Open access peer-reviewed chapter

Idaho State University AGN-201 Low Power Teaching Reactor: An Overlooked Gem

Written By

Chad L. Pope and William Phoenix

Submitted: 24 September 2021 Reviewed: 10 June 2022 Published: 16 July 2022

DOI: 10.5772/intechopen.105799

From the Edited Volume

Nuclear Reactors - Spacecraft Propulsion, Research Reactors, and Reactor Analysis Topics

Edited by Chad L. Pope

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A category of reactors called university research and teaching reactors, includes relatively high-power pool-type and low-power solid-core reactors. Many high-power university reactors are largely used for irradiations and isotope production. Their almost constant operation tends to impede student access. A university reactor can be particularly relevant to the university’s mission of preparing well-rounded students who have theoretical knowledge, reinforced by focused laboratory reactor experience. The solid-core Idaho State University Aerojet General Nucleonics (AGN) model 201 reactor operates at such a low power (5 W maximum) that it is not useful for isotope production activities. However, the AGN-201 reactor is well suited for teaching and research activities. The solid-core AGN-201 reactor requires no active cooling system, uses a simple shielding arrangement, and the very low operating power results in trivial burnup providing an operating lifetime exceeding many decades. It is thus worthwhile to examine the Idaho State University AGN-201 nuclear reactor more closely because it offers a wide range of research and teaching capabilities while being widely available to students.


  • reactor
  • solid-core
  • research reactor
  • university reactor
  • low-power reactor

1. Introduction

University research and teaching reactors are fundamentally intended to help prepare nuclear engineering and other students for entry into the nuclear workforce. They introduce students to the disciplined, structured environment of operating a reactor licensed by the Nuclear Regulatory Commission (NRC). They also offer students hands-on experience, provide opportunities to demonstrate the operation of reactors and a variety of the traditional applications of reactors such as neutron activation, and introduce them to the application of nuclear instrumentation, applied principles of health physics, and more. They can be useful to a wide range of people beyond university nuclear engineering students, including those from National Laboratories, utilities, regulators, and others.

The Idaho State University Aerojet General Nucleonics (AGN) model 201 nuclear reactor is an example of a very safe, low-power, solid-core reactor designed with students and teaching in mind. It was developed in the late 1950’s by AGN to satisfy the need of university nuclear engineering departments for a relatively inexpensive, safe, flexible and available reactor with a long design life. The AGN-201’s safety results from, inter alia, its ‘thermal fuse’ that terminates excessive sustained operation at high power, a large negative temperature coefficient (−0.035%Δk/k °C−1), and low available excess reactivity (nominally 0.18% Δk/k ($0.24) at 20°C) [1]. These safety features, and other design features, make it an ideal teaching reactor in an environment with rapid turnover of student operators and other personnel.

The small teaching reactors generally preceded the higher-power reactors at universities. As the university’s interest moved to the higher-power reactors, reactors like the AGN-201 s fell into disuse and most were decommissioned. Recently however, there has been a renewed interest in the utility of AGN-201 nuclear reactors [2]. In addition to discussing the potential uses for the AGN-201, this chapter includes discussions of the challenges of replacing obsolete components to facilitate continued operation. To address this issue, Idaho State University teamed with members of the community whose expertise in project management, instrumentation and control, licensing and other subjects complemented the university’s expertise and resources.

A nuclear reactor is an example of the integrated operation of many systems to support the operation of a nuclear core. Simple reactors can be excellent examples of the integrated operation of the core, nuclear instrument systems, the reactor operator or ‘human in the loop’ and control rods and their controls. Although the AGN-201 is a simple reactor, it can be used to measure the operation of the core and understand and gain insight into its operation. It is intended to support teaching, training and research in a wide variety of subjects. For example, human/machine interface studies could even be conducted with the operator to test novel display concepts.

