U.S. NUCLEAR REGULATORY COMMISSION May 2008

OFFICE OF NUCLEAR REGULATORY RESEARCH Division 1

DRAFT REGULATORY GUIDE

Contact: Satish Aggarwal

(301) 415-6005

This regulatory guide is being issued in draft form to involve the public in the early stages of the development of a regulatory 

position in this area. It has not received final staff review or approval and does not represent an official NRC final staff position. 

Public comments are being solicited on this draft guide (including any implementation schedule) and its associated regulatory 

analysis or value/impact statement. Comments should be accompanied by appropriate supporting data. Written comments may 

be submitted to the Rulemaking, Directives, and Editing Branch, Office of Administration, U.S. Nuclear Regulatory 

Commission, Washington, DC 20555-0001; emailed to NRCREP@nrc.gov; submitted through the NRC’s interactive rulemaking 

Web page at http://www.nrc.gov; faxed to (301) 415-5144; or hand-delivered to Rulemaking, Directives, and Editing Branch, 

Office of Administration, US NRC, 11555 Rockville Pike, Rockville, MD 20852, between 7:30 a.m. and 4:15 p.m. on Federal 

workdays. Copies of comments received may be examined at the NRC’s Public Document Room, 11555 Rockville Pike, 

Rockville, MD. Comments will be most helpful if received by July 25, 2008. 

Electronic copies of this draft regulatory guide are available through the NRC’s interactive rulemaking Web page (see above); the 

NRC’s public Web site under Draft Regulatory Guides in the Regulatory Guides document collection of the NRC’s Electronic 

Reading Room at http://www.nrc.gov/reading-rm/doc-collections/; and the NRC’s Agencywide Documents Access and 

Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html, under Accession No. ML080570075. 

DRAFT REGULATORY GUIDE DG-1195 

(Proposed Revision 1 to Regulatory Guide 1.93, dated December 1974) 

(Original Draft Regulatory Guide was issued as DG-1153, dated October 2006) 

AVAILABILITY OF ELECTRIC POWER SOURCES 

A. INTRODUCTION 

This regulatory guide describes the operating procedures and restrictions that the staff of the U.S. 

Nuclear Regulatory Commission (NRC) considers acceptable for implementation if the available electric 

power sources are less than the limiting conditions for operation (LCO). This regulatory guide is 

applicable to single- and multi-unit plants. 

In Title 10, Part 50, of the Code of Federal Regulations (10 CFR Part 50), “Domestic Licensing 

of Production and Utilization Facilities,”1

 Section 50.36(d)(2), (10 CFR 50.36(d)(2)) requires that the 

technical specifications include the LCO, which are defined as the lowest functional capability or 

performance levels of equipment required for safe operation of the facility. Furthermore, the same 

regulations require that, when an LCO of a nuclear reactor is not met, the licensee shall shut down the 

reactor or follow any remedial action the technical specifications permit until the condition can be met. 

With respect to available electric power sources, the LCO establish the required capability of the 

electric power system that satisfies General Design Criterion (GDC) 17, “Electric Power Systems,” as set 

forth in Appendix A, “General Design Criteria for Nuclear Power Plants,” to 10 CFR Part 50, by 

including the following electric power sources: 

 

1

 10 CFR Part 50 is available electronically through the Electronic Reading Room on the NRC=s public Web site, at 

http://www.nrc.gov/reading rm/doc collections/cfr/. Copies are also available for inspection or copying for a fee from 

the NRC’s Public Document Room (PDR) at 11555 Rockville Pike, Rockville, MD; the mailing address is USNRC 

PDR, Washington, DC 20555; telephone (301) 415-4737 or (800) 397-4209; fax (301) 415 3548; and e mail 

PDR@nrc.gov. 
DG-1195, Page 2 

• Two physically independent circuits from the offsite transmission network, each of which is 

either continuously available or can be made available within a few seconds following a loss-ofcoolant accident (LOCA) 

• Redundant onsite alternating current (ac) power sources. 

• Redundant onsite direct current (dc) power sources. 

