ML20071N325
| ML20071N325 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 09/20/1982 |
| From: | Baxter F YANKEE ATOMIC ELECTRIC CO. |
| To: | Srinivasan M Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8210070160 | |
| Download: ML20071N325 (12) | |
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o NRC QUESTION Provide the results of an analysis to prove that any challenges to Class lE Circuits from associated circuits do not prevent the safe shutdown of the plant.
RESPONSE
A.
General In accordance with the provisions of Section 4.Sa of FSAR Appendix =8A, Sections 4.5(1) and 4.6.1 of IEEE 384-1974, and Position C4 of Regulatory Guide 1.75, Revision 2, we have elected to associate all the Non-Class 1E circuits with Class lE circuits.
This application of associated circuits allows the plant to be designed with one less separation group; that 18, instead of having.five. separation groups consisting of four safety-related separation groups and one non-safety-related sepadaict.
group, Seabrook has only four separation groups. The major advantages of this approach are the ability to provide greater separation distances between the groups as well as to reduce th.: raceway' system's exposure to fire.
As-a result af the this design, 'all plant circuits are specifically assigned to one of the following four separation groups as noted in Figure 1.
Group A - Train A, Channel I and Trair. A Associated Circuita r
l Group B - Train B, Channel II and Train B Associated Circuits Group C - Channel III i
Group D - Channel IV i
The great majority of associated circuits are with Group A, a very limited number are with Group B, and none are with Groups C and D.
The circuits that are associated with Train A consist of:
DRAF
.I.
1.
No,n-Class lE power, control, acJ instrument circuits contained within the Nuclear Island.
2.
Non-Class IE power, control, and instrumentation circuits that traverse the Nuclear Island boundary.
3.
Non-Class lE power, control, and instrument circuits outside the Nuclear Island.
The circuits that are associated with Train B consist of:
1.
Non-Class lE power, control, and instrument circuits contained within the Ne: lear Island.
2.
Non-Class IE power, control, and instrumentation circuits that traverse the Nuclear Island boundary.
The Nuclear Island boundary is shown in Figure 1.
This figure denotes the buildings, structures, duct banks, etc., which are part of the Nuclear Island. All other buildings, structures, etc., are considered to be outside the Nuclear Island.
The following analysis examines the design features and modes of failure of associated circuits of each separation group to determine any interaction and challenges with other separation groups. The overall l
objective is to assure that the ability to achieve a saf e plant shutdown under Design Basis Event (DBE) conditions is not compromised.
B.
Train A Associated Circuit Analysis I
1.
Associated Circuits Contained within the Nuclear Island l
i Non-Class lE circuits that remain within the Nuclear Island are permitted to share the same raceway as Train A Class lE circuits.
These circuits are classified as Train A Associated Circuits and are i
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designed and installed to meet all the requirements placed on ssociated circuits as required by FSAR Appendix 8A.
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D, l
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Ch,allenges to Class IE circuits, because of failure in an associated circuit, have been examined and determined to have' no detrimental effect because:
Wher, Class lE power supplies are utilized, failure of a a.
Non-Class lE motor, load, or device connected to this power supply will.be promptly isolated by operation of Class lE protective devices.
b.
In cases where Non-Class lE powee supplies, such as switchgear, motor control centers, and distribution panels, are utilized, these are of identical design to the Class IE counterparts and have been purchased to the same specification requirements inclusive of quality control. Mounting of the Non-Class lE power suppNpswithin the Nuclear Island is identical.to the mounting of their Class lE counterparts; therefore, credit can be taken for this equipment to function under DBE conditions.
c.
The probability of an ensuing fire is minimized because all cables utilized for these associated circuits are specified, designed, manufactured, and installed to the same criteria as Class lE cables. Factors that have been taken into consideration include flame retardancy, non propagating and self-extinguishing properties, splicing restrictions, appropriate limitations on raceway fill, appropriate cable derating, and environmental qualifications.
d.
Degradation of an associated circuit because of a raceway failure during a DBE, has been eliminated because all electrical raceway systems within the Nuclear Island are seismically analyzed.
e.
Other design considerations that contribute to the integrity of these associated circuits are:
Cables associated with one train are never routed in raceways containing cable of another train or channel.
D A-M. - -
All cables for instrumentation circuits utilize shielded construction which minimize any unacceptable interaction between Class IE and associated circuits.
All circuits entering the reactor containment are provided with protective devices complying with Regulatory Guide 1.63.
Based on the above design features and analysis, we do not consider these associated circuits.to pose any challenges to any Class IE circuits.
Therefore, the ability for safe plant shutdown under DBE conditions has not been jeopardized.
2.
Train A Associated Circuits That Traverse the Nuclear Island Boundary For analysis purposes, the associated circuits that traverse the Nuclear Island boundary can be further subdivided into two basic types:
(a) those that have their protective device located in the Nuclear Island and (b) those that have their protective device outside the Nuclear Island. It should be noted that there are a limited number of power cables in these categories.
a.
Associated Circuits That Have Protective Device Located in the Nuclear Island These circuits are also designed and installed to meet all the requirements as outlined in Sections B.la, b, e and e.
Though the raceway system outside 'the Nuclear Island is not seismically analyzed; this is of no concern because tha circuit protective devices inside the nuclear island are assumed to perf orm their protective function. It is therefore concluded that the ability for safe plant shutdown under DBE conditions has not been jeopardized by these associated circuits.
