View source for Information Notice 1996-11, Ingress of Demineralizer Resins Increases Potential for Stress Corrosion Cracking of Control Rod Drive Mechanism Penetrations

{{Adams
| number = ML031470664
| issue date = 02/14/1996
| title = Ingress of Demineralizer Resins Increases Potential for Stress Corrosion Cracking of Control Rod Drive Mechanism Penetrations
| author name = Crutchfield D, Grimes B
| author affiliation = NRC/NRR
| addressee name = 
| addressee affiliation = 
| docket = 
| license number = 
| contact person = 
| document report number = IN-96-011
| document type = NRC Information Notice
| page count = 3
}}
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Home > Electronic Reading Room > Document Collections > General Communications > Information Notices > 1996 > IN 9 UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, D.C.     20555 February 14,   1996 INFORMATION NOTICE 96-11:     INGRESS OF DEMINERALIZER RESINS INCREASES POTENTIAL

FOR STRESS CORROSION CRACKING OF CONTROL ROD DRIVE

MECHANISM PENETRATIONS

==Addressees==
All holders of operating licenses or construction permits for pressurized

water nuclear power reactors.

==Purpose==
The U.S. Nuclear Regulatory Commission       NRC) is issuing this information

notice to alert addressees to the increased likelihood of stress corrosion

cracking of pressurized water reactor (PWR) control rod drive mechanism (CRDM)
penetrations if demineralizer resins contaminate the reactor coolant system

(RCS).  It is 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 supplement are not NRC requirements; therefore, no specific action or

written response is required.

Background

In 1990, the NRC staff issued Information Notice 90-10,         Primary Water Stress

Corrosion Cracking (PWSCC) of Inconel 600,- informing PWR licensees that PWSCC

was an emerging technical issue.      PWSCC was noted in Inconel 600 pressurizer

heater sleeve penetrations at a domestic PWR facility.         The NRC staff

determined that the safety significance of the cracking was low because the

cracks were axial, had a low growth rate, and were in a material with an

extremely high flaw tolerance (high fracture toughness).         Accordingly, the

cracks were unlikely to propagate very far.

In December 1991, after cracks were found in a CRDM penetration in the reactor

head at a French plant, an NRC action plan was implemented to address PWSCC at

all U.S. PWRs.    The NRC staff met with the Westinghouse Owners Group, the

Babcock and Wilcox Owners Group, and the Combustion Engineering Owners Group

to discuss their respective programs for investigating PWSCC of Inconel 600
and to assess the possibility of cracking of CRDM penetrations in their

respective plants.    Subsequently, the staff asked the Nuclear Management and

Resources Council, now the Nuclear Energy Institute, to coordinate future

industry actions because the issue was applicable to all PWRs.          Each owners

9602090038.                                                                      IN 96-11 February 14, 1996 group submitted individual safety assessments, dated February 1993, through

Nuclear Energy Institute to the NRC on the CRDM penetration cracking issue.

In July 1993, the Institute submitted to the NRC proposed acceptance criteria

for flaws identified during inservice examination of CRDM penetrations.            On

the basis of the owners group analyses and the European experience, the NRC

staff concluded, in a safety assessment dated November 19, 1993, (NRC

Accession No. 9403020162), that there is a high probability that CRDM

http://www.nrc.gov/reading-rm/doc-collections/gen-comm/info-notices/I 996/in9601 I.html                03/13/2003

Information Notice No. 96-11 penetrations at U.S. plants may contain similar axial cracks caused by PWSCC.

The Electric Power Research Institute is engaging in ongoing research on

methods for mitigating PWSCC. They also have developed a demonstration

program to ensure that inspections performed on CRDM penetrations are highly

reliable in detecting and determining the size of flaws.

The first of three U.S. inspections took place in the spring of 1994 at the

Point Beach Nuclear Generating Station. No indications were uncovered in the

CRDM penetrations. The eddy current inspection at the Oconee Nuclear Station, Unit 2, in the fall of 1994 revealed 20 indications in one penetration.

