ML19056A408

Virgil C. Summer Nuclear Station NPDES Permit No. SC0030856 Renewal Application, Thermal Mixing Zone Evaluation, Addendum: Additional Modeling Cases for Revised Reservoir Ambient and Discharge Temperatures

ML19056A408
Person / Time
Site:	Summer
Issue date:	02/28/2014
From:	GeoSyntec Consultants, South Carolina Electric & Gas Co
To:	Office of Nuclear Reactor Regulation
Shared Package
ML19056A440	List: ML19056A404 ML19056A406 ML19056A407 ML19056A408 ML19056A409 ML19056A410 ML19056A411 ML19056A412 ML19056A413 ML19056A414 ML19056A415 ML19056A416 ML19056A417 RC-19-0012, NPDES Permit No. SC0030856 Renewal Application, Operational Status
References
RC-19-0012
Download: ML19056A408 (22)

Text

ATTACHMENTS Prepared for South Carolina Electric and Gas 100 SCANA Parkway . Cayce, SC 29033 THERMAL MIXING 7.DNE EVALUATION VIRGIL C. SUMMER NUCLEAR STATION NPDES PERMIT FAIRFIELD COUNTY, SOUTH CAROLINA ADDENDUM:

ADDITIONAL MOQELING -CASES FOR REVISED RESERVOIR AMB]ENT AND DISCHARGE TEMPERATURES

~MMI engineers

• scientists

• innovators Prepared by Geosyntec

<<:> consultants engineers 1

• scientists I innovators 1255 Roberts Boulevard, Suite 200 Kennesaw, Georgia 30144 Project Nrunber GK5460 February 2014

~MMI GeosyntecD consultants TABLE OF CONTENTS 1. IN"1RODUCTION

................................................................................................

1 2. MODELED TEMPERA TURES ..........................................................................

2 2.1 Reservoir Ambient Temperature

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............. 2.2 Nuclear Station Cooling Water Discharge Temperature

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3 3. MODELED SCEN"ARIOS

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............. , .... 4 4. CO:tvIPUTA TIONAL MODEL .............................

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6 4.1 Geometry and Mesh ...............................................................................

.. :_.. 6 4.2 Bounqary and Initial Conditions

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6 4.3 CoIIIputational Models .............

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'.6 4.4 Numerical Models .........................................................

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6 5. RESULTS ..............................................................................................

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8 5.1 Preceding Work ...........................................................................................

8 5 .2 Current Work ...............................................................................................

9 5.3 Results Discussion-Winter Condition

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10 5.4 Results Discussion-Summer Condition

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11 6. CONCLUSIONS

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12 GK5460/GA140069

_Thennal Eva! Addendtllll.cbcx 02.05.14

~MMI Geosyntec e> consultants Table 1: Table 2: Table 3: Figure 1: Figure 2:*

• Figure ,3:. -Figure 4: Figure 5: TABLE OF CONTENTS (Continued)

LIST OF TABLES Scenarios Calculated in the C1UTent Work Calculated Plume S:izes Repeated from the Preceding Work Calculated Plume S:izes from the Current Work LIST OF FIGURES Scenario 1: Winter -High Water; No Flow through FPSF Scenario 2: Winter -Low Water; No Flow through FPSF Scenario 3: Winter -Low Water; FPSF Pmnpjng Back To Reservoir. .Scenario 4: Summer -High Water; FPSF Generating (Di$charging from Reservoir).

Scenario 4: Summer -High Water; FPSF Generating (Discharging from _ Reservoir).

GK.5460/GAl 400 69 _ Thermal Eva! Addendum.

cbcx ii 02.05.14 Geosyntec t> consultants

1. INTRODUCTION South Carolina Electric and Gas Company (SCE&G, a subsidiary of SCANA Corporation) is :makmg an application to the South Carolina Department of Health and Environmental Control (SCDHEC) for a renewal of its National Pollutant Discharge Elimination System (NPDES) pennit for Unit 1 of the Virgil C. Summer Nuclear Station (VCSNS). VCSNS is located in Fairfield County near Jenkinsville, South Carolina.

