1. The expected balance closes exactly
For the CWS, 38,825 gpm makeup equals 29,100 gpm evaporation + 25 gpm drift + 9,700 gpm blowdown. Adding 752 gpm of consumptive groundwater use gives the whole published basis:
39,577 = 29,877 + 9,700 gpm
Published2 × AP1000
Westinghouse two-loop PWRs.
Published6,800 MWt
Licensed thermal power, two units.
Published≈2,234 MWe
Approximately 1,117 MWe per unit.
PublishedNatural draft
Closed-cycle wet cooling towers.
What “real data” means here
The flow rates are project-specific values published in the Vogtle combined-license environmental record, not generic nuclear-industry averages. They are design-basis flows, not a claim of metered 2025 consumption. EIA Form 923 reports Plant Vogtle cooling under plant ID 649 and cooling-system ID “PLANT,” so its public table does not isolate Units 3 and 4 from the four-unit site. A defensible unit-specific actual balance cannot be reconstructed from that file alone. EIA-923 data page ↗
Operating point
Units
Published cooling-water balance
expected operation · Units 3 + 4Savannah River—CWS tower makeup
→
Circulating-water system2 × natural-draft towersClosed-cycle heat rejection
→
Atmosphere—evaporation + drift
Savannah River—cooling-tower blowdown
Separate groundwater withdrawal: —. The licensing table identifies this as consumptive groundwater use; it is not added to CWS blowdown.
CWS closure: —
Published stream table
source values + exact conversions| Stream | Status | m³/h | MGD | Share of river makeup |
|---|
“Consumption” follows the licensing table: CWS evaporation plus drift, with groundwater separately described as consumptive use.
Whole-basis result
river + groundwaterExternal withdrawal—
—
Total consumption—
—
Liquid return—
—
Withdrawal intensity—
at ≈2,234 MWe
Consumption intensity—
at ≈2,234 MWe
CWS return fraction—
blowdown ÷ river makeup
Published-basis closure: —
Per-unit equivalent
derived equal split · not measuredDesign basis versus withdrawal permits
do not confuse a design maximum with an authorized operating rate
| Quantity | Published value | Equivalent | Interpretation |
|---|---|---|---|
| Expected CWS river makeup | 38,825 gpm | 55.908 MGD | COL environmental design value for Units 3 + 4. |
| Maximum CWS river makeup | 61,145 gpm | 88.049 MGD | Short-term design maximum; not itself a withdrawal authorization. |
| Surface-water permit 017-0191-11 | 74.0 MGD max day | 51,389 gpm | Active-permit list value for Savannah River withdrawal. |
| Surface-water permit 017-0191-11 | 62.0 MGD monthly average | 43,056 gpm | Normal expected makeup is below this monthly limit. |
| Expected groundwater use | 752 gpm | 1.083 MGD | COL environmental design value; two units. |
| Maximum groundwater use | 2,797 gpm | 4.028 MGD | Below the listed groundwater permit limits. |
| Groundwater permit 017-0003 | 5.5 MGD yearly average | 6.0 MGD monthly average | Georgia EPD active-permit list, December 2024. |
Important comparison: the 88.049 MGD maximum CWS design flow exceeds the 74.0 MGD permitted maximum-day withdrawal. That is not a mass-balance error; it means the licensing design envelope and the operating permit have different functions. The maximum design case must not be presented as authorized continuous river withdrawal.
Why older Vogtle figures differ
ESP values were superseded by the later COL application basis
| Two-unit CWS quantity | Earlier ESP basis | Later COL basis used here | Change |
|---|---|---|---|
| Expected river makeup | 37,224 gpm | 38,825 gpm | +4.30% |
| Maximum river makeup | 57,784 gpm | 61,145 gpm | +5.82% |
| Expected evaporation | 27,900 gpm | 29,100 gpm | +4.30% |
| Expected blowdown | 9,300 gpm | 9,700 gpm | +4.30% |
| Maximum groundwater withdrawal | 3,140 gpm | 2,797 gpm | −10.92% |
NUREG-1947 Appendix I places the ESP and COL values side by side. The later COL column is the appropriate basis for this case study.
Engineering interpretation
what the numbers do—and do not—establish
2. “Maximum” is a different operating case
Maximum evaporation changes little, while blowdown rises from 9,700 to 30,560 gpm. The resulting return fraction rises from about 25.0% to 50.0%. Do not interpret that maximum row as a typical annual average.
3. Annual volumes are not claimed
Multiplying a design flow by 8,760 hours would produce a continuous-flow equivalent, not metered annual use. Outages, power level, weather, chemistry and permit controls all affect actual annual withdrawal and consumption.
4. Safety inventory is separate
Each AP1000 containment has an exterior tank holding more than 750,000 gallons for passive cooling. It is stored inventory for accident response—not a routine cooling withdrawal—and must not be added as a continuous flow.
