ML20055A913
| ML20055A913 | |
| Person / Time | |
|---|---|
| Site: | Fermi  |
| Issue date: | 07/15/1982 |
| From: | Tauber H DETROIT EDISON CO. |
| To: | Youngblood B Office of Nuclear Reactor Regulation |
| References | |
| EF2-57-987, NUDOCS 8207200123 | |
| Download: ML20055A913 (3) | |
Text
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Harry Tcuber Erg nd Construct!on Detroit Edson Edisin>>-
July 15, 1982 EF2 - 57,987 Mr. B. J. Youngblood U. S. Nuclear Regulatory Commission Licensing Branch No. 1 Division of Licensing Washington, D. C. 20555
Dear Mr. Youngblood:
Re ferences :
(1)
Enrico Fermi Atomic Power Plant, Unit 2 NRC Docket No. 50-341 (2)
Letter of May 5, 1982, B. J. Youngblood to H. Tauber
Subject:
Errors in BWR Water Level Indication This is in response to your letter of May 5, 1982 regarding errors in BWR-water level indication.
Reactor vessel water level indication is accomplished on BWR designs by employing the hydraulic differential pressure measurement method. The particular design implemented on Fermi 2 is the cold reference leg-design. Condensing chambers connected to the steam space in the vessel are used to generate a fixed reference level for the cold reference. leg.
Pressure taps at different elevations in the water space of the vessel are employed as the variable leg of each dif-ferential pair.
No hydraulic connection or path exists normally between the two differential legs of the measurement at the instrument end.
Each leg includes a restriction orifice near the primary coolant pressure boundary and an excess flow check valve at the primary containment wall.
The differen-tial pressure instruments are mounted on racks which are located in the reactor building near the drywell wall.
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i it The Fermi 2_ design utilizes two types'of level trainsmit-
.J ters, the Rosemount 1151 series andtthe Gener59 E16ctr/c i
GE-MAC 555.
The Rosemount is a.capacitivv sens'er design with a 4 to'20. milliampere output, and the Q
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General Electric is a bellows / force balance primary senk J,' /
sor design with a-10 to 50 milliampere output span.
The level instrument designations *and arrangements are
/4 shown on Figurc 7 3-9 of the FSAR.,
All of the. Fermi N
level indicators are referenced to ~ the. top o'f active fuel as discussed in Section H. ILK.3 27 of the FSAR.-
h 3
Reactor vessel. taps, lines, racks and' instrument's are
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divided into two divisional groups to maintain spatisi d
diversity.
The ability of the ECCSisystems to'N'i,thstan'd a single failure is dependent upon the physical.sepaga-tion inherent in the level sensing logic desigd.i
'I In order to minimize the effects of drywell;t[emperature -
'I changes, each pair of sensing linea is run withiapproxi-r/
mately equal vertical drops within the drywell.
This J
j approach essentially eliminates the effectfof drywell temperature changes on level by producing-a self-i compensating effect.
A further measure to preclu.de potential level measurement errors is limiting the ver-i tical drop of both sensing lines within the drywell..-
Only the amount of slope necessary to assure self-venting g/
of the lines is maintained within the drywell... As a result, the potential error due to a loss of liquid in7'
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the sensing lines is minimized.
The nominal lev'el sen-sing line vertical drop in the drywell is.; sixteen y
inches.
This distance is measured from vessel tap ele-1 Ii vation to the drywell penetration.
h As a result of the preceding design features;'drywell
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temperature effects on level instruments are judged to be very minor.
Potential for' instrument line vaporiza-f.
tion (flashing) is very nearly zero due to the' fact that c
cold reference leg designs have a saturation pressure of 118 psia when the drywell is at the maximum predicted temperature of 3400F.
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An analysis of the potential failures which result in high drywell air temperatures has,beenfperformed by
'/4 General Electric Company and the'results published in
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NEDE-24801, " Review of BWH Reactor Vessel Water Level
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Measurements".
This report conc'lu' des! that the cold
, r, reference leg level measurement design wit)f parallel lines in the drywell and restricted serftical drop will
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.r perform adequately under any postulated degradation without further modification. In addition, the Fermi 2 level measurement system includes a degree of enhan-cement to allcw the plant to withstand failures beyond the design basis as discussed in Section 2.4 of the e
Edison has concluded that supplemental procedures in addition to those presently developed in response to the emergency procedure guidelines are not necessary.
Should you have any additional questions, please con-
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tact L.' E. Schuerman, (313) 649-7652.
Sincerely,
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L. L. Kintner
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