Geosyntec Consultants (Geosyntec

), and its wholly-owned subsidiary Miv1I Engineering (Mivil), have supported SCE&G in the pennit application process by providing modeling studies to determine the . size of thermal mixing zones in Monticello Reservoir due to. cooling water discharges from VCSNS Unit 1. This was reported in Geosyntec report Thermal. Mixing Zone Evaluation Virgil C. Summer Nuclear Station NP DES Permit (Geosyntec Project reference GR4796; date January 9, 2012). SCDI:IEC has since reviewed the report on the thermal pluwe sizes and has. requested . . further information from SCE&G. This has included*

a request for additional modeling to determine the thermal plume sizes under the discharge conditio~

stated. on the . *NPDES permit application and with revised ambient temperatures representing the highest and lowest ambient temperatures recorded over a* longer period than used in the earlier modeling work. This report is an addendum to the earlier thermal mixing zone report to provide the results of the additional models. As fur as possible, the same model set ups have been used as in the original reported work with changes made only to the boundary and initial conditions in Monticello Reservoir to meet SCDHEC's request. This report is focused to provide principally the results of the additional modeling scenarios and does not include the full background to the work and computational model detail As such, it should be read in cortjunction with the original report.

• GK.5460/GAl 40069 _Thennal Eva! Addendum.di ex 02.05.14

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2. MODELED TEMPERATURES

2.1 Reseivoir

Ambient Temperature The preceding work used ambient temperatures in Monticello Reservoir which were based on Discharge Monitoring Report (DMR) temperature data for VCSNS unit 1 for 2010, the most recent complete year of temperature monitoring data at* the time. These ambient reservoir temperatures were:

• Summer Condition:

86.4°F .-this was the highest monthly-averaged temperature measured at the Unit 1 intakes in 2010.

• Winter Condition:

66.6°F -this was the reservoir temperature when the highest monthly-averaged*

change in temperatlrre

(~T) was reco,rded in 2010 between the reservoir.

ambient conditions and the Unit 1 cooling water discharge.

To address . SCDBEC questions about the original rno.~el runs, SCE&G compiled DMR temperature data for VCSNS Unit 1 for a 10-year period from 2003 through 2012. Inspection of the 10-year data set revealed that the monthly average intake temperature of 86.4°F recorde.d in August 2010, which was used .in the modeling of summer critical conditions, was the highest monthly average intake temperattrre in the 10-year data set. Based on review of the longer-term data and SCE&G's proposal to maintain l 13°F as a daily maxnnum discharge . limit year-round, SCDHEC requested additional modeling runs using the highest and lowest ambient temperatures from the 10-year temperature data set. Specifically, SCDHEC requested that the additional model scenarios use the highest possible discharge temperattrre of 113 °F for summer and winter model runs and these ambient reservoir temperattrres:

• Summer Condition:

87 .9°F -this was the highest daily maxnnmn Unit 1 intake temperature recorded from 2003 through 2012 (July 2010).

• Winter Condition:

46.4°F -this was . a low monthly-averaged Unit 1 intake temperature recorded from 2003 through 2012 (January 2010). GK5460/GA140069_Thenna1Eva1Addendum.chcx 2 02.05.14 Geosyntec t> consultants

2.2 Nuclear

Station Cooling Water Discharge Temperature In the preceding work, the VCSNS Unit 1 cooling water discharge temperahrres were set to 113°F (summer) and 98.7°F (winter).

For the ctnTent calculations, the cooling water discharge temperatlrre has been set to 113 °F for both summer and winter conditions to match the NPDES pennit application and as requested by SCDHEC. GK.5460/GA140069_Thenna1Eva1Addendum.chcx 3 02.05.14

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3. MODELED SCENARIOS There are four principal scenarios for Monticello Reservoir which were tested in the preceding work for both summer and winter temperature conditions:

I. Scenario 1 -Thermal discharge mder peak load and discharge flow with Monticello Reservoir elevation mder high water-slack conditions (no flow through Fairfield Pumped Storage Facility [FPSF]). 2. Scenario 2 -Thermal discharge mder peak load and discharge flow with Monticello Reservoir elevation mder low water-slack conditions (no flow through FPSF). 3. Scenario 3 -Thermal discharge mder peak load and discharge flow with Monticello Reservoir elevation illlder low water-rising conditions (FPSF pump-back);

and 4. *

• Scenario 4 --:--: Thermal discharge under peak load and discharge fl.ow with Monticello Reservoir elevation mder high water-fulling conditions (FPSF generation).

All four scenarios were calculated in the preceding work, as it was not possible to determine a priori which scenario would provide the worst case in terms of the 90°F plume size (summer) and ~T > 5°F plrnne size (winter).

For the current work under summer conditions, it has been judged that there is only a small change in temperatures compared with the preceding work -the discharge temperature remains the same (113 °F) and the ambient temperature has

• increased by only l.5°F. It can be reasonably assrnned that the worst scenario previously calculated would also be the worst case for the new temperature conditions.

This was Scenario 4 (High water Levei FPSF generating), which is the only slll11l!ler condition case to have been recalculated in the current work. Under winter conditions, the current requirement for discharge and ambient temperatures has changed more considerably compared with the preceding calculations (discharge temperature has increased from 98.7°F to I l3°F; ambient temperature has decreased from 66.6°F to 46.4°F). Given these large variations, it has not been possible GK.5460/GA140069_Therma1Eva1Addendum.cbcx 4 02.05.14

~~MMI Geosyntec t> consultants reasonably to assmne that the worst case will remain the same as previously calculated.

Hence, all four winter scenarios have been re-calculated in the current work. The cases which have been calculated in the current work are surmnarized in Table 1. Scenarios denoted with a 'W" are the winter nms and the scenario denoted with an "S" :is the summer nm. Table 1. Scenarios Calculated in the Current Work Water Level FPSF Discharge Ambient Cooling Case Scenario Temp Temp Water Flow (feet) (cfs) (0 F) (0 F) (gpm) 1 lW 425.0 0 113 46.4 532,000 2 2W 420.5 0 113 46.4 532,000 3 3W 420.5 41800 113 46.4 532,000 4 4W 425.0 -50400 113 46.4 . 532,000 5 4S 425.0 -50400 113 87.9 532,000 GK5460/GA140069_Thenna1Eva1Addendum.cbcx 5 02.05.14

}MMI Geosyntec t> consultants

4. COMPUTATIONAL MODEL . As fur as was possible, the same . modeling conditions were applied to the computational model in the clilTent work as were used in the preceding work. This has been considered essential for direct comparison of cases. The changes that have been made and their potential effect on the results are noted in the following sub-sections.

4.1 Geometry

and Mesh The exact same geometry and mesh that were used in the preceding work have been used in the clilTent work. 4.2 Boundary and Initial Conditions All boundary and initial conditions have been applied in the same manner, with the only changes being to the specified values of ambient and cooling water discharge temperatures.

4.3 Computational

Models The

• thermodynamic model has retained the same dependence of water density on temperature only using the same tested polynomial relationship.

The same Shear Stress Transport (SS1) turbulence model has been used for all calculations.

4.4 Numerical

Models The preceding work used the ANSYS-CFX vl2.0 software to perform the calculations; this is a commercially available, general purpose Computational Fluid Dynamics (CFD) software package which is widely applied throughout a range of industries.

The clilTent work has used a later release of the same software ANSYS-CFX v14.0 1. There are no changes to the solution method between these releases.

1 ANSYS releases a new version of the code generally every 12 months; the new versions typically have new models for more esoteric calculations (combustion; 2-phase flow; reaction kinetics, etc.) and some bug fixes. However the underlying engine of the software has not changed since they released v5 in the mid 1990's. There have been no changes between vl2 and vl4 to the sub-set of models we are using in this analysis.

GK.5460/GA140069_Thenna1Eva1Addendum.cbcx 6 02.05.14

}MMI Geosyntec t> consultants The preceding work used time-dependent

(transient")

calculations to determine the plume sizes. Although there was no variation of the flow conditions with time, a dependent solution method is required to resolve the thermal buoyancy forces which are significant in large parts of the reservoir.

The same approach has been used in the current work. For spatial discretization 2 , the preceding work used a specified blend factor between :first and second order schemes for all transported variables, with a blend factor of 0.5. In the current work a hybrid differencing scheme has been used, which applies order differencing as widely as possible in the domain, only reverting to :first-order differencing in regions of high gradients in the transported variables.

This was largely a change in style, rather than substance.

The hybrid scheme has the potential to be marginally more accurate, but with perhaps slightly less stability.

For temporal discretization 3 , the preceding work used *a second-order implicit Euler scheme. In the current work, a :first-order implicit Euler scheme was used as the second-order scheme is only considered essential where there are true transient

• *conditions, rather than using a transient scheme to reach.a steady solution.

Convergence in the preceding work was judged to be achieved by three metrics: (i) when the Root-Mean-Square (RMS) residuals were reduced below l.Oe-4 for all transport equations solved at each time step in the time-dependent solution; (ii) when the variable imbalances for all conserved variables were less than 1 percent; (fu) when the thermal plume sizes were observed not to vary in time. The same approach has been used in the current work with the exception that RMS residuals were reduced to l.Oe-5. This was largely a change in style, rather than substance.

2 Discretization describes a numerical technique which is used in computational models. The flow domain -in this case the reservoir-is split into a ~ery large number of grid cells, typically 10 5 -10 6 and the flow details (velocity, pressure, temperature, turbulence) are calculated in each grid cell. The numerical method must have some means of passing information between neighbouring cells and other near-neighbours

-this is the spatial discretization scheme. 3 Similarly the flow data must be passed between time steps -this requires the temporal discretization scheme GK.5460/GA140069_Thenna1Eva1Addendum.cbcx 7 02.05.14

~MMI Geosyntec t> consultants

5. RESULTS 5.1 Preceding Work The principal results for plume sizes which were calculated in the preceding work are repeated here for comparison.