Ultrasonic testing did not reveal the depth of these indications because they

were shallow. These indications may be associated with the original

fabrication and may not grow; however, the licensee has committed to reexamine

this penetration during the next refueling outage. An examination of the CRDM

penetrations at the Donald C. Cook Nuclear Plant Unit 2 in the fall of 1994 revealed three clustered indications in one penetration. The indications were

46 mm (1.7 in.), 16 mm (0.63 in.), and 7 mm (0.28 in.) in length and the

deepest flaw was 6.8 mm (0.27 in.) deep. The tip of the 46 mm (1.7 in.) flaw

was just below the J-groove weld. These results are consistent with the PWR

owners group analyses, the NRC staff safety evaluation of the owners group

analyses, and the PWSCC found in the CRDM penetrations in European reactors.

The results of these inspections are documented in Safety Evaluation Reports

dated January 1995 for the D.C. Cook Plant (Accession Nos. 9504050173,
9504050168, 9503220149) and January 1995 for the Oconee Plant (Accession

No. 9503270178).

==Description of Circumstances==
Early in 1994, an inspection for PWSCC at a reactor in Spain identified cracks

which were apparently initiated by high sulfate levels in the reactor coolant

system. Two cation resin ingress events had occurred at the reactor. In

August 1980, 40 liters of cation resin entered the coolant system.    In

September 1981, a mixed-bed demineralizer screen failed and five to eight

times as much resin entered the coolant system as that entering in the August

1980 event.  The coolant conductivity remained high for at least 4 months

after the ingress. The increase in conductivity was attributed to acid .

February 14, 1996 sulfate. Sulfates were found around the crack areas and on the fracture

surfaces. It is important to note that sulfate cracking occurs in lower

stress regions than does PWSCC. The Spanish reactor has 37 CRDM penetrations, of which 20 are active and 17 are spare.   Of the 17 spare penetrations, 16 showed stress corrosion cracking and intergranular corrosion. The cracks were

both axial and circumferential. Four of the active CRDM penetrations had

significant axial and circumferential cracking.

Westinghouse notified the Westinghouse Owners Group plants, the Babcock and

Wilcox Owners Group plants, and the Combustion Engineering Owners Group plants

of the Spanish reactor incident by issuing NSAL-94-028. Westinghouse informed

the NRC staff, during a public meeting on August 24, 1995, that NSAL-94-028 recommends that PWR licensees review their primary coolant system water

chemistry to verify that they have not had significant primary system resin

bed intrusions, and that U.S. PWRs review their RCS chemistry and other

operating records relative to sulfur ingress events. Westinghouse also

reported during this meeting that no other plant had been found worldwide that

has experienced cracking similar to that at the Spanish reactor and that the

U.S. plant inspection results agreed in general with the worldwide experience.

The Westinghouse staff further reported that U.S. plants routinely monitor RCS

conductivity, follow the Electric Power Research Institute guidelines on

primary water chemistry, and monitor for sulfates three times a week.

Westinghouse concluded that no immediate safety issue exists and that the

conclusions in its CRDM safety evaluation, dated February 1993 (WCAP-13565, NRC Accession No. 9312090177), remain valid.

Discussion

The NRC staff is not aware of any significant primary system resin bed

intrusions at any U.S. PWR.   However, if any significant resin intrusions have

occurred at U.S. PWRs, residual stresses are likely sufficient to cause

circumferential intergranular stress corrosion cracking. The NRC staff has

agreed to meet with National Electric Institute and the PWR owners groups in

early 1996 to continue discussions on this issue.

http://www.nrc.gov/reading-rmldoc-collections/gen-comm/info-notices/l 996/in960 11 .html 03/13/2003

Information Notice No. 96-11 On the basis of the results of the inspections at three U.S. PWRs, the NRC

staff continues to conclude, as stated in the 1993 safety evaluation, that

there is a high probability that CRDM penetrations at other plants may contain

similar axial cracks caused by PWSCC.

IN 96-11 February 14, 1996 This information notice requires no specific action or written response. If

you have any questions about the information in this notice, please contact

the technical contacts listed below.

signed by B.K. Grimes

Dennis M. Crutchfield, Director

Division of Reactor Program Management

Office of Nuclear Reactor Regulation

Technical Contacts:  Keith A. Wichman, NRR

(301) 415-2757 internet:krw@nrc.gov

James A. Davis, NRR

(301) 415-2713 internet:jadQnrc.gov

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