For nuclear power plants that are not licensed in accordance with GDC 17, the updated final 

safety analysis report provides the applicable design criteria. This guide sets forth criteria similar to GDC 

17, which requires that an offsite power system be provided to ensure the continued functioning of certain 

structures, systems, and components in the event of anticipated operational occurrences and postulated 

events. 

Operating nuclear power plants for which only one of the two required offsite circuits can be 

made available within a few seconds following a LOCA must justify the delayed offsite circuit 

availability to support the core cooling systems. 

The NRC issues regulatory guides to describe to the public methods that the staff considers 

acceptable for use in implementing specific parts of the agency’s regulations, to explain techniques that 

the staff uses in evaluating specific problems or postulated accidents, and to provide guidance to 

applicants. Regulatory guides are not substitutes for regulations and compliance with them is not 

required. 

This regulatory guide contains information collection requirements covered by 10 CFR Part 50 

approved by the Office of Management and Budget (OMB) under OMB control number 3150-0011. 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 

Background 

Electric loads important to safety in a nuclear power plant are served by an electric power system 

pursuant to GDC 17. Nuclear power plants with more power sources than required by GDC 17 may be 

able to withstand the loss of one or more sources and still satisfy the LCO. However, during the normal 

course of operation, any nuclear power plant may lose power sources to the extent that the LCO are not 

met. This regulatory guide addresses such cases. 

1. Loss of Offsite Power 

The technical specifications of operating nuclear power plants include the operational restrictions 

resulting from the loss of power sources. In general, plant technical specifications require the operability 

of the offsite power system as a part of the LCO and specify actions to be taken when the offsite power 

system is inoperable. Plant operators should be aware of (1) the capability of the offsite power system to 

supply power during operation, and (2) situations that can result in a loss of offsite power or inadequate 

voltage following a trip of the plant or other transmission contingencies (which could potentially degrade 

the offsite power supplies) identified by the grid operator. If the offsite power system is not capable of 

providing the requisite power in either situation, the system should be declared inoperable and pertinent 

plant technical specification provisions should be followed. 
DG-1195, Page 3 

A licensee’s ability to comply with technical specifications for offsite power may depend on grid 

conditions and plant status; in particular, maintenance on, and degraded conditions of, key elements of the 

plant switchyard and offsite power grid can affect the operability of the offsite power system, especially 

during times of high grid load and high grid stress. A communication interface with the plant’s 

Transmission System Operator combined with training and other local means to maintain nuclear power 

plant operator awareness of changes in the plant switchyard and offsite power grid is important to enable 

the licensee to determine the effects of these changes on the operability of the offsite power system. 

Analysis tools give the transmission system operator the capability to determine the impact of the loss or 

unavailability of various transmission system elements (called contingencies) based on the condition of 

the transmission system. The transmission systems can generally cope with several contingencies without 

undue impairment of grid reliability, but it is important that the nuclear power plant operator know when 

the transmission system near the nuclear power plant can no longer sustain plant voltage based on the 

transmission system operator’s analysis of a contingency. This knowledge helps the operator maintain 

awareness of the nuclear power plant’s offsite power system. Additionally, the nuclear power plant 

operator should know the grid’s condition before taking pertinent risk-significant equipment out-ofservice, and should monitor it for as long as the equipment remains out-of-service. 

For the passive plant designs that are exempted from providing the two offsite ac sources required 

by GDC 17 or for passive plant designs that fully meet the requirements of GDC 17 are not required to 

have any technical specification requirements for their offsite ac source(s) because passive plant designs 

rely on passive safety-related systems for core cooling and containment integrity. These passive safetyrelated systems only require electric power for valves and the related instrumentation. If no offsite power 

is available, it is expected that the non-safety-related onsite diesel generators would be available for 

important plant functions. These non-safety-related diesel generators do not require any technical 

specification requirements because they are treated under regulato0ry treatment of non-safety systems 

(RTNSS). The RTNSS basis applies to those non-safety systems that perform risk-significant functions, 

and therefore, are candidates for regulatory oversight. However, if an offsite power system or a diesel 

generator is found to be inoperable at these plants, it is expected that the licensees would make a 

concerted effort to restore inoperable offsite ac source or the diesel generator to operable status within a 

reasonable time period. 

