A 5-Watt Plastic Reactor

This area is for discussions involving any fusion related radiation metrology issues. Neutrons are the key signature of fusion, but other radiations are of interest to the amateur fusioneer as well.
Post Reply
Robert Dwyer
Posts: 86
Joined: Sun Sep 04, 2016 5:34 pm
Real name: Robert Dwyer

A 5-Watt Plastic Reactor

Post by Robert Dwyer »

Hello All,

I hope everyone is doing well! I had been compiling data and images for some reports for my universities' research reactor, and remembered that the design and engineering of fission reactors occasionally pops up on these forums, and I thought I might share.

Since the early 1960s the nuclear engineering department has operated and AGN-201 research reactor. A mass produced research by the aerojet nucleonics corporation with the intent of a mass-produced small reactor that would find itself in universities', industry, and maybe even high-schools. While aerojet's dreams did not come to fruition at that scale, some of the reactors were in fact built and licensed. This is one of three remaining and two operating AGN-201 cores in the U.S. The other two are at Idaho State University and Texas A&M with the A&M reactor currently being rebuilt/re-licensed.
One of the flyers for the AGN-201 reactor
One of the flyers for the AGN-201 reactor
In 2019 I underwent the UNM Reactor Operator (RO) training program to become an NRC licensed reactor operator. This included a practical, hands-on course in radiation protection, reactor kinetics, and of course, NRC regulations and procedures. Before taking a formal class in kinetics or neutorn transport I had learned the basics of rod drops, the Inhour equation and some neutron diffusion theory just by learning to operate a real nuclear reactor. I must say even nuclear engineering as I am about to graduate the program as I am in my senior year, this type of experience is one of the quite unique things about small reactor facilities like this. Very few programs, even nuclear engineering programs really let students at the entry-level undergraduate level get hands-on experience with reactors. Due to delays from the coronavirus pandemic I did not undergo my license examination until late 2020, and was officially licensed in 2021.
AGN Full Core Schematic (taken from unknown online-source that is for another operating AGN.  Better than the old mechanical drawings I currently have access to).
AGN Full Core Schematic (taken from unknown online-source that is for another operating AGN. Better than the old mechanical drawings I currently have access to).
The core has a rather unique design in that it is, to my knowledge, the only homogenous core that utilizes low density polyethylene plastic. Yes that is right the core is made of plastic! 100-200 micron UO2 beads are dispersed throughout the fuel giving them a unique black plastic color. The fuel is enriched to 19.5% U-235 with, wait for it, a total U-235 mass of 666.6 grams of U-235. Yes 666.... Images of these fuel plates are given below:
Image of a bototm fuel plate with the control rod penetrations.
Image of a bototm fuel plate with the control rod penetrations.
Image of the upper fuel plates removed during a student approach to critical experiment.
Image of the upper fuel plates removed during a student approach to critical experiment.
The core is surrounded by a graphite reflector and lead shield to shield against gamma radiation. The core is then surrounded by a water tank that acts as a neutron shield. The initial rated power of the core was 100mW but the UNM reactor has a license modification that allows us to operate at 5W of thermal power with additional shielding from concrete blocks.
A view of the open upper core and an image of the core removed from the tank.
A view of the open upper core and an image of the core removed from the tank.
The fuel is stacked inside of a core-tank made of aluminum which is hermetically sealed. The core tank acts as a fission-product barrier due tot he fuel being unclad. The core tank and lower fuel plates are penetrated by four control rods that are inserted via magnetically-coupled drives that come up from the bottom of the core. The control rods are made of fuel material with two safety rods, a course control rod, and a smaller fine control rod. Operation cannot commence without the two safety rods inserted fully into the core. Operators can adjust the critical geometry with the course rod and fine rod as they desire. Images of the control rod drives, and a video of myself and Carl Willis doing a SCRAM test for one of the rods are given below along with the core tank diagram :
Drawing of the AGN core tank.
Drawing of the AGN core tank.
Image of the control rod mechanisms
Image of the control rod mechanisms
Image of the UNM core being assembled for the first time.
Image of the UNM core being assembled for the first time.

https://www.youtube.com/watch?v=H40PEHTpniE

Many people in here may ask why the rods come from the bottom. That is due to them being fueled. Therefore they insert positive reactivity. When the reactor is SCRAMMED the rods fall out of the core from gravity as the magnetic coils that hold the rods lose power current and a spring system pulls the rods out as an extra safety feature if gravity fails (It really just adds redundancy and works to increase the time it takes for rods to be inserted).

