1. Sources of Radiation Research Reactors
Day 4 – Lecture 4

2. To discuss the types and uses of Research Reactors
Objective
To discuss the types and uses of Research Reactors

3. Contents Types of Research Reactors Uses of Research Reactors
Pool Type Reactor
TRIGA Reactors
Other Reactors/ Critical Assemblies
Uses of Research Reactors

4. Introduction Research Reactors Not used to generate electrical power
Produce neutrons for various uses
Use higher enriched 235U than power reactors
Approximately 266 in operation worldwide (January 2014)
Research reactors comprise a wide range of civil and commercial nuclear reactors which are generally not used for power generation. The primary purpose of research reactors is to provide a neutron source for research and other purposes. Their output (neutron beams) can have different characteristics depending on use. They are small relative to power reactors whose primary function is to produce heat to make electricity. Their power is designated in megawatts (or kilowatts) thermal (MWth or MWt). Most range up to 100 MW, compared with 3000 MW (i.e MWe) for a typical power reactor. In fact the total power of the world's 283 research reactors is little over 3000 MW.
Research reactors are simpler than power reactors and operate at lower temperatures. They need far less fuel, and far less fission products build up as the fuel is used. On the other hand, their fuel requires more highly enriched uranium, typically up to 20% U‑235, although some older ones use 93% U‑235. They also have a very high power density in the core, which requires special design features. Like power reactors, the core needs cooling, and usually a moderator is required to slow down the neutrons and enhance fission. As neutron production is their main function, most research reactors also need a reflector to reduce neutron loss from the core.

5. Types Pool type (61 units)* Curved aluminum clad fuel plates
Control rods
Water for moderation and cooling
Beryllium or graphite neutron reflectors common
Empty channels for experiments
Apertures for neutron beams
Tank Type (27 units)*
There is a much wider array of designs in use for research reactors than for power reactors, where 80% of the world's plants are of just two similar types. They also have different operating modes, producing energy which may be steady or pulsed.
A common design (67 units) is the pool type reactor, where the core is a cluster of fuel elements sitting in a large pool of water. Among the fuel elements are control rods and empty channels for experimental materials. Each element comprises several (e.g. 18) curved aluminium‑clad fuel plates in a vertical box. The water both moderates and cools the reactor, and graphite or beryllium is generally used for the reflector, although other materials may also be used. Apertures to access the neutron beams are set in the wall of the pool. Tank type research reactors (32 units) are similar, except that cooling is more active.
* Research Reactors data is from Jan. 2014

6. Pool Type Reactor
A swimming pool, Materials Testing (MTR) type reactor.
The Reactor has been utilized for studies in solid state physics, neutron diffraction, nuclear structure, fission physics, studies of geological, biological and environmental samples by Neutron Activation Analysis (NAA) techniques, radioisotope production and for training of scientists.

7. Test Reactors
The Materials Test Reactor (MTR) completed in 1952 in Idaho was the workhorse of the U.S. Atomic Energy Commission's test reactor program for many years. It was the first reactor to be built
Argonne designed many reactors for specific types of testing such as materials or transient testing, but also for university research and training.
solely for testing materials to be used in other reactors.

8. Types
TRIGA (37 units)*
cylindrical fuel elements (36 mm diameter)
Uranium fuel and zirconium hydride moderator
Water for moderation and cooling
Beryllium or graphite neutron reflectors common
Operate at thermal power levels from less than 0.1 to 16 megawatts and pulsed to 25,000 MW
* Data from Jan. 2014
The TRIGA reactor is another common design (40 units). The core consists of 60‑100 cylindrical fuel elements about 36 mm diameter with aluminum cladding enclosing a mixture of uranium fuel and zirconium hydride (as moderator). It sits in a pool of water and generally uses graphite or beryllium as a reflector. This kind of reactor can safely be pulsed to very high power levels (e.g. 25,000 MW) for fractions of a second. Its fuel gives the TRIGA a very strong negative temperature coefficient, and the rapid increase in power is quickly cut short by a negative reactivity effect of the hydride moderator.

