A 5-Watt Plastic Reactor
Posted: Tue Mar 22, 2022 10:07 pm
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.
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.
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:
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.
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 :
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:
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
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.
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.
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:
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.
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 :
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:
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