United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 87-20: Hydrogen Leak in Auxiliary Building

                                                   SSINS No.: 6835 
                                                        IN 87-20 

                                  UNITED STATES
                          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 

Addressees: 

All nuclear power reactor facilities holding an operating license or a 
construction permit. 

Purpose: 

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 
(ENS). 

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 
where little 

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                                                    IN 87-20 
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                                                            Page 2 of 3 

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. 

Discussion: 

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 
hydrogen lines. 

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. 

                                                    IN 87-20 
                                                            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 
                      (301) 492-9005 

                      Frank Witt, NRR 
                      (301) 492-9440 

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