Radiation levels are measured through portable neutron and gamma detectors as well as portable gamma detectors placed around various areas of the reactor facility. Three neutron detectors are used to measure the neutron output, and therefore power level inside of the core. The first, a U-235 fission chamber called "Channel-1" is used as the low-power monitor. Typically only used for "previous readings" measurements comparing the early states of the core while it is subcritical to previous operating conditions. The other two are channels 2/3 which are boron-lined ion chambers which provide a linear current output proportional to the neutron flux. These are each calibrated at low and high power levels and run the low and high level trips respectively. The low level trip is required as operators must have a measurable neutron flux in order to adequately look at the multiplication rate of neutrons in the system. In order to provide a minimum neutron flux even when the reactor is scrammed, a PuBe neutron source enters the side of the reactor through a port in the side of the core. This can be inserted and retracted from the core as required. Schematics of the core instrumentation are shown below:
Top-down view of the safety channels placed in shielded feedthroughs into the water tank.  These measure the neutron flux at three different positions outside of the core.
Top-down view of the safety channels placed in shielded feedthroughs into the water tank. These measure the neutron flux at three different positions outside of the core.
The reactor ports which penetrate the water tank and lead shielding.  Auxiliarry channels for operator aids and experiments are often in these ports as well as the PuBe source drive.
The reactor ports which penetrate the water tank and lead shielding. Auxiliarry channels for operator aids and experiments are often in these ports as well as the PuBe source drive.
An image of operators at the AGN-201M core
An image of operators at the AGN-201M core
The reactor facility is unique as it is one of the few "low-power" research reactors. The maximum licensed power if 5W with the maximum achievable steady-state power being ~10W due to thermal feedback. The students use the reactor for many experiments, the most exciting being the "approach to critical" were students must dress out in "bunny suits" and handle unclad fuel and due stack the fuel plates measuring the change in reactivity from each addition. The lab teaches students about reactivity and criticality safety as well as how to deal with working in contaminated areas where they must be frisked and deal with health physics staff and strict controls on reactivity changes and fuel additions. The reactor is also used by other departments for some other experiments involving neutron activation analysis.

While not fusion related, I hope some people may find this interesting, given that sometimes the radiation aspects of the forum drift over to the general nuclear physics or fission side of things! I have also attached a youtube link below to a video-tour of the AGN facility at UNM done by the head of the reactor lab, Carl Willis, who was a long-time contributor to this forum for those interested in some more details:

https://www.youtube.com/watch?v=j-tjRh_l0Do
If we throw more money at it, it will have to work... right?
User avatar
Richard Hull
Moderator
Posts: 13903
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: A 5-Watt Plastic Reactor

Post by Richard Hull »

Thanks Robert. I really enjoyed this post mightily. In the scram test you tube video I got to see the current iteration of Carl. He is less skeletal and the Thelonious Monk beard looks good on him.

I like that a very few universities have not yielded to the temptation to remove all of their experimental reactors installed in the late 50's and 60's.
UVA here had a nice swimming pool reactor that I would often visit by just walking in back in the early 70's. Now long gone.

You are right in that many of our former fusor.net folks are now nuclear engineers or are physicists and engineers in related fields. They are gainfully employed and beginning family life in many instances. I am proud of what they learned from me and value all that I learned from them. All seem to have valued my insistence on the "hands-on" approach to science. Many, of course, arrived here with that mentality in full bloom.

I really enjoyed the advert from Aerojet General in the first image and all the other images by which I got the real feel for how this great low power fission reactor functions. Really cool! Again thank for this and the URLs to watch. Fission is where future power lies, fusion is a struggling dream of consistent failure at the multi-billion dollar level.

