Information Notice 2005-24, Nonconservatism in Leakage Detection Sensitivity
| ML051780073 | |
| Person / Time | |
|---|---|
| Site: | Catawba, Callaway, McGuire  |
| Issue date: | 08/03/2005 |
| From: | Hiland P NRC/NRR/DIPM/IROB |
| To: | |
| Hodge, CV, NRR/DIPM/IROB, 415-1861 | |
| References | |
| TAC M50628 IN-05-024 | |
| Download: ML051780073 (4) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
August 3, 2005 NRC INFORMATION NOTICE 2005-24:
NONCONSERVATISM IN LEAKAGE DETECTION
SENSITIVITY
ADDRESSEES
All holders of operating license or construction permits for nuclear power reactors, except those
that have permanently ceased operations and have certified that fuel has been permanently
removed from the reactor.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees that the reactor coolant activity assumptions for containment radiation gas channel
monitors may be nonconservative. As a result, the containment gas channel may not be able to
detect a 1 gallon-per-minute (1-gpm) leak within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. It is expected that the 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 are not NRC
requirements; therefore, no specific action or written response is required.
DESCRIPTION OF CIRCUMSTANCES
Several nuclear power plant licensees have reported problems with the detection capabilities of
containment radiation gas channel monitors. The following gives several examples of these
reports.
On May 2, 2005, the McGuire nuclear power plant licensee reported that the containment
atmosphere radioactivity monitors were not sensitive enough for their intended function of
detecting a 1-gpm reactor coolant system (RCS) leak within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> (Licensee Event Report
(LER) 50-369/2005-01, ADAMS Accession No. ML051310167). This resulted in a Severity
Level IV noncited violation.
The McGuire licensee declared the atmosphere monitors inoperable and performed
compensatory actions in accordance with plant technical specifications. The compensating
actions were to (1) establish temporary alarm setpoints to provide earlier notification should a
significant RCS leak occur, (2) instruct operators on other methods of RCS leak detection, (3)
establish sensitivities as low as practical based on actual RCS radioactivity levels, (4)
periodically review the sensitivities for revision as needed, (5) provide additional training as
needed, and (6) consider submitting a license amendment request to clarify the capabilities of
the leak detection instrumentation.
In February 2005, NRC inspectors at the Catawba nuclear power plant identified a noncited
violation of Technical Specification 5.4.1.a, Written Procedures, because the licensee failed to
establish and maintain an adequate procedure for the required containment atmosphere
radioactivity monitor surveillance in that the associated alarm function was not set or tested to
alarm at a value equivalent to 1 gpm in 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> for a realistic current reactor coolant activity level
(NRC Integrated Inspection Report 50-413/2005-02 and 50-414/2005-02, ADAMS Accession
No. ML051160367).
The Catawba licensee also declared these channels to be inoperable and is performing
compensatory actions in accordance with plant technical specifications.
In June 2003, an NRC inspection made a similar finding at Callaway (NRC Inspection
Report 50-483/2003-04, ADAMS Accession No. ML032020562) that resulted in a noncited
violation. The gas channel monitor was not capable of performing its design basis function of
detecting a 1 gpm RCS leak within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The calculation for the gas channel monitor
response used an RCS source term corresponding to an assumed 0.1 percent failed fuel but, because of improved fuel performance and RCS chemistry control, the plant operated with an
RCS source term several orders of magnitude smaller.
The Callaway licensee responded to this situation similarly by (1) declaring the gas channel out
of service to prevent its being credited for leakage detection and (2) considering a license
amendment request to revise the final safety analysis report and technical specification bases
to reflect actual leakage detection capabilities.
DISCUSSION
The NRC requires licensees to use a means of detecting and, to the extent practical, identifying
the location of any sources of RCS leakage (Title 10 of the Code of Federal Regulations, Part 50, Appendix A, General Design Criteria [GDC] for Nuclear Power Plants, Criterion 30,
Quality of Reactor Coolant Pressure Boundary). The NRC provided guidance on meeting
GDC 30 in Regulatory Guide (RG) 1.45, Reactor Coolant Pressure Boundary Leakage
Detection Systems. Some licensees committed to using RG 1.45 as the basis for meeting
RG 1.45 states that an acceptable means would provide for adequate sensitivity and response
time of all leakage detection systems to detect a leakage rate of 1 gpm in less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />.
Further, the acceptable means would employ at least three separate detection methods. Two
of these methods are monitoring sump level and sump flow and monitoring airborne particulate
radioactivity. The third method is either monitoring the condensate flow rate from air coolers or
monitoring airborne gaseous radioactivity. The guide also states that a realistic primary
radioactivity concentration should be assumed when analyzing the sensitivity of leak detection
systems.
During original plant licensing, the typical calculation for the technical specification for gas
channel monitor response used an RCS source term corresponding to an assumed 0.1 percent
failed fuel. Nowadays, because of improvements in fuel performance and RCS chemistry
control, the actual RCS source term can be orders of magnitude smaller. Though desirable, a small source term can result in reduced leakage monitoring capabilities. Using a realistic RCS
source term, a 1 gpm RCS leak would likely not be detected by a gas channel monitor for a
much greater time than within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />. The 0.1-percent failed fuel assumption introduces a
nonconservatism into the technical specifications. Guidance on resolving such a
nonconservatism is given in NRC Administrative Letter 98-10, Dispositioning of Technical
Specifications That Are Insufficient to Assure Plant Safety.
The consistency of leakage detection systems with RG 1.45 has been questioned at several
nuclear power plants. See NUREG/CR-6861, Barrier Integrity Research Program, December
2004 (ADAMS Accession No. ML043580207) for a good discussion of detector sensitivities.
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contact(s) listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/ By David C. Trimble Acting For/
Patrick L. Hiland, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts:
Michael Peck, RIV
Vernon Hodge, NRR
573-676-3181
301-415-1861 E-mail: msp@nrc.gov
E-mail: cvh@nrc.gov
Note: NRC generic communications may be found on the NRC public Website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
ML043580207) for a good discussion of detector sensitivities.
This information notice requires no specific action or written response. Please direct any
questions about this matter to the technical contact(s) listed below or the appropriate Office of
Nuclear Reactor Regulation (NRR) project manager.
/RA/ By David C. Trimble Acting For/
Patrick L. Hiland, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts:
Michael Peck, RIV
Vernon Hodge, NRR
573-676-3181
301-415-1861 E-mail: msp@nrc.gov
E-mail: cvh@nrc.gov
Note: NRC generic communications may be found on the NRC public Website, http://www.nrc.gov, under Electronic Reading Room/Document Collections.
DISTRIBUTION:
IN File
ADAMS ACCESSION NUMBER: ML051780073 OFFICE EMEB:DE
Tech Editor
BC:EMCB
BC:SPLB
PM:DLPM
NAME
CVHodge
(VH for Paul Kleene)
WHBateman
JNHannon
JNDonohew
DATE
07/12/2005
06/27/2005
07/30/2005
07/12/2005
07/28/2005 OFFICE PM:DLPM
TL:OES:IROB:DIPM
SC:OESIROB:DIPM
C:IROB:DIPM
NAME
SEPeters
IJung
MJRoss-Lee
PLHiland
(DTrimble for)
DATE
08/01/2005
08/01/2005
08/02/2005
08/03/2005