Fort St. Vrain Power Station History

Built in the shadow of the majestic Rocky Mountains, Fort St. Vrain (FSV) was Colorado's only Nuclear Power Plant and America's only commercial High Temperature Gas Cooled reactor design.  Plans to construct FSV were announced in 1965.  Work began at the site in 1968.  Initial hot flow testing of the reactor began in 1972, and several years of design problem work followed.  The first commercial electric power using the reactor was generated from the plant in December 1976.  Nuclear operations came to a close in 1989 due to continuing problems with the plant.  Decommissioning of the reactor, as well as shipping of all nuclear fuel off-site to a U.S. Department of Energy managed facility, was complete in 1992.  Fort St. Vrain was the first commercial nuclear generating plant in the United States to be decommissioned.  In 1996, generation from FSV began again, this time with a combustion turbine burning natural gas and generating 130 megawatts of power.  A heat recovery steam generator (HRSG) was added, and steam was provided to the old main steam turbine.  A second gas turbine with HRSG was added in 1998, making  FSV capable of 500 megawatts.  In May 2001 a third combustion turbine with HRSG was added, making the rated output of the plant 720 megawatts.  In 2009 two more simple cycle combustion turbines were added bringing the plants total output to the grid just over 1,000 megawatts.
The Rest of the Story

Public Service Company of Colorado (PSCo) was researching alternative power generation as early as the late 1950s and plans to build Fort St. Vrain were announced on March 13, 1965.  On November 1st of that year, PSCo, General Atomic, and the U.S. Atomic Energy Commission signed a three-way contract launching the effort to build a 330,000-kilowatt nuclear electric plant utilizing a high temperature, gas-cooled nuclear reactor.  The application to construct FSV was filed with the Atomic Energy Commission on October 20, 1966.  It would be the first commercial scale high temperature gas cooled reactor plant in the United States.  The plant was to be named after the historic frontier fort of the same name, once located about a mile north of the power plant site.  

Preliminary construction work on FSV began in April 1968 after receiving approval from the Colorado Public Utilities Commission.  The U.S. Atomic Energy Commission issued it's construction permit on Sept. 18, 1968 and concrete work on the reactor building began.  Gulf General Atomic (GA) was the prime contractor.  Sargent & Lundy subcontracted to GA for architectural and engineering and Ebasco was the principal constructor. 
To meet the earthquake design criteria the reactor building was engineered to rest on bedrock.  This proved to be a problem right away because bedrock was 50 feet down through sandy soil and a water table at 20 feet.  This major obstacle was overcome by freezing the ground around the area to be excavated.  A total of 360 fifty-five foot long U-tube assemblies, all connected together, were installed in the ground in an oval shape around what would become the reactor building.  A freezing brine solution was pumped through these pipes.  Three huge refrigeration systems maintained the brine at minus 11 degrees Fahrenheit.  The "freeze wall," as it was known, was started on May 6th, and by June 3, 1968, the majority of the wall was frozen.  The foundation was actually dug down 25 feet below the normal surface of the bedrock.  Once they reached the shale bedrock during excavation, it was found that it deteriorated rapidly upon exposure to air.  Final excavation and concrete pours were carefully coordinated to minimize the deterioration.  
Also in June 1968 construction of the reactor bottom head assembly was begun west of the reactor building while the building foundation and support ring for the pre-stressed concrete reactor vessel  (PCRV) were being constructed.  This assembly consisted of the steel liner, penetrations, and core support floor columns and weighed in at 400 tons.  In February 1969 it was moved on rails to temporary supports within the support ring.  The support ring was completed on Feb 13, 1969.  It is a cylinder, 50 feet in diameter with highly reinforced walls 3-1/2 foot thick and 33 feet high.  It required 575 cubic yards of concrete and was completed in one 18 hour continuous pour. 
A different approach was used in the construction of the turbine building foundation.  Sixty-six caissons were drilled into the bedrock and casing were installed.  Once the casings were in place they were pumped dry and the bedrock was drilled out an additional 6 feet.  When that was done, reinforcing steel was lowered into the casing and then the concrete was poured. 
Turbine building structural steel was 70% complete by Oct. 1, 1969.  Turbine generator erection was started at this time. 

Hot Flow testing was begun in June 1972.  The pelton wheels disintegrated due to cavitation.  A pelton cavity nitrogen pressurization system was designed and implemented by May 1973.