Only the results for the cases which have been re-nm in the current work are shown in Table 2. The average depths have been updated to be somewhat greater, as they were not presented correctly in the preceding report4; the plume volume, area, and average depth are the same. The following thermal conditions were used in the preceding work:

• Winter: ambient temperature:

66.6°F; discharge temperature:

98.7°F.

• Summer: ambient temperature:

86.4°F; discharge temperature:

I l3°F. Table 2. Calculated Plume Sizes Repeated from the Preceding Work Case Scenario 1 lW 2 2W 3 3W 4 4W 5 4S Volume (acre-ft)

Suiface Area (acre)

• Winter Conditions L1T = 5°F 799 77 1,005 107 1,148 120 1,043 110 Summer Conditions T = 90°F 1,790 163 Average Depth (ft) 10.4 9.4 9.6 9.5 6.1 .Maximum Depth (ft) 40 36 36 40 40 4 The results :from the preceding analysis were originally provided in the tables in Section 7 "Results Summary -T = 90°F Plume" and Section 8 "Results Summary -AT= 5°F Plume" of report: Thermal Mixing Zone Evaluation Virgil C. Summer Nuclear Station NP DES Permit (Geosyntec Project reference GR.4796; date January 9, 2012). GK.5460/GA140069_Therma!Eva!Addendum.chcx 8 02.05.14 Geosyntec t> consultants

5.2 Current

Work 'f4e equivalent resuhs for the plume sizes calculated in the CID.Tent work are shown in .

• Table 3. The following thermal conditions were used in the CID.Tent work:

• Winter: ambient temperature:

46.4°F; discharge temperature:

113°F.

• Summer: ambient temperature:

87.9°F; discharge temperature:

l 13°F. Case 1 2 3 4 5 Table 3. Calculated Phnne Sizes from the CID.Tent Work Scenario lW 2W 3W 4W 4S Volume (acre-ft)

Surface Area (acre) Winter Conditions L1T= 5°F 1,031 125 1,109 388 -1,246 130 1,503 218 Summer Conditions T = 90°F 4,841 378 Average Depth (ft) 8.2 2.9 9.6 6.9

• 12.8 Maximum Depth (ft) 40 36 36 40 40 Contour plots showing the extent of the thermal plumes at the surface of the reservoir for each case are presented in Figures 1 through 5. The resuhs for plume volume are . considered to be accurate to arolllld 5 percent. GK5460/GA140069

_Thennal Eva! Addendum.ch ex 9 02.05.14

}MMI

• Geosyntec 1> consultants

5.3 Results

Discussion

-Winter Condition The preceding work. showed that the worst case :in winter was Scenario 3 (low water; pump-back operation at FPSF). This was the worst case for both the LlT = 5°F plume volume and area on the reservoir surface. In the current work, the worst case for Ll T > 5°F plume volume is Scenario 4 (high water; generation at FPSF) and the worst case for area on the surface of the reservoir is Scenario 2 (low water; no flow through FPSF) (Table 3). The LlT > 5°F plume remains to the east of the island at the end of the jetty (Figures 1, 3, and 4) for all cases except Scenario 2, where it just passes armmd the northernmost extent of the island (Figure 2). In generai the plumes calculated with the ambient temperature 46.4°F and discharge temp~rature 113°F (Table 3) have greater volume and great~r extent on the surface of the reservoir than _the equivalent plumes :in the preceding work with ambient temperature 66.6°F and discharge temperature 98.7°F (Table 2). There are a number of effects which * :influence this. Firstly, the higher discharge temperature results :in a greater body of water. with LlT > 5°F; the lower ambient temperature also acts to increase this plume size. However, counter to that, the lower ambient temperature also provides a greater cooling effect and has the potential to reduce the thermal plume size. Overall, it appears that the increased discharge temperature and lower ambient temperature act to :increase the size of the winter thennal plume, as defined by Ll T > 5°F, to a greater extent than the lower ambient temperature provides cooling. Scenario 2 is also slightly unusual in that the average plume depth (or thickness)

JS shallow; this :increases its area on the surface of the reservoir relative to the other scenarios.

This is most likely due to the low water level used :in Scenario 2, which is set at 420.5 ft mean sea level (msl), compared with the high water level cases using 425 ft msl Scenario 3 also has the low water levei but there is increased mixing in the reservoir due. to pump-back operations at FPSF. GK5460/GA140069_Thenna1Eva1Addendum.cbcx 10 02.05.14

~MMI Geo syn.tee t>

• consultants

5.4 Results

Discussion

-Summer Condition The T = 90°F thermal phnne for Scenario 4 (high water; generation at FPSF) is considerably larger for the clllTent conditions than in the preceding work. The increase is evkient in the volume, extent on the surface area, and depth of the thermal plume (Tables 2 anci 3). The only change in the conditions for this scenario was the increase in the ambient temperature from 86.4°F to 87.9°F. Although this is a small increase, it is significantly closer to the T = 90°F limit that defines the thermal phnne, and thus less able to cool the discharged water. As shown in Figure 5, the thermal plume remains to the east 9f the island and does not extend towards the FPSF or the VCSNS Unit 1 cooling water intake structtrre.

GK5460/GA140069_Thenna1Eva1Addendum.cbcx 11 02.05.14

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6. CONCLUSIONS Additional calculations have been carried out for cooling water discharges from VCSNS Unit 1 into Monticello Reservoir.

The additional calculations have been made at the request of SCDHEC tci :investigate a nmnber of effects: lower ambient temperature in the winter; higher ambient temperature in the sunnner; and cooling water discharge of 113 °F in the winter. In winter, reduc:ing the ambient temperature in the reservoir and increasing the cooling water discharge temperature has the effect of increas:ing slightly the ti T > 5°F thermal plmne size. The worst case for plume volmne is Scenario 4 (high water; FPSF pump:ing back to Monticello Reservoir) and worst case for plmne area on the reservoir smfuce is Scenario 2 (low water; no flow through FPSF). The ti T > 5°F plmne remains to the east of the island at the end of the jetty (located .between the VCSNS cooling water intake* structure and the discharge po:int) for all cases except Scenario 2, where it just passes around the northernmost extent of the island. In summer, increas:ing the ambient temperature in the reservoir to 87 .9°F bas a large

• effect on the T = 90°F thermal. plume. This is because there is little cooling potential in *the reservoir when the. ambient temperature is already close to the thermal plume limit. However, the thermal plmne remains to the east of the island. The accuracy of the CFD calculations used to produce these results is estimated to be around 5 percent on the volmne of the thermal plmnes. Both winter and summer cases show larger thermal plmnes than were calculated in the preced:ing work, due to the revised ambient and discharge temperatures specified by SCDHEC. However, it is significant that in all cases calculated, the thermal plumes due to the cooling water discharge remain entirely or predominantly to the east of the island that separates the VCSNS cooling water :intake structure and discharge.

The thermal plmnes do not approach the FPSF :intake, the VCSNS Unit 1 cooling water intake structure, or the northern reach of Monticello Reservoir.

GK5460/GA140069_Thenna1Eva1Addendwn.cbcx 12 02.05.14 SffilflDid Temperature Contour 1 113.0 90.0 1J 70.0 NORTH 51.4 46.4 ISLAND [F] Figure 1. Scenario 1: Winter -High Water; No Flow through FPSF. Contour plot showing the extent of the AT> 5°F piume which for Tambient = 46.4°F bas the value Tp1ume = 51.4°F Temperature Contour 1 113.0 90.0 70.0 51.4 46.4 [FJ 1J NORTH 500 00 1000.00 (m) 250.00 750.00 Figure 2. Scenario 2: Winter -Low Water; No Flow through FPSF. Contour plot showing the extent of the AT> 5°F plume which for Tambient = 46.4°F has the value Tptume = 51.4°F Temperature Contour2 113.0 90.0 70.0 51.4 46.4 [F] Figure 3. Scenario 3: Winter -Low Water, FPSF Pumping Back to Reservoir.

1J NORTH Contour plot showing the extent of the AT> 5°F plume which for Tambient = 46.4°F has the value Tplume = 51.4°F Temperature Contour2 113.0 90.0 70.0 51.4 46.4 [F] Figure 4. Scenario 4: Winter -High Water; FPSF G~nerating (Discharging from Reseivoir).

n NORTH Contour plot showing the extent of the AT> 5°F plume which for Tambicnt = 46.4°F has the value Tplumc = 51.4°F Temperature Contour 3 [F] 113.0 92.9 90.0 87.9 Figure 5. Scenario 4: Summer -High Water; *FPsF* Generating (Discharging from Reservoir).

Contour plot showing the exte: nt of the T = 90°F plume; also shown is AT> 5°F plume which for Tanibi~nt = 87.9°F has the value Tptume = 92.9°F NORTH