The AGN-201 has a variety of attractive design features. The reactor has direct access to the core via the so-called ‘glory hole’ that runs horizontally through the reactor center. It also has a graphite thermal neutron column at the top of the reactor and beam ports in the radial portion of the graphite reflector. The core is enriched to a nominal 19.5% and given the reactor’s low power, the core should essentially never require replacement [1]. The reactor has extremely low background neutron and gamma flux levels that along with the reactor’s unusually sensitive nuclear instrument systems, facilitate a wide range of measurements including some that might not be possible in other reactors. For example, it is possible to observe individual chains of fissions when the core is just barely subcritical and flux has been allowed to decay to very low levels thus allowing measurement of the prompt neutron decay constant using Rossi’s-α method [3]. Neutron flux near the allowed maximum power level is high enough to usefully activate foils and illustrate reactor physics principles but too low to result in the accumulation of large amounts of fission products.

The AGN-201 provides and supports a number of potential opportunities for demonstrations and tests that complement the theory from the classroom, research and problem solving. A wide range of demonstrations and tests can introduce students to the instrumentation and activities that are conducted by reactor engineers and reactor operators at higher-powered test and research reactors and commercial power reactors. This knowledge can help an instrumentation and control designer or engineer to produce circuits that are more forgiving of noise and to help a technician to differentiate between electronic noise and normal operation of the detector channel and be more successful in reducing noise.


2. Reactor description

The AGN-201 nuclear reactor is a solid-core reactor with no active cooling system. The core is constructed of nine 25.6-cm diameter fuel disks (see Figure 1). Four of the disks are 4-cm thick, three of the disks are 2-cm thick and two of the disks are 1-cm thick. Each 4-cm thick fuel disk contains 96 g of 235U, each 2-cm thick fuel disk contains 58 g of 235U, and each 1-ck thick fuel disk contains 29 g of 235U. The overall core height is 24 cm. A graphite reflector surrounds the core both radially and axially. The graphite reflector is 20-cm thick and has a density of 1.75 g/cm3. The reactor fuel consists of slightly less than 20 wt. % enriched uranium. The uranium is in the form of 15-micron diameter particles of UO2. The UO2 particles are pressed with 100-micron diameter polyethylene particles. The density of 235U in the UO2-polyethelyene fuel is 61 mg/cm3 and the overall uranium density in the fuel is 305 mg/cm3. The mass ratio of uranium to polyethylene is 1:3.16. The approximate critical mass of the AGN-201 reactor is 665 g 235U [1].

Figure 1.

AGN-201 reactor core, reflector, and control rods [1].

The reactor uses a total of four control rods; two safety rods, one adjustable coarse rod, and one adjustable fine rod. The control rods are made from the same UO2-polyethyelene fuel as the core. To ensure safety, the fueled control rods enter the core from the bottom (see Figure 1) so that gravity, along with compressed springs, ensure rapid removal upon reactor SCRAM. The bottom four fuel disks as well as the lower reflector have holes drilled through them to accommodate the control rods.

In addition to the control rods, the AGN-201 reactor is equipped with a thermal fuse as an ultimate reactor safety shutdown device. The thermal fuse is located just below the core center line (see Figure 1). The fuse is similar in construction to the reactor fuel with two key differences. First, rather than polyethylene, the fuse uses polystyrene. Second, the density of uranium in the fuse material is double the value used in the fuel. The two differences coupled with the location of the fuse results in maximizing the fission rate in the fuse compared to all other locations in the core. In the event of a runaway power transient, heat will be generated in the thermal fuse at a greater rate than any other location in the core. As the fuse temperature rises, it will tend to soften when it reaches 100°C and will melt before any the reactor fuel reaches its melting point of 200°C. The AGN-201 reactor design has the lower portion of the core and reflector held in place by the thermal fuse. In the event of the thermal fuse melting, the lower portion of the core and reflector will move downward approximately 5 cm compared to the upper portion of the core which is stationary since it is supported separate from the thermal fuse. The net result will be a dramatic increase in neutron leakage which will terminate the transient. It must be noted that the thermal fuse is a single use safety device.

The reactor core and a portion of the reflector are contained within a gas tight core tank. The core tank is then located within the remainder of the graphite reflector (see Figure 2). Surrounding the graphite reflector is a 10-cm thick lead shield. The lead shield is primarily used for gamma ray shielding. The reactor core, reflector, and lead shielding are located within the reactor tank. A graphite thermal column is located on the top lead shielding to support experiments and measurements involving thermalized neutrons. The reactor tank is then located within a 200-cm diameter water filled tank. The radial thickness of the water is approximately 55 cm. The water filled tank is used to absorb neutrons that escape from the core.

