Information Notice 2004-21, Additional Adverse Effect of Boric Acid Leakage: Potential Impact on Post-Accident Coolant Ph
| ML043280614 | |
| Person / Time | |
|---|---|
| Issue date: | 11/24/2004 |
| From: | Hiland P NRC/NRR/DIPM/IROB |
| To: | |
| Hodge, CV, NRR/DIPM/IROB, 415-1861 | |
| References | |
| IN-04-021 | |
| Download: ML043280614 (7) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 November 24, 2004 NRC INFORMATION NOTICE 2004-21: ADDITIONAL ADVERSE EFFECT OF BORIC
ACID LEAKAGE: POTENTIAL IMPACT ON POST-
ACCIDENT COOLANT pH
ADDRESSEES
All holders of operating licenses or construction permits for pressurized water reactors (PWRs),
except those who have ceased operations and have certified that fuel has been permanently
removed from the reactor vessel.
PURPOSE
The U.S. Nuclear Regulatory Commission (NRC) is issuing this information notice (IN) to inform
addressees of potential adverse effects of boric acid leakage that may not have been previously
considered and to reemphasize concerns regarding boric acid accumulations on reactor plant
equipment inside containment. The primary concern regarding boric acid leakage is corrosion
of ferritic steel components. However, if boric acid deposits of sufficient magnitude are present
in containment, dissolution of these deposits may also affect the pH of the reactor coolant in the
containment sump. The NRC anticipates that recipients will review the information for
applicability to their facilities and consider appropriate actions. However, suggestions contained
in this IN do not constitute NRC requirements; therefore, no specific action or written response
is required.
DESCRIPTION OF CIRCUMSTANCES
During refueling outages throughout the 1990s, personnel at the Davis-Besse nuclear power
plant performed visual inspections of the reactor pressure vessel (RPV) head surface that was
accessible through the service structure weep holes. Visual inspections performed below the
RPV head insulation found some accumulation of boric acid deposits on the RPV head. The
boric acid buildup was due to leaking control rod drive mechanism flanges and reactor coolant
pressure boundary leakage. Many areas of the RPV head were not visible because of
persistent boric acid deposits that the licensee did not clean. In addition to the significant
buildup of boric acid on the reactor pressure vessel head, a substantial amount of boric acid
built up inside the containment at Davis-Besse.
After a loss-of-coolant accident (LOCA) at a pressurized water reactor, chemical agents would
be used to ensure that the reactor coolant pH is kept neutral or slightly basic. At the Davis- Besse plant, trisodium phosphate (TSP) is used. The TSP is kept in designated storage
baskets in the containment building. However, large deposits of boric acid in containment may
adversely affect the pH of the reactor coolant in the containment sump.
DISCUSSION
Boric acid deposits can occur inside a pressurized water reactor containment as a result of
reactor coolant system leakage. The deposits typically accumulate at any point where moisture
condenses inside containment (e.g., cooling water pipes, ventilation systems, containment liner
surfaces). If these deposits are not promptly identified and routinely removed, they could
accumulate and impact the sump pH. Therefore, it is important to have procedures and
programs to routinely identify and remove boric acid deposits.
After a LOCA, the iodine released from the damaged core is removed from the containment
atmosphere by spraying borated water accumulated in the containment sump. To keep iodine
in solution, the pH of the sump water should be at least 7. Maintaining a pH of 7 or slightly
greater is also necessary to minimize chloride stress corrosion cracking in austenitic stainless
steel components exposed to the sump water. The amount of TSP depends on how much
boric acid from all sources has accumulated in the containment. Failure to control and remove
accumulations of boric acid deposits inside containment may challenge whether the reactor
coolant in the containment sump is chemically neutral or slightly basic.
Boron concentration in the reactor coolant and the impact on containment sump pH are
discussed in NRC Bulletin 77-04, ?Calculational Error Affecting the Design Performance of a
System for Controlling pH of Containment Sump Following a LOCA, available at ADAMS
Accession No. ML031200570 and on the NRC Web site at
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/bulletins/1977/bl77004.html.
During recent years, the nuclear power industry has become more sensitive to leakage of
borated water from the reactor coolant system or auxiliary systems. The NRC issued several
generic communications to inform the industry of the serious consequences of such leakage
and took other actions to ensure that such leakage is addressed if and when it occurs. Several
actions to address boric acid leakage are described in Attachment 1 of Regulatory Issue
Summary (RIS) 2003-13, NRC Review of Responses to Bulletin 2002-01, <Reactor Pressure
Vessel Head Degradation and Reactor Coolant Pressure Boundary Integrity. This RIS is
available at ADAMS Accession No. ML032100653 and the NRC Web site at
http://www.nrc.gov/reading-rm/doc-collections/gen-comm/reg-issues/2003/ri200313.pdf.
CONTACT
This information notice requires no specific action or written response. If you have any
questions about the information in this notice, please contact one of the technical contacts
listed below or the appropriate project manager from the NRCs Office of Nuclear Reactor
Regulation (NRR).
/RA/
Patrick L. Hiland, Chief
Reactor Operations Branch
Division of Inspection Program Management
Office of Nuclear Reactor Regulation
Technical Contacts: K. Parczewski, NRR C. Vernon Hodge, NRR
301-415-2705 301-415-1861 E-mail: kip@nrc.gov E-mail: cvh@nrc.gov
Attachment: List of Recently Issued NRC Information Notices
ML043280614 DOCUMENT NAME: G:\DIPM\OES\Staff Folders\Hodge\vern cmt IN TSP3-25.wpd
OFFICE OES:IROB:DIPM TECH EDITOR EMCB EMCB C:EMCB:DE
NAME CVHodge PKleene KIParczewski ALLund WHBateman
DATE 11/09/2004 11/09/2004 11/09/2004 11/09/2004 11/10/2004 OFFICE RIII LD3:DLPM DLPM A:SC:IROB:DIPM C:IROB:DIPM
NAME JAGrobe JAHopkins ACMcMurtray THBoyce PLHiland
DATE 11/02/2004 11/17/2004 11/16/2004 11/23/04 / /2004
Attachment LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2004-20 Recent Issues Associated with 11/24/2004 All holders of operating licenses
NRC Medical Requirements for for nuclear power reactors and
Licensed Operators research and test reactors, except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2004-19 Problems Associated with 11/04/2004 All holders of operating licenses
Back-up Power Supplies to for nuclear power reactors, Emergency Response except those who have
Facilities and Equipment permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor vessel.
2004-18 Recent Safety-related Event at 10/26/2004 All licensees authorized to
Panoramic Wet-source- possess and use sealed sources
storage Irradiator in panoramic wet-source-storage
irradiators, and irradiator vendors.
2004-17 Loose Part Detection and 08/25/2004 All holders of operating licenses
Computerized Eddy Current for pressurized-water reactors
Data Analysis in Steam (PWRs), except those who have
Generators permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2004-16 Tube Leakage Due to a 08/03/2004 All holders of operating licenses
Fabrication Flaw in a for pressurized-water reactors
Replacement Steam Generator (PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
Note: NRC generic communications may be received in electronic format shortly after they are
issued by subscribing to the NRC listserver as follows:
To subscribe send an e-mail to <listproc@nrc.gov >, no subject, and the following
command in the message portion:
subscribe gc-nrr firstname lastname
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit