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Research Reactor Design

Need for Neutrons
Neutrons are used for research and in many industrial and medical applications. Sources capable of producing high neutron fluxes with desired spectrum are needed to perform material research, radiography and cancer therapy among other important uses. Research reactors (RR) are one possible source of neutrons. The flux and spectrum of neutrons and availability of irradiation facilities determine the types of applications and, therefore, usefulness of a reactor. New RRs continue to be developed. Restriction on level of enrichment in these reactors has led to some constraints on their designs. However, with improved simulation and design tools, it is now possible to explore design features that would have been difficult to analyze with an earlier generation of design tools, and thus it is becoming possible to mitigate at least some of the restrictions posed by fuel enrichment levels by more thoroughly exploring the design parameter space than was possible earlier.

Modern Research Reactor Facilities
Modern multi-purpose RRs are characterized by small and compact cores designed to facilitate the leakage of neutrons to the reflector, where they can be used for different purposes. The MTF (Maximum Thermal Flux) and core life are both important parameters of such facilities as they determine the kind and quality of experiments that may be placed on the RR. Characteristics of state of the art RR facilities are summarized in the following table:

RR (location)

MTF *1014

(n×cm-2s-1)

Enrichment

Core Life  (days)

Power

(MW)

MTF per Mega

Watt*1013

HFIR (USA)

25.5

HEU

23

85

3.0

FRM-II (Germany)

8.0

HEU

52

20

4.0

HANARO (Korea)

4.5

LEU

28

30

1.7

JRR-3M (Japan)

2.0

LEU

26

20

1.0

OPAL (Australia)

3.0a

LEU

> 30

20

1.5

aPerturbed 

New Designs 
The objective of this work is to develop new RR core designs that optimize the neutron production per unit power, constrained to the use of standard fuel material, core life requirements and neutron spectrum requirements. The first design proposed is the asymmetric cylindrical core in two versions: the standard and the compact version. For a 10 MW of power, these designs allow to achieve a MTF of 4.2 x 1014 n×cm-2s-1 and 5.0 x 1014 n×cm-2s-1respectively.

Detailed heterogeneous asymmetric model. An enlarged view of a segment of the thin FE is shown on the left. FE, F and T initials refer to fuel element, fast irradiation position and thermal irradiation position, respectively .
                                                                               a)
                                                                                b)
Thermal neutron flux distribution in the central horizontal plane. a) standard model and b) compact model (fluxes are in 1014 n×cm-2s-1 units) . Note that the inner and outer radii of the core are shown in both pictures.


Publications
1) Teruel, F., Rizwan-uddin, An innovative research reactor design. Nuclear Engineering and Design. 2009, 239, 395-407. (PDF)

2) Teruel, F., Rizwan-uddin, 2006. Detailed core design and flow coolant conditions for neutron flux maximization in research reactors. In: Proceeding of International Conference on Nuclear Engineering 2006, Miami, USA, July 2006.

3) Teruel, F., Rizwan-uddin, 2005. An alternative model for neutron flux maximization in research reactors. In: Proceeding of the International Topical Meeting of Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear and Biological Applications 2005, Avignon, France, September 2005. 

Contact info: teruel@cab.cnea.gov.ar, rizwan@illinois.edu