A Glowing Review
Knoll Labs Nuclear Reactor Site
Connecticut is currently home to one nuclear powerplant: Millstone in Waterford. We used to have another – Connecticut Yankee in Haddam, now decommissioned – and there are, of course, nuclear submarines stationed in Groton. But there was another nuclear reactor here from 1959 to 1993 in… Windsor.
I don’t remember when I first learned of this surprising fact, but I do recall being, well, being surprised. Right there – right off of Day Hill Road in the woods next to the landfill near Northwest Park, behind what is now a bunch of businesses and a new massive “mixed use” complex, near the Farmington River… for over 30 years… was a nuclear reactor and testing station.
Apparently, the true nature of the facility was secret. The people living nearby had no idea. I can’t imagine the secret was too closely guarded, but I can’t know. (A commenter below says that it was not a very well-kept secret.)
It was a small reactor called the S1C prototype, designed for the United States Navy to provide electricity generation and propulsion on warships. The S1C designation stands for:
S = Submarine platform
1 = First generation core designed by the contractor
C = Combustion Engineering (C-E) was the contracted designer
All of the information about this place is from the excellent Coldwar-Ct.com, which is the CTMQ of all things Cold War. In Connecticut. Obviously.
S1C achieved the first self-sustaining nuclear chain reaction in Connecticut and was a prototype for the experimental USS Tullibee submarine. The Knoll Labs propulsion plant was unusual in that the steam turbines powered an electric motor, rather than a set of reduction gears. The electric motor was in turn connected to an electrical generator. By changing the load on the generator the load on the reactor system could be changed.
Yeah, I have no idea what that means either.
The facility consisted of naval nuclear propulsion plants, administrative offices, training facilities, an equipment service building, boiler house, and waste-handling facilities. A full scale 100% operational mock-up of the reactor and engineering spaces of a submarine served as the training platform.
Throughout the Cold War, the S1C Prototype at the Nuclear Propulsion Training Unit (NPTU) at the Windsor Site supported the submarines and surface ships of the Navy’s nuclear fleet by testing new equipment and training naval propulsion plant operators. Over 14,000 Naval operators were trained there.
You see what I mean about it being “secret?”
“Oh look, Billy, another caravan of buses containing young men with buzzcuts going through that gate manned by uniformed officers during WWII and all through the Cold War. I’m sure it’s just some sort of summer camp or something. Let’s eat lunch!”
The facility was initially operated by Combustion Engineering for the Department of the Navy and the Department of Energy. In 1960, the S1C site was sold to the U.S. government although CE continued to manage operations until 1970, when Knolls Atomic Power Laboratory (KAPL) took over operations. In the eighties Westinghouse would be involved.
In the mid 80s construction started on a new building that would be nick-named “Castle Gray Skull”. It was of very sturdy construction with heavy rebar in the walls, massive doors and massive screens on the diesel generator air intakes to protect them from debris during hurricanes and tornadoes.
Just popping back in here to say that the real Castle Grayskull (no space) is a fortress located on the planet Eternia. It’s where He-Man and Skeletor had many battles to be the titular Master of the Universe. And as far as hurricanes and tornadoes, remember that a tornado did cause extensive damage just north of here in Windsor Locks in 1979, right before Castle Gray Skull was built.
The diesel generators could provide emergency power and cooling to the reactor in the event of a utility power failure. There were fully redundant systems and the generators would be on line supplying power within 30 seconds of an outage. The building was earthquake and bomb proof. There were utility tunnels connecting this building with other parts of the site. There was a large control room where plant management could go during an emergency and cots, water, food and other survival supplies were kept on hand as the building could serve as a emergency shelter. Reportedly there were large tanks of borated water contained in the building that could be used flood the reactor compartment in the event of a loss of coolant accident.
Hurricanes, tornadoes… okay. Earthquakes and bombs? I’m sure the locals would have been pleased as punch to learn that there was a fear of the Soviets dropping a bomb in their backyards. On a nuclear reactor. And really, shouldn’t residents have been made aware of any potential fallout danger? The movie “Red Dawn” was released in 1984. Ivan Drago killed Apollo Creed in 1985 before Rocky beat him in the fourth installment of that franchise. Real talk.
Here’s my favorite story about this place:
In the early 90s there was a security scare at the facility. A group of armed individuals came running from the woods towards the plant and showed up in the parking lot with weapons drawn. There was a tense few minutes until the plant guards sorted things out. The “intruders” were members of the Hartford Police SWAT team who were supposed to be conducting a force on force exercise at the Combustion Engineering nuclear fuel fabrication plant next door.
The reactor was shut down in 1993 and closed shortly thereafter. Full clean up of the site was completed in 2006 and the parcel was the first ever unrestricted radiological and chemical release of a nuclear reactor site. I think that means you and I can just walk around it now… or that large mixed use apartment and retail complexes can be built right next to it.
(The two roads into the site are gated and signs warn off anyone looking to take a walk. However, the field is easily accessed via any number ways, from all directions. If you’re so inclined.)
And finally, check this out. I’ve driven the western end of Day Hill Road every day for years – both for work when I’ve worked there and to take my son to school – and have driven over the train tracks there. In recent years, it has seen more and more activity. In fact, just this morning on Cottage Grove Road in Bloomfield, I was stopped at the same rail line. I swear. Proof:
Anyway, its northern terminus is at the Bloomfield/Windsor line on Day Hill Road. Weird, right? Well, there is an explanation for this:
The Griffin Line railroad which extends from downtown Hartford out to northern Bloomfield was used starting in the late fifties to transport nuclear material to and from the nearby Knolls Atomic Power Labs in Windsor. The line was all but abandoned for over a decade but was rebuilt in the late 90’s to aid in the decommissioning of the Knoll Labs. Highly radioactive materials from the lab, including spent fuel rods and the actual reactor core were initially transported via this line to their ultimate disposal location in Idaho.
So the short little rail line spur that I drive over at least twice a day, every day, either on Day Hill Road or Cottage Grove Road was built solely to supply a secret nuclear reactor site in Windsor… and then rebuilt more recently to transport “highly radioactive” materials to our capital city for ultimate removal to Idaho.
In 2021 I currently work on Day Hill Road and my son still goes to school in Windsor. If there ever was an “interesting story in my own backyard,” this is it.
And this is why I continue to love writing this dingdong website.
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Debbie saysDecember 8, 2021 at 7:20 am
Dave saysDecember 8, 2021 at 8:08 am
Fascinating article. growing up in East Granby on Hatchet Hill Road, the reactor was a poorly kept secret piece of Nutmeg history.
Tim Wescott saysDecember 8, 2021 at 9:17 am
Fascinating. Those train tracks border my company’s property (we are at the corner of Griffin Rd S and Day Hill Rd), I always assumed it was for the Home Depot distribution center.
Steve saysDecember 8, 2021 at 9:36 am
I thought that too. Remember around 2016 or so they’d just drive that one green engine back and forth all the time? I figured it was going to Hartford to pick up lumber and shingles (I recall seeing lots of lumber and shingles on train cars too) for the HD distribution building back there. But these days they’ve been building it back up around Cottage Grove and improved the crossing in “downtown” Bloomfield as well. Used to be a guy with a little orange flag would hop out and stop traffic. All this work is probably still for the Home Depot deliveries. Who knows.
Albert M. Passy saysJune 28, 2022 at 11:10 pm
So, I actually attend that prototype as a young Ensign in the USN in 1989. The existence of the plant was in NO WAY a secret, but there weren’t any billboards either. We weren’t told not to talk about it. Matter of fact, I was a volunteer firefighter in the Windsor FD, which technically had first-response duties, and it was always a topic of discussion as to how many might even turnout for a fire.
Needless to say, NPTU Windsor planned on their own fire response.
Dale saysJuly 14, 2022 at 5:17 pm
I worked there from the late 70’s through the next 10 to 15 years. Started off with GE and went to Martin Marietta then Lockheed Martin. All subcontractors for the DOE AND NAVY. It was the greatest job ever, knowing I was supporting our country.
