ML20005A070
| ML20005A070 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 06/23/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Kay J YANKEE ATOMIC ELECTRIC CO. |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR LSO5-81-06-096, LSO5-81-6-96, NUDOCS 8106290328 | |
| Download: ML20005A070 (5) | |
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June 23, 1981 g3?!
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@k Docket No. 50-29 LS05-81-06-096 I N I M 2 6 lSgg 5 5 I' " W % j 2
Mr. James A. Xay y
Senior Engineer - Licensing
-, p' Yankee Atomic Electric Company W Ji.'
s 25 Research Driva Westborough, Massachusetts 01581
Dear Mr. Kay:
RE: SEP TOPIC VIII-4, ELECTRICAL PEfiETRATIONS OF REACTOR CONTAINMENT (Yankee-Rowe)
Draft Technical Evaluation Reports (TER) on Topic VIII-4 have been prepared and forwarded to all SEP Licensees for coement. Comments from some licensees (e.g., Northeast Utilities letters dated August 29, 1980 and January 29, 1981) indicated concern with the model used and assumptions made in the initial conditions and naterial properties.
Unfortunately, most respondents have not provided sufficient technical information nor detailed schematics to support th
,;oments.
Our audit calculations failed to establish that the fault current protec-tion for containment electrical penetrations in SEP facilities is generally adequate. This does not necessarily mean that the protection is inadequate.
Our calculations were simplified and conservative so that there is room to improve the result by using more realistic models.
In addition, licensee coments have indicated that there may be some errors in our calculations. Nevertheless, our audit did not put the natter to rest and, thus, you are requested to evaluate the adequacy of all electrical penetrations in your facility in accordance with the enclosed position.
Generally, where needed, our position calls for mt.re realistic calcula-tions than were used in our audit.
In relation to current licensing criteria, it provides relief from the need for redundant circuit protective devices in certain instances and specifically provides for using fuses as an altermative to circuit breake s.
Other straightforward alternatives r
such as daenergizing circuits are also provided for.
If any instsnces arise where your calculations cannot demonstrate circuit protection in accordance with our position, you are requested to inform us of your intended correctivc actions.
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. In order to couplete our review of Topic VIH 4, please provice a report describing the calculations performed and criteria used for evaluating the penetrations for the specific circuits identified in the staff's previous report for your plant within 30 days of receipt of this letter.
The report as a minimum should address' the following items:
1.
Backup protection for the low voltage and de penetrations.
2.
Protection of parallel conductors and seals if an open circuit should develop.
The requested infornation will be used to revise our topic Safety Evaluation Report and will be used in the preparation of the integrated assessment for your plant.
Sincerely, Dennis M. Crutchfield, Chief Operating Reactors Branch #5 Division of Licensing
Enclosure:
As stated cc w/ enclosure:
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June 23,1981 Docket No. 50-29
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LS05-81-06-096 Mr. James A. Kay Senior Engineer - Licensing Yankee Atomic Electric Company 25 Research Drive Westborough, Massachusetts 01581
Dear Mr. Kay:
RE: SED TOPIC VIII-4, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT (Yankee-Rowe)
Draft Technical Evaluation Reports (TER) on Topic VIII-4 have been prepared and forwarded to all SEP Licensees for comment.
Comments from some licensees (e.g., Northeast Utilities letters dated August 29, 1980 and January 29, 1981) indicated concern with the model used and,
assumptions made in the initial conditions and material properties.
Unfortunately, most respondents have not provided sufficient technical information nor detailed schematics to support their comments.
Our audit calculations failed to establish that the fault current protec-tion for containmant electrical penetrations in SEP facilities is generally adequate. This does not necessarily mean that the protection is inadequate.
Our calculations were simplified and conservative so that there is room to improve the result by using more realistic models.
In addition, licensee comments have indicated that there may be some errors in cJr calculations.
Nevertheless, our audit did not put the matter to rest and, thus, you are requested to evaluate the adequacy of all electrical penetrations in your facility in actordance with the enclosed position.
Generally, where needed, our position calls for more realistic calcula-tions than were used in our audit.
In relation to current licensing criteria, it provides relief from the need for redundant circuit protective devices in certain instances and specifically provides for using fuses as an alternative to circuit breakers.
Other streightforward alternatives such as deenergizing circuits are also provided for.
If any instances arise whue your calculations cannot demonstrate circuit protectior, in accordance with our position, you are requested to inform us of your intended corrective actions.
~.
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In order to complete our review of Topic VIII 4, please provide a report describing the calculations performed and criteria used for evaluating the penetrations for the specific circuits identified in the staff's previous report for your plant within 30 days of receipt of this letter.
The report as a minimum should address the following items:
1.
Backup protection for the low voltage and de penetrations.
2.
Protection of parallel conductors and seals if an open circuit should develop.
The requested information will be used to revise our topic Safety Evaluation Report and will be used in the preparation of the integrated assessment for 'your plant.
Sincerely, y.