Figure 2.

Reactor tank assembly [1].

To provide access for experiments, a 2.54-cm diameter hole traverses the reactor tank, lead shielding, graphite reflector, and reactor fuel. The hole through the center of the reactor core is commonly referred to as the “glory hole”. The glory hole aluminum pipe ensures the core, reflector, lead shield, and water remain properly sealed. When not in use, the glory hole is typically open to the air atmosphere. When starting the reactor, a neutron source is placed in the glory hole and when the reactor is shut down and not in use, a cadmium neutron absorber is placed in the glory hole to ensure reactor startup cannot occur. In addition to the glory hole, there are four access ports located in the graphite reflector (see Figure 2). The access ports are 10.16 cm in diameter and penetrate through the reactor tank, lead shielding and graphite reflector. When not in use, the access ports are typically filled with graphite, lead, and wood (to simulate water).

The reactor radial thermal flux profile is provided in Figure 3. The flux profile shows a general Bessel function trend in the core region followed by an exponential drop in the reflector, lead, and water regions. It should be noted that, unlike water reflected thermal reactors, the AGN-201 reactor does not experience an increase in the thermal neutron flux as neutrons enter the reflector. This is primarily due to the difference in neutron scattering properties of water compared to graphite. The flux profile plot demonstrates the effectiveness of the neutron shielding associated with the water shielding tank. The thermal neutron flux at the outer edge of the shielding tank is four orders of magnitude lower than at the center of the reactor.

Figure 3.

Reactor radial flux profile [1].

Reactivity control is carried out using four control rods. Two safety rods, each with a reactivity worth of 1.25% Δk/k ($1.68), are operated in a binary fashion. When starting the reactor, the safety rods are driven fully into the core. No intermediate stopping locations are used for the safety rods. When the reactor is SCRAMed, the safety rods are completely removed form the core. The removal mechanism relies on both gravity as well as compressed springs. A single coarse control rod with a reactivity worth identical to the safety rods (1.25% Δk/k ($1.68)) is raised into the core region during reactor startup. Typically, the coarse control rod is driven to its maximum insertion location, although there are scenarios where the coarse control rod is stopped short of the maximum insertion location. Similar to the safety rods, upon reactor SCRAM, the adjustable coarse control rod is rapidly ejected from the core by relying upon gravity and compressed springs. Finally, the fine control rod has a reactivity worth of 0.31% Δk/k ($0.42). The fine control rod is typically driven into the reactor until criticality occurs. Adjustments in the coarse control rod and the fine control rod can then be made to adjust the desired reactor power. Unlike the safety rods and the coarse control rod, the fine control rod is not rapidly ejected from the core when the reactor is SCRAMed. Rather, the fine control rod is driven out of the core at the same rate that it can be driven into the core.

Three monitoring channels are used in the ISU AGN-201 reactor. The three monitoring channel detectors are located within the water filled reactor tank as shown in Figure 4. The AGN-201’s nuclear instrumentation consists of three different nuclear instrument channels and offer students the opportunity to understand the functions performed by separate portions of the circuit as the incoming signal is processed. Students can study the nuclear instrument channels in a laboratory and then observe them at the reactor.

Figure 4.

Reactor assembly plan view [1].

The three channels are comprised of commercial-grade components. They are more accessible than power plant channels to students and others who wish to study them and their operation over a wide range of neutron flux at an actual reactor. Students can study the instrument systems and their theory and design, and then observe the systems in operation at a wide range of neutron flux. Analog and digital designs of nuclear instrument systems, with a variety of neutron detectors, can be evaluated by using the AGN-201. The AGN-201’s nuclear instrumentation consist of the three commonly-found types of nuclear instrument channels that follow the same operating approaches and perform the same functions as the nuclear instrument channels typically found in most reactors. Each channel has a unique but complementary principle of operation. Together, they provide the reactor operators and others with indications of reactor power and the rate of change in power over the entire operating range. Of course they also supply signals for reactor trips.

