[DNFSB
LETTERHEAD]
October 17, 2005
The Honorable Linton Brooks
Administrator
National Nuclear Security
Administration
U.S. Department of Energy
1000 Independence Avenue, SW
Washington, DC 20585-0701
Dear Ambassador Brooks:
The Defense Nuclear Facilities
Safety Board (Board) has been closely following various safety aspects of the
National Nuclear Security Administration’s design project for the Pit Disassembly
and Conversion Facility (PDCF), including ventilation, safety analysis,
criticality safety, seismic criteria, process safety, and fire protection. The PDCF design project is nearing completion
of the final design stage, and the Board will continue its safety reviews as
the project progresses. The electrical
design aspect of the project is anticipated to achieve 90 percent of final
design within the next several months. The Board’s staff conducted a review of the electrical
system at the 60-70 percent completion stage of the final design. The concerns identified during this review are
provided as an enclosure to this letter.
Subsequent to the review,
discussions with your staff and the Board’s staff have continued and the issues
discussed appear to be headed toward resolution. The enclosure is provided for your information
and use, as appropriate.
Sincerely,
A.
J. Eggenberger
Chairman
c: Mr. Mark B. Whitaker, Jr.
Enclosure
DEFENSE
NUCLEAR FACILITIES SAFETY BOARD
Staff
Issue Report
September
19, 2005
MEMORANDUM
FOR: J. K. Fortenberry, Technical
Director
COPIES: Board Members
FROM: A. Matteucci
SUBJECT: Review of Electrical System of
the Pit Disassembly and Conversion Facility
The purpose of this report is to
document a review of the electrical system of the Pit Disassembly and
Conversion Facility (PDCF). The review
was conducted at the National Nuclear Security Administration’s (NNSA) design
contractor’s (Washington Group, International [WGI]) facilities in Denver,
Colorado on August 24, 2005, by the Defense Nuclear Facilities Safety Board
(Board) staff A. Gwal, H. Massie, and A. Matteucci.
Background. The
primary mission of the PDCF is to (1) receive surplus weapons plutonium in the
form of pits and other plutonium metals, (2) convert the plutonium metal to plutonium
oxide, and (3) remove any residual classified attributes through blending of
the converted plutonium oxide. The PDCF
design project, being lead by WGI, is in the final design stage. Although the design stage of the overall
project is near the 90 percent final design stage, the electrical aspect of the
project is at about 60-70 percent final design. The electrical design aspect of the project is
anticipated to achieve 90 percent of final design in late 2005.
Safety
Analysis. The preliminary documented
safety analysis (PDSA) for the PDCF has been submitted. The PDCF was determined to be a Hazard
Category 2 facility, and based on hazard analysis and associated unmitigated
accident analysis results, there is a potential for significant onsite
consequences. An assessment of safety
controls has been completed and documented in the PDSA.
The scope of the electrical
design addresses normal, standby, uninterruptible, and emergency power systems.
Within this scope, the electrical design
for the PDCF incorporates controls which are designated both safety-class and
safety-significant. Presently, the
portion of the electrical system designated as safety-class includes the
emergency generators and fuel system, automatic transfer switches, electrical
distribution system, and the 125 volt battery system.
Electrical
System. Overall, the design of the
electrical system is progressing well. However, there were several
concerns identified by the staff during the review.
Standby
Diesel Generators―The staff believes that the present
rating of the two standby diesel generators may not be adequate to handle the
necessary loads during restart from a loss of off-site power, especially the
restart of a 700 horsepower (hp) chiller motor. During restart of the PDCF after a loss of
off-site power, the facility would be restarted in a limited operational mode. During normal operations with off-site power,
two 700 hp chillers are operating. The
limited mode would require operation of only one 700 hp chiller. To provide the necessary power to perform a
successful restart of the facility in a limited mode, the standby generators
may need to have an increased rating. The PDCF project team desires to maintain the
current footprint of the facility. The
staff is concerned that efforts to maintain the current footprint may drive a
final electrical system that cannot support operation of the facility in a
standby mode. The staff suggested the
contractor perform the calculations for restarting the facility with all
necessary loads, including a 700 hp chiller motor, to confirm the adequacy of the
rating for the standby diesel generators.
Non-Safety
Loads on
the Safety-Class or Safety-Significant Busses―The PDCF electrical design criteria
references the appropriate Institute of Electrical and Electronic Engineers
(IEEE) standards (e.g., IEEE Standard 384, Standard
Criteria for Independency of
Class IE Equipment and Circuits) related to the connection of
non-safety-related loads to safety-class busses. However, the requirements regarding the
connecting of non-safety-class loads on a safety-class bus are missing in
design documents. The explicit inclusion
of the requirements relating to connecting non-safety-class loads to the
safety-class bus would ensure these requirements are adhered to during the
electrical design process.
Fast
Reclosing―Section 20.85 of the National
Electrical Manufacturers Association (NEMA) M G-1-1993,
Revision 2, states
that “Induction machines are inherently capable of developing transient current
and torque when exposed to an out-of-phase bus transfer or momentary voltage
interruption and reclosing on the same power supply”.
The magnitude of the transient torque
may range from 2-20 times the rated torque and is a function of machine parameters
and switching time.
The staff suggested an
evaluation of the transient torque for the 700 hp chiller motor during a fast reclosing after a loss of power for a very short duration
and that suitable protective devices be provided, if
required, for the protection of the chiller motor.
4160 Switch Gear―The current PDCF design makes partial use of fuses in lieu of
circuit breakers in the electrical system. The design of typical switch
gear systems do not employ both circuit breakers and fuses. Although fused switches may be used in lieu of
circuit breakers, coordinating a line-side circuit breaker with a load-side
fuse is difficult. The staff suggested
that NNSA thoroughly
evaluate the coordination of protective devices, specifically the fuses for the
700 hp chiller motor and upstream circuit breakers.
Procurement
Specifications―Procurement specifications for safety-class
electrical equipment do not include the seismic requirements. The contractor had planned to include the seismic
requirements in the procurement specification by referencing a separate
document, which might be confusing to the equipment bidder. As a
result of discussion with the staff, the contractor has now decided to include
the seismic requirements for electrical equipment directly in the procurement
specifications.