCC for plants designed by Combustion Engineering. The CEOG recomnended a
visual inspection program for the thermal sleeves.
the thermal sleeves varied, depending on the degree of susceptibility of the
sleeve materials. The sleeve susceptibility was rated by the elements described
above. The staff notes that at CC-2 the yield strength of the thermal sleeve
material is higher than that of the instrument nozzle material. However, PWSCC
occurred in both heats o f materials. This circumstance may indicate that the
yield strength of the material is not necessarily a reliable screening criterion
for PWSCC susceptibility. The CEOG is performing additional work to address.
PWSCC of Inconel 600. The CEOG programs include the following activities:
evaluations to gain better understanding of the cracking mechanism in
pressurizer thermal heater sleeves and instrument nozzles; an analytical
determination of a temperature profile for the heater sleeves; review of
the fabrication history of all Inconel 600 penetrations in the primary system
components; conduct of a test that is primarily a system leakage test on a
mock-up of the flawed components; and improvement of NDE methods for cracking
eva 1 ua t ion.
PWSCC of Inconel 600 is not a new phenomenon. However, very little special
attention has been given to the inspect.ion for PWSCC in Inconel 600 applica- tions other than that associated with the steam generator tubing. As a result
of the recently reported instances of PWSCC in the pressurizer heater thermal
sleeves and instrument nozzles in several domestic and foreign PWRs, it may be
prudent for licensees of all PWRs to review their Inconel 600 applications in
augmented inspection program.
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structural integrity of the components and most likely will result in a small
However, limited circumferential cracking was reported in the instrument
The difference in the cracking morphology has
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The appearance of the
The inspection program for
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the primary coolent pressure boundary, and when necessary, to iniplement an
I N 90-10
February 23, 1990
Page 4 o f 4 This information notice requires no specific action o r written response.
you have any questions about the information i n t h i s notice, please contact one
o f the technical contacts l i s t e d below o r the appropriate NRR project manager.
If
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e
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harles E. Rossi. D rector
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts:
William H. KOO, NRR
Robert A.
Hermann, NRR
(301) 492-0928
.
(301) 492-0911 A,,achment:
L i s t o f Recently Issued NRC Infirmation Notices