Channel 1 is the startup, source range, channel and uses a BF3 filled proportional counter. The source range channel illustrates a standard approach that allows the source range channel to display a very low neutron flux in the presence of significant gamma radiation. A proportional-type BF3 neutron detector produces pulses when gamma radiation and neutrons interact with the BF3 that fills the detector. The pulses are amplified and shaped, the lower-amplitude pulses due to gamma interactions within the detector are rejected while the remaining higher-amplitude pulses from neutron interactions are further amplified and displayed. The channel displays count rates from the reactor without a source to well above critical. Channel 1 is designed to initiate a SCRAM signal for low power situations when the count rate falls below the setpoint.

Channel 2 is used to monitor the reactor power using a log scale as well as for indication of the reactor period. The channel 2 detector is a BF3 filled ionization chamber. Channel 2 generates a SCRAM signal when the reactor power falls below 3 x 10−13 W or when the reactor power exceeds 5 W. Additionally channel 2 generates a scram signal if the reactor period is less than 5 seconds. The wide range logarithmic neutron instrument channel (channel 2) illustrates a standard approach that allows the channel to detect and display a current signal that is proportional to power over 7 decades. Channels 1 and 2 rely on different applications of wide-range logarithmic amplifiers. The source range nuclear instrument channel’s wide-range logarithmic amplifier converts the frequency of incoming pulses from neutron interactions to voltage. The wide range logarithmic current channel’s amplifier converts a direct current to a voltage. In both cases, variations in count rate or current level that are due to the normal and expected variations in neutron flux are often misinterpreted as ‘noise’ that can lead to the period meters having too much variation to be useful indicators to the reactor operators, and the period circuits spuriously tripping. Circuit designers frequently assume the neutron signal is relatively constant and do not anticipate the large noise component that is inherent due to sources. The AGN-201 provides the actual variations in neutron flux that drive oscillations in period meters and indications of reactor power and can be used to evaluate the effect of circuit modifications to reduce the amplitudes of the oscillations.

Channel 3 is used to monitor reactor power using a linear scale. The channel 3 detector is a BF3 filled ionization chamber. Channel 3 generates a SCRAM signal when the reactor power exceeds 5 W or whenever the linear rotating switch indicator is less than 5% or greater than 95% of full scale.

Figure 5 shows the SCRAM circuit arrangement for the three monitoring channels. It is important to recognize that the SCRAM circuit arrangement is a single signal SCRAM [4]. If any one of the channels identifies a situation that triggers a SCRAM, the reactor will be SCRAMed. That is, the AGN-201 SCRAM circuit is not a two-out-of-three arrangement.

Figure 5.

SCRAM circuit arrangement [1].

In addition to the monitoring channels, a series of additional interlock circuits are used to prevent reactor startup or to SCRAM the reactor in the event of undesired situations (see Figure 6) [4]. The reactor shielding tank water temperature is monitored to ensure that the maximum allowed excess reactivity is not exceeded. If the reactor water temperature falls below 15°C the reactor excess reactivity is unacceptably large and reactor operation is prevented or discontinued. The reactor shielding tank water level is monitored to ensure sufficient shielding is present. Finally, a seismically activated switch is used to prevent reactor operation or discontinue reactor operation in the case of a seismic event. Similar to the reactor monitoring channels, the interlocks follow a series approach so that if any one of the interlocks is triggered, the reactor will not be allowed to operate.

Figure 6.

Interlock circuit [1].

The reactor is operated from a relatively simple console located in the same room as the reactor. The original console was used for approximately fifty years. In 2020, the original console was replaced with an upgraded console (see Figure 7). The primary motivation for upgrading the console centered on the use of vacuum tubes for the SCRAM circuits in the old console. Obtaining replacement vacuum tubes became very difficult since these items are no longer manufactured in large quantities. The upgraded console uses solid state relays rather than vacuum tubes. In addition to the use of solid-state relays, the upgraded console has all new wiring, instrumentation, switches, and knobs.

Figure 7.

Upgraded console installed in 2020 [1].