Mark Backhaus saysJuly 14, 2022 at 5:41 pm
Your statement “So the short little rail line spur that I drive over at least twice a day, every day, either on Day Hill Road or Cottage Grove Road was built solely to supply a secret nuclear reactor site in Windsor” is not true. This railroad spur is all that remains of an abandoned railroad that went much further than Windsor. In fact, it once reached to the Hudson River in Dutchess County, New York. It was built in the late 1800s, and was known as the Central New England Railway (see Wikipedia). From Hartford, it went through Tariffville, Winstead, Canaan, Millerton, NY, Poughkeepsie, NY, and Rhinecliff, NY. Starting in the 1920s, decreasing traffic and redundant rail lines caused portions of the railway to be abandoned in stages until only this spur remained, probably as far back as the 1930s.
Otto Leinhauser saysFebruary 13, 2023 at 10:17 am
I attended NPTU S1C prototype in summer of ’72 as a Machinist Mate before being assigned to my fisrst sub.. It was not a secret but run as a research facility by Combustion Engineering for training. Our automobile parking pass was a S1C sticker on the front windshield, I believe parking was open. As I remember, the only gate was to get into the facility where we showed our Navy ID.
There were quonset huts inside you were assigned if you got behind in your studies. Fortunately I stayed out of them.
Another thing I remeber were all the tobacco farms and a small store at the edge of the woods at the beginning of the access road.
Chris C saysFebruary 24, 2023 at 4:55 pm
I grew up in Windsor, Like others have said not advertised but not really a secret (thou I’m sure alot of what actually happened there was very secret).
As a kid I didn’t really know about it until I was a teenager. When I got my drivers license a few of my friends would go up to the back of the nearby tobacco fields to get down to the farmington river. If you look on a map to the west you can see outlines of the old fields and the gravel pit that was back there we used to go thru to get to the river.
This was in the mid to late 90’s so the facility was closed but still being dismantled. my friends mentioned that there were armed gourds with Jeeps if you got too close, and sure enough i did see guards sitting at the corner of the entrance roads in a Jeep a few times. I currently work in defense contracting and now know those were some serious guards and were very well armed.
Karen saysMarch 14, 2023 at 2:34 pm
I came across this site today as my husband and I are composing a memory book of his naval career. He spent 22 years as a submariner, then 23 years working at Millstone Power Station, Dominion Nuclear., in Waterford, CT
In February of 1979 my husband began his tour of duty as an instructor at the Windsor site. We lived in Plainville on Cassidy Drive, units that were mostly occupied by military recruiters and their families.
My most vivid memory of our time at this facility took place on the afternoon of October 3, 1979. My mother, daughter, and I had been shopping at the West Farms mall when a torrential rain storm hit as soon as we began our trip home. I knew that my husband and two other instructors would be leaving for work and I was concerned for their safety.
We didn’t travel long before I stopped beneath an underpass as the rain made it impossible to see and dangerous to drive. Thunder and lightning were all around us and I had hoped to get back home to warn my husband before he left. After about 10 minutes we resumed our trip, struggling to see but anxious to get home to safety.
When we got back to our house and settled inside the thunder grew even stronger. One particular unrelenting roar sounded more like a freight train approaching, and I recalled a friend, who was born and raised in Missouri, who once described the familiar sound of a tornado. I ignored that thought because, after all, this was Connecticut and we were fairly insulated from that threat.
When I turned on the TV all local stations were broadcasting requests for medical personnel to return to the hospitals. Weather reports were stating that a tornado had just ripped through Windsor, CT. I called my neighbor, whose husband was the driver of the car pool, to ask if they had left on time and if she knew if they arrived to work safely. When I finally heard from my husband, he told me that his 1/2 hour trip turned into a 2 1/2 hour plight.
They weren’t far from home when the rain caused massive flooding on their route. The 3 of them were stuck in high waters and had to push the vehicle toward higher ground. Some of the roads in which they traveled to work were in the path of the tornado. I believe that the flooding they encountered actually kept them out of harm’s way of the tornado.
Dan Murphy saysMay 27, 2023 at 10:19 pm
I worked at CENRD Sep 1960 – Nov 1961, for Combustion Engineering. Left to join Army, I was draft bait. In the subsequent years I have encountered only two people from the NPTU, one on them for several years. Good memories.