5. NPDES governs discharge quality
Permit GA0039420 identifies cooling-tower blowdown internal outfalls and requires final-outfall flow reporting. It sets monitoring and effluent conditions; the published permit does not establish one numeric design-flow cap that replaces this balance.
6. Per-unit values are only equivalents
The brackets in the licensing table give a two-unit total, while individual units share the same design. Dividing by two is useful for comparison, but it is not evidence that actual Unit 3 and Unit 4 flows are always equal.
Data lineage and limitations
published, derived and unavailable information kept separate
| Item | Status | How used | Limitation |
|---|---|---|---|
| CWS makeup, evaporation, drift and blowdown | Published | Direct COL values in NUREG-1947 Appendix I, Table I-1. | Design basis, not metered annual operation. |
| Groundwater consumptive use | Published | Direct COL expected and maximum two-unit values. | Does not itemize every end use. |
| SI conversions, totals, fractions and intensity | Derived | Calculated with 1 US gpm = 0.22712470704 m³/h and ≈2,234 MWe. | Intensity is an instantaneous full-output equivalent. |
| Per-unit equivalent | Derived | Two-unit value divided by two. | Not a unit-specific meter reading. |
| 2024/2025 actual Units 3 + 4 water balance | Not publicly isolated | Not substituted with plant-wide EIA data. | EIA cooling record is filed at Plant Vogtle “PLANT” level. |
References
primary and official sources first
[1] U.S. NRC — Vogtle Units 3 and 4 combined-license application. Official application index linking Part 3, Environmental Report, and the NRC review record. NRC application page ↗
[2] NRC, NUREG-1947 — Draft Supplemental Environmental Impact Statement. Appendix I, Table I-1 (PDF pp. 287–291) reproduces the site-characteristic values for both the ESP and later COL bases. The COL two-unit values used here are: makeup 38,825/61,145 gpm; evaporation 29,100/30,560 gpm; drift 25 gpm; blowdown 9,700/30,560 gpm; CWS consumption 29,125/30,585 gpm; groundwater consumptive use 752/2,797 gpm. GovInfo PDF ↗
[3] NRC, NUREG-1947 — Final Supplemental Environmental Impact Statement. Final NRC environmental review, ADAMS Accession No. ML11076A010. Final NRC PDF ↗
[4] NRC, NUREG-1923 — Safety Evaluation Report for the Vogtle Early Site Permit. Sections 2.4.12 and 2.4.13 document Savannah River makeup, closed-cycle towers, the older 57,784 gpm maximum and the passive ultimate-heat-sink concept. GovInfo PDF ↗
[5] Georgia EPD — active surface-water withdrawal permits. Revised January 2017 list includes permit 017-0191-11 at 74 MGD maximum day and 62 MGD monthly average for the Savannah River. EPD workbook ↗
[6] Georgia EPD — active groundwater withdrawal permits. December 2024 list includes Plant Vogtle permit 017-0003 at 5.5 MGD yearly average and 6.0 MGD monthly average. EPD workbook ↗
[7] Georgia EPD — NPDES Permit GA0039420. Official discharge permit for Units 3 and 4; identifies the final discharge and internal cooling-tower blowdown outfalls and monitoring requirements. Permit PDF ↗
[8] Southern Nuclear — Plant Vogtle media guide. Current plant description, AP1000 cooling-system overview and the “more than 750,000 gallons” passive containment cooling-water inventory for each new unit. Media guide PDF ↗
[9] Southern Nuclear — Plant Vogtle. Current reactor types and approximate electrical output: Units 3 and 4 are two-loop AP1000s at about 1,117 MW each. Plant page ↗
[10] U.S. EIA — Form EIA-923 detailed data. Schedule 8D is the official public cooling-system operations dataset used to check whether unit-specific actual flows were available. EIA-923 page ↗
Values transcribed and independently reconciled on 25 August 2026. Regulatory compliance must be assessed against current issued permits and licensee records, not this educational reconstruction.
Frequently asked questions
scope, figures and interpretation
How much water do Vogtle Units 3 and 4 withdraw?
The published expected design basis is 38,825 gpm of Savannah River cooling-tower makeup plus 752 gpm of consumptive groundwater use, or 39,577 gpm total external withdrawal for Units 3 and 4 together.
Are these measured annual water-use figures?
No. They are project-specific design-basis flows from the Vogtle combined-license environmental record. Public EIA cooling data do not isolate actual Units 3 and 4 water use from the four-unit site.
Why does the maximum design flow exceed the permit limit?
The 88.049 MGD cooling-water-system design maximum and the 74.0 MGD permitted maximum-day withdrawal serve different purposes. The design value is not an authorization for continuous withdrawal.