For evolutionary plant designs that have three or four safety trains and have excess redundancy in 

their onsite power systems, the restrictions imposed on such plants on the loss of required onsite power 

sources may differ from those recommended in this guide and should be evaluated on a case-by-case 

basis. 

2. Operational Restrictions 

The operational restrictions in the technical specifications are based on the following three 

assumptions: 

2.1 Meeting the Limiting Condition for Operation

The LCO of nuclear power plants are met when all electric power sources required by GDC 17 

are available at the required voltage and capacity for the nuclear station and capable of withstanding a 

system contingency such as: (a) a single failure involving loss of generation by the nuclear unit, any other 

critical generation source, or loss of power from a transmission system element; or (b) a double failure 

involving a loss of power from the transmission network and the loss of one train of onsite ac power. 
DG-1195, Page 4 

2.2 Period of Continued Operation

Under certain conditions, it may be safer to continue operation at power for a limited time, rather 

than to implement an immediate shutdown upon loss of some required electric power sources. Such 

decisions should be based on an evaluation that balances the risks associated with immediate shutdown 

against those associated with continued operation. If, on balance, immediate shutdown is the safer 

course, the unit should promptly be brought to an orderly shutdown. For example, the risks associated 

with immediate shutdown upon loss of the onsite ac power source during a period of light transmission 

system load with high operating reserve would tend to be less than those resulting from shutdown during 

a peak load period with less operating reserve because the electrical grid may be able to accommodate a 

loss of power generation. If, on balance, continued power operation is the safer course, the period of 

continued operation, with appropriate approvals, should be used to restore the lost power system elements 

(generation, transmission, and capacitor banks) and prepare for orderly shutdown, provided, of course, 

that these activities do not risk further degradation of the electric power system or in any way jeopardize 

the unit’s safety. 

2.3 Orderly Shutdown

If the LCO has not been achieved, the unit should be promptly brought to an orderly shutdown 

after the allowed time for continued power operation has elapsed and to a cold shutdown state as soon as 

possible, thereafter. The premise here is that the time allowed for continued operation could have been 

used to enhance the safety of the imminent shutdown. For example, the dispatcher could take such 

system wide actions as increasing generation at other units or dropping selected loads to ensure that the 

shutdown does not cause power grid instability or inadequate offsite power voltage. In addition, if the 

loss of power sources beyond the LCO were to occur during a peak load period, the time allowed for 

continued operation could be used to defer the shutdown to an off-peak period when the electric grid has 

sufficient operating reserve to accommodate a loss of generation. 

3. Levels of Power System Degradation 

To develop bases for specific guidance, seven levels of power system degradation are described 

below, in order of increasing severity. 

3.1 The Available Offsite AC Power Sources Are One Less Than the LCO

This degradation level means that one of the required offsite ac sources is not available and, thus, 

the offsite ac power system has no redundancy. However, the remaining offsite power system retains full 

capability (voltage, frequency and capacity) to affect safe shutdown and mitigate the effects of a designbasis event. Operation could, therefore, safely continue if the availability of the remaining power sources 

is verified; however, since the system is degraded below the LCO, a time limit on continued operation is 

warranted. Operating experience indicates that availability and reliability are higher for typical offsite 

power sources. Thus, if risk is evaluated in terms of availability and capability, the risk associated with 

the loss of an offsite power source (the source with higher availability) would appear to be more severe. 

However, this apparent difference in severity is usually offset by maintainability considerations; that is, 

the time required to detect and restore an unavailable offsite source is generally much less, especially 

when the grid operator uses real-time contingency analysis. 
DG-1195, Page 5 

However, the loss of an offsite source resulting from an event associated with extensive 

consequences, such as a severe ice storm or forest fire, would have more severe implications. The risks 

associated with such an offsite loss would be compounded because: 

• the maintainability advantage of the offsite sources would be lost; 

• the remaining offsite circuit could be susceptible to the same cause; 

• the consequential trip probability of a number of units would be higher because of the potential 

loss of loads; and 

• the availability and capability of the offsite power system might be affected. 

Thus, the loss of an offsite source resulting from such a cause should be treated as equivalent to 

the loss of both required offsite sources. 

Licensees should make a concerted effort to restore the offsite ac power source during this 

restricted time period, and should ensure that the remaining power source can accommodate the imminent 

shutdown. 

3.2 The Available Onsite AC Power Sources Are One Less Than the LCO

This degradation level means that one train of the onsite ac power system is not available for safe 

shutdown or to mitigate the effects of an event. In a single-unit plant, this typically means that one diesel 

generator is inoperable. In certain multi-unit plants that share onsite ac supplies, this typically means that 

the available onsite supply does not have the capacity to mitigate the effects of events in both units. 

Since any inadvertent generator trip could potentially result in a total loss of ac power, the time 

allowed for continued operation should be severely restricted. In the absence of one onsite power source, 

the intent is twofold: 

• Avoid the risk associated with immediate shutdown. 

• Minimize the risk associated with this level of degradation by severely limiting its exposure time. 

Licensees should make a concerted effort to restore the onsite ac power source during this 

restricted time period, and should inform the grid operator to ensure that the offsite power system can 

accommodate the imminent shutdown. 

3.3 The Available Offsite AC Power Sources Are Two Less Than the LCO

This degradation level means that the offsite power system cannot affect a safe shutdown and 

mitigate the effects of an event; however, the onsite ac system is not degraded. Thus, this level generally 

corresponds to total loss (inadequate capacity, voltage, or frequency) of the immediately accessible offsite 

power sources. 

Because of the normally high availability of offsite sources, this level of degradation may appear 

to be more severe than the next two degradation levels discussed below. However, two factors tend to 

decrease the severity of this degradation level as compared to the next two degradation levels listed. 

First, the configuration of the redundant onsite ac power system that remains available for this 

degradation level is not susceptible to a single bus or switching failure, whereas the next degradation level 

may be susceptible. Second, the time required to detect and restore an unavailable offsite power source is 

generally much less than that required to detect and restore an unavailable onsite ac power source. 

This level of degradation can be caused by a variety of events, including the loss of two offsite 

circuits, an unavailable electric grid, or any other condition that renders offsite power unavailable for safe 
DG-1195, Page 6 

shutdown and emergency purposes. Since the onsite power system is not degraded and a loss of offsite 

power simultaneous with a LOCA was postulated as a design basis, a brief interval of continued operation 

may be justified if an onsite source of ac power, independent of grid condition, is readily available and 

can act as a substitute train of ac power. Note that some nuclear power units are designed to cause an 

automatic shutdown or initiate load rejection at this level of degradation. Units designed to undergo an 

automatic shutdown at this level of degradation need no further discussion; however, those that initiate 

load rejection are considered to remain operating within the context of this regulatory guide. 

3.4 The Available Offsite and Onsite AC Power Sources Are Each One Less Than the LCO 

This level of power system degradation results from the loss of individual redundancy in both the 

offsite and onsite ac power systems. However, since power system redundancy is provided by two 

different sources of power, the reliability and, hence, the safety of this degradation level appears to be 

slightly higher than that of the previous degradation level. However, the susceptibility of this power 

system to a single bus or switching failure could offset this apparent improvement. For example, the 

failure of an emergency power distribution bus that is energized by either the single available offsite 

circuit or the single available onsite ac supply could render all emergency ac power from that source 

ineffective. Moreover, if the offsite and onsite power were available to only one train, a bus fault could 

render all emergency power unavailable. 

Based on these considerations, the operating restrictions imposed at this level of degradation 

should be similar to those of the previous degradation level. However, the allowed operating time should 

be shortened because the onsite ac power system has been degraded, and a loss of offsite power 

simultaneous with a LOCA (or any event that causes a generator trip) is a design-basis event. 

3.5 The Available Onsite AC Power Sources Are Two Less Than the LCO

This degradation level means that the onsite ac power system cannot effect a safe shutdown and 

mitigate the effects of an accident in the event of a loss of offsite power. In a single unit, this usually 

means that two diesel generators are inoperable. In multiple units that share onsite ac supplies, this 

degradation level usually means that the available onsite supplies, if any, do not have the capacity to 

mitigate the effects of an event in one unit and safely shut down the other unit(s). 

Since the offsite power system is the only source of ac power at this level of degradation, the risk 

associated with continued operation for a very short time could be less than that associated with 

immediate shutdown. (Immediate shutdown could cause grid instability resulting in a total loss of ac 

power.) However, since any inadvertent generator trip could potentially result in a total loss of ac power, 

the time allowed for continued operation should be severely restricted. In addition, all work that could 

potentially trip the unit should be suspended. The intent is twofold: 

• Avoid the risk associated with immediate shutdown. 

• Minimize the risk associated with this level of degradation by severely limiting its exposure time. 

Licensees should make a concerted effort to restore at least one onsite ac power source during this 

restricted time period, and take systemwide actions to ensure that the offsite power system can 

accommodate the imminent shutdown. 

3.6 The Available Onsite DC Power Sources Are One Less Than the LCO

This degradation level means that the available dc power sources do not have the required 

redundancy; however, the remaining train(s) of the dc power system has (have) full functional capability 

to effect a safe shutdown and mitigate the effects of an event. Since a subsequent degradation in an onsite 
DG-1195, Page 7 

ac or dc system could jeopardize unit safety (e.g., a subsequent single failure could render the entire 

power system ineffective on a generator trip), the time allowed for continued operation should be severely 

restricted. If the affected dc source is restored within this time period, unrestricted operation may 

resume. If not, the unit should promptly be brought to an orderly shutdown. The required functions of 

the dc system should be critically monitored during the shutdown period and corrective actions taken, if 

required, to ensure safety. 

The passive designs that depend heavily on dc power systems for core cooling and containment 

integrity have batteries that last for 72 hours. The design of batteries to meet the long duration constant 

current demands that is required of passive designs may have different monitoring requirements 

(recommended by their manufacturers) than those required in current designs. Therefore, the required 

functions of these batteries should also be critically monitored during the shutdown period and corrective 

actions taken, if required, to assure that these batteries will perform their functions for the long duration 

as designed. 

3.7 The Available Inverters Are One Less Than the LCO

This degradation level means that the available inverters do not have the required redundancy; 

however, the remaining trains of the inverter power system have full functional capability to prevent a 

reactor trip. Since a subsequent single failure of another inverter could cause a reactor trip, the time 

allowed for continued operation should be severely restricted. If the affected inverter is restored within 

this time period, unrestricted operation may resume. If not, the unit should promptly be brought to an 

orderly shutdown. 

The outage times provided in Section C of this regulatory guide reflect an acceptable regulatory 

practice for designs with two or more onsite ac sources, two or more dc power sources, inverters, and two 

offsite power sources. Specific outage times are expected to be specified in the technical specifications. 

Further, the regulatory positions in Section C are based on the grid operators’ capabilities to ensure the 

adequacy of the offsite power system through contingency evaluations, as well as the unit’s capabilities to 

manage risk-significant maintenance and outages. 

C. REGULATORY POSITION 

The intent of each of the following regulatory positions is to ensure that a nuclear power plant is 

in an acceptably safe operating mode whenever the available electric power sources are less than the 

LCO. Accordingly, this section discusses the various levels of degradation of the electric power system, 

in order of increasing degradation; the technical specifications should incorporate the regulatory position 

for each degraded level. Whenever the technical specifications allow unrestricted operation to resume, 

such resumption should be contingent on verification of the capability of the restored sources. Similarly, 

whenever the technical specifications allow power operation to continue during a specific degradation 

level, such continued power operation should be contingent upon: 

a. immediate verification of the availability and capability of the remaining sources; 

b. verification that the required maintenance activities do not further degrade the power system or 

in any way jeopardize plant safety; and 

c. compliance with the additional conditions stipulated for each specific degradation level specified 

in the plant specific technical specifications. 

The conduct of maintenance or surveillance activities should be evaluated to determine their 

compliance with 10 CFR 50.65, “Requirements for Monitoring the Effectiveness of Maintenance at 

Nuclear Power Plants.” 
DG-1195, Page 8 

1. The Available Offsite AC Power Sources Are One Less Than the LCO 

If the available offsite ac power sources are one less than the LCO, power operation may continue 

for a period that should not exceed the time period allowed for continued operation as specified in the 

plant specific technical specifications. 

If the affected source is restored within the time period specified in the plant specific Technical 

Specifications, unrestricted operation may resume. Conversely, if the conditions for continued power 

operation are met, but the source is not restored within the time period specified in the plant specific 

technical specifications, the unit should be brought to shutdown. 

2. The Available Onsite AC Power Sources Are One Less Than the LCO 

If the available onsite ac power sources are one less than the LCO, power operation may continue 

for a time period that should not exceed the time period allowed for continued operation as specified in 

the plant specific technical specifications, provided the redundant diesel generator is assessed within 24 

hours to be free from common-cause failure. 

If the affected source is restored within time period specified in the plant technical specifications, 

unrestricted operation may resume. Conversely, if the conditions for continued power operation are met, 

but the source is not restored within the time period specified in the plant specific technical specifications, 

the unit should be brought to shutdown. 

3. The Available Offsite AC Power Sources Are Two Less Than the LCO 

If the available offsite ac power sources are two less than the LCO, power operation may 

continue for the time period specified in the plant specific technical specifications if it appears likely that 

at least one of the offsite sources can be restored within that time. If these conditions for continued power 

operation are met and both offsite sources are restored within the time period specified in the plant 

technical specifications, unrestricted operation may resume. If only one offsite source is restored within 

the time period specified in the plant specific technical specifications, power operation may continue for a 

total time that should not exceed the specified time in accordance with the conditions described in 

Regulatory Position 1. Conversely, if no offsite source is restored within the first period of continued 

power operation, the unit should promptly brought to shutdown based on plant specific technical 

specifications. 

4. The Available Offsite and Onsite AC Power Sources Are Each One Less Than the 

LCO 

If the available offsite and onsite ac power sources are each one less than the LCO, power 

operation may continue for a short time period as specified in the plant technical specifications. 

If these conditions for continued power operation are met and both sources are restored within 12 

hours, operation may resume. If either an offsite or an onsite ac source is restored within the time period 

specified in the plant specific technical specifications, power operation may continue for a total time that 

should not exceed the time period specified in accordance with the condition described in Regulatory 

Position 1 for the loss of one ac source. Conversely, if neither an offsite source nor an onsite source is 

restored within the first time period of continued power operation, the unit should be brought to shutdown 

based on plant specific technical specifications. 
DG-1195, Page 9 

5. The Available Onsite AC Power Sources Are Two Less Than the LCO 

If the available onsite ac electric power sources are two less than the LCO, power operation may 

continue for a period that should not exceed time period specified in the plant specific technical 

specifications. If both onsite ac electric power sources are restored within this time period unrestricted 

operation may resume. If only one onsite ac power source is restored within this time period power 

operation may continue but power operation should not exceed the specified time period, in accordance 

with the conditions described in Regulatory Position 2 for the loss of one onsite ac source. Conversely, if 

no onsite ac source can be restored within the first time period of continued power operation, the unit 

should be brought to cold shutdown based on plant specific technical specifications. 

6. The Available Onsite DC Power Sources Are One Less Than the LCO 

If the available onsite dc power sources are one less than the LCO, power operation may continue 

for a period that should not exceed the time period specified in the plant specific technical specifications. 

If the affected dc source is restored within this time period, unrestricted operation may resume. If not, the 

unit should be brought to hot shutdown based on plant specific technical specifications. 

7. The Availability of Inverters Are One Less Than the LCO 

If the available inverters are one less than the LCO, power operation may continue for a period 

that should not exceed the time period specified in the plant specific technical specifications. If the 

affected inverter is restored within this time period, unrestricted operation may resume. If not, the unit 

should be brought to hot shutdown based on the time period specified in the plant specific technical 

specifications. 

D. IMPLEMENTATION 

The purpose of this section is to provide information to applicants and licensees regarding the 

NRC’s plans for using this draft regulatory guide. The NRC does not intend or approve any imposition or 

backfit in connection with its issuance. 

The NRC has issued this draft guide to encourage public participation in its development. The 

NRC will consider all public comments received in development of the final guidance document. In 

some cases, applicants or licensees may propose an alternative or use a previously established acceptable 

alternative method for complying with specified portions of the NRC’s regulations. Otherwise, the 

methods described in this guide will be used in evaluating compliance with the applicable regulations for 

license applications, license amendment applications, and amendment requests. 
DG-1195, Page 10 

REGULATORY ANALYSIS 

1. Statement of the Problem 

The NRC published Regulatory Guide 1.93 in December 1974 to provide licensees with guidance 

for complying with the regulations for the availability of electric power sources in the then current version 

of 10 CFR Part 50. The implementation of a risk-informed and performance based approach as well as 

multiple revisions and additions to 10 CFR Part 50 make the current regulatory guide obsolete. 

An earlier draft guide 2

 (DG-1153) was issued in October 2006 but later withdrawn to resolve 

multiple comments. The NRC has made major modifications to the earlier draft guide to address these 

comments and concerns and is issuing this new draft guide to promulgate the NRC’s viewpoint. 

Therefore, revision of this regulatory guidance is issued to provide licensees with more modern guidance 

that incorporates the risk-informed and performance-based approach currently favored by the NRC. 

2. Objective 

The objective of this regulatory action is to provide a more useful and up-to-date version of the 

guidance acceptable to the NRC when the availability of electric power sources is less than the limiting 

conditions for operation for the facility. 

3. Alternative Approaches 

The NRC staff considered the following alternative approaches: 

• Do not revise Regulatory Guide 1.93. 

• Update Regulatory Guide 1.93. 

3.1 Alternative 1: Do Not Revise Regulatory Guide 1.93 

Under this alternative, the NRC would not revise this guidance, and the original version of this 

regulatory guide would continue to be used. This alternative is considered the baseline or “no action” 

alternative and, as such, involves no value/impact considerations. 

3.2 Alternative 2: Update the Regulatory Guide 1.93 

Under this alternative, the NRC would update Regulatory Guide 1.93, taking into consideration 

the need to address current regulations and prepare for multiple new license applications. This action 

would address an important aspect of safe nuclear power plant operation in the event of a loss of power 

onsite and offsite power sources that result in a failure to meet the LCO. This revised regulatory guide 

will replace old, outdated, and inapplicable guidance with updated guidance that focuses on a regulatory 

framework that has changed since Regulatory Guide 1.93 was first written. 

 

2

 Draft Regulatory Guide DG-1153 is available electronically under Accession Number ML062840370 in the NRC’s 

Agencywide Documents Access and Management System (ADAMS) at http://www.nrc.gov/reading-rm/adams.html. 

Copies of this draft regulatory guide are available through the NRC’s interactive rulemaking Web page (see above); the 

NRC’s public Web site under Draft Regulatory Guides in the Regulatory Guides document collection of the NRC’s 

Electronic Reading Room at http://www.nrc.gov/reading-rm/doc-collections/; and the NRC’s Accession No. 

ML080220459. 
DG-1195, Page 11 

The costs to the NRC would be the one time cost of issuing the revised regulatory guide (which is 

expected to be relatively small) and applicants would incur little or no cost. 

4. Conclusion 

Based on this regulatory analysis, the staff recommends revision of Regulatory Guide 1.93. The 

staff concludes that the proposed action will enhance reactor safety by providing a more risk-informed 

and performance-based approach to the loss of onsite and offsite electrical power sources that result in a 

failure to meet the LCO. It could also lead to cost savings for the industry, especially with regard to 

applications for standard plant design certifications and combined licenses.