Fuel loading to the reactor began on December 27, 1973, after the operating license was issued.  Fuel loading was completed on January 16, 1974, and initial criticality was reached on January 31, 1974.  The rest of the year and into the early spring of '75 was spent working on problems with the control rod drives, moisture ingress into the reactor, and pelton wheel cracks.

Rise-To-Power testing to 2% occurred in April 1975.  However, as a result of the Browns Ferry fire, an internal PSC cable segregation audit was conducted.  In June, the Nuclear Regulatory Commission (NRC) ordered a full audit of all essential and associated non-essential cables with respect to compliance with the Final Safety Analysis Report.  The reactor remained shut down during all these audits.  Another problem, internal leakage in 15 of the control rod drive assemblies, required the rest of '75 and early '76 to resolve.

On July 6, 1976, FSV reached power levels greater than 2%.  However, the "C" helium circulator had to be replaced due to excessive purified helium leakage from the penetration interspace into the pre-stressed concrete reactor vessel (PCRV).  October to November saw rise-to-power testing and minor modifications to the startup bypass pressure control system and steam/water dump relay system.

First Power Generation

On December 11, 1976, FSV generated its first electrical power to the grid using reactor power.

Core thermal fluctuations were observed on November 23, 1977.  Reactor power was reduced to 68% power.  Then a small steam generator tube leak was detected on November 30th, and the reactor was manually shut down so repairs could be made.

The turbine was again placed on line on April 3, 1978, and testing was begun to determine the nature of the thermal fluctuations observed earlier.  The NRC had imposed a 70% reactor power limit (which was below the threshold of the thermal fluctuations).

The reactor was shut down for first refueling on February 8, 1979.  Refueling was completed on May 2nd and the reactor was taken critical on May 26th.  In June, PSC signed an agreement to assume ownership of the plant from General Atomics (GA).  The reactor was operated at less than 2% power for testing until July, when the turbine was once again put on line to generate electrical power.  Commercial operation of the plant officially began on August 1, 1979. 

In October, the reactor was shut down for the installation of region constraint devices, better known as "Lucy Locks."   The lucy locks were installed to address the core fluctuations.  Research by GA and PSC engineering had come to the conclusion that the blocks were shifting around slightly under power.  They reasoned that the Lucy locks would hold the the block columns together and prevent the fluctuations.  Lucy locks in place, the reactor was taken critical on December 25th.  Our fluctuation problems were cured.  However a problem was found on the "B" helium circulator primary seal, and the reactor was soon shut down again.

The "B" helium circulator was replaced (a huge job), and the turbine was back on line on March 16, 1980.  In August, the plant was shut down for required surveillance (testing) and planned maintenance but was back on line, generating power on October 8th.

Excessive interspace leakage on the Loop 2 steam generator penetrations required a shutdown on March 22, 1981, but FSV was back on line with the generator on April 13.  However, turbine high vibration caused a turbine trip, resulting in a reactor scram on May 13th.  

Rather than start back up, the second refueling outage was begun a little ahead of schedule.  Refueling was completed, the reactor taken critical, and the generator was back on line on July 26, 1981.  On November 6th, the reactor reached 100% power.  This was great day!  However, the reactor was shut down on November 9th to begin the "loop split" outage in order to create two independent paths for buffer helium for better reliability.

The loop split modifications were completed and the reactor taken critical on February 11, 1982.  On Feb. 22nd, the reactor was manually scrammed due to high moisture, and two control rods failed to properly insert.  Three additional rods exhibited a tendency to stick in the full-out position.  A program was initiated to exercise the control rods and all were operating properly by February 23rd.  The reactor was taken critical on April 2nd and the generator put on line on April 4 but the plant was shut down again on April 20th to repair a core support floor tube leak and test the reserve shutdown system.  On May 3rd the reactor was taken critical again and the generator was placed on line on May 7th.  FSV scrammed again on September 30th.  In October the NRC granted release from the 70% power limitation imposed during the thermal fluctuations.  The reactor was taken critical for training during the first week of November but high primary coolant moisture problems kept FSV at low power or shutdown.

