ML20151U854
| ML20151U854 | |
| Person / Time | |
|---|---|
| Issue date: | 08/10/1988 |
| From: | Murley T Office of Nuclear Reactor Regulation |
| To: | Franklin F PROFESSIONAL ANALYTICAL & CONSULTING ENGINEERS, INC. |
| Shared Package | |
| ML20151U858 | List: |
| References | |
| NUDOCS 8808190279 | |
| Download: ML20151U854 (5) | |
Text
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AUG 1 0 1989 Mr. Frederick F. Franklin, P.E.
President Professional Analytical and Consulting Engineers, Inc.
4325 Indeco Court Cincinnati, Ohio 45241
Dear Mr. Franklin:
This letter is provided in response to your letter of July 15, 1988 in which you referred to a newspaper article stating that nuclear power plants may have bought used circuit breakers that were falsely labeled as new. Your letter indicates that even new North American circuit breakers are riot properly designed to prevent short circuit fires, particularly in residential and commercial installations. Although you do not specifically mention any problems in nuclear power plants, we conclude that your concern extends to them also.
The information you submitted indicates that your research concentrated on 15-and 20-ampere circuit breakers. You note that most househo'd short circuits result in a 150- to 400-ampere short and that the magnetic (qnick) trips of North American circuit breakers may be set in excess of this range.
You state that the thermal (slow) trip may require several seconds at 100 amperes.
Further, you note that European breakers are designed to magnetically trip at lower ratings than North American breakers.
Our concern regarding the nuclear power plant circuit breakers that may have been falsely labeled as new, as mentioned in the newspaper article, is with their ability to function as they are supposed to do. As we understand it, your concern is with the designed magnetic trip settings of North American circuit breakers, particularly that they may not trip fast enough during a short circuit to preveat a household fire. We will attempt to address this concern as it may relate to nuclear power plants.
First, we note that the European-style breakers that you appear to be reconinending have not been approved by Underwriters Laboratories, Inc. (UL).
One of the reasons given by UL for this circumstance is that the interrupting ratings of European breakers are not sufficient for most North American applications. This fact would be particularly significant in a nuclear power plant where the protection of safety-related equipment is a primary concern.
Second, nuclear power plants have extensive fire protection, fire detection Q
and fire mitigation requirements. These include:
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Identification of fire hazards I '
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Automatic fire detection systems j/7 Automatic fire suppression systems si 8808190279 880810 P
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F. Franklin,bG 1 0 1933 Fire barriers and barricades Separation of cables from combustible material Onsite fire brigades Personnel training and periodic surveillance of cables and equipment (8) Enclosure of cables' and equipment In addition to these requirements, nuclear plant regulations also require rigorous design and testing of electrical equipment and circuits to ensure a high level of reliability of safety systems. The design requires redundancy of electrical circuits and separation of the redundant circuits.
Flame tests, in accordance with Institute of Electrical and Electronics Engineers Standard 383, are required to ensure that cables are fire resistant and will not propagate a fire. Thus, it is unlikely that a relatively low-amperage short circuit as you described would cause a significant fire. Finally, experience does not indicate that a fire hazard exists at nuclear piants because of low-amperage short circuits.
Of greater concern are high-amperage faults that are not cleared and that may cause equipment damage or may propagate to other systems.
Finally, designing or setting circuit breakers to trip at five times the breaker ampere rating could result in spurious trips of the breakers during motor starting.
Such a trip could disable s&,ty equipment and safety systems when they are most needed to prevent or to mitigate an accident condition.
Although we do not anticipate any significant problems at nuclear power plants from the types of short circuits you described, we appreciate the insight you have provided regarding this phenomena and will consider it in our ongoing safety reviews. We thank you for your concern.
Sincerely, OPI inal signed by, 8
Dua3 E. Murloy Thomas E. Murley, Director Office of Nuclear Reactor Regulation
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F. Franklin (1 Identification of fire haza ds 2
Automatic fire etection sy tems 3
Automatic fire s ppression systems
- 4) Fire barriers an barrica es
- 5) Separation of cabl s fro combustible material
- 6) Onsite fire brigad
- 7) Personnel training nd eriodic surveillance of cables and equipment (8) Enclosure of cables a equipment In addition to these requirements, nuclea
)lant regulations also require rigorous design and testing of electrica e'uipment and circuits to ensure a high level of reliability of safety sys ms.
The design requires redundancy of electrical circuits and separation o the edundant circuits.
Flame tests, in accordance with Institute of Electr al an Electronics Engineers Standard 383, are required to ensure that cable are fi e resistant and will not propagate a fire. Thus, it is unlike' that a elatively low-amperage short circuit as you described would cause i fire.
F1 ally, experience does not indicate that a fire hazard exists a nuclear p1 ts because of low-amperage short circuits. Of greater concern re high-ampe age faults that are not cleared and that may cause equipmen damage or ma propagate to other systems.
Also, designing or setting circuit reakers to trip at five times the breaker ampere rating could result in spur ous trips of the reakers during motor starting. Such a trip could remov safety equipment and safety systems when they are most needed to prevent o to mitigate an ac dent condition.
Although we do not anticipate an problenis at nuclear ower plants from the types of short circuits you des ibed, we appreciate t insight you have provided regarding this phenomer a and will consider it n our ongoing safety reviews. We thank you for your concern.
Sincerely, Thomas E. Murley, Director Office of Nuclear Reactor Regulation
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Ident\\iicationoffirehazard a
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Automat 1 fire detection sys ems c
Automatic fire suppression stems d
Fire barri rs and barricade e
Separation f cables from ombustible material f
Onsite fire igades g
Personnel tra ing and pe iodic surveillance h
Enclosure of c les and e uipment In addition to the fire protection re uirem ts, nuclear plant regulations require rigorous design and testing of electri al e uipment and circuits to assure a high reliability of safety systems. The des gn equires redundancy of electrical circuits and separation of the redundant circuits Flaue tests, in accordance with IEEE Standard 383, are required to ensure that cables are fire resistant and will not propagate a fire. Thus, it is unlikely t a relatively low amperage short circuit as described by you would propag te into a fire.
Finally, experience does not suggest a firc. hazard at nuclear pl ts ue to low amperage short circuits.
Of greater concern are high amperage fa its w ich are not cleared and which may result in equipment damage or may prop gate to other systems.
Also, designing or setting circuit br akers to t ip at five times the breaker ampere rating could result in spuriou trips of t e breakers during motor 4 tarting requirements. Such a trip could rem ve safety equ pment and safety systems when they are nost needed to prevent or itigate an acci ent condition.
Although we do not foresee any im diate concern at n clear plants resulting from the types of short circuits descri ed by you, we appr iate the insight you have provided regarding this phenomena and will consider i in our ongoing safety reviews. We thank you for this ntribution to our kno ledge.
Thomas E. Murley, Direct r Office of Nuclear Reacto Regulation i
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F. Franklin -
Distributior::
.1 Central Files SELB Rdg.
j NRC PDR A.Toalston(PF)
J. E. Knight.
F. Rosa NRC Editor A. Thadani L. Shao (YT 889133)
T. Martin J. Sniezek T. Murley B. Grimes D.Mossburg(YT 889133)
J. Norberg F. Gillespie S. Ebneter j
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