ML20083P922

Discusses Plans for Upgrading Core Exit Thermocouple Sys,Per 840322 Telcon.Illustration of Sys Components Encl

ML20083P922
Person / Time
Site:	Summer
Issue date:	04/16/1984
From:	Dixon O SOUTH CAROLINA ELECTRIC & GAS CO.
To:	Harold Denton Office of Nuclear Reactor Regulation
References
NUDOCS 8404200264
Download: ML20083P922 (4)

Text

i SOUTH CAROLINA ELECTRIC & GAS COMPANY POST OPriC8 764 cotuusia. soutw canotina aoaie April 16, 1984 w ete.a o

..no S Mr. Harold R. Denton, Director Office of Wclear Reactor Regulation U.S. Nuclear Regulatory Consnission Washington, D.C. 20555

Subject:

Virgil C. Sumner Wclear Station Docket No. 50/395 Operating License No. NPF-12 Inadequate Core Cooling

Dear Mr. Denton:

In a telephone conference held with the Staff on March 22, 1984,. plans for upgrading the Virgil C. Stamer Welear Station (bre EKit %ermoccuple (CET)

Systen were discussed. %e Staff requested that a sumnary description of the CEr System be provided to supplenent previous subnittals dated Wrch 5, 1983, August 26, 1983 and February 17, 1984.

%e attached figure illustrates the system couponents described below.

Qualified cable, connectors and penetrations will be installed for all fifty-one (51) CETs inside the Reactor Building. With the exception of the area where the thermocouples exit the reactor vessel head, the circuits will be divided into two trains and electrical separation will be maintained. In addition, the circuits will be seisnically supported. We need for reference junction bones inside the Reactor Building will be eliminated through the use of electrical penetrations with cremel and alumel conductors.

Outside of the Reactor Building, the circuits will be routed from the penetrations to the thermoccuple transmitter / isolation cabinets maintaining electrical separation and utilizing qualified cable and seimnic supports.

A thernrw=gle transnitter/ isolation cabinet will be provided for each train containing electronic modules which provide cold junction compensation and lE electrical isolation for each thermoccuple. his electrical isolation will assure that any credible faalts on the nm lE circuits connected to the output of the isolators will not degrade the lE thermocouple circuits connected to the input of the isolators. %ese cabinets will be located in the cable spreading area one floor below the Control Roan.

%e signals fran the output of the isolators will then be wired to the input of two computers and the microprocessor haw =*maling monitors.

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s Mr. Harold R. Denton Inadequate Core Cooling April 16, 1984 i

Page #2 s

t All 51 signals are inputs to both the plant process conputer,(primary display) and the Technical Support Center computer (Safety Parmter Display Systen [SPDS] and Technical Support Center /Baergency Operations j

Facility displays). Eight A-Train signals (two per' core gudant) are g

J input to the A-Train subcooling monitor and eight B-Train signals (tw per core quadrant) are input tc' the B-Train aihmnling monitor; Since separation cannot be maintained for inputs to the ccuputers, all

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circuits from the output of the isolators will be routed as X-Train.

7, The subcooling monitors are micnoprem.sser haaarl systems that calculate 1

subcooling margin based on Reactor coolant System tenperature and pressure inputs. The inputs to each monitor include two hot leg and two cold leg wide range reaperatures (Hesistance Temperature Detectors), one' narrow range and two wide range pressures;- and eight core exit thermoccuple tenperatures -(two per core quadranti.. Each monitor calculates two subcooling marginy.one based on auctioneered high wide range taiperature and auctioneered low pressure; and a aamnr1 haaarl on auctioneered high core exit temperature and auctioneered Iciw prammire. Both calculated mihmnling

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margins'and all of the input values.can be callarl up on an alpha-numeric j

display on the nonitors which are located in the Control Rocat. Both subcooling margins frtsriboth nonitors are displayed continuously on four j

separate vertical indfcators on the main control board.-

The CET readout on.the aihmnling nonitors is'a harimn to the plant process i

1, c<mputer and SPDS displays-available Tin 'the Control Rcica., Althcugh a fully h= anted seisnic qualification of the subcooling' nonitors has not been ccupleted, the monitors and the cabinet in which they ar'e mounted were designed and built to be seisatically qualified. Preliminary selenic tests have confirmed;the adequacy'cfithis design.

Should the CET tenperatures bkrequired following 'a seimnic event which disables all of-the Control Race CET raarlmts, the CEF signals can be read manually at the input to the thermocouple transnitter/ isolator cabinets withJa handheld ther=nrmple meter. This operation will be included in a h==nted training program for operators.

considering the confidence we have in the seismic design'of the subcooling j

monitors, the low peabability of inadequate core cooling conditions resulting from a'seimnic event and the ready access ~ to fully qualified j'

signals for manual'=mamirement, South Carolina Eiect'ric and Gas Ocapany (SPEEG) considers this design adequate'to address the intent'of-the 5

requirement!s for display of sthis infornstion.-

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~In crder to satisfy license condition 2'.C.23(d), we are prr M ing with

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. design and procurement of thisf system as. described to support (installation '

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Mr. Harold R. Denton Inadequate Core Cooling April 16, 1984 Page #3 l

during the first refueling outage.

If you have any further questions, please advise.

Very truly yours, f f.

O. W. Dixon)-Of.

AW/OiO/gj Attacment:

cc:

V. C. Sumner C. A. Price T. C. Nichols, Jr./O. W. Dixon, Jr.

C. L. Ligon (NSRC)

E. H. Crews, Jr.

K. E. Nodland E. C. Roberts R. A. Stough W. A. Williams, Jr.

G. Percival D. A. Natsnan C. W. Hehl J. P. O'Reilly J. B.' Knotts, Jr.

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