ML19350C390
| ML19350C390 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 03/27/1981 |
| From: | Crutchfield D Office of Nuclear Reactor Regulation |
| To: | Counsil W NORTHEAST NUCLEAR ENERGY CO. |
| References | |
| TASK-08-04, TASK-8-4, TASK-RR LSO5-81-03-062, LSO5-81-3-62, NUDOCS 8104010325 | |
| Download: ML19350C390 (5) | |
Text
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, ff UNITED STATES y
,,, ( [,g NUCLEAR REGU,LATORY COMMISSION g.g ^ /. E WASHINdTON, D. C. 20555 MAR.'. 7 7gg(
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P Docket No. 50-245 l3h E'
LS05 03-062 g gggg, Mr. W. G. Coun:.11, Vice President Nuclear Engineering and Operations
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Northeast Nuclear Energy Company Post Office Box 270 Hartford, Connecticut 06101
Dear Mr. Counsil:
SUBJECT:
SEP TOPIC VIII-4, ELECTRICAL PENETRATIONS OF REACTOR CONTAINMENT (MILLSTONE NUCLEAR POWER STATION UNIT 1)
Your letter of January 29, 1981 did not provide sufficient information upon which we could evaluate the coments you have provided. We understand that you do not agree with the model used and assumptions made in the initial conditions and material properties.
Unfortunately, you have not provided sufficient technical information nor detailed schematics to support your comments. For exar:ple, we consider the test results presented for the electrical penetrations do not establish that the leakage rates would be acceptable.at temperaures above 0
177 C since no test data was provided to support the 250 C temperature limit for the material stated by NNECo. Further, credit is claimed for seals at both ends of a penetration where only one seal appears to be tested.
Our audit calculations failed to establish that the fault current protection for containment electrical penetrations in SEP facilities is generally adequate.
This does not necessarily mean that the protection is inadequate. Our calcula-tions were simplified and conservative so that there is room to improve the result by using more realistic models. Thus, you are requested to evaluate the adequacy of the electrical penetrations in your facility in accordance with the enclosed position.
Generally, where needed, our position calls for more realistic calculations than were used in cur 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 straightforward alternatives such as deenergizing circuits.are also provided for.
OW If any instances arise where your calculations cannot demonstrate circuit 3
protection in accordance with our position, you are requested to inform us of your intended corrective actions.
E iB10.4010 M f
MAR 0 7 ;3g; -
- 4 In order to complete our evaluation of Topic VIII-4, please provide a report
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describing the calculations performed and criteria for evaluating the penetrations for the specific circuits identified in the staff's previous report within 30 days of receipt of this letter.
The report as a minimum should address the following items:
1.
Backup protection for penetrations like X-101 A and X-105D.
2, Protection of parallel conductors and seals if an open circuit should develop.
3.
Circuit design and theory of operation for differential current protection of pump motor circuits for
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(a) Motor Faults (b) Conductor Faults at the penetration (single phase and bolted faults).
4.
An analysis of how the design of the differential protection satisfies the single failure criterion.
5.
A description of testing methods and results for both seals on electrical penetrations.
6 The basis for your assumption that single failures in electrical circuits will be short circuits instead of open circuits in parallel conductors.
7, You should also provide a copy of an relevant proprietary data relating to c;alification of the electrical penetrations.
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, ennis M, Crutch te d, C e Operating Reactors Bran No. 5 Division of Licensing
Enclosure:
As stated cc w/ enclosure:
See next page
.m-.
EN;LOSURE POSITION ON PROTECTION OF CONTA!EENT ELECTRICAL PENEiRATIONS AGAINil FAILURES CAUSED ET FAULT AhD OVERLOAD CURREh15 FOR SEP PLANTS Introduction As part of the Systematic Evaluation Program (SEP) the NRC staff performed an audit, conparing sample containment electrical penetrations in SEP facilities eith current licensing criteria for protection against fault and overload currents following a postulated accioent. The simplified and conservative codel used did not show that the SEP facilities meet current licensing criteria nor did it show the existing circuit prctection to be adequate.
Accordingly, e
the SEP licensees are requested to demnstrate, using rore realistic calcula-tions where necessary, that the circuit protection is adequate in accordance eith the position described belo=.
