Information Notice 2002-15, Hydrogen Combustion Events in Foreign BWR Piping
| ML020980466 | |
| Person / Time | |
|---|---|
| Issue date: | 04/12/2002 |
| From: | Beckner W NRC/NRR/DRIP/RORP |
| To: | |
| Dozier J, NRR/RORP 415-1014 | |
| References | |
| TAC MB4660 IN-02-015 | |
| Download: ML020980466 (10) | |
UNITED STATES
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, DC 20555-0001 April 12, 2002 NRC INFORMATION NOTICE 2002-15: HYDROGEN COMBUSTION EVENTS IN
FOREIGN 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 information notice to inform
addressees about two recent hydrogen combustion events in piping at foreign boiling water
reactors (BWRs). These BWRs were not of domestic (U.S.) manufacture; however, the
affected systems where the hydrogen combustions occurred are similar to those in some
domestic BWRs. The events were publicly reported in the respective countries news media.
No injuries to personnel or radioactive releases to the environment were reported.
It is expected that 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
The first foreign event occurred on November 7, 2001, while the BWR/4-type unit was operating
at rated power. The utility was performing a periodic surveillance of the high pressure coolant
injection (HPCI) system. Immediately after the test began, the HPCI system automatically
isolated and the reactor building fire detectors actuated. The unit was then manually shut
down. An examination of the residual heat removal (RHR) system revealed that a pipe elbow
had ruptured near the high point in the RHR branch steam supply line leading to one of the two
RHR heat exchangers (steam condensing mode line), in the reactor building as shown in
Figure 1. Fragments from the piping rupture caused some damage to equipment in the
general area, but no significant damage to any safety-related equipment. The subject line
supplies steam to the RHR heat exchanger when the heat exchanger is operated in the steam
condensing mode. The utility had modified the RHR piping by adding a water barrier upstream
of the RHR steam supply isolation valve in order to reduce leakage through this valve.
The utility initially reported the pipe rupture as a water hammer event; however, subsequent
investigation has led the utility to re-characterize the rupture as a combustion event. This re- characterization was based in part on an analysis of gases in the sister BWR unit at the same
RHR piping location. This analysis found the hydrogen levels to be 46 percent by volume
(percent vol), 23 percent vol oxygen, and 31 percent vol steam. A metallurgical analysis of the
resulting piping fragments indicated ductile fracture from excessive internal over-pressure.
The second foreign event occurred on December 14, 2001, while the unit was operating at 100-
percent power. The utility interpreted a containment pressure increase, concurrent with an
acoustic monitoring response, as a flange leak in the reactor head spray line. The utility uses
the reactor head spray after shutdown to shorten outages (see Figure 2). The utility isolated
the drain-and-keep-fill line valve for the reactor head spray, which appeared to stop the leak.
The utility notified its regulatory authority, but did not shut down the unit until February 21, 2002, when the regulatory authority performed an inspection to determine the cause of the
containment pressure increase. The inspection found that 2 to 3 meters (6.25 to 10 feet) in
length of the 10-centimeter (about 4-inches) diameter head spray line had been destroyed;
however, the effects of the ruptured piping were not reported to have caused any significant
damage to any nearby safety-related equipment. Although the root cause of the pipe rupture
has not yet been established, the utility is investigating the possibility of a hydrogen combustion
event inside the pipe as a result of the buildup of hydrogen and oxygen gases created by
radiolysis.
Discussion
Radiolysis occurs normally in the reactor core region when radiation decomposes some reactor
coolant system (RCS) water into hydrogen and oxygen. Excess hydrogen and oxygen that
does not recombine into water is normally removed by the off-gas system. Hydrogen is added
in those BWRs utilizing hydrogen for reactor water chemistry control in order to scavenge
In these two foreign events, it appears that hydrogen and oxygen gases accumulated in system
high points instead of being removed by the plants off-gas system. Further, since the ignition
energy for the above combustion events is predicted to be extremely small, the ignition
source(s) may not be conclusively identified.
These events show the importance of preventing combustible gas mixtures from accumulating
in piping. In both of the above described events, hydrogen and oxygen gases apparently
accumulated to a combustible level which then catastrophically failed these piping systems.
Proper venting or other considerations to prevent accumulation of combustible gases in piping
high points might alleviate conditions leading to hydrogen combustion.
Related Generic Communications
The following NRC generic communications describe related reactor operating experience:
- Information Notice (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," October 4, 1990 * Generic Letter (GL) 93-06, Research Results on Generic Safety Issue 106, Piping
and the Use of Highly Combustible Gases in Vital Areas," October 25, 1993
- IE Bulletin No. 78-03, "Potential Explosive Gas Mixture Accumulations Associated
With BWR Offgas System Operations," 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 NRCs 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: C. E. Carpenter, NRR Jerry Dozier, NRR
(301) 415-2169 (301) 415-1014 E-mail: cec@nrc.gov E-mail: jxd@nrc.gov
(301) 415-6764 E-mail: cem3@nrc.gov
Attachments:
1. Figures 1 and 2
2. List of Recently Issued NRC Information Notices
ML020980466 DOCUMENT NAME: G:\REXB\DOZIER\H&BIN1.WPD Template: NRR-052 OFFICE RSE:RORP:DRIP Tech Editor ME:EMCB:DE BC:EMCB:DE
NAME IJDozier PKleene* CECarpenter* WHBateman*
DATE 04/05/2002 04/05 /2002 04/08/2002 04/11/2002 OFFICE BC:EMCB:DE (A)SC:RORP:DRIP PD:RORP:DRIP BC:MEB:RES
NAME JWermiel* CDPetrone WDBeckner NCChokshi
DATE 04/09/2002 04/10/2002 04/12/2002 04/12/2002
Attachment 1 Figure 1. High Pressure Coolant Injection System and Residual Heat
Removal System Branch Line
Figure 2. Head Spray System
Attachment 2 LIST OF RECENTLY ISSUED
NRC INFORMATION NOTICES
_____________________________________________________________________________________
Information Date of
Notice No. Subject Issuance Issued to
_____________________________________________________________________________________
2002-14 Ensuring a Capability to 04/08/2002 All holders of operating licenses
Evacuate Individuals, Including for nuclear power reactors, Members of the Public, From including those who have ceased
the Owner-Controlled Area operations but have fuel on site.
2002-13 Possible Indicators of Ongoing 04/04/2002 All holders of operating licenses
Reactor Pressure Vessel Head for pressurized water nuclear
Degradation power reactors, except those who
have permanently ceased
operations and certified that fuel
has been permanently removed
from the reactor.
99-28, Supp 1 Recall of Star Brand Fire 03/22/2002 All holders of licenses for nuclear
Protection Sprinkler Heads power, research, and test
reactors and fuel cycle facilities.
2002-12 Submerged Safety-Related 03/21/2002 All holders of operating licenses
Electrical Cables or construction permits for
nuclear power reactors
2002-11 Recent Experience with 03/12/2002 All holders of operating licenses
Degradation of Reactor for pressurized-water reactors
Pressure Vessel Head (PWRs), except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-10 Nonconservative Water Level 03/07/2002 All holders of operating licenses
Setpoints on Steam for nuclear power reactors, Generators except those who have
permanently ceased operations
and have certified that fuel has
been permanently removed from
the reactor.
2002-09 Potential for Top Nozzle 02/13/2002 All holders of operating licenses
Separation and Dropping of for nuclear power reactors, and
Certain Type of Westinghouse non-power reactors and holders
Fuel Assembly of licenses for permanently
shutdown facilities with fuel
onsite.
______________________________________________________________________________________
OL = Operating License
CP = Construction Permit