9. TRIGA

10. Types Critical assemblies (zero power) Test reactors
Number*
Critical assemblies (zero power) 79
Test reactors 15
Training facilities 21
Prototypes 2
Generating electricity 1
Research
138
. As expensive scientific facilities, they tend to be multi‑purpose, and many have been operating for more than 30 years.
Some produce radioisotopes
* Data from Jan. 2014

11. Types Some moderated by heavy water (10) or graphite
Some are fast reactors (no moderator and mixed U - Pu fuel)
Other research reactor designs are moderated by heavy water (12 units) or graphite. A few are fast reactors, which require no moderator and can use a mixture of uranium and plutonium as fuel.
Homogenous type reactors have a core comprising a solution of uranium salts as a liquid, contained in a tank about 300 mm diameter. The simple design made them popular early on, but only five are now operating.

12. Uses Analysis and testing of material Production of radioisotopes
Fusion research
Environmental science
Advanced material development
Drug design
Nuclear medicine
Research reactors have a wide range of uses, including analysis and testing of materials, and production of radioisotopes. Their capabilities are applied in many fields, within the nuclear industry as well as in fusion research, environmental science, advanced materials development, drug design and nuclear medicine.

13. Uses

14. Uses
Neutron scattering experiments to study structure of materials at atomic level
Neutron activation for detecting presence of small amounts of material
Neutron beams are uniquely suited to studying the structure and dynamics of materials at the atomic level. Neutron scattering is used to examine samples under different conditions such as variations in vacuum pressure, high temperature, low temperature and magnetic field, essentially under real‑world conditions.
Using neutron activation analysis, it is possible to measure minute quantities of an element. Atoms in a sample are made radioactive by exposure to neutrons in a reactor. The characteristic radiation each element emits can then be detected.

15. Uses Radioisotope production
90Y from 89Y for treatment of liver cancer
99Mo from fission of 235U foil to produce 99mTc for nuclear medicine
Neutron activation is also used to produce the radioisotopes, widely used in industry and medicine, by bombarding particular elements with neutrons. For example, yttrium‑90 microspheres to treat liver cancer are produced by bombarding yttrium‑89 with neutrons. The most widely used isotope in nuclear medicine is technetium‑99, a decay product of molybdenum‑99. It is produced by irradiating U‑235 foil with neutrons and then separating the molybdenum from the other fission products in a hot cell.

16. Uses Industrial processing
Neutron transmutation doping of silicon crystals
Study changes resulting from intense neutron bombardment (e.g., embrittlement of steel)
Research reactors can also be used for industrial processing. Neutron transmutation doping makes silicon crystals more electrically conductive for use in electronic components. In test reactors, materials are subject to intense neutron irradiation to study changes. For instance, some steels become brittle, and alloys which resist embrittlement must be used in nuclear reactors.
Like power reactors, research reactors are covered by IAEA safety inspections and safeguards, because of their potential for making nuclear weapons.

17. Chicago Pile Reactors CP-2
The Chicago Pile (CP) reactors were small reactors which, in general, demonstrated new concepts or were designed for research purposes.
Operation of CP‑1 was terminated in February 1943 and the reactor dismantled and moved to a new site. It was reconstructed using CP‑1 materials but enlarged with a radiation shield and named CP‑2. It began operation in March 1943.

18. Zero Power Reactor
zero‑power full‑scale reactor core mockup assemblies used to:
gain understanding of a variety of reactor concepts
assist in the engineering design of these reactor systems
Zero Power Reactors - The ZPRs (ZPR‑2 and ZPR‑6) were essentially zero‑power full‑scale reactor core mockup assemblies used to gain understanding of a variety of reactor concepts and to assist in the engineering design of these reactor systems (the Submarine Thermal Reactor (STR) and the Savannah River reactors).