1 Dennis M. Crutchfield, C ' ef Operating Reactors Branch #5 Division of Licensing
Enclosure:
As stated cc w/ enclosure:
See next page i
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ECLOSURI
. POSITION ON PROTECTION OF CONTAINENT ELECTRICAL PENETRATIONS AGAIN51 FAILURES CiuSED e,Y f AULT AND OVERLOAD CURRENTS FOR SEP PLAN 15 Introduction As part of the Syster tic Evaluation Program (SEP) the NRC staff performed an audit, cor:p,aring sample containment electrical penetrations in SEP facilities with current licensing criteria for protection against f ault and overload currents following a postulated accident. The simplified and conservative model used did not sho= that tne SEP facilities meet current licensing criteria e
nor did it show the existing circuit protection to be 3dequate. Accordingly, the SEP licensees are requested to demonstrate, using rore realistic calcula-tions where necessary, that the circuit protection is adequate in accordance with the position described below.
Eactemund In licensing new plants, the staff requires coc;1iance with the recocmendations of Regulatory Guide 1.63 or an acceptable alternative method.
For each containment electrical penetraticn, tne retective systems provide primary and backup circuit protection cevices to prevent a singl.e failure in con-junction with a circuit overload from impairing centainment integrity. The prir.ary and backup protection devices have trip time vs. current response charac-teristics which assure protection against penetration failure. The protection devices are periodically tested to verify trip se: points and adequacy of response.
No single failure all'ows excessive currents in the pewtration' conductors which will degrade the penetration seals. Where external control power is usec for l
actuating the protection systems the power for primary and backup breakers are derived from separate sources. Overcurrent signals for tripr en; primary and backup syste devices are electrically indepencent and physically separated.
Staff Audit
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The safety objective of SEP Topic,III-4, " Electrical Penetrations of Reac*ar Containment," is to assure that C.1 electrical penetrations in the containment structure are designed not to fail from electrical faults during a high energy line break (LOCA or secondary syste: line break).
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We have perforced preliminary evaluations, on a conservative bash, of tha icuir, current protection for three samle contain.en: electrical penetrations for each of the eleven SEP plants. The entire penetration was assumed to be initially i at the peak calculated LOCA temerature. Then, for a given fault current, the time to heat the wire to the liciting raterial'tegerature (usually the ce.iting point of the seal raterial) was calculatea This tire was co: pared to the tice for the protective device (s) to interrupt the fault current.
On this basis, several penetrations exceed l'miti~ g tegeratures if the prirary i
n protection device fails.
Others do so without postulating prirary device failure.
Two of the samle penetrations even have reiting tegeratures less than the peak 1.00A tegerature and thus exceed the limits of this rodel even if there is no f ault current.
(Reference.c 1through11)
This does not.necessarily mean that the penetrations would actually fail.
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The analysis was conservative, particuluriy in assuming that the penetration tras initially r. the peat calculated containcent te.perature. The per,etraticris would not reach such a temerature folleving an accident.
In addition, licensee co rents have indicated that there ray be sore errors in the calculations.
(For
-exagle, Northeast utilities letter dated August 29, 1950, Doc', et No. 50-245, '
providing connents on the staff calculations for Millstona Unit 1).
Nevertheless, this auBit clearly did not put the ratter to rest.
Position Each SEP licensee is requested to evaluate the adequacy of the existing fault current protection for centainant electrical penetrations in accordance with the position discussed in rare detail below and to propese re:edies where needed in order to reet the position.
1.
The basic requirement of Regulatory Guide 1.63 that all penetration circuits, Class IE or non-Class IE, be provided with overturrent protection in confom.ance with the redundancy and testability requirements of IEEE Std 279-1971 should be-met; 2.
A si6gle ctreuit breaker to protect a penetration serving a Clasc IE circuit or F
a non-safety circutt containing only components that are qualified to Class IE requirements is acceptable provided that each component of such circuit is L
qualificd to the accident environment; 3.
A circuit 'ahose loads insida containment are not required to mitigate the _
consequences of accidents may be automatically disconnected from its power source on receipt of an accident signal or it may be maintained dcenergized by positive means such as those outliend in Branch Technical Position ICSB 18 (PSS) of Appendix 8A to the Standard Review Plan whenever c'unt&inment integrity is required.
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Notes For the purpose of evaluating the adequacy' cf protection for containment protection, faults should be postu'=ted up to a bolt,ed cable fault inside containment at the penetration (a, sited three phase fault for thres phase circuits ).
The primary protection device should have a trip time vs. current response characteristic that assures against penetration failure under all fault conditions.
Circuit breakers should be tested periodically to verify their trip setting value and response tire. Breakers should be designed to interrupt the rarim;m possible f ault current for the circuit or backup protection fast response current limiting fuses should be provided.
e In addition, fuses ray be used. 'n lie'u of circuit brealers as protective devices.
Where fuses are used, documentati,on of their response characteristics derived f rom producpion testing should be availa,ble_for audit.
It is acceptable to use less conservative rodels than were insed in our preliminary evaluations provided that they address f ault currents up to belted f aults and still provide reasonable assurance that the penetration will not fail.
For exarple, a more realistic initial terperature of the containrent cenetration could be determined rather than assuming the penetratian has reached the peal calculate: cor.tainman; atresphere temp-e rature.
- ircuits may be modified to reduce the short circuit current to accep*able values by the use of current limiting devices (such as resistors, isolation.e transformers, and changing transfo. mar taps) external to the containment.
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