The turbine generator was placed on line on January 1, 1983 but high primary coolant moisture scrammed the reactor again on January 28th.  The generator was back on line again on February 8th but the reactor was manually scrammed on February 14th after the loss of  the "B" instrument power inverter.  The reactor was kept shut down while a possible core support floor leak was investigated.  The generator was back on line on March 9th and scrammed again on high moisture on March 17th.  The reactor was brought on line again on May 24th, but power was limited due to high moisture.  The moisture gradually decreased, and the generator was finally placed on line on July 16th.  Things ran pretty well for a while.  

Next, FSV experienced high vibration problems with "C" boiler feed pump.  Reactor power was taken to 80%.  Vibration problems continued with the boiler feed pump.  Consultants were called in and various avenues were tried to solve the problem to no avail. By October reactor power was up to 85%.  However, on November 9th, the boiler feed pump seized up and tripped.  If that wasn't enough, on December 8th the reserve auxiliary transformer deluge system was activated by high winds resulting in a turbine trip and reactor scram.  The reactor was immediately taken critical and the steamer was back in service on December 11th.

On January 20, 1984, the reactor was shut down for refueling, a turbine overhaul and electrical modifications.  In February the Colorado State Public Utility Commission recommended a $526,000.00 rebate to the Public Service customers, due to the poor performance of the plant.  

In March an inspection of the PCRV tendons revealed failed strands in the tendon bundles.  

In April, while FSV was awaiting release to go to power from 2%, problems arose with sticking orifices in regions 12 and 30.  The region 12 control rod drive assembly had to be replaced, but region 30 freed up after exercise.  Permission to go above 2% power was received from the NRC on May 16th, after their evaluation of the PCRV tendon wire degradation.  The process of drying out and gradual reactor power increase continued until June 12 when the generator was placed on line.  However, due to moisture, reactor power could only slowly be increased.  Then on June 22nd a sudden pressure relay on the 4160/480V transformer #1 caused a trip of the 480VAC essential bus 1A and subsequently tripped the "A" helium circulator, due to a bearing water upset.  Trying to recover from this incident, we scrammed on high reactor pressure on June 23.  During this event, six of the thirty-seven control rod pairs failed to automatically insert.  A powered insertion to the stuck rods was successful.  Cold shutdown conditions were achieved by the initial scram, however.  This scram signaled the beginning of an extensive control rod drive refurbishment program.

During a test of the reserve shutdown system in November 1984 for control rod drive #21, the boron balls failed to discharge properly from their hopper.  A event report was filed with the NRC. In December, helium circulator A was removed and shipped to San Diego for repairs on an interspace bearing water leak.

By February 1985, control rod drive refurbishment was in full swing.  The helium circulator was returned from San Diego in March.  During the repair work at San Diego, GA Technologies discovered chloride stress corrosion on some of the internal bolting.  Therefore, the rest of the circulators would have to be removed and inspected.  One by one, the circulators were removed, repaired and reinstalled.  The on-going control rod drive work was completed in June 1985, at about the same time as the circulator repair work.

Permission to start up the reactor (at loads up to 15% until Environmental Qualification issues were resolved) was received on July 19 and the reactor was taken critical the next day.  A high moisture scram occurred on July 23rd, and the reactor remained shutdown for a time for primary coolant cleanup.  A new digital valve that had been installed on on "A" circulator experienced leakage and was replaced with the original valve.

The reactor was taken critical a few times during the summer of 1985 to try to dry out the primary coolant but the turbine was never placed on line.  In November the reactor was shutdown for mandated Environmental Qualification modifications.

In January 1986, while returning a clearance on "D" helium circulator, a water ingress into the PCRV of approximately 300 gallons occurred.  The reactor was taken critical on February 14th and power was slowly increased during March, while primary coolant cleanup continued.  On April 3, a major snow storm caused voltage upsets on the grid, resulting in an automatic shutdown of Loop 2 and the isolation of "B" purification train.  Management directed a manual scram.  The reactor was up again on April 6th, and the turbine on line on April 11th.  On April 27, an automatic reactor scram was generated accidentally due to a routine surveillance test on the plant protective system (PPS).  The generator was placed back on line on April 29.

On May 6th, an electrical grid transient occurred which increased reactor power to a maximum of 39.2% (FSV was limited to 35% power at the time by the NRC).  Leakage through a main steam bypass pressure control valve upset the overall plant, but the problem was corrected and operation returned to normal.  Steps were taken to prevent reactor power from increasing above 30%.


