Information Notice 2014-04, Potential for Teflon Material Degradation in Containment Penetrations, Mechanical Seals and Other Equipment
| ML13330B698 | |
| Person / Time | |
|---|---|
| Issue date: | 03/26/2014 |
| From: | Michael Cheok, Kokajko L Division of Construction Inspection and Operational Programs, Division of Policy and Rulemaking |
| To: | |
| M Banic, 301-415-2771 | |
| References | |
| TAC MF1921 IN-14-004 | |
| Download: ML13330B698 (6) | |
ML13330B698 UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
OFFICE OF NEW REACTORS
WASHINGTON, DC 20555-0001
March 26, 2014
NRC INFORMATION NOTICE 2014-04: Potential for Teflon Material Degradation in
Containment Penetrations, Mechanical Seals
and Other Components
ADDRESSEES
All holders of an operating license or construction permit for a nuclear power reactor under
Title 10 of the Code of Federal Regulations (10 CFR) Part 50, Domestic Licensing of
Production and Utilization Facilities, except those that have permanently ceased operations
and have certified that fuel has been permanently removed from the reactor vessel.
All holders of and applicants for a power reactor early site permit, combined license, standard
design approval, or manufacturing license under 10 CFR Part 52, Licenses, Certifications, and
Approvals for Nuclear Power Reactors. All applicants for a standard design certification, including such applicants after initial issuance of a design certification rule.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of the potential for Teflon1 material degradation affecting containment
penetrations, containment personnel airlocks, pump seals, and other components. The NRC
expects that recipients will review the information for applicability to their facilities and consider
actions, as appropriate. Suggestions contained in this IN are not NRC requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
Fort Calhoun Station
On May 1, 2012, the Omaha Public Power District (the licensee or OPPD) at Fort Calhoun
Station (FCS) submitted Licensee Event Report (LER) 2012-002-00, Inadequate Qualifications
for Containment Penetrations Renders Containment Inoperable, (Agencywide Documents
Access and Management System (ADAMS) Accession No. ML12208A313) and follow up report
LER 2012-002-01, dated July 2, 2013 (ADAMS Accession No. ML13184A270). These reports
informed the NRC that an environmental qualifications (i.e., qualifications to ensure that
equipment will be capable of withstanding the ambient conditions under an accident scenario)
review identified multiple containment electrical penetrations that use Teflon seals.
1 Teflon or polytetrafluoroethylene (PTFE) material is a synthetic fluoropolymer of tetrafluoroethylene that has
numerous applications. The most well-known brand name of PTFE is Teflon which is a registered trademark of the
DuPont Company. The containment seals consist of an inboard and outboard section of Teflon for each electrical
The licensee had previously identified and replaced Teflon seals on safety related (Class 1E2)
containment electrical penetrations but did not replace them on the non-Class 1E penetrations.
The remaining seals were classified incorrectly as non-safety-related based solely on their
electrical function, even though they have a safety function to maintain containment integrity.
Following a review of environmental qualification records in May 2012, OPPD performed a dose
analysis on the non-Class 1E containment penetration electrical seals to determine if they would
maintain containment leak integrity. The analysis determined that the inboard and outboard
Teflon seals would receive failure threshold doses during a design basis accident (DBA). The
degraded inboard seal would fail in a DBA environment, reducing the safety margin. The leak
integrity would then depend on the outboard Teflon seal. Additional functional testing on seals
in the laboratory confirmed this finding but also indicated that the external seal would be
exposed to less severe environmental conditions and would remain in place due in part to the
surrounding electrical penetration and electrical cables. However, the testing did not reproduce
conditions that would exist following a DBA.
On June 10, 2013, the NRC staff completed a team inspection at FCS
(Inspection Report No. 05000285/2013008 (ADAMS Accession No. ML13197A261). The NRC
inspection team determined that from initial construction to the present, the licensee did not
perform adequate analysis and/or post-accident condition functional testing of the Teflon
insulated and Teflon sealed electrical penetration assemblies to determine if they were suitable
for expected post-accident conditions. As a corrective action, the licensee replaced or capped
all Teflon-insulated containment electrical penetration assemblies.
