Unit 1: July 4, 1960 Unit 2: June 9, 1970 Unit 3: November 16, 1971
Decommission date
Unit 1: October 31, 1978
Construction cost
Unit 1: $423 million (2010 USD) or $557 million in 2022 dollars[1] Unit 2: $856 million (2010 USD) or $1.13 billion in 2022 dollars[1] Unit 3: $828 million (2010 USD) or $1.09 billion in 2022 dollars[1]
Dresden Generating Station (also known as Dresden Nuclear Power Plant or Dresden Nuclear Power Station) is the first privately financed nuclear power plant built in the United States. Dresden 1 was activated in 1960 and retired in 1978. Operating since 1970 are Dresden units 2 and 3, two General Electric BWR-3 boiling water reactors. Dresden Station is located on a 953-acre (386 ha) site in Grundy County, Illinois, at the head of the Illinois River, near the city of Morris. It is immediately northeast of the Morris Operation—the only de facto high-level radioactive waste storage site in the United States. It serves Chicago and the northern quarter of the state of Illinois, capable of producing 867 megawatts of electricity from each of its two reactors, enough to power over one million average American homes.
In 2004, the Nuclear Regulatory Commission (NRC) renewed the operating licenses for both reactors, extending them from forty years to sixty.[2]
Unit 1
Inside the Dresden 1 nuclear power plant
After the Atomic Energy Act of 1954 allowed private companies to own and operate nuclear facilities, Commonwealth Edison contracted with General Electric to design, construct, and place into operation the 192 MWe Dresden Unit 1 for $45M in 1955.[3] One-third of the contract price was shared by a consortium of eight companies comprising the Nuclear Power Group Inc.
The core contained 488 fuel subassemblies, 80 control rods, and 8 instrument nozzles. Each subassembly contained 36 fuel rods in a Zircaloy-2 channel. The fuel was uranium dioxide clad in Zircaloy-2 tube. The core thermal power was 626 MWt. The reactor vessel was rated to 1015 psia and measured 12 ft. 2 in. diameter and 42 ft. tall.
Dresden 1 Nuclear Flow Diagram featured a secondary steam generator for load following
The reactor featured a dual cycle, with steam coming from both the stream drum and steam generators. This made for rapid response to changes in power demand. Reactor power was regulated by actuation of the secondary admission valve by the turbine's governor. Decreasing the rate of secondary steam reduces reactor power, and vice versa. Thus, the secondary pressure varies with the external load.
Cooling
The plant has three cooling modes:
Direct open-cycle mode:[d] Intake from canal leading to the Kankakee River,[e] discharge directly to the Illinois River. The cooling canal system, cooling lake, and the supplementary cooling towers are completely bypassed in this mode of operation.
Indirect open-cycle mode:[f] Intake from canal leading to the Kankakee River,[e][g] discharge to cooling canal leading to Dresden Cooling Lake,[h] discharged from lake through return cooling canal that eventually discharges into the Illinois River. Use of the cooling towers for supplemental cooling of canal system water is usually necessary during this mode of operation.
Closed-cycle mode:[i] Intake from return cooling canal leading back from Dresden Cooling Lake,[j] discharge to cooling canal leading to Dresden Cooling Lake.[h] Use of the cooling towers for supplemental cooling of canal system water is usually not necessary during this mode of operation.
Between the 1970s and 1996, Dresden was fined $1.6 million for 25 incidents.
June 5, 1970: A false high pressure signal due to instrument failure on the Dresden II reactor pressure control system caused turbine valves to dump steam (a "turbine trip"), which in turn automatically initiated a SCRAM. Void collapse in the reactor water caused the reactor water level to drop, which resulted in an automatic increase in feedwater flow. The feedwater pumps then tripped on low suction pressure. One pump turned back on automatically when the low suction pressure signal reset, feeding water rapidly into the now lower-pressure reactor vessel. Water level in the reactor rose rapidly until water entered the main steam lines. At this point, the false high pressure signal disappeared. The turbine dump valves closed, increasing back pressure in the reactor vessel and slowing the feedwater inlet flow. Cooling reactor water temperature caused further void collapse. Reactor water level began to rapidly lower once again. This again automatically caused the feedwater system to increase the flow rate into the vessel, and began to raise reactor water level. As cooler feedwater was again rapidly pumped into the reactor, void collapse caused water level to lower. The feedwater system responded by increasing feedwater flow. However, the indicator needle on the water level recorder stuck, which caused the operator to assume level had stopped rising in the reactor. The operator began increasing feedwater flow in order to raise water level in the reactor, manually overriding the automatic control system. The operator never checked a second indicator that showed the increasing level. Reactor water level continued rising and flooded the main steam lines. Two minutes later, the operator tapped on the water level recorder and the water level needle became unstuck, at which point the operator began reacting to the now high water level by manually reducing feedwater flow. At this point, the operator manually opened a steam line relief valve to reduce rising reactor pressure. However, due to the earlier introduction of water into the main steam lines, a hydrostatic shock occurred in the steam lines, which caused a safety valve to open, admitting steam and water into the drywell causing drywell pressure to increase. This caused the initiation of safety injection systems, and for the next 30 minutes reactor water level and pressure seesawed as the operators attempted to stabilize the reactor. It was not until two hours later that reactor level, reactor pressure and drywell pressure were reduced to normal.[5] The movie The China Syndrome bases its initial plot device on this event, with the needle becoming unstuck when the operator taps the recorder.[6]