While the AGN-201’s core will essentially never be exhausted, support systems such as the instrument systems and their neutron detectors, reactor controls and control rod drives require periodic upgrading. The current financial state of universities and the perceived difficulty in conforming to regulatory requirements tends to encourage using the original 60-year-old tube-based control systems and other equipment until their failure rates leave no choice but to modernize. The cost of the engineering and manufacturing of upgraded instrumentation and equipment by outside firms can be too great for universities. Idaho State University recruited community volunteers with experience in project management and expertise in the design, construction, operation and startup of instrumentation and control, licensing of reactors and other relevant subjects for the university’s second attempt to replace the original tube-based control system. The first attempt involved the design and construction of a complex, multiple-level printed circuit board that could not easily be modified. The second and successful attempt used a breadboard approach of circuit boards with holes that could be used to mount components. The second attempt had very few changes to the design, a likely result of the lifetimes of experience of the community members in designing, repairing and maintaining analog systems. One of the main considerations was if the replacement system was to be analog or digital. The advantages and disadvantages of replacing the existing analog control system with a functionally equivalent analog system or attempting to replace it with a digital system were weighted. A replacement analog functional replacement appeared to be simpler and easier from a regulatory standpoint.

From a lifecycle cost standpoint, the analog system’s lifetime was envisioned to be decades, whereas digital technology is rapidly advancing, and the lifetime of a digital system was envisioned to be a few years. Analog enjoys far superior cyber security than digital, and maintaining cyber security appeared to be an unnecessarily potential burden to the university. It was decided to replace the system under a 10 CFR 50.59 evaluation. The community expert in licensing helped write the 10 CFR 50.59 document and helped ensure applicable codes and standards had been followed. The community member also purchased and donated some of the components. Another community member and two graduate students worked with the community members to document the project in their thesis. One of the community members became the Project Manager and kept the project moving even during the height of the COVID-19 pandemic shutdown. He also reviewed the design and construction and assisted with troubleshooting. The collaboration of community and university personnel worked well to produce and complete the replacement instrumentation and had the time to transfer knowledge. It is anticipated that the same model will be applied to other modernization efforts going forward.


3. Capabilities

The nuclear instrument systems, convert the neutron flux at the detectors adjacent to the core into instrument readings that the operator interprets to control the core. Each part of the loop can be tested. The neutron flux at neutron detectors is often assumed by designers to be essentially constant at a given power level, whereas from very low to moderate levels of neutron flux, such as found during very low power and shutdown operation, the neutron flux can vary considerably in amplitude in a random manner. The random manner results from the characteristic random nature of the decay of neutron sources that supply the reactor with neutrons at low power and shutdown.

One consequence of the variation in neutron flux is that it appears as an unwanted variation in the display of a channel and might result in inadvertent period trips. Nuclear instrument channel ‘noise’ is generally considered an unwanted (and often misunderstood) variation in a signal. It can be electronic noise that is externally introduced to the circuit and must be minimized so it does not distort the true readings or the ability of the reactor operator to identify the average signal. It can also be due to the normal random decay of a neutron source, where it is a valid part of the signal. It can be very difficult to visually identify if the noise is due to the valid operation of the core, or if it is due to electrical interference.

A statistical test called the ‘Chi-Squared’ test can be applied to data from pulse-type channels such as the startup channel. A Chi-Squared test is often used at power reactors to verify the startup channels and any temporary startup-range neutron detectors used for loading fuel are displaying counts from neutrons rather than noise. The Chi-Squared test will identify if the noise is electronic interference or valid and due to a neutron source, although it will not identify the source of the electric noise.

The AGN-201 offers the opportunity for training and evaluating the nuclear instrument channels with a very low neutron signal, lower than typically encountered at commercial power reactors. The neutron flux at a detector must be low enough that the channels will display changes in signal (jumps) from individual neutron interactions, and the channels must support attaching a scaler-timer. The test is useful when the AGN-201 is shut down and a neutron source is supplying neutrons. If neutron flux is low enough, as it is when the neutron source is inserted, even the channel 2 and 3 ion chambers might be evaluated with the Chi-Squared test. In both cases, a scaler-timer is required to total the counts in a given time interval.