In addition, LER 2013-006-00, Use of Teflon in LPSI [low-pressure safety injection] and CS
[containment spray] Pump Mechanical Seals, dated May 3, 2013 (ADAMS Accession No.
ML13126A121) and follow-up report LER 2013-006-01, dated August 26, 2013 (ADAMS
Accession No. ML13239A120) identified that the mechanical seals used in certain safety related
pumps at FCS also contain Teflon. The increased radiation during a DBA could rapidly
degrade the Teflon and the increased pressure, temperature, and steam could penetrate the
seals, resulting in failure of the associated safety systems.
As described in LER 2013-06-00, the Teflon mechanical seals used in LPSI pumps and CS
pumps might adversely affect the integrity of the pumps under certain accident conditions.
LER 2013-06-01 stated, Failure of Teflon seals may have hindered the pumps' ability to
operate in post-accident conditions. A failure of one or more pumps could have resulted in
insufficient cooling water to keep the core and the containment cooled . Causal analysis
determined the original construction specifications did not adequately specify a compatible
material for the pump seals. As corrective actions, the licensee is performing a material
compatibility review and will restrict the use of Teflon. The licensee replaced the affected
pump seals prior to startup.
In addition to the recent experience at Fort Calhoun, the potential for Teflon material
degradation affecting components has been discussed in 10 CFR Part 21, Reporting of defects
2 Institute of Electrical and Electronics Engineers (IEEE), IEEE 323-1974, IEEE Standard for Qualifying Class 1E
Equipment for Nuclear Power Generating Stations, Piscataway, NJ. NOTE: The terms Class 1E equipment and
safety related electric equipment are synonymous. and noncompliance notifications, LERs, and NRC Inspection and Enforcement Circulars
associated with experience at Vermont Yankee, Fermi 2, and with Foxboro transmitters.
Vermont Yankee
On June 19, 1985, the licensee at Vermont Yankee issued 10 CFR Part 21 Notification 85-287 (ADAMS Accession No. ML14052A079) that identified four Conax containment personnel
airlock electrical penetrations which contained Teflon insulation and sealant materials. As part
of the corrective actions, the licensee stated that it intended to replace the penetrations with
ones that contain materials which are more radiation resistant and further recommended that all
licensees using Conax electrical penetrations investigate the construction of all safety and non- safety related electrical penetrations to determine if they contained Teflon.
On November 2, 1990, the licensee submitted LER 90-014-00 (ADAMS Accession
No. 90111601823) which stated that Teflon seal material existed in the containment personnel
airlock. The seals were located where shafts penetrate a bulkhead and in stem packing and
seals for equalizing valves. The Teflon that existed in the airlock seals had characteristic
material damage limits in the range of 104 to 106 rad. For containment design, the Vermont
Yankee DBA radiation dose is 8 x 107 rad, one order of magnitude greater than that required for
Teflon material damage. Therefore, the Teflon material could potentially fail under accident
conditions and compromise primary containment. The licensee took prompt corrective actions
to comply with the DBA dose limit by replacing the Teflon in the shaft seals with graphite and
the equalizing valves with equivalent valves that use metallic seats.
Fermi 2
On February 28, 1991, the Fermi 2 licensee was notified by Whittaker Electronic Resources
Division that a flow switch manufactured by Chem-Tec for the Exo-Sensor Hydrogen/Oxygen
monitoring system could contain Teflon, rather than Tefzel, lead wire insulation. Teflon is not
qualified for the postulated radiation environment encountered following a design basis Loss of
Coolant Accident. See LER 05000341/ 91-003-01, ADAMS Accession No. 91061202384. The
root cause of this condition was a breakdown in the procurement process between Whittaker
Electronic Resources Division and their flow switch supplier, Chem-Tec, and inadequate work
instructions for the Raychem repair of the flow switch. Whittaker filed a 10 CFR Part 21 report
with the NRC and the flow switch was replaced during the units next Refueling outage with a
flow switch containing Tefzel insulated lead wires.