D AF--
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b.,
Associated Circuits That llave Protective Device Outside the Nuclear Island Non-Class IE switchgear, motor control centers, and distribution panels outside the nuclear island have been purchased to the same specification requirements as their Class lE counterparts; therefore, the probability of failure under DBE conditions is greatly minimized. Nevertheless, for circuits under this category, a failure of the Non-Class IE protective device,'the Non-Class lE load, and the Non-Class lE power supply must be postulated under DBE conditions. As a result, since the Ncn-Class lE power supply is lost,-all Non-Class IE equipment becomes de-energized; therefore, no possible interaction of the failed Non-Class lE associated circuit with a Class lE circuit is possible.
If, however, one selectively postulates the failure of the Non-Class lE protective device and the Non-Class 1E load, but not of the Non-Class IE power supply, then under this scenario, a failure of the associe*.ed circuits may occur. Possible consequential degradation of a Train A, Class lE circuit is discussed below:
Because the design considerations as outlined in Sections B.lc and e are applicable to these associated circuits, such as cable qualifications, no cable hopping becween separation groups, shielded cable for instrumentation circuits, and because of the conservative nature of our design and our insistance on high quality equipment even for Non-Class 1E applications, we feel the potential for degradation, even under this scenario, is practically non-existent. Ilowever, even if degradation of the Class lE circuits within one separation group were assumed, there would be no effect on the other redundant separation groups.
For the above reasons, we conclude that the ability for the safe plant shutdown under DBE conditions has not been D R AFgj Lged by these circuits.
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3.
Train A Associated Circuits Outside the Nuclear Island The design features, analyses, and conclusions listed under Section B.2.b are applicable to all these circuite.
C.
Train B Associated Circuit Analysis 1.
Associated Circuits Contained Within the Nuclear Island Non-Class lE circuits that remain within the Nuclear Island are permitted to share the same raceways as Train B Class 1E circuits.
These circuits are classified as Train B Associated Circuits and are designed and installed to meet all the requirements placed on associated circuits as required by FSAR Appendix 8A.
Challenges to Class IE circuits because of f ailure in an associated circuit will have no detrimental effect because all Train B power supplies utilized by these circuits such as motor control centers, distribution panels, etc., and their protective devices are Class IE equipment. Failure of a Non-Class lE motor, load, or device connected to the Class lE power supply will be promptly isolated by operation of a Class lE protective device. Therefore utilizing the anlaysis performed for Train A associated circuits in Section B.1 we conclude that the ability for the safe plant shutdown under DBE conditions has not been jeopardized by these circuits.
2.
Associated Circuits That Traverse the Nuclear Island Boundary For analysis purposes, the associated circuits that traverse the Nuclear Island boundary can be further subdivided into two basic types:
(a) those that have the protective devices located in the Nuclear Island and (b) thor,e that have their protective devices outside the Nuclear Island.
DRAF a.,
Associated Circuits That Have Protective Devices Located in the Nuclear Island There are very few Train B associated circuits that traverse the Nuclear Island. boundary. These circuits are unavoidable either because of plant design constraints, such'as the need for interlocks and permissives.for the preferred power supply circuits to Train B emergency buses, or because of features provided to improve plant reliability, such as power supply and control for the station service air compressors fed frca Train B buses. The portion of these circuits which are outside the Nuclear Island are routed in dedicated embedded or exposed conduits; thea ' ore, the potential of harmful interactions with other associated circuits is minimized.
The design features described in Section Col for associated circuits contained within the Nuclear Island, are also applicable to these circuits. Though the conduit system cutside the Nuclear Island is not seismically analyzed, this is of no concern because the circuit protective devices located in the Nuclear Island are assumed to perform their protective f'
function.
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Based on the above, we conclude that the ability for the. safe plant shutdown under DBE conditions has not been jeopardized by these few circuits.
b.
Associated Circuits That Have Protective Devices Outside the Nuclear Island i
The only circuits under this category are the 15 kV cables to the reactor coolant pumps for motor feeders and potential transformers. These interlocked armor cables are routed in embedded conduit outside the Nuclear Island and are in dedicated seir.mically analyzed raceway systems in the Nuclear Island. Furthermore, the portion of the circuit entering the containment is protected by qualified fuses located in the.
DRA' T
electrical penetration area which would open the circuit in the event of a failure of a reactor coolant pump.
The 15 kV cables used on these circuits meet all the construction and material requirements placed on the 5 kV Class lE cables, i.e.,
flame retardancy, etc., but do not have LOCA/MSLB qualifications.
Based on the above design features, we -conclude that these circuits do not pose any challenges to Class lE circuits.
D.
Gtoup C and D Circuits Separation Groups C and D, which are comprised of circuits for Channels III and IV, do not have any associated circuits. The Channel III and IV circuits remain within the Nuclear Island except for the turbine trip inputs to the Reactor Protection System (RPS). These circuits outside the Nuclear Island are routed in conduits dedicated to each separation group.
Based on the above design features, and since these channels meet all requirements as defined in FSAR Appendix 8A, these channels are not susceptible to any challenges from any associated circuits; therefore, the ability for the safe plant shutdown under a DBE cannot be jeopardized.
E.
Results of Analysis Based on the above discussion, it is concluded that under any Design Basis Event the Safe Shutdown capability of the plant has not been impaired.
DRAFT t
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ror 480 VAC, 120 VAC 6125 VDC feeders requiring cables 2/0 AWG and sr. aller.
h Reserved for Control Rod Drive power feeders only.
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