On May 30th the turbine was taken off line, and on May 31st the reactor shut down for government mandated Environmental Qualification (EQ) modifications.  In June, clearances were hung on the circulating water system, resulting in flooding the pump pit.  All affected motors were removed for inspection and repair.  During the EQ outage, staff at the plant swelled to an all time high of 965.  This number included contractor and PSCo personnel.

Next, on July 7, 1986, the NRC imposed civil penalties on Fort St. Vrain for the May 6 over power event ($75,000) and for inadequate protection of protected and vital areas ($65,000).  

On September 24, 1986, Public Service reached an agreement to settle all litigation concerning Fort St. Vrain.  The settlement removed FSV from the company's rate base, provided customer refunds, and reduced electric rates.  The plant was to be run essentially as an independent power producer and could charge 4.8 cents per kWh. 

In March 1987 FSV completed the Environmental Qualification program, and on June 17th the NRC voted to allow FSV to return to power, not to exceed 82%.  Unfortunately, on July 28th a purified helium leak was found in the interspace of "D" circulator.  The reactor was shutdown again and "D" circulator was removed and sent back to San Diego.  A spare circulator was installed.  The reactor was again taken critical on September 30.

On October 2 a hydraulic oil fire broke out in the area of a hydraulic valve (HV-2292) in the turbine building.  A manual reactor scram was inserted because of an indicated loss of primary and secondary coolant flow.   The fire was extinguished by the plant fire brigade.  Repairs were made.

The reactor was again taken critical on December 11th.  By January 16 1987, FSV was at 77% reactor power, beginning the first sustained period above 72% power since 1983.

FSV set a new record for total net generation during a single month of 160,184 MWhe during March 1988.  In April more problems arose again and the plant was up and down, due to circulating water problems and electrical system upsets.  However, in June FSV set another new record for generation.

End of Nuclear Operation Announced

However, in December 1988 the decision was made by the board of directors of Public Service Company that Fort St. Vrain would be shut down for good.  The NRC was notified that the plant would shutdown no later than June 30, 1990.

In March 1989 the independent safe fuel storage installation (ISFSI) request for proposal was sent out.  The preliminary decommissioning plan was submitted in June.  In July a new generation record for a one-month period was attained and Foster Wheeler was selected as the ISFSI vendor.

The plant was returned to power service on April 9 following a reserve shutdown problem.  FSV reached 80% reactor power on May 29. 

The summer of '89 was a hot one and Public Service set an all time record for power output.  For once, FSV was up and fully loaded!

On July 30th the plant recorded an all time monthly record power production of 178,221 net megawatt-hours.  On August the 4th FSV employees celebrated the outstanding recent performance of the plant and the new record with a picnic on the front lawn.  There was volleyball, horseshoes, a dunk tank (proceeds of payment to "dunk your favorite boss" went to United Way) and enough food for 500 employees.

The End Came Early!

On August 18th during routine surveillance testing a control rod drive assembly was found to malfunction.  The plant was shut down and preparations for repair and return to service were begun.  However, during a routine walkdown by one of the plant engineers, hairline cracks were found in the inconel steel main steam ring header immediately below the reactor.  This ring header received steam from the steam generators in the reactor prior to the steam's short trip to the turbine generator.  The hairline cracks proved to be the last straw for Fort St. Vrain.  Based on this turn of events, the PSC Board of Directors announced the decision to terminate operations at Fort St. Vrain effective on August 29, 1989.

In early 1989 the computer engineering team at Ft. St. Vrain developed a way to run the fuel handling machine control system with a new 16-bit computer replacing the old DEC PDP-8/s (12-bit) system that was failing and unmaintainable.  This pioneering work was reviewed by Rockwell International and accepted by the NRC.  The system ran so well that from November 1989 through February 1990, fuel was removed from twelve reactor regions without any computer system problems.  This was 5 months and 15 days ahead of schedule saving PSCo approximately $2M a day in operations costs.  The fuel was stored in the storage wells located on the fuel deck in the plant reactor building.