December 8, 1971: Events similar to the ones the year earlier on Dresden II occur on Dresden III.[5]
May 15, 1996: Lowering water levels around the nuclear fuel in unit 3[7] reactor's core prompt a shut down at Dresden Generating Station and placement on the NRC's "watch list" that merit closer scrutiny by regulators. Dresden was on the NRC watch list six out of nine years between 1987 and 1996, longer than any of the 70 other operating plants in the nation.[8]
July 15, 2011: Plant declared an Alert at 10:16 a.m after a chemical leak of sodium hypochlorite restricted access to a vital area that houses plant cooling water pumps.[9]
Surrounding population
The Nuclear Regulatory Commission defines two emergency planning zones around nuclear power plants: a plume exposure pathway zone with a radius of 10 miles (16 km), concerned primarily with exposure to, and inhalation of, airborne radioactive contamination, and an ingestion pathway zone of about 50 miles (80 km), concerned primarily with ingestion of food and liquid contaminated by radioactivity.[10]
The 2010 U.S. population within 10 miles (16 km) of Dresden was 83,049, an increase of 47.6 percent in a decade, according to an analysis of U.S. Census data for msnbc.com. The 2010 U.S. population within 50 miles (80 km) was 7,305,482, an increase of 3.5 percent since 2000. Cities within 50 miles include Chicago (43 miles to city center).[11]
Ownership
Both currently operating units are owned and operated by Constellation Energy following separation from Exelon, which also owns and is responsible for the decommissioning of Unit 1. Prior to August 3, 2000, all three units were owned by Commonwealth Edison.[12][13]
Seismic risk
The Nuclear Regulatory Commission's estimate of the risk each year of an earthquake intense enough to cause core damage to the reactor at Dresden was 1 in 52,632, according to an NRC study published in August 2010.[14][15]
Averted closure
In August 2020, Exelon announced they would close the plant in November 2021 for economic reasons, despite the plant having licenses to operate for about another 10 years and the ability to renew the licenses for an additional 20 years beyond that. On September 13, 2021, the Illinois state senate passed a bill subsidizing the Byron and Dresden nuclear plants,[16] which Governor J. B. Pritzker signed into law on September 15,[17] and Exelon announced it would refuel the plants.[18]
Notes
^Currently only allowed when both units are out of service, rarely used.
^Used from June 15 through September 30, or approximately 8.5 months of the year.
^Currently only allowed when both units are out of service, rarely used.
^ abcDuring periods of low river flow, intake water may also be indirectly drawn from the Des Plaines River.
^Used from June 15 through September 30, or approximately 8.5 months of the year.
^Up to 940,000 US gallons per minute (59 m3/s) is withdrawn from the river by six pumps each rated at 157,000 US gallons per minute (9.9 m3/s)).
^ abWater is pumped from the cooling canal into the 1,275 acres (516 ha) cooling lake via a lift station with 6 × 167,000 US gallons per minute (10.5 m3/s) pumps. The cooling lake has 5 zones through which the water slowly travels over the course of 2.5 days before it exits the cooling lake.
^Limited amounts (up to 70,000 US gallons per minute (4.4 m3/s)) of makeup water is drawn from the Kankakee River as needed,[e] and limited discharge (up to 50,000 US gallons per minute (3.2 m3/s)) to the Illinois River happens in order to minimize dissolved solids concentrations in the cooling canals/lake.
^Prior to 2000, supplemental cooling was provided via spray canals (spray systems installed in both the hot and cold (return) cooling canals) rather than the current cooling towers.
^1 × 12-cell tower (single-wide, built between 2000 and 2001), 2 × 18-cell towers (double-wide, built in 2000), and 1 × 6-cell tower (single-wide, built between 2003 and 2004) with an overall total of 54 cells. The 12-cell tower is only used for supplementary cooling of the cold (return) cooling canal as necessary in order to maintain discharge water temperatures within permitted levels, while the three other cooling towers are used for the supplementary cooling of water in the hot cooling canal. The three hot canal cooling towers are fed by 7 pumps rated at 135,067 US gallons per minute (8.5214 m3/s) each (total flow of 735,469 US gallons per minute (46.4009 m3/s)). The single 12-cell cold (return) canal cooling tower is fed by 24 pumps rated at 8,800 US gallons per minute (0.56 m3/s) each (total flow of 211,200 US gallons per minute (13.32 m3/s)). The 6-cell tower was added to provide additional cooling for the extended power uprates (+17%) on Units 2 & 3 that Exelon requested in December 2000, which were approved by the NRC in December 2001, although it was not until the end of 2002 that the uprates were implemented at both units (the units were also not operated at the uprated power for most of 2003 due to steam dryer cracking problems), and this additional cooling tower meant to provide additional cooling capacity to accommodate the additional thermal output from the outrate was not added until sometime between 2003 and 2004.
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