The AGN-201 offers a unique opportunity to explore the variations the current signal of a current neutron instrument channel without the time pressure and limitations on connecting test instruments at a power plant. A properly designed test can demonstrate that current signals from a neutron detector consist of a number of pulses of very small electrical charges, each resulting from the individual disassociation of B10 upon absorbing a neutron.

Teaching-reactors such as the AGN-201 provide the opportunity to measure a wide range of characteristics, and to gain experience and practice in conducting the same measurements that are performed at power reactors during low power physics testing following the loading of the first core, following refueling, and even during power operation to characterize the stability of the reactor. The tests generally involve changing a parameter such as reactor temperature or control rod position, and observing the corresponding change in rate of change in reactor neutron flux. Commercial reactors use a so-called ‘Reactivity Computer’ to infer the change in reactivity from a change in a parameter. The AGN-201 allows students to build, operate and evaluate the operation of analog and digital reactivity computers themselves [5, 6].

The AGN-201 could be used to evaluate and improve test procedures that would be used on future first-of-a-kind reactors, and to train future reactor engineers and other operating staff. In addition to gaining experience and practice in conducting the measurements, students can develop the skills required to write test procedures and to conduct high-quality test programs in a low-risk environment. The AGN-201 can also potentially offer realistic simulations of conditions at other reactors so newly written test procedures can be conducted and improved prior to being used at the reactor. Test engineers, reactor operators and others, including regulators, from other facilities can benefit from the training available at the AGN-201. The AGN-201 can be useful in observing the principles and some of the parameters being tested at other reactors, thereby allowing the test procedures to be validated and problems discovered.

The AGN-201 operates at very low power levels (microwatt range), often termed ‘zero-power’ where its operation closely resembles most other reactors when they are operated at low power levels, below the point of adding sensible nuclear heat. Even at power reactors, many of the core physics measurements that are made following refueling or core alterations occur with the core subcritical or with the reactor just critical on delayed neutrons at low power level. They include monitoring the core during shutdown operation, while core alterations during refueling are being made, during the approach to criticality, and reactor state point measurements and core physics parameter measurements in a suite of ‘low power physics tests.’ Some measurements are made at both low power and at-power, and only a few are restricted to high power operation. The AGN-201 is therefore capable of providing conditions for most of the core physics measurements found at power reactors [7].

The explanations and demonstrations of the theory and measurement techniques of subcritical core physics can be of interest to reactor physicists, instrumentation and control technicians and engineers, operators and managers of nuclear facilities, health physicists and criticality safety personnel. The phenomena of subcritical multiplication of source neutrons requires a ‘multiplying medium,’ neutron source and neutron detector. The common technique that is used at reactors is an ‘inverse multiplication ratio’ or ‘1/M’ plot. The increase in count rate as control rods are moved in steps, and corresponding decrease in ‘1/M’ plot are readily apparent. The plot is typically used to infer the point of criticality, in this case the position of the control rods. The reactivity of the AGN-201’s control rods have been characterized well enough to illustrate the increases in count rate as positive reactivity is added. The demonstration can be relevant for power reactors to illustrate monitoring techniques during core alterations such as fuel loading and about establishing boron dilution warning setpoints. At pressurized water reactors with a soluble boron shim, the source range channels include the ability to establish a setpoint whose warning will help operators stop a dilution that could lead to an inadvertent reactivity change. The count rate at typical alarm setpoints can be low enough that the random variations in neutron production by the source becomes apparent. The resulting variation in source range channel readings, coupled with the requirement for a response time, can make it difficult to establish a setpoint that provides for enough warning but does not have false alarms.

Subcritical measurements to measure the values of parameters that formerly were measured during low power physics testing can save utilities considerable time and money. One is measuring the reactivity worth of control rods by raising and then dropping control rods, which can also be demonstrated in the AGN-201. Control rod drop times are also measured following refueling and other core alterations. The techniques and difficulties in measuring the positions of the controls during the drop, and the response of the nuclear instrumentation can be demonstrated in the AGN-201.