Foxboro Transmitters
NRC Inspection and Enforcement Circular 81-06, Potential Deficiency Affecting Certain
Foxboro 10 To 50 Milliampere Transmitters, (ADAMS Accession No. 80110402884) was issued
after the NRC staff received a Technical Letter from Foxboro regarding deficiencies identified in
certain E-10 Series Foxboro transmitters which could adversely affect their operation during
DBA conditions. According to Foxboro, the Teflon insulation material in question had
demonstrated a tendency to embrittle and deteriorate when subjected to an integrated radiation
dose of 200 megarads. A total integrated dose of 200 megarads was called for in the
qualification test sponsored by the Utility Transmitter Qualification Group which led to Foxboros
discovery of the Teflon insulation qualification deficiency.
3 The text of this document is available in the legacy library portion of ADAMS.
4 The text of this document is available in the legacy library portion of ADAMS.
DISCUSSION
Although previous industry efforts have addressed the replacement of Teflon material for
equipment that are relied upon to remain functional during and following design basis events, Teflon seals and insulation may remain in use as recently identified at FCS. General Design
Criteria require among other things that reactor containment penetrations, regardless of their
electrical classification, be designed so that the containment structure and its internal
compartments can accommodate, without exceeding the design leakage rate and with sufficient
margin, the calculated pressure and temperature conditions resulting from any loss-of-coolant
accident. In other words, the non-Class 1E electrical penetration seals have a pressure- boundary safety-related function for maintaining containment integrity. Therefore, they must be
able to accommodate the effects of, and to be compatible with, the environmental conditions
associated with normal operation, maintenance, testing, and postulated accidents, including
loss-of-coolant accidents as required by the General Design Criteria. Similarly, safety related
mechanical equipment such as pump seals and valve seats must maintain their integrity under
accident conditions as required by the General Design Criteria.
With respect to maintaining containment integrity, all containment electrical penetrations should
be designated safety-related, designed to American Society of Mechanical Engineers (ASME)
Section III, seismic category 1, and should be Type B tested under 10 CFR Part 50 Appendix J,
Primary reactor containment leakage testing for water-cooled power reactors.
In addition, specific requirements pertaining to qualification of certain electric equipment
important to safety are contained in § 50.49, "Environmental Qualification of Electric Equipment
Important to Safety for Nuclear Power Plants," of 10 CFR Part 50. Section 50.49 requires that
three categories of electric equipment important to safety be qualified for their application and
specified performance and provides requirements for establishing environmental qualification
methods and qualification parameters. These three categories are (1) safety-related electric
equipment (Class lE), (2) non-safety-related electric equipment (non-Class lE) whose failure
under postulated environmental conditions could prevent satisfactory accomplishment of safety
functions by safety-related equipment, and (3) certain post-accident monitoring equipment. This
equipment is relied upon to remain functional during and following design basis events to
ensure the integrity of the reactor coolant pressure boundary; the capability to shut down the
reactor and maintain it in a safe shutdown condition; or the capability to prevent or mitigate the
consequences of accidents that could result in potential offsite exposures comparable to the
guidelines in § 50.34(a)(1), § 50.67(b)(2), or § 100.11.
In accordance with paragraph 50.49(k), applicants for and holders of operating licenses are not
required to requalify electric equipment important to safety (replacement equipment excepted) in
accordance with the provisions of this section if the NRC has previously required qualification of
that equipment in accordance with "Guidelines for Evaluating Environmental Qualification of
Class IE Electrical Equipment in Operating Reactors" (DOR Guidelines), or NUREG-0588,
"Interim Staff Position on Environmental Qualification of Safety-Related Electrical Equipment."
These applicants and licensees may continue to use the criteria in these documents for
qualifying electric equipment important to safety in the affected plants, with the exception of
replacement equipment. The following documents contain additional related information and guidance.
A.
Electrical Power Research Institute, Guidance for Accident Function Assessment for
[Risk-Informed Safety Class] RISC-3 Applications, Final Report 1009748, October 2005, Palo Alto, CA (ADAMS Accession No. ML12041A226). (Note: This
EPRI document has not been endorsed by the NRC.) This document specifically
discusses exclusion of Teflon from components in elevated radiation environments.
