ML20052C061
| ML20052C061 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 04/30/1982 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| RTR-NUREG-0737, RTR-NUREG-737, TASK-2.F.2, TASK-TM NUDOCS 8205040317 | |
| Download: ML20052C061 (5) | |
Text
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_ p Mr. Harold R. Denton, Director ys f
Office of Nuclear Reactor Regulation
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U. S. Nuclear Regulatory Comnission My 4'
Washington, D.C.
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Subject:
Virgil C. Sumner Nuclear Station Docket No. 50/395 NURED 0737, Item II.P.2 Incore Thermocouple Qualification
Dear Mr. Denton:
In a recent telephone conference with the NRC Staff, South Carolina Electric and Gas Conpany (SCE&G) was requestcd to supply additional information about the existing incore thernocouple installation at the Virgil C. Summr Nuclear Station to supplement the information provided in our letter dated M1rch 16, 1982. Specifically, the Staff requested information that muld indicate the expected reliability or usefullness of the existing incore thermocouple installation during and following an event which produces a harsh environment insi& tM reactor buildig.
The attached figure provides a schematic of our existing incore thermocouple installaticn insi& tM Reactor Buildig. The 51 stainless steel sheathed chrcxnel alumel incore thernocouple assemblies exit the reactor vessel head and terminate to thernocouple extensicn wire usig Thermo Electric connectors. The thermocouple extension wire used between the thermocouples and the reference juncticn boxes consists of four(4) 15 pair cables. These cables are routed from the reactor vessel head through four mnnectors located cn a plugboard which facilitates removal of the reactor vessel head and control rod drive mrhanisms. From the plugboard the cables are routed to the two reference junction boxes which are located outside tM primary ard secondary shield mils in a location accessible during operation. Individual twisted shielded pair copper cables are routcd fran the reference junction boxes to electrical penetrations sere the signals exit the Reactor Building.
The followig paragraphs provide descriptions of the connectors, cable, reference junction boxes and penetrations with an assessmnt of their expected performance in a harsh environmnt. These assessents are based on engineering jtdgamnt and similarity to other qualified equipment where possible.
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'Ihermoccuple Connectors
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'Ihe thernocouple extension wire connectors are 'Iherno Electric catalog f[
number MSP/)Sj-kx connectors supplied by Westinghouse with the thernoccuples.
'Ihey are nude of lightweight shatterproof thernosetting plastic which exhibits a low noisture absorption rate ard is
- rated for 425"F continuous service. The flat polarized connector pins are nude of thernoccuple materials. They are sprim loaded for positive connections and use screws for wire connecticn 8205040SnA
b Mr. Harold Dmton April 30, 1982 Page 2 directly to the pins. Epoxy resin is applied in the connector cavity to prevent loosenirg of the screw. After fuel loadirg the mated connectors will be sealed with either a heat shrink tubing or a silicon potting ocxnpound to protect the connector frm the environnent. The normal environmental conditions for these connnectors are 40*-200*F at 100% humidity with maxinum radiation of 10 RAM (Ganna). This type of connector has been used successfully on Westinghouse units for years. When installed as described above these connectors are expected to function acceptably in a harsh environment.
hermocouple Extension Cable The thermocouple extension cable used between the thernocouples and the reference junction boxes is 15 pair chrmel alumel wire with tefzel insulation and a tefzel jacket. his cable ms purchased m a safety related purchase order frcm tM Okonite Conpany and is similar in construction and materials to other cable on that order which is qualified for IOCA environnents to IEE-323-74. Based on this qualification report, which has been reviewed and accepted by SCE&G, this cable is expected to function acceptably in a harsh environment.
Plugboard Connectors The pitgboard connectors are nanufactured by Litton Precision Products for use inside tM Reactor Buildirg and are designM for 302 F continuous operating ternperature at 100% relative humidity and 108 rads TID. The connector shells are stainless steel ard utilize silicone rubber for inserts, o-rirg seals between connector halves and cmpression grcxmets sich seal the connector backshell to tM cable jacket. Considerity the moistureproof design ard the unterials used these connectors are expected to function acceptably in a harsh environment.
