ML12227A520
| ML12227A520 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 08/09/2012 |
| From: | Dominion Nuclear Connecticut |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| 12-474A 98-ENG-02405D2, Rev 2 | |
| Download: ML12227A520 (6) | |
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I :ýý w. .1 I~ I I Calculation 98-ENG-02405D2, Revision 2 Attachment 6
Calculation No. 98-ENG-02405D2. Revs Process Conditions Mider which the Service Water Inlet Souice Tempei!ature is Homogeneous Tile following ififormation is provided by Robert L McGuinness via e-mail, the elements pertinent to this calculation are underlined:
Rob-._ _ _ _ _ _ _ _ _ _
M4ik-e-F~i~ffla~
Ir-e -yoll could use some lfpu*-7o-fdr d&-t;Y-M-nn-gilfi" acceptableto averagethe Intake / UHS temperatureinstrumentsat Unit 2.
- 1) As we know, the Tech Spec Bases 3/4. 7.11 describes that we shall use the highest readingvalid temperatureobtainedfrom the Unit 2 intake structure (2 instruments)and the inlets to the CirculatingWater System waterboxes (4 instruments)to verilfy the UHS temperatureis < 70-degF.
- 2) The Tech Spec Bases also descriLe that rf temperatureIs above 70-degF, that monitoring is performed at the Vital A CSwitchgearService Water heat exchanger inlets; orat the RB heat exchangerinlets if the*
temperaturecannot be taken at the Vital ACswirchgearheat exchanger inlets.
Temperature averagingmay help determine a more accuratetemperaturein all four cases (Intake, Waterboxes, Vital AC, andRB inlets)- I understandthat temperatureinstrumentaveraging may help reduce an unnecessarilyhigh reading,on average, up to approximatelyX-degree. Of course, an Engineering basis would be needed to proceed with averaging. In all cases,the individual temperaturescan deviate from normal due to temporarythermal transients caused by main condenser waterbox backflushes and by thermal mussel cooks performed in individualbays. The temporary transientsaffect individual temperatureinstruments immediately atthe beginning of the flush or cook, then exponentially return to normal within an hour.
Regards, Bob -6855 Temperature data was obtained from the MPS2 Plant Process Computer (PPC) during both a thermal backwash (Figure A-l) and a mussel cook (Figure A-2) evolution. The temperature measurements recorded are the PPC inputs the "C" bay water quality monitor (T6690) and the four circulating water temperatures at the inlet of the condenser water boxes (T6557, T6564, T6596, and T6589). The assumption is that the circulating water temperature is representative of the inlet bay temperature in each of the four intake structure bays when the respective circulating water pump is in operation.
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Calculation No. 98-ENG-02405D2. Rev 12 Figure A-i shows the temperatures resulting from a thermal backwash evolution. Upon commencement of thermal backwash the temperature in the associated circulating water pipe immediately increases reflecting the introduction of condenser heated water into the line. The backwash has been completed and normal operation commenced when the temperature in the associated circulating water pipe decreases reflecting the return of the colder seawater back into the line. This is followed by a period of normalization where the intake bays recover from the i nirntdnctH c n-f candeiser 1eat+/-9 Ffli-d, f-rc-t~~Vws
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If3¶h7 Wo1tib Vtapers gr alitemperatures Irnt e circulating water lines have returned to their pre-backwash condition and are stable after approximately 30 minutes. In the figure, the temperature measured by the water quality monitor in bay* "C" continues to decay and is also stable after approximately 50 minutes.
Figure A-2 shows the temperatures resulting from a mussel cook evolution. Upon commencement of mussel cook the temperature in the associated circulating water pipe immediately increases.
reflecting the introduction of condenser heated water into the line. The mussel cook has been completed and normal operation commenced when the temperature in the associated circulating water pipe decreases reflecting the return of the colder seawater back into the line. This again is followed by a period of normalization where the intake bays recover from the.
introduction of condenser heated fluid from the mussel cook evolution. In Figure A-2 it appears that temperatures in the circulating water lines have returned to their pre-mussel cook condition after apptoximately 30 minutes. In the figure, there appear to be some continued oscillations in the temperature measurements after the 30 minute period however the temperatures are all oscillating together suggesting a condition affecting all bays equally.* In this evolution there does not appear to be as pronounced an impact on the temperature measured by the water quality monitor in bay "C" as there was in the thermal backwash evolution.
In the above two evolutions it appears that the intake structure bays have returned to a homogeneous condition after 30 minutes of normal operation following completion of each evolution. It is unknown why the response of the water quality monitor appears to lag behind the circulating water line temperature recovery.
This might be a response time issue associated with the equipment, or some other dynamic not clear from the data presented. However, the circulating water pipe temperature data does show a clear recovery within 30 minutes. To provide Page A13 of 14 1
Cal n.llytion No. 98-ENG-02405D2, Rev2
.margin, a recovery period of 45 minutes before taking a Technical Specification UtS reading using the average of TI-6928, TI-6929, and TI-6930 will be specified.
The above information supports the following limitation on when temperature indicators TI-6928, TI-6929, and TI-6930 may be averaged to improve their temperature measurement accuracy, and the average temperature measurement used for the purposes of compliance with MEPS2 Technical Specification 3/4.7.11:
"emperature averaging or- "'i--*z-'-W 2Y9, a-n-and 6930 may be utilized whenever the intake structure bays are at a homogeneous temperature that will ensure essentially equal inlet temperature conditions in both service water trains. This is expected to occur under all plant operating conditions, except when main condenser waterbox backflushes and thermal mussel cooks are being performed in any intake bay.
Following the completion of either of these evolutions a minimum 45 minute period of normal system line up and operation will return the intake bays to a homogeneous temperature condition that will support averaging of the above temperature measurements."
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