UNITED STATES

NUCLEAR REGULATORY COMMISSION

OFFICE OF NUCLEAR REACTOR REGULATION

WASHINGTON, DC 20555-0001

May 6, 2003

NRC INFORMATION NOTICE 2002-15, SUPPLEMENT 1: POTENTIAL HYDROGEN

COMBUSTION EVENTS IN BWR

PIPING

Addressees

All holders of operating licenses for light water reactors, except those who 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 supplement to inform

addressees about the status of the followup actions taken by the staff and the Boiling Water

Reactor Owners Group (BWROG) after the issuance of Information Notice (IN) 2002-15 on

April 12, 2002. The original information notice discussed hydrogen combustion events in piping

at foreign boiling water reactors (BWRs). 

The NRC expects recipients to review the information for applicability to their facilities and

consider actions, as appropriate, to avoid similar problems. However, suggestions contained in

this IN are not NRC requirements; therefore, the NRC requires no specific action or written

response .

Background

The NRC issued IN 2002-15, “Hydrogen Combustion Events in Foreign BWR Piping,” on 

April 12, 2002, to inform addressees about the hydrogen combustion events at two foreign

BWRs. The NRC requested that recipients review the information and consider actions, as

appropriate, to avoid similar problems in U.S. plants. At a BWROG/NRC senior management

meeting on July 25, 2002, the NRC staff asked the BWROG to submit a written report about the

group’s followup activities in response to the foreign events. The BWROG submitted the

information to the staff in a letter dated December 20, 2002 (ADAMS Accession No.

ML023610269).

Description of Circumstances

In response to the foreign hydrogen combustion events, General Electric (GE) convened a task

force. The BWROG participated in the GE task force to study the events. The task force

concluded that although the probability of similar events in U.S. BWRs is small, such events

cannot be completely precluded. GE issued GE Service Information Letter (SIL) No. 643,

“Potential for Radiolytic Gas Detonation,” dated June 14, 2002, to all BWR licensees

recommending that piping systems (primary and secondary ) susceptible to accumulation of

noncondensable gases be reviewed and actions taken where necessary to avoid the problem. 

ML031210054
IN 2002-15, Sup 1

Page 2 of 3

Based on its review of GE SIL No. 643, the BWROG concluded that piping configurations and

conditions conducive to radiolytic gas accumulation are expected to be rare, and therefore the

likelihood of hydrogen combustion events in U.S. BWRs is small. However, the possibility could

not be ruled out, particularly in the case of degraded performance that may not be immediately

recognizable. Very unusual combinations of geometry and plant material condition are required

for radiolytic gas to accumulate, but should the gas accumulate, there is a potential for

detonation, resulting in piping failure. 

Consequently, the BWROG formed a Hydrogen Accumulation Committee to develop detailed

guidance for U.S. BWR utilities on identifying, disposing of, and mitigating potential radiolytic

hydrogen and oxygen in plant piping and equipment. The committee did the following:

1. Identified the most significant generic plant equipment that could be subject to rapid

hydrogen accumulation.

2. Surveyed BWR licensee members about plant areas with the greatest potential for

hydrogen/oxygen accumulation and about actions taken to address this configuration.

3. Reviewed the recommendations of Generic Letter (GL) 91-18, “Information to Licensees

Regarding NRC Inspection Manual Section on Resolution of Degraded and

Nonconforming Conditions,” to ensure that operability with hydrogen accumulation is

properly addressed.

4. Developed a guidance document, “BWR Piping and Component Susceptibility to

Hydrogen Detonation,” which provides detailed guidance on identifying equipment subject

to hydrogen accumulation and potential rupture. This document also identifies short-term

and long-term mitigation strategies for such equipment.

At the February 2003 BWROG/NRC senior management meeting, the BWROG said it will

provide a final summary report to the NRC later in 2003 to document the results of the

implementation of the BWROG guidance on this issue.

Conclusion

This IN provides a summary of the actions taken by the BWROG and NRC in response to the 

hydrogen combustion events in foreign BWRs initially described in IN 2002-15. The NRC staff

is continuing to monitor the BWROG activities related to hydrogen accumulation.

Related Generic Communications

The following documents describe reactor operating experience with gas intrusion and

combustion events:

• IN 88-23, “Potential for Gas Binding of High-Pressure Safety Injection Pumps,” with five

supplements, the latest dated April 23, 1999.

• IN 90-64, “Potential for Common-Mode Failure of High Pressure Safety Injection

Pumps,” dated October 4, 1990.
IN 2002-15, Sup 1

Page 3 of 3

• GL 93-06, “Research Results on Generic Safety Issue 106, ‘Piping and the Use of

Highly Combustible Gases in Vital Areas,’” dated October 25, 1993.

• IE Bulletin No. 78-03, “Potential Explosive Gas Mixture Accumulations Associated With

BWR Offgas System Operations,” dated February 8, 1978.

This information notice does not require any 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 in the NRC’s Office of Nuclear Reactor

Regulation (NRR).

/RA/

William D. Beckner, Program Director

Operating Reactor Improvements Program

Division of Regulatory Improvement Programs

Office of Nuclear Reactor Regulation

Technical contacts: George Thomas, NRR Jerry Dozier, NRR

(301) 415-1814 (301) 415-1014

E-mail: gxt@nrc.gov E-mail: jxd@nrc.gov

Attachment: List of Recently Issued NRC Information Notices