I have put this URL up before but Carl and any serious rad freak would love to be at the Hanford B reactor fuel transport car as seen in the video at the 18:30 point in this URL. You can see the gleam in Carl's eyes as the radiation gets more and more intense. ( For the train buffs the two diesel locomotives are RS-1s of the 1940s...acronym for RoadSwitcher-1)

https://www.youtube.com/watch?v=k6j7wksLhaw

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
User avatar
Jim Kovalchick
Posts: 630
Joined: Wed Apr 13, 2011 8:00 pm
Real name:

Re: A 5-Watt Plastic Reactor

Post by Jim Kovalchick »

46708535_10217821611150864_2268786370686222336_o.jpg
This year marks the 40th anniversary of my first pulls to critical on both of the UVA reactors, the CAVALIER and the UVAR, and my NRC license docket on the latter dates to 1982. I was one of many students whose nuke careers were kick started by operating the UVAR. It makes me sad that a nervous provost insisted on closing her, but I'm encouraged that the remaining university reactors are hanging in there.
Jim K
User avatar
Richard Hull
Moderator
Posts: 13903
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: A 5-Watt Plastic Reactor

Post by Richard Hull »

Yes, In the early 70's I use to get time on the McCormick 26-inch refractor at UVA as head of the Richmond Astronomical Society. I would often go up early in the afternoon before dark and wander into the swimming pool reactor building where a friend worked. We would go to lunch and often bring it back to eat at the facility and talk all things nuclear. I loved to look over the edge into the warm blue glow of the Cherenkov radiation from the working core. The reactor used rather highly enriched uranium at that time. Very soon, the access was quickly controlled as terrorist attacks became a staple of the mid-late-70s.

As a kid born in the 40's I became intensely interested in the mid-50's with all things nuclear. I took advantage of the atoms for peace program where young students could get radio-active isotopes sent from Oak Ridge to my home. My mom signed for my first orders in 1957 when I was 12. Later in high school my science teacher would sign and even bought two of the 9 packs for me using his own money! The mailman would just show up with the boxes with the radiation stickers on them and leave them in the doorway. I guess I had about 3 of the two packs and over 10 of the 9 packs delivered between 1957 and 1966. Lots of rads to the nads as a kid.

I attach a couple of catalogs offering the raw chemical isotopes. (note: these were not sealed check sources but the raw chemical isotopes!) I monkeyed about with these all through the late 50s and into my college days in the 60s. Growing up back then was great! A kid could get all manner of really dangerous crap back then! Life was good....

Richard Hull
Attachments
These were my favorites!!  I cut grass and did some TV-Radio repair jobs to earn money to get these Abbott labs super value-packs of many isotopes.
These were my favorites!! I cut grass and did some TV-Radio repair jobs to earn money to get these Abbott labs super value-packs of many isotopes.
Universal Atomics was another of my major suppliers back in the 60's
Universal Atomics was another of my major suppliers back in the 60's
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.
User avatar
Dennis P Brown
Posts: 2600
Joined: Sun May 20, 2012 10:46 am
Real name: Dennis P Brown
Location: Glen Arm, MD

Re: A 5-Watt Plastic Reactor

Post by Dennis P Brown »

Thanks for the information of the reactor - the reactor core/uranium binding agent being plastic certainly is unexpected! Hopefully, with the possible development of a liquid ceramic/uranium fuel core local reactors will become available in the not-to-distant future (yet again!)
Jerry Biehler
Posts: 938
Joined: Tue Nov 24, 2009 3:08 am
Real name:
Location: Beaverton, OR

Re: A 5-Watt Plastic Reactor

Post by Jerry Biehler »

Reed college here in Portland has a reactor too: https://www.youtube.com/watch?v=pLBcp3nJlFQ
Emma Black
Posts: 23
Joined: Wed May 11, 2022 9:42 am
Real name: Emma Black

Re: A 5-Watt Plastic Reactor

Post by Emma Black »

Really interesting, reminds me of a paper on critical mass reduction (attached) and the Comet machine they used. The mass described in the paper was highly enriched and was around 250 grams!
Attachments
00314721.pdf
(229.58 KiB) Downloaded 28 times
Post Reply

Return to “Neutrons, Radiation, and Detection (& FAQs)”