Reference Junction Boxes
%e reference junction boxes provide a uniform cold junction tenperature for the incore thermocouples at the transition point from chromel alunel wire to copper wire. %is transition is required inside the Reactor Building since the penetrations utilize copper conductors. The reference junction boxes are manufactured by Celesco Corporation and were supplied by Westinghouse. The reference junction tenperature is maintained at 160*F by a heater and tenperature controller. Each reference junction has two platinum RTD's which provide the cmputers and the subcoolirg monitors with the actual cold junction temperature for use in cxxtpensation. The cables are routed frcxn the cable tray through conduit and a pull box into the reference junction boxes. The reference junction box and pull box both have gasketed covers to prevent noisture entry.
Any noisture entering the reference junctim boxes muld have to travel up the conduit through the pull box and throtyh nore conduit to tne reference junction boxes. The passive conponents in the reference junction box
f Mr. Harold Dmton April 30, 1982 Page 3 (reference junction & RTD's) are expected to function acceptably in the harsh environment to which they might be exposed.
If the active ocxrponents (heater and tenperature controller) wre to fail ard tM tenperature of the reference junction varied up or down frcxn 160 F the RID's will still provide the necessary cold junction tenperature for cmpensaticn. The subcooling monitors will provide accurate tenperature cxmpensation as lorg as the cold junction tenperature is between 50*F and 350 F.
If the tenperature exceeds this range an alarm sounds, the referen tenperature is defaulted to 160*F and the actual reference value is displayed. A default value other than 160*F can be entered manually by the operator.
The plant process cmputer provides normal conpensation with the reference tenperature between 155' ard 165 F.
If the tenperature exceeds this range it is alarmed, all resulting displays are designated as unreliable by an "*" symbol, and tM last reliable reference value is used for conpensatim.
The technical support center conputer also displays incore thernocouple tenperaturm to the operators and to the technical support center staff. This system provides an alarm which propogates through all displays when the referenm tenperature is not betwen 155* and 165 F.
If the reference tenperature exceeds 180 F or the tenperature difference between the two R1D's in a reference junction is greater than 2*F the inputs are considered bad quality.
Bad quality is propagated through all displays and is indicated by "x's" instead of conpensaticn values.
Based m the design and location of the reference junction boxes and the fact that failure of the active conponents will not render the systm useless, they are expected to function acceptably in a harsh environnent. The operator should not be misled in the event of failures due to the alarns incorporated in the indication systems.
Instrument Cable The instrunent cable used between the reference junction boxes and the Reactor Building penetratios is single twistal shielded pair copper cable nunufactured by Samuel bbore Ccmpany utilizing EPDM and HYPALON Insulation.
This cable was purchascd as safety related and is qualified for IOCA environnents. This qualification report has been review d and accepted by SCE&G.
Electrical Penetrations The electrical penetration assmbly used to carry these electrical signals outsich of tM Reactor Buildirg is a 12 inch nodel M-56 penetration manufactured by D.G. O'Brien. This nodule has been qualified by D.G. O'Brien. The nodel
Mr. Harold Denton April 30, 1982 Page 4 C-32 connectors utilized with this penetration have been through qualification testiry where sme anmolles were reported. After investigation of the anmolies they were largely determined to be a result of test nethods used for accelerated aging arri should not be of concern for these circuits carrying millivolt signals. Similar penetrations are currently in use in operating nuclear power plants. Based on this information the electrical penetrations are expected to function acceptably for these millivolt signal applications in a harsh environment.
In summry, SCE&G believes that the existing incore thermocouple installation at the Virgil C. Sumner Nuclear Staticn is very likely to function acceptably during and following a high energy line break inside the Reactor Building. Based on this and other information providal in previous submittals on this subject, SCE&G believes that full power operation is justified until the new fully qualified equipment can be installed durity the first major shutdown or refueling cutage following June,1983.
If you have additional questions, please let us know.
Very truly yours,
/
/
T. C. Nichols, Jr.
SbC:'IG:tdh Attachmmt cc:
V. C. Sunner (w/o attach.)
G. H. Fischer (w/o attach. )
- 11. N. Cyrus T. C. Nichols, Jr.
(w/o attach.)
M. B. Whitaker, Jr.
J. P. O'Reilly
- 11. T. Babb D. A. Naunnn C. L. Ligon (NSIC)
W. A. Williams, Jr.
R. B. Clary O. S. Bradham A. R. Koon M. N. Browne G. J. Braddick J. C. Ruoff J. L. Skolds J. B. Knotts, Jr.
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Aussad aturon Venet Virgil C. Summer Nuc14ar Station Existing Incore Themocouple Installation Attachment to 4/30/82 letter
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