[ RadSafe ] query - Fort St. Vrain

Sandy Perle sandyfl at cox.net
Mon Dec 17 11:29:00 CST 2007

Everything you ever wanted to know about Fort St. Vrain:


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 final rated output of the
plant 720 megawatts.  


The Rest of the Story


Public Service Company of Colorado (PSC) was researching alternative power
generation as early as the late 1950s.  Plans to build Fort St. Vrain were
announced on March 13, 1965 and the application to construct FSV was filed
with the Atomic Energy Commission <http://www.nrc.gov/>  on October 20,
1966.  It would be the first commercial scal high temperature gas cooled
reactor plant in the United States.  The plant was to be named after the
historic frontier fort <http://stvrainsfort.homestead.com>  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 <http://www.dora.state.co.us/puc/>
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 <http://www.gat.com/>  (GA) was the
prime contractor.  Sargent  <http://www.slchicago.com/home/> & 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.  The 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
contol rod drives, moisture ingress into the reactor, and pelton wheel


Rise-To-Power testing to 2% occured in April 1975.  However, as a result of
the Browns Ferry fire <http://www.ccnr.org/browns_ferry.html> , an internal
PSC cable segregation audit was conducted.  In June, the Nuclear Regulatory
Commission <http://www.nrc.gov/>  (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


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 surveillances (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 supposrt 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 Untility 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
excercise.  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 paris 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 Novemeber 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 Environmetal
Qualification issues were resolved) was rececived on July 19 and the reactor
was taken critical the next day.  A high moisture scram occured 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


In January 1986, while returning a clearance on "D" helium circulator, a
water ingress into the PCRV of approximately 300 gallons occured.  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 accidently 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 occured 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




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 independant 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 <http://www.fwc.com/>  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 hairlinge 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.


>From November 1989 through February 1990, fuel was removed from twelve
reactor regions and stored in the fuel storage wells located on the fuel
deck in the plant reactor building.


The Nuclear Regulatory Commission (NRC) issed 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


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 <http://www.inel.gov/> .  Also in
October, all non-union employees were required to bid on the remaining
positions for "early dismantlement".  This was a very tramatic 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-radioacive
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.



(FSV rides again!)


Construction of the first gas turbine, a General Electric Frame 7
ms7001fa.jsp/>  called FSV Unit 2, was nearing completion in March 1996 and
the unit was test fired a few times.  Black
<http://www.bv.com/bv/index.htm> & 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.  Pubic Service initally 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 syncronized 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 <http://www.ueplaza.com/>
Engineering.  Unit 3 was started up in simple cycle (without the HRSG) on
January 12, and syncronized to the grid.  On April 24, the unit was fired in
combined cycle and the steam turbine was syncronized 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) <http://www.tic-inc.com/>  was their principal


On October 2nd, Public Service Company of Colorado officially became Xcel
<http://www.xcelenergy.com/>  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 <http://www.mhi.co.jp/indexe.html>  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 is believed to be the final configuration of the Fort St. Vrain
power station.  The plant is now rated at 720 megawatts.




Sander C. Perle 


Global Dosimetry Solutions, Inc. 

2652 McGaw Avenue

Irvine, CA 92614


Tel: (949) 296-2306 / (888) 437-1714 Extension 2306 

Fax:(949) 296-1144


E-Mail: sperle at dosimetry.com

E-Mail: sandyfl at cox.net 


Global Dosimetry: http://www.dosimetry.com/ 

Mirion Technologies: http://www.mirion.com/ 



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