The Nuclear Regulatory Commission (NRC) issued the Confirmatory Shutdown Order for FSV in May 1990.  In June, the Independent Spent Fuel Storage Installation (ISFSI) license application, safety analysis report, and environmental reports were submitted to the NRC.  The ISFSI was needed because plans to ship Fort St. Vrain's spent fuel to the Department of Energy facilities in Idaho under a 1965 contract were halted by a lawsuit filed by the State of Idaho.  So, the ISFSI was considered as a contingency.

In July the Westinghouse team was selected as the decommissioning contractor.  

The decision to proceed with construction of the ISFSI was made in January 1991, and construction began in February.  In May, a "possession only" license was issued by the NRC.  The Final Safety Analysis Report was submitted to the NRC in July 1991.

In October 1991, three shipments (eighteen fuel elements) of spent fuel were sent to the Idaho National Engineering Lab.  Also in October, all non-union employees were required to bid on the remaining positions for "early dismantlement".  This was a very traumatic time that none of us will forget.  An employee either got picked for a position or got a 90-day notice.  Simple.  On November 22nd the names of 38 non-barganing unit personnel were announced.  The union employees went through a similar procedure based on seniority.

The NRC issued the Materials License and Safety Analysis Report for ISFSI in November 1991 and the first load of spent fuel was deposited there on December 27th.  Fuel shipping was completed  into the ISFSI on June 10, 1992 and the nuclear security and nuclear fitness for duty programs were terminated shortly thereafter.  Fort St. Vrain received the Public Service Company Eagle Award as recognition for completing defueling "months ahead of schedule--saving the company millions of dollars."  The PSCo Times noted that the award was "even more impressive considering many of those employees were literally working themselves out of a job."

On June 26th more than 700 past and present employees came together to celebrate the final defueling of the reactor at Fort St. Vrain.  A grand time was had by all on the front lawn of the now silent plant.  At this time, Del Hock, president, chairman and CEO of PSCo, presented the 1991 President's Safety Award to the employees of the plant for the most hours worked without a lost-time injury.


Decommissioning of the plant--returning it to a safe and non-radioactive site--began immediately after defueling was complete.  Decommissioning was expected to take 3 years.  Also at this time, plans to convert the plant to natural gas were being considered.

In the October 4, 1993 issue, of the PSCo Times, Bob Gunnerson, decommissioning project engineer, reported that the last section of the 15-foot thick concrete reactor top head (the top of the reactor vessel) had been removed.  Diamond wire saws were used to cut the tophead apart.  In all there were 12 pie shaped pieces, each weighing around 110 tons, or in total, 17,500 cubic feet of concrete.

With the tophead removed, work could begin to remove the top of the PCRV steel liner and then go on to the 1,500 graphite blocks which made up the remainder of the reactor core (after the removal of the fuel blocks during defueling).  The reactor was flooded with constantly filtered water to provide as much shielding from the remaining radiation as possible.

The reactor core support floor, weighing in at 340 tons, was removed Feb 8, 1995.  With the reactor vessel still flooded, divers actually had to swim under the core support floor to cut it lose from the core support floor posts with torches.  It was then sectioned into two pieces and lifted out, using the reactor building overhead crane.

Repowering with Natural Gas
(FSV rides again!)

Construction of the first gas turbine, a General Electric Frame 7FA called FSV Unit 2, was nearing completion in March 1996 and the unit was test fired a few times.  Black & Veatch was the primary contractor on this unit.  On May 6, 1996, the unit came on line for commercial operation at the "repowered" Fort St. Vrain.  Public Service initially billed the plant as a "peaking unit capable of 130 megawatts (MW) of power."  The June 24, 1996 issue of the PSCo Times quoted station director, Marty Block, about the repowering:  "Start up of the combustion turbine marked an important day for all of the employees here--and certainly for all those who worked so hard over the years when this was a nuclear facility. . .We're just glad to be back as a power plant."

Meanwhile, construction of the heat recovery steam generator (HRSG) for unit 2 proceeded at a rapid pace.  The HRSG would take the hot exhaust from the combustion turbine and make steam to power the old steam turbine in the main plant building.  The HRSG also has supplemental natural gas burners to provide additional heat during times where peak load is required.  On March 21, 1998, unit 2 was fired with the damper door open to the HRSG for initial heat up and testing.  On May 5, 1998, with HRSG testing completed, steam was admitted to the original steam turbine and the unit was synchronized to the grid for the first time in 9 years.  At this point, FSV was capable of about 230 MW of power total to the grid.

