Regulatory Guide 1.81
| ML003740343 | |
| Person / Time | |
|---|---|
| Issue date: | 01/31/1975 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| References | |
| RG-1.81, Rev 1 | |
| Download: ML003740343 (2) | |
Revision 1 January 1975 U.S. NUCLEAR REGULATORY COMMISSION
REGULATORY GUIDE
REGULATORY GUIDE 1.81 SHARED EMERGENCY AND SHUTDOWN ELECTRIC
SYSTEMS FOR MULTI-UNIT NUCLEAR POWER PLANTS
A. INTRODUCTION
General Design Criterion 5 has resulted in development of onsite emergency electric power systems that are General Design Criterion 5,, "Sharing of Structures, shared among the units of the plant. The degree of Systems, and Components," of Appendix A, "General sharing in these designs has varied from sharing of only Design Criteria for Nuclear Power Plaits," to 10 CFR one Source to sharing of all sources and their distribution
. Part 50, "Licensing of Production and Utilization Facil systems. A device is considered to be shared among units i ties,r prohibits structures, systems, and components if it is designied to perform the same function in all units important to safety from being shared among nuclear as required.
power units unless it can be shown that such sharing will Sharing of onsite power systems at multi-unit power not significantly impair their'ability to perform their plant sites generally results in a reduction in the number safety functions. These safety functions include the and capacity cf the onsite power sources to levels below capability -to perform an orderly shutdown and cool those required for the same number of units located at down of the remaining units in the event of an accident separate sites. The reduced capacity could cause unde-.'
in one unit. This regulatory guide describes a method ac sirable interactions. Examples of such interactions are ceptable to the NRC staff for complying with the Nuclear (1) the interconnection of engineered safety feature Regulatory Commission's requirements with respect to (ESF) control circuits of each unit such that failures and the sharing of onsite emergency and shutdown electric maintenance or testing operations in one unit affect the'
systems for multi-unit nuclear power plants. With availability of ESF in other units, (2) coordination respect to the sharing of d.c. systems, this guide applies required between unit operators in order to cope with an to all multi-unit plants. With respect to the sharing of accident in one unit and safe shutdown of the remaining a.c. systems, this guide applies to the multi-unit plants unit(s), and (3) system overload conditions as a conse whose a.c. power is supplied by diesel generators. The quence of real accident in a unit coincident with a false Advisory Committee on Reactor Safeguards has been or spurious accident signal in another unit.
consulted concerning this guide and has concurred in the All of the applicants with shared onsite power regulatory position. systems at multi-unit plants reviewed to date have been required by the staff to provide improvements in capacity and/or a reduction in system interactions in
B. DISCUSSION
order to resolve concerns with regard to these unde.
sirable interactions. Further, the staff has, since 1973, The staff has determined that, because of the low advised several applicants for construction permits that probability of a major reactor accident, a suitable design sharing of onsite power systems should not be incorpo basis for multi-unit nuclear power plants is the assump rated into their designs. Inasmuch as most, if not all, of tion that an accident occurs in only one of the units at a the applications for construction permits presently time, with all remaining units proceeding to an orderly under review and those in the planning stages are for shutdown and a maintained cooldown condition. Use of multi-unit plants comprising from two to six units, the this design basis in conjunction with the requirements of staff has concluded that the onsite emergency electric power systems for these plants should be designed to minimize undesirable interaction effects.
This revision reflects comments received from the
"Lines indicate substantive changes from previous issue.
public and additional staff review.
USNRC REGULATORY GUIDES Copies of published guides may be obtained by request indicating the divisions desired to the U S Nuclear Regulatory Commission. Washington. D.C. M5556.
Regulatory Guides are issued to describe and make available to the public Attention Director of Standards Development Comments and suggestions for methods acceptable to the NRC staff of implementing specilic parts of the improvements in these guides are encouraged and should be sent to the Commission's regulatiot~ss to delineate techniques used by the staff in Secretary of the Commission U S Nuclear Regulatory Commission.
evaluating specific problems or postulated accidents. or to provide guidance to Washington. D C 20566. Attention Docketing end Service Section.
applicants Regulatory Guides are not substitutes for regulations and compliance with them is not required. Methods and solutions different from those set out in The guides are issued in the following tan broad divisions the guides will be acceptable if they provide a basis for the findings requisite to the issuance or continuance of a permit or license by the Commission 1 Power Reactors 6 Products
2. Research and Test Reactors 7 Transportation
3 Fuels and Materials Facilities 8 Occupational Health Published guides will be revised periodically, as appropriate, to accommodate 4. Environmental and Siting I Antitrust Review comments and to reflect new information or experience S Materials and Plant Protection 10 General
C. REGULATORY POSITION
d. The interaction between each unit's engineered I.,
safety feature electric circuits should be limited such
1. D.C. systems in multi-unit nuclear power plants that any allowable combination of maintenance and test should not be shared. operations in the units will not preclude the capability to automatically supply power to minimum ESF loads in
2. Multi-unit nuclear power plants now under con any unit, assuming a loss of offsite power.
struction or for which construction permit application e. Coordination between the unit operators should was made before June 1, 1973, will be reviewed on an not be necessary in order to meet Regulatory Positions individual-case basis. For these plants, the design of 2.b and 2.c. Coordination required to meet Regulatory shared onsite emergency and shutdown a.c. electric Position 2.d should be minimized.
systems should satisfy the following: f. Complete information regarding the status of the a. The sharinig of onsite a.c. electric systems should shared systems should be provided for each unit opera be limited to two units. tor.
b. A single failure (a false or spurious accident signal g. The design should conform to the recommenda at the system level in the non-accident unit should be tions contained in Regulatory Guides 1.6 (Safety Guide considered as a single failure) should not preclude the 6), 1.9 (Safety Guide 9), and 1.47.
capability to automatically supply minimum engineered safety feature (ESF) loads in any one unit and safely shut down the remaining unit, assuming a loss of the 3. In the case of multi-unit nuclear power plants for offsite power. which the construction permit application was made on c. Onsite power capacity should be provided to or after June 1, 1973, each unit should have separate energize sufficient Seismic Category I equipment to and independent onsite emergency and shutdown attain a safe and orderly cold shutdown of all units, electric systems, both a.c. and d.c., capable of supplying assuming the loss of offsite power and the most severe minimum ESF loads and the loads required for attaining (in terms of power drain) design basis event and a single a safe and orderly cold shutdown of the unit, assuming a failure in the onsite electric system. single failure and loss of offsite power.
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