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REGULATORY GUIDE T he U .S . N uclear R egulatory C om m ission (N R C ) issues regulatory guides to describe and m ak e available to the public m ethods that the N R C staff
considers acceptable for use in im plem enting specific parts of the agencys regulations, techniques that the staff uses in evaluating specific problem s
or postulated accidents, and data that the staff need in reviewing applications for perm its and licenses. Regulatory guides are not substitutes
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U.S. NUCLEAR REGULATORY COMMISSION
M arch 2007
Revision 4
REGULATORY GUIDE
OFFICE OF NUCLEAR REGULATORY RESEARCH
REGULATORY GUIDE 1.9
(Draft was issued as DG -1172, dated November 2006)
APPLICATION AND TESTING
OF SAFETY-RELATED DIESEL GENERATORS
IN NUCLEAR POWER PLANTS
A. INTRODUCTION
General Design Criterion 17, Electric Power Systems, of Appendix A, General Design Criteria
for Nuclear Power Plants, to Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50),
Domestic Licensing of Production and Utilization Facilities (Ref. 1), requires that onsite electric power
systems have sufficient independence, capacity, capability, redundancy, and testability to ensure that
(1) specified acceptable nuclear fuel design limits and design conditions of the reactor coolant pressure
boundary are not exceeded as a result of anticipated operational occurrences, and (2) the core is cooled
and containment integrity and other vital functions are maintained in the event of postulated accidents,
assuming a single failure.
General Design Criterion 18, Inspection and Testing of Electric Power Systems, of Appendix A
to 10 CFR Part 50 requires that electric power systems important to safety be designed to permit
appropriate periodic inspection and testing to assess the continuity of the systems and the condition
of their components.
Criterion III, Design Control, and Criterion XI, Test Control, of Appendix B, Quality
Assurance Criteria for Nuclear Power Plants and Fuel Reprocessing Plants, to 10 CFR Part 50 require
that (1) measures be provided for verifying or checking the adequacy of design through design reviews,
the use of alternative or simplified calculational methods, or the performance of a suitable testing program
and (2) a test program be established to ensure that systems and components perform satisfactorily
and that the test program include operational tests during nuclear power plant operation. Rev. 4 of RG 1.9, Page 2
10 CFR 50.63, Loss of All Alternating Current Power, requires that each light-water-cooled
nuclear power plant must be able to withstand and recover from a station blackout [i.e., loss of offsite
and onsite emergency alternating current (ac) power systems] for a specified duration. The reliability
of onsite ac power sources is one of the main factors contributing to the risk of core melt as a result
of a station blackout.
Most onsite electric power systems use diesel generators as the chosen onsite emergency power
source. This regulatory guide provides guidance that the staff of the U.S. Nuclear Regulatory Commission
(NRC) considers acceptable to comply with the Commissions regulations for safety-related diesel
generators intended for use as onsite emergency power sources in nuclear power plants specifically,
that the emergency diesel generators be selected with sufficient capacity, be qualified, and have
the necessary reliability and availability for design-basis events.
This regulatory guide relates to information collections that are covered by the requirements
of 10 CFR Part 50 and 10 CFR Part 21, Reporting of Defects and Noncompliance (Ref. 2),
which the Office of Management and Budget (OMB) approved under OMB control number 3150-0011
and 3150-0035, respectively. The NRC may neither conduct nor sponsor, and a person is not required
to respond to, an information collection request or requirement unless the requesting document displays
a currently valid OMB control number.
B. DISCUSSION
An emergency diesel generator selected for use in an onsite electric power system should have
the capability to (1) start and accelerate a number of large motor loads in rapid succession, while
maintaining voltage and frequency within acceptable limits, (2) provide power promptly to engineered
safety features if a loss of offsite power (LOOP) and a design-basis event occur during the same time period,
and (3) supply power continuously to the equipment needed to maintain the plant in a safe condition
if an extended (e.g., 30-day period should be considered with refueling every 7 days) LOOP occurs.
The Institute of Electrical and Electronics Engineers (IEEE) Standard 387, IEEE Standard Criteria
for Diesel-Generator Units Applied as Standby Power Supplies for Nuclear Power Generating Stations
(IEEE Std 387-1995), issued in 1995 (Ref. 3), delineates principal design criteria and qualification
and testing guidelines to ensure that selected diesel generators meet performance requirements.
Working Group SC 4.2 of Subcommittee 4 (Auxiliary Power) of the IEEE Nuclear Power Engineering
Committee developed IEEE Std 387-1995, and the IEEE Standards Board approved the standard
on December 12, 1995.
A knowledge of the characteristics of each load is essential to establish the bases for selection
of an emergency diesel generator that is able to accept large loads in rapid succession. The majority
of these emergency loads are large induction motors. At full voltage, this type of motor draws a starting
current of five to eight times its rated full-load current. These sudden large increases in current drawn
from the diesel generator as a result of the startup of induction motors can result in substantial voltage
reductions. This lower voltage could prevent a motor from starting (i.e., accelerating its load to rated speed
in the required time), or could cause a running motor to coast down or stall. Other voltage-sensitive loads
might also be lost because of low voltage or if their associated contactors drop out. Recovery from
the transient caused by starting large motors, or from the loss of a large load, could cause diesel engine
overspeed that, if excessive, might result in a trip of the engine (i.e., loss of the safety-related power source).
These same consequences can also result from the cumulative effect of a sequence of more moderate transients
if the system is not permitted to recover sufficiently between successive steps in a loading sequence. Rev. 4 of RG 1.9, Page 3
General industry practice is to specify a voltage reduction of 1015 percent when starting
large motors from large-capacity power systems, and a maximum voltage reduction of 2530 percent
when starting these motors from limited-capacity power sources such as diesel generators. Voltage reduction
during load sequencing should be evaluated in light of the plant-specific equipment to prevent
load interruption. Large induction motors can achieve rated speed in less than 5 seconds when powered
from adequately sized emergency diesel generators that are capable