Information Notice No. 87-20: Hydrogen Leak in Auxiliary Building
SSINS No.: 6835
NUCLEAR REGULATORY COMMISSION
OFFICE OF NUCLEAR REACTOR REGULATION
WASHINGTON, D.C. 20555
April 20, 1987
Information Notice No. 87-20: HYDROGEN LEAK IN AUXILIARY BUILDING
All nuclear power reactor facilities holding an operating license or a
This notice is to alert addressees of the potential for a hydrogen leak in
portions of the plant where the potential for the leak may not have been
adequately, considered. Recipients are expected to review the information for
applicability to their facilities and consider actions, if appropriate, to
preclude similar problems occurring at their facilities. However, suggestions
contained in this information notice do not constitute NRC requirements;
therefore, no specific action or written response is required.
Description of Circumstances:
On February, 20, 1987, the Vogtle nuclear power plant reported a hydrogen leak
inside the auxiliary building. This plant was recently licensed, had never
been critical, and was in cold shutdown at the time of the event.
The discovery of this problem was as a result of an unassociated event
involving the activation of a chlorine monitor in the control building. When
additional samples indicated no chlorine gas, the shift supervisor ordered
further investigation into other plant areas. Because there was no installed
detection equipment, portable survey instruments were used to determine
gaseous mixtures. Hydrogen was detected in the auxiliary building and percent
of the lower flammability limit (LFL) for hydrogen. A level of about
30percent of LFL corresponds to about 1.2 percent hydrogen by volume. This
reading was erroneously reported to the control room as 20 to 30 percent
hydrogen by volume. The on-shift supervisor declared an unusual event (UE)
with a subsequent report to the NRC via the emergency notification system
When hydrogen was discovered in the auxiliary building, the licensee isolated
the cryogenic hydrogen skid outside the turbine building and soon located the
source of the leak as packing on a globe valve in a small line to the volume
control tank (VCT). The licensee opened doors that quickly caused the
hydrogen to dissipate. The globe valve was of a conventional design and had
no special packing. The globe valve was located in a vertical pipe chase
April 20, 1987
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ventilation was present because of ongoing HVAC testing. Besides being used
as a cover gas in the VCT, hydrogen from the skid also is used in the plants
waste gas system and to cool the generator.
The lessons of this event fall into five categories: (1) proper in-plant
communications during events, (2) proper valve application for use with
hydrogen, (3) excess flow check valve set point, (4) heating ventilation and
air conditioning (HVAC) maintenance and flow testing, and (5) hydrogen line
routing. The licensee is examining ways to improve communications in the plant
during events and the training of personnel in reading portable instruments.
As another corrective measure, the licensee is examining the use of other
types of valves, such as valves with a diaphragm or bellows rather than
conventional stem packing, in lines containing hydrogen.
The licensee also is examining the set point for the excess flow check valves
the hydrogen lines. These check valves are designed to limit the flow of
hydrogen in the event of a large leak so that when combined with proper
ventilation in rooms with hydrogen lines, hydrogen levels would remain within
specified limits throughout the plant.
This plant had HVAC flow balancing problems during the preparation for plant
startup. Generally HVAC flow balance is based on the heat loads and the
resultant room temperatures under normal and accident conditions. However,
this event demonstrates that hydrogen concentrations also may need to be
considered to set a lower limit on the ventilation in rooms that contain
Although this licensee has reexamined the routing of hydrogen lines throughout
the auxiliary building and found no problems, licensees with older plants may
not have examined this question in detail.
The NRC staff is currently reviewing an EPRI/BWROG topical report titled
"Guidelines for Permanent BWR Hydrogen Water Chemistry Installation," 1987
revision. Included in this document are guidelines for design, operation,
maintenance, surveillance, and testing of hydrogen supply systems.
Other Recent Reactor Events Involving Hydrogen
On March 3, 1987 an unusual event was reported at Waterford Unit 3 plant.
While unloading hydrogen from a truck into the storage tank, the storage tank
rupture disc failed and a deflagration and fire ensued. The fire burned
itself out in about an hour with no apparent damage to the storage facility.
April 20, 1987
Page 3 of 3
On January 12, 1987, an explosive mixture of hydrogen and oxygen was
discovered in the number 1 holdup tank of the gaseous radwaste system at Zion
Unit 1. Prompt action was taken to isolate the tank and dilute the gaseous
content with a nitrogen purge to reduce the hydrogen concentration below
explosive limits. Investigation showed that the holdup tank was placed in
service on January 6, 1987. However, the tank was left isolated from the
automatic waste gas analyzer until January 12, 1987. This violated the
technical specifications requiring daily analysis of the waste gas system for
oxygen and hydrogen.
A report that may be useful in considering hazards and some methods for
improving the safe handling of pressurized gas is NUREG/CR-3551, ORNL/NOAC-214
"Safety Implications Associated with In-Plant Pressurized Gas Storage and
Distribution Systems in Nuclear Power Plants," published in May 1985.
No specific action or written response is required by this information notice.
If you have questions about this matter, please contact the Regional
Administrator of the appropriate NRC regional office or this office.
Charles E. Rossi, Director
Division of Operational Events Assessment
Office of Nuclear Reactor Regulation
Technical Contacts: Eric Weiss, AEOD
Frank Witt, NRR
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