B.
Westinghouse Electric Company, AP1000 Design Control Document, Rev. 19, Tier 2 Chapter 3, Appendix 3D, Methodology for Qualifying AP1000 Safety-Related
Electrical and Mechanical Equipment (ADAMS Accession No. ML11171A437)
addresses new reactors. In Attachment C, Effects of Gamma Radiation Doses
Below 1E4 Rads on the Mechanical Properties of Materials, beginning on page
3D-87, this document summarizes the available information about the effects of
gamma radiation on the material mechanical properties of Teflon and indicates that
it is susceptible to alteration at a gamma dose of less than 105 rads.
C.
ASME QME-1-2007, Qualification of Active Mechanical Equipment Used in Nuclear
Facilities, as endorsed by Regulatory Guide 1.100, Revision 3, Seismic
Qualification Of Electrical And Active Mechanical Equipment And Functional
Qualification Of Active Mechanical Equipment For Nuclear Power Plants, provides
guidance for the qualification of nonmetallic parts used in nuclear safety-related
active mechanical equipment that can be used for new reactor design and
construction.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to one of the technical contacts listed below or to the appropriate Office of Nuclear
Reactor Regulation (NRR) or Office of New Reactors (NRO) project manager.
/RA/
/RA/
Michael C. Cheok, Director
Lawrence E. Kokajko, Director
Division of Construction Inspection
Division of Policy and Rulemaking
and Operational Programs
Office of Nuclear Reactor Regulation (NRR)
Office of New Reactors (NRO)
Technical Contacts: Joseph Sebrosky, NRR
Swagata Som, NRR
301-415-1132
301-415-8491 E-mail: Joseph.Sebrosky@nrc.gov
E-mail: Swagata.Som@nrc.gov
301-415-1081 E-mail: Andrea.George@nrc.gov
Note: NRC generic communications can be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
ML12041A226). (Note: This
EPRI document has not been endorsed by the NRC.) This document specifically
discusses exclusion of Teflon from components in elevated radiation environments.
B. Westinghouse Electric Company, AP1000 Design Control Document, Rev. 19, Tier 2 Chapter 3, Appendix 3D, Methodology for Qualifying AP1000 Safety-Related
Electrical and Mechanical Equipment (ADAMS Accession No. ML11171A437)
addresses new reactors. In Attachment C, Effects of Gamma Radiation Doses
Below 1E4 Rads on the Mechanical Properties of Materials, beginning on page
3D-87, this document summarizes the available information about the effects of
gamma radiation on the material mechanical properties of Teflon and indicates that
it is susceptible to alteration at a gamma dose of less than 105 rads.
C. ASME QME-1-2007, Qualification of Active Mechanical Equipment Used in Nuclear
Facilities, as endorsed by Regulatory Guide 1.100, Revision 3, Seismic
Qualification Of Electrical And Active Mechanical Equipment And Functional
Qualification Of Active Mechanical Equipment For Nuclear Power Plants, provides
guidance for the qualification of nonmetallic parts used in nuclear safety-related
active mechanical equipment that can be used for new reactor design and
construction.
CONTACT
This IN requires no specific action or written response. Please direct any questions about this
matter to one of the technical contacts listed below or to the appropriate Office of Nuclear
Reactor Regulation (NRR) or Office of New Reactors (NRO) project manager.
/RA/
/RA/
Michael C. Cheok, Director
Lawrence E. Kokajko, Director
Division of Construction Inspection
Division of Policy and Rulemaking
and Operational Programs
Office of Nuclear Reactor Regulation (NRR)
Office of New Reactors (NRO)
Technical Contacts: Joseph Sebrosky, NRR
Swagata Som, NRR
301-415-1132
301-415-8491 E-mail: Joseph.Sebrosky@nrc.gov
E-mail: Swagata.Som@nrc.gov
301-415-1081 E-mail: Andrea.George@nrc.gov
Note: NRC generic communications can be found on the NRC public Web site, http://www.nrc.gov, under NRC Library.
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