Construction of Unit 3, FSV's second gas turbine and HRSG, was completed by January 1999 by principal contractor, Utility Engineering.  Unit 3 was started up in simple cycle (without the HRSG) on January 12, and synchronized to the grid.  On April 24, the unit was fired in combined cycle and the steam turbine was synchronized to the grid for the first time using unit 3 steam.  Now FSV was capable of just over 500 megawatts on a cool day.  (The units outputs are highly effected by the ambient temperature.)

Construction of FSV Unit 4, the third and final gas turbine and HRSG, was begun in the summer of 2000.  First fire of unit 4 was early May 2001.  Utility Engineering was also the primary contractor for this unit and The Industrial Company (TIC) was their principal constructor. 

On October 2nd, Public Service Company of Colorado officially became Xcel Energy.  Xcel Energy was the result of the merger of New Centuries Energies and Northern States Power on August 18th.  Headquarters for the new company are in Minneapolis.  At this time, Xcel Energy had 11,800 employees in 12 states and served 3.1 million customers. 

In February 2001, Fort St. Vrain exceeded the total output generated by the plant during the nuclear days.  This was a bittersweet date for those who were at FSV in those days.

On April 25, 2001, unit 4 was put on the turning gear in preparation for first fire.  Unit 4 has a selective catalytic reduction system (SCR) for reducing stack emissions of the oxides of nitrogen (NOx).  The SCR was manufactured by Mitsubishi Heavy Industries.  First fire was a brief flame on the 28th.  A sustained flame was attained on the 29th and on the 30th, and the unit was run for about 4 hours at full speed and no load.  As with the first two combustion turbines, these events began the arduous task of combustion tuning (for most stable flame and lowest emissions), steam blows (to clean out the HRSG and steam lines), and stack certification testing (to certify the stack emissions monitoring system).

On May 21, 2001, unit 4 was put into service for the first time, purely to produce power for the grid.  It ran in simple cycle and full load during the combined cycle startup of unit 3 as FSV began putting the other units and steam turbine back on line for the summer.  On May 22nd, unit 4 was put in combined cycle for the first time, supplying steam to the steam turbine.  On May 24, 2001, unit 4 was pronounced "commercial," bringing to a close the $283 million repowering of FSV.  On May 31st all 3 combustion turbines were running in combined cycle mode, supplying steam to the old steam turbine, for the first time.  The new plant uses 1800 psig and 1000 deg. F. main steam.  This was believed to be the final configuration of the Fort St. Vrain power station.  The plant was now rated at 720 megawatts.

FSV Units 5 & 6
(More Power)

But wait! In early 2008 ground was broken for two additional GE Frame 7 simple cycle combustion turbines.  Constructed by TIC, each unit was capable of 150MW of additional power to the grid.  FSV Unit 5 was first fired for testing and checkout on March 31, 2009.  It's main power transformer failed upon being energized and lit up the night sky!  Fortunately there were no injuries but the transformer had to be replaced.  Unit 5 was first synchronized to the grid on April 22, 2009 and all testing and environmental checks were completed on May 21, 2009.

Unit 6 was first fired on April 24, 2009 and synchronized to the grid the following day.  All testing and environmental checks were completed on May 20, 2009.

This brought Fort St. Vrain's total power capability up to just over 1,000 megawatts.

Photo by Toby Grotz
This photo of FSV, taken prior to the construction of unit 4, and shows the stacks of the unit 2 and 3 heat recovery steam generators (HRSGs), located behind the main plant building.  The main building houses the old steam turbine and the decommissioned nuclear reactor plant.
Drawings of the Freeze Wall
Drawing of the "Freeze-Wall"
Reactor Building Excavation
Photo of excavation
FSV as of October 1969
Destroyed Pelton Wheel
PCRV Support Ring
Reinforcing steel of the PCRV support ring.
Botton Head Assembly
Helium Circulator
The late Wilbur Franklin
Reactor Operator Wilbur Franklin at the controls.
GA Startup Console
Helium Circulator 
GA Startup Console
Pelton Wheel
Oct. 1969
FSV on May 21, 2001
A piece of 'tophead pie."
Tophead concrete.
Diver in PCRV
Final concrete removal
Click to view larger photo!
First Combustion 
Turbine comes on line!
FSV in 2009