The state-point measurements of a reactor are measurements of parameters whose values define the operating condition, or ‘state’ of the reactor. Examples of parameters include reactor temperature and control rod positions are made to evaluate the reactivity of the reactor, and for comparison with core physics code predictions. Accurate state-point measurements are crucial in assessing the operation of the core and are made when the reactor is first brought critical after a refueling outage, and periodically throughout core life. The technique is simple and involves adjusting parameters such as control rod position, temperature and boron concentration in reactors with soluble neutron poison so the reactor is just critical at a given power level. A careful measurement, where reactor power is essentially constant, provides the best data. The AGN-201 allows operators and reactor engineers to explore their ability to establish just critical conditions, and to compare the measurements of parameters with calculations.

Low power physics measurements are conducted with a critical reactor whose power level is below the point of adding observable sensible nuclear heat, also known as ‘reactors without feedback.’ The measurements include the state-point measurement mentioned earlier, control rod reactivity worth, moderator temperature measurements, core stability measurements using a ‘core oscillator’ with variable, regular changes in reactivity, delayed neutron lifetime, irradiation of metallic foils to determine reactor power and more.

The operation of the AGN-201 is licensed and regulated by the Nuclear Regulatory Commission. The reactor and its conduct of operations are periodically inspected, particularly its documentation, and orderly documentation requires timely, accurate, truthful completion of forms, operating logs and more. Operating a nuclear reactor requires developing the valuable skills of discipline, focus and attention to detail, communication and more. The AGN-201 requires the same attitudes and abilities as higher-power test reactors. The full force of regulations is applied to the AGN-201. The opportunity to operate a nuclear reactor, regardless of size, is a unique experience that can benefit people who choose to put forth the time and effort. Students have opportunities to participate in a disciplined, regulated environment that is required of operators of a nuclear reactor that can shape their outlook on life and work ethic at a pivotal point in their lives. Students and other potential operators are invited to study, pass exams, and be responsible for the operation of a nuclear reactor providing a valuable and unique experience for those considering entering the field of nuclear power.


4. Conclusion

The Idaho State University AGN-201 reactor is a very safe, low-power, solid-core reactor designed with students and teaching in mind. It was developed in the late 1950’s by AGN to satisfy the need of university nuclear engineering departments for a relatively inexpensive, safe, flexible and available reactor with a long design life. The AGN-201 reactor is well suited for teaching and research activities. The solid-core AGN-201 reactor requires no active cooling system, uses a simple shielding arrangement, and the very low operating power results in trivial burnup providing an operating lifetime exceeding many decades. The AGN-201 reactor is used to help prepare nuclear engineering and other students for entry into the nuclear workforce. The reactor introduces students to the disciplined, structured environment of operating a reactor licensed by the Nuclear Regulatory Commission. The reactor offers students hands-on experience, provides opportunities to demonstrate the operation of reactors and a variety of the traditional applications of reactors such as neutron activation, and introduces them to the application of nuclear instrumentation, applied principles of health physics, and more. With the recently installed reactor console upgrade, the ISU AGN-201 reactor is poised to serve students for many decades to come.


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  2. 2. Skoda R, Peddicord K. Rebirth of AGN-201M: Practical ways of using the proven training reactor. In: 19th International Conference on Nuclear Engineering. Chiba Japan: ICONE19-44136; 2011
  3. 3. Pope C. Prompt Neutron Decay Constant Measurement Using Rossi’s α Method [Thesis]. Pocatello: Idaho State University; 1993
  4. 4. Malicoat A, Pope C. Design improvements to the ISU AGN-201 reactor SCRAM, interlock, and magnet circuits. Annals of Nuclear Energy. 2020;136
  5. 5. Levinskas D. Installation of an Automatic Reactivity Control System into the AGN-201 Reactor at Idaho State University [Thesis]. Pocatello: Idaho State University; 1990
  6. 6. Smith C. Reactivity Measurement Software System for the AGN-201 Reactor Using Inverse Point Kinetics [Thesis]. Pocatello: Idaho State University; 1990
  7. 7. Baker B. Comparison of Open Loop and Closed Loop Reactivity Measurement Techniques on the ISU-AGN-201 Reactor [Dissertation]. Pocatello: Idaho State University; 2013

Written By

Chad L. Pope and William Phoenix

Submitted: 24 September 2021 Reviewed: 10 June 2022 Published: 16 July 2022