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 POSTACCIDENT 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. 

ML043280614
IN 2004-21

Page 2 of 3

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 DavisBesse 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.
IN 2004-21

Page 3 of 3

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 NRC’s 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
______________________________________________________________________________________

OL = Operating License

CP = Construction Permit

IN 2004-21

Page 1 of 1

LIST OF RECENTLY ISSUED

NRC INFORMATION NOTICES

____________________________________________________________________________________

Information Date of 

Notice No. Subject Issuance Issued to

____________________________________________________________________________________

2004-20 Recent Issues Associated with

NRC Medical Requirements for

Licensed Operators

11/24/2004 All holders of operating licenses for

nuclear power reactors and 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

Back-up Power Supplies to

Emergency Response

Facilities and Equipment

11/04/2004 All holders of operating licenses for

nuclear power reactors, except those

who have permanently ceased

operations and have certified that

fuel has been permanently removed

from the reactor vessel.

2004-18 Recent Safety-related Event at

Panoramic Wet-source-storage

Irradiator

10/26/2004 All licensees authorized to possess

and use sealed sources in

panoramic wet-source-storage

irradiators, and irradiator vendors.

2004-17 Loose Part Detection and 

Computerized Eddy Current

Data Analysis in Steam

Generators

08/25/2004 All holders of operating licenses for

pressurized-water reactors (PWRs),

except those who have permanently

ceased operations and have certified

that fuel has been permanently

removed from the reactor.

2004-16 Tube Leakage Due to a

Fabrication Flaw in a

Replacement Steam Generator

08/03/2004 All holders of operating licenses for

pressurized-water reactors (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