TRANSMITTED TO M. WHITAKER 4/11/97

DEFENSE NUCLEAR FACILITIES SAFETY BOARD

June 3, 1996

1. Purpose: This memorandum documents a trip to the Pantex Site to: (1) review diesel generator (DG) and Uninterruptible Power Supply (UPS) systems; and (2) determine if the emergency electrical systems provide required power to emergency systems for the specified duration. The review was performed May 16, 1996, by Defense Nuclear Facilities Safety Board (Board) staff member A. K. Gwal.

2. Summary:

a.There are several buildings at Pantex that require only low power to feed the critical safety load. In such buildings UPS system may meet National Fire Protection Association (NFPA) requirements, if it is rated for 1 1/2 hours. However, some of these Pantex buildings have UPS systems that are rated at only 30 minutes. For these buildings, DG systems have been provided to extend UPS system rating to 1 1/2 hours.

Whenever there is a need for maintaining differential pressure between various zones of a building, to limit spread of contamination, the large electric motors driving the heating, ventilation, and air conditioning (HVAC) fans often require DGs. For example, Building 12-116 may need such a system.

b.Prior to the visit by the Board's staff, HVAC system in building 12-116 had failed and was still inoperable at the time of the tour. Without this system in operation, there is a significant potential for hydrogen buildup in an electrical equipment room containing lead- acid batteries. Hydrogen could accumulate near the ceiling of the room and create a potential for explosion. In addition, Mason and Hanger (M-H) was unable to confirm that the room complies with the American National Standards Institute (ANSI) C2 National Electric Safety Code.

3. Background: During an earlier trip to Pantex, the Board's Technical Director observed that many buildings at Pantex do not have DG systems as backups, and use only UPS systems to feed electric power to critical systems. It appeared possible that during loss of normal electric power, the UPS system might not perform its intended function for the required duration, as specified by applicable industry codes and standards. The present review of electrical backup systems was based on the Critical Safety Systems Manual (CSSM MNL-1101), Rev 3C, dated December 1, 1995; various Technical Procedures; design bases for the Technical Procedures; design documents related to actual loading of the DG and UPS; and discussions with M-H personnel.

4. Discussion/Observations:

Electrical distribution systems feeding critical safety systems of most buildings at Pantex are classified as safety-significant. Some of the critical systems they supply include: Emergency Lighting, Alpha Continuous Air Monitoring System (Alpha CAMS), Radiation Alarms and Monitoring System (RAMS), and Fire Detection and Alarm Systems. Buildings at Pantex use combinations of UPS systems, DG systems, and normal electric power supply to feed these critical systems.

Requirements for emergency lighting are delineated in NFPA-101, Life Safety Code, which requires that emergency illumination be provided for a period of 1 1/2 hours, in the event of failure of normal lighting. The Pantex Critical Safety Systems Manual (CSSM MNL-1101) states:

"The basis for emergency lighting is to provide the required illumination automatically in the event of any interruption of normal lighting. This lighting will allow safe shutdown of operations in and egress from the effected [sic] facility in the event of a loss of power. The loss of the emergency lighting system could severely hinder evacuation of the facility, potentially leading to many different types of industrial accidents."

One line diagram, panel load list, and actual loads from load tests performed in accordance with Pantex technical procedures were reviewed by the Board's staff to assess specific load requirements, with the following results:

a. Buildings with UPS systems only (no DG):

Buildings with UPS systems only require low power to feed critical systems, such as emergency lights. The review revealed that the UPS systems for these buildings do have 1 1/2 hour ratings and meet applicable loading requirements. For example, the following data are taken from actual tests of the UPS system for Building 12-44.

b. Buildings with both DG and UPS Systems:

The Board's staff noted that many Pantex DG systems were lightly loaded. DG systems were provided in these buildings primarily to extend the ratings of UPS systems from 30 minutes to 1 1/2 hours as required by NFPA-101. The following data, taken from actual tests of DGs located in the indicated buildings, illustrate the low power demands on these systems.

c. Diesel Generator Systems for Auxiliary Power:

DG Systems at Pantex are required only in the event of a long-term failure of normal electrical power (>30 minutes). They are not relied upon to place facilities in a safe and stable configuration; for this, UPS systems are relied upon to provide electrical power to critical systems.

d. Confinement Systems:

At Pantex, very few buildings need to maintain differential pressures between zones to limit contamination spread. Such air handling requirements demand large, continuously running electric motors that must be supplied by a DG system during a loss of normal power. UPS systems are typically rated at 1 1/2 hours and cannot feed such large loads on a continuous basis. For example, Building 12-116 may need such a system to maintain differential pressure.

The Board's staff was briefed by the facility manager about the mission and conceptual design of Building 12-116. During a tour of the existing facility, the Board's staff observed that the HVAC was out of service in an electrical equipment room that contains many lead-acid batteries. For rooms containing lead-acid batteries, the ANSI C2 National Electric Safety Code requires adequate ventilation and an alarm for loss of ventilation to ensure hydrogen does not build up. In this case, there is neither a local nor a remote indicator, nor is there an alarm or a flow switch to alert plant operators to a failure of battery room exhaust/ventilation. The Board's staff is concerned that hydrogen generated by the batteries may accumulate and create a potential for explosion. The facility manager agreed to evaluate this condition and to provide protective measures to resolve this issue.

5. Future Staff Actions:

The Board's staff will continue to follow the resolution of concerns involving the ventilation system of the electrical equipment room, and will perform a detailed review of the HVAC system during its design review of electrical and control systems of Building 12-116.