Information Notice 1996-11, Ingress of Demineralizer Resins Increases Potential For Stress Corrosion Cracking of Control Rod Drive Mechanism Penetrations
| ML031470664 | |
| Person / Time | |
|---|---|
| Issue date: | 02/14/1996 |
| Revision: | 0 |
| From: | Crutchfield D M, Grimes B J Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| IN-96-011 | |
| Download: ML031470664 (3) | |
Information Notice No. 96-11 Index I Site Map I FAQ I Help Glossary I Contact Us A Search AU.S. Nuclear Regulatory CommissionHome llWho We Are lWhat We Do ll Nuclear ll Nuclear llRadioactive n Public lReactors Materials Waste InvolvementHome > Electronic Reading Room > Document Collections > General Communications > Information Notices > 1996 > IN 9UNITED STATESNUCLEAR REGULATORY COMMISSIONOFFICE OF NUCLEAR REACTOR REGULATIONWASHINGTON, D.C. 20555February 14, 1996INFORMATION NOTICE 96-11: INGRESS OF DEMINERALIZER RESINS INCREASES POTENTIALFOR STRESS CORROSION CRACKING OF CONTROL ROD DRIVEMECHANISM PENETRATIONS
Addressees
All holders of operating licenses or construction permits for pressurizedwater nuclear power reactors.
Purpose
The U.S. Nuclear Regulatory Commission NRC) is issuing this informationnotice to alert addressees to the increased likelihood of stress corrosioncracking 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 forapplicability to their facilities and consider actions, as appropriate, toavoid similar problems. However, suggestions contained in this informationnotice supplement are not NRC requirements; therefore, no specific action orwritten response is required.BackgroundIn 1990, the NRC staff issued Information Notice 90-10, Primary Water StressCorrosion Cracking (PWSCC) of Inconel 600,- informing PWR licensees that PWSCCwas an emerging technical issue. PWSCC was noted in Inconel 600 pressurizerheater sleeve penetrations at a domestic PWR facility. The NRC staffdetermined that the safety significance of the cracking was low because thecracks were axial, had a low growth rate, and were in a material with anextremely high flaw tolerance (high fracture toughness). Accordingly, thecracks were unlikely to propagate very far.In December 1991, after cracks were found in a CRDM penetration in the reactorhead at a French plant, an NRC action plan was implemented to address PWSCC atall U.S. PWRs. The NRC staff met with the Westinghouse Owners Group, theBabcock and Wilcox Owners Group, and the Combustion Engineering Owners Groupto discuss their respective programs for investigating PWSCC of Inconel 600and to assess the possibility of cracking of CRDM penetrations in theirrespective plants. Subsequently, the staff asked the Nuclear Management andResources Council, now the Nuclear Energy Institute, to coordinate futureindustry actions because the issue was applicable to all PWRs. Each owners9602090038. IN 96-11February 14, 1996 group submitted individual safety assessments, dated February 1993, throughNuclear Energy Institute to the NRC on the CRDM penetration cracking issue.In July 1993, the Institute submitted to the NRC proposed acceptance criteriafor flaws identified during inservice examination of CRDM penetrations. Onthe basis of the owners group analyses and the European experience, the NRCstaff concluded, in a safety assessment dated November 19, 1993, (NRCAccession No. 9403020162), that there is a high probability that CRDMhttp://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 onmethods for mitigating PWSCC. They also have developed a demonstrationprogram to ensure that inspections performed on CRDM penetrations are highlyreliable in detecting and determining the size of flaws.The first of three U.S. inspections took place in the spring of 1994 at thePoint Beach Nuclear Generating Station. No indications were uncovered in theCRDM 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 theywere shallow. These indications may be associated with the originalfabrication and may not grow; however, the licensee has committed to reexaminethis penetration during the next refueling outage. An examination of the CRDMpenetrations at the Donald C. Cook Nuclear Plant Unit 2 in the fall of 1994revealed three clustered indications in one penetration. The indications were46 mm (1.7 in.), 16 mm (0.63 in.), and 7 mm (0.28 in.) in length and thedeepest flaw was 6.8 mm (0.27 in.) deep. The tip of the 46 mm (1.7 in.) flawwas just below the J-groove weld. These results are consistent with the PWRowners group analyses, the NRC staff safety evaluation of the owners groupanalyses, and the PWSCC found in the CRDM penetrations in European reactors.The results of these inspections are documented in Safety Evaluation Reportsdated January 1995 for the D.C. Cook Plant (Accession Nos. 9504050173,9504050168, 9503220149) and January 1995 for the Oconee Plant (AccessionNo. 9503270178).
Description of Circumstances
Early in 1994, an inspection for PWSCC at a reactor in Spain identified crackswhich were apparently initiated by high sulfate levels in the reactor coolantsystem. Two cation resin ingress events had occurred at the reactor. InAugust 1980, 40 liters of cation resin entered the coolant system. InSeptember 1981, a mixed-bed demineralizer screen failed and five to eighttimes as much resin entered the coolant system as that entering in the August1980 event. The coolant conductivity remained high for at least 4 monthsafter the ingress. The increase in conductivity was attributed to acid .February 14, 1996 sulfate. Sulfates were found around the crack areas and on the fracturesurfaces. It is important to note that sulfate cracking occurs in lowerstress 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, 16showed stress corrosion cracking and intergranular corrosion. The cracks wereboth axial and circumferential. Four of the active CRDM penetrations hadsignificant axial and circumferential cracking.Westinghouse notified the Westinghouse Owners Group plants, the Babcock andWilcox Owners Group plants, and the Combustion Engineering Owners Group plantsof the Spanish reactor incident by issuing NSAL-94-028. Westinghouse informedthe NRC staff, during a public meeting on August 24, 1995, that NSAL-94-028recommends that PWR licensees review their primary coolant system waterchemistry to verify that they have not had significant primary system resinbed intrusions, and that U.S. PWRs review their RCS chemistry and otheroperating records relative to sulfur ingress events. Westinghouse alsoreported during this meeting that no other plant had been found worldwide thathas experienced cracking similar to that at the Spanish reactor and that theU.S. plant inspection results agreed in general with the worldwide experience.The Westinghouse staff further reported that U.S. plants routinely monitor RCSconductivity, follow the Electric Power Research Institute guidelines onprimary water chemistry, and monitor for sulfates three times a week.Westinghouse concluded that no immediate safety issue exists and that theconclusions in its CRDM safety evaluation, dated February 1993 (WCAP-13565,NRC Accession No. 9312090177), remain valid.DiscussionThe NRC staff is not aware of any significant primary system resin bedintrusions at any U.S. PWR. However, if any significant resin intrusions haveoccurred at U.S. PWRs, residual stresses are likely sufficient to causecircumferential intergranular stress corrosion cracking. The NRC staff hasagreed to meet with National Electric Institute and the PWR owners groups inearly 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 NRCstaff continues to conclude, as stated in the 1993 safety evaluation, thatthere is a high probability that CRDM penetrations at other plants may containsimilar axial cracks caused by PWSCC.IN 96-11February 14, 1996 This information notice requires no specific action or written response. Ifyou have any questions about the information in this notice, please contactthe technical contacts listed below.signed by B.K. GrimesDennis M. Crutchfield, DirectorDivision of Reactor Program ManagementOffice of Nuclear Reactor RegulationTechnical Contacts: Keith A. Wichman, NRR(301) 415-2757internet:krw@nrc.govJames A. Davis, NRR(301) 415-2713internet:jadQnrc.govhttp://www.nrc.gov/reading-rm/doc-collections/gen-comnm/info-notices/1 996/in960 11 .html 03/13/2003