19. Zero Power Reactor
ZPR‑2, a heavy‑water reactor, began operation in 1952 and was used in the development of the Savannah power reactors used for plutonium production

20. Zero Power Reactor
ZPR‑6, designed to advance fast reactor technology for civilian power use, went into operation in July 1963

21. SLOWPOKE Central control rod Small sample irradiation tube
Large sample irradiation tube
SLOWPOKE is an acronym for Safe Low‑Power Kritical Experiment ("K" is the traditional symbol for "criticality" in the field of reactor physics). SLOWPOKE represents a low‑power, compact‑core reactor technology developed by AECL in the late 1960's.
The idea of building a safe research nuclear reactor with a tiny core is credited to George A. Jarvis and Carroll B. Mills of the Los Alamos Scientific Laboratory of the University of California, Los Alamos, New Mexico. They published a report on March 22, 1967 entitled "Critical Mass Reduction", the abstract of which reads "A new low value for the critical mass of 235U in a critical reactor assembly has been determined. This value is 250 grams of 235U in a polyethylene core surrounded by a thick beryllium reflector."
Beryllium annulus
Lower beryllium reflector

22. SLOWPOKE
prime functions are to perform nondestructive elemental analysis and produce quantities of selected radioactive material for use in industry and medicine
SLOWPOKE laboratories have been utilized in a number of different fields such as:
Trace element identification
Radiotracer supply
Forensic science
Environmental analysis
Radioactivity counting

23. SLOWPOKE Reactor Specifications Type Pool and Tank
Licensed limit 20 kW
Fuel Extruded Uranium/aluminum alloy
Moderator Light water
Cooling Convection/conduction
Core diameter/height 22cm/22.1cm
Critical mass 235U g
Fuel life 6.4 x 1019 nvt (at small inner sites)
Irradiation Parameters
Parameter Inner Sites Outer Sites
Thermal flux 1 x x 1012
These reactor specifications are for a Particular Reactor in Canada

24. High Flux Isotope Reactor
Oak Ridge National Laboratory (ORNL) - USA
Historical Background
In 1958 the Atomic Energy Commission recommended that a high‑flux reactor be designed, built, and operated at ORNL, with construction to start in FY 1961 to produce transuranic isotopes. Criticality was achieved on August 25, 1965.
The preliminary conceptual design of the reactor was based on the "flux trap" principle, in which the reactor core consists of an annular region of fuel surrounding an unfueled moderating region or "island." Such a configuration permits fast neutrons leaking from the fuel to be moderated in the island and thus produces a region of very high thermal‑neutron flux at the center of the island. This reservoir of thermalized neutrons is "trapped" within the reactor, making it available for isotope production. The large flux of neutrons in the reflector outside the fuel of such a reactor may be tapped by extending empty "beam" tubes into the reflector, thus allowing neutrons to be beamed into experiments outside the reactor shielding. Finally, a variety of holes in the reflector may be provided in which to irradiate materials for later retrieval.
Notable accomplishments include the production of californium‑252, which is used for reactor startup sources, scanners for measuring the fissile content of fuel rods, neutron activation analysis, and fissile isotope safeguards measuring systems. In addition, californium‑252 is used as a medical isotope to treat several types of cancer. The Fusion Energy Program has also been supported by the HFIR.
The HFIR is a beryllium‑reflected, light‑water‑cooled and ‑moderated, flux‑trap type reactor that uses highly enriched uranium‑235 as the fuel. This image is a cutaway of the reactor that shows the pressure vessel, its location in the reactor pool, and some of the experiment facilities.
The reactor core assembly is contained in a 2.44‑m diam pressure vessel located in a pool of water. The top of the pressure vessel is 5.18 m below the pool surface, and the reactor horizontal midplane is 8.38 m below the pool surface. The control plate drive mechanisms are located in a subpile room beneath the pressure vessel. These features provide the necessary shielding for working above the reactor core and greatly facilitate access to the pressure vessel, core, and reflector regions.

25. Where to Get More Information
Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009)
International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002)
IAEA Research Reactor Database