Beck m und In licensing new plants, the staf f requires compliance with the recocnende.tions of Regulatory Guide 1.63 or an acceptable alternative method.
For each containment electrical penetratien, tne >retective systems provide primary and backup circuit protection devices to prevent a single failure in con-junction with a circuit overload from impairing containment integrity. The primary and backup protection devices have trip tire vs. current response charac-teristics which assure protection against penetration failure.
The protection devices are periodicallp tested to verify trip setpoints and adequacy of response.
No single failure allows excessive currents in the penetration conductors which will degrade the penetration seals. Knere external control power is used for actua'cing the protection systems the power for primary and backup breakers are derived from separate sources. Overcurrent signals for tripping primary and backup system devices are electrically indepencent and physically separated.
Staff Audit The safety objective of SEP Topic VIH-4, " Electrical Fenetrations of Reactor Containment," is to assure that all electrical penetrations in the containment structure are designed not to fail from electrical faults during a high energy line break (LOCA or secondary system line break).
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We have performed preliminary evaluations, on a conservative basis, of the f alt, current protection for three samle containcent electrical penetrations for each of the eleven SEP plants.
The entire penetration was assumed to be initially at the peak calculated LOCA temerature. Then, for a given fault current, the time to heat the wire to the limiting raterial temerature (usually the reiting point of the seal raterial) was calculated.
This tire was cc pared to the ~tice for the protective device (s) to interrupt the fault current.
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On this basis, several penetrations exceed limiting tegeratures if the prirary protection device fails.
Others do so without postulating prirary device failure.
Two of the sa@le penetrations even have relting temeratures less than the peak LOCA temerature and thus exceed the limits of this rodel even if there is no f ault current.
(References 1 through 11)
This does not necessarily mean that the knetrations would actually fail.
The analysis was conservative, partieularly in assuming that the penetration was initially at the peal calculated containrent temerature. The penetrations would not reach such a temerature following an eccident.
In addition, licensee co. rents have indicated that there ray be so e errors in the calculations.
(For exagle, Northeast Utilities letter dated August 29, 1930 Dock et No. 50-245, providing coments on the staff calculations for Millstone, Unit 1). Nevertheless, this audit clearly did not put the ratter to rest.
Position Each SEP licensee is requested to evaluate the adequacy of tne existing fault current protection for containrent electrical penetrations in accordance with the position discussed in core detail below and to propese remedies where neeoed in order to neet the position.
1.
The basic requirement of Regulatory Guide 1.63 that all penetration circuits, Class IE or non-Class IE, be provided with overcurrent protection in conforr,ance with the redundancy and testability requirements of IEEE Std 279-1971 should be met; l
2.
A single circuit breaker to protect a penetration serving a Class IE circuit or i
a non-safety circuit containing only components that are qualified to Class IE requirements is acceptable provided that each component of such circuit is qualified to the accident environment; 3.
A circuit whose loads inside 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 deenergized by positive means such as those outliend in Branch Technical Position ICSB 18 (PSB) of Appendix 8A to the Standard Review Plan whenever cbntainment integrity is required.
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P00R R GllCI.
Notes For the purpose of evaluating the adequacy of protection for containment protection, faults should be postulated up to a bolted cable fault inside containeent at the penetration (a bolted three phase fault for three phase circuits). The prinary protection device should have a trip tire vs. current response characteristic that assurts 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 rarimum possible fault current for the circuit or backup protection fast response current limiting fuses should be provided.
m In addition, fuses may be used in lieu of circuit breakers as protective devices.
Where fuses are used, documentati.on of their response characteristics derived from production testing shoald be available_for audit.
It is acceptable to use less conservative rodels than were used in our preliminary evaluations provided that they eddress f ault currents up to bolted faults and still provide reasonable assurance that the penetration will not f ail.
For example, a core realistic initial terperature of the containment penetration could be determined rather than assuming the penetration has reached the peak calculated containment atmosphere te=p-erature.
Circuits may be modified to reduce the short circuit current to acceptable values by the use of current limiting devices (such as resistors, isolation transformers, and changing transformer taps) external to the containment.
t P00R BRIGRAL o
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