Feasibility Study Part – II Fission Mo-99 Production by the Irradiation of a LEU Metallic Uranium Foil at Tajoura Research Reactor

Feasibility Study Part – II Theoretical Calculations of Fission 99Mo Production by the Irradiation of LEU Metallic Uranium Foil at Tajoura

Research Reactor

Bsebsu, F. M.1,Elwaer S.2

Renewable Energies and Water Desalination Research CenterP.O. Box 30878 Tajoura (Tripoli), Libya

AbstractThe Renewable Energies and Water Desalination Research

Center (REWDRC), Libya, will implement the technology for 99Mo isotope production using LEU foil target (This target is made of a LEU metallic uranium foil inserted between two concentric aluminium cylinders), to obtain new revenue streams for the Tajoura nuclear research reactor and desiring to serve the Libyan hospitals by providing the medical radioisotopes.

This paper will present the preliminary results for the neutronic and activity calculations of 99Mo, taking into account different irradiation and decay times.

1. Introduction The Tajoura reactor is a pool type reactor, moderated and cooled by

light water located at the Renewable Energies and Water Desalinization Research Center (REWDRC). The reactor is designated to carry out experiments in field of nuclear physics and nuclear engineering, neutron activation analysis, solid state physics and isotope production. The reactor was put into operation at a power level of 10 MW in September 1983. [1]

The reactor is completely converted to Low Enriched Uranium (LEU, 19.7% of 235U) fuel of type IRT-4M at the end of 2006; the new fuel is an alloy (matrix) of aluminum and uranium-dioxide (UO2–Al) with aluminum cladding. The moderation and core cooling are provided through forced convection of de-mineralized water. [2]The compact core loading of Tajoura reactor core consists of 16 IRT-4M fuel assemblies type (10 (6TFA) + 6 (8TFA)) with LEU 19.7% 235U enrichment.

1 Dr. Bsebsu, Farag Muftah, Reactor Department, Calculation Unit, Head of, [email protected] 2 Dr. Elwaer, Sami, Radiochemistry Department, Head of, [email protected]

2VCR 1VCR

3VCR 4VCR

5VCR 6VCR

7VCR 8VCR

9VCR 10VCR

11VCR 12VCR 13VCR

14VCR

15VCR 17VCR 18VCR

16VCR

19VCR

1 6

1VCV 2VCV

3VCV 4VCV

5VCV

7VCV

9VCV

6VCV

8VCV

10VCV

5 4 3 2

6

4

3

1

2

5

Figure 1. Tajoura Reactor Core Horizontal

Cross Section.

The Tajoura reactor has 44 vertical irradiation channels (6 in the 8TFA fuel assemblies, 9 in removable Beryllium reflector units, 19 VCR in the stationary reflector blocks, and 10 VCV in reactor core Al vessel). Figure 1 shows the Tajoura core horizontal cross section. The study of this analysis includes the neutronic and activity analysis of 99Mo, where Figure 2 shows the LEU target configuration, dimensions, and specifications [3]

Figure 2. LEU Target Horizontal, Vertical Cross Sections, and Dimensions.

2. Neutronic and Activity CalculationsThe neutronic calculations were performed for the present core

configuration of Tajoura reactor using neutronics computer package [4] codes, neutronic programs used routinely in the fuel management of this reactor. Different cell models were needed to

Table 1Energy five-group structure used in the diffusion theory

calculationsBroad Grou

ps

Fine Group

s

Energy Interval [eV]

1 1 – 5 0.821 E+06 – 1.000 E+07

2 6 – 5.530 E+03 – 0.821

generate appropriate cross sections for the various reactor regions in an energy five-group structure. The WIMS-D4 code was used to generate the multi-group nuclear constants library for different regions as a function of burn-up, the main transport calculation was performed in 69 energy groups, condensing to 7 groups for the diffusion theory calculations as shown in Table 1.

In order to calculate the cross sections for fuel assembly, a complete fuel assembly and a homogeneous extra zone was used. The extra region includes the aluminum in the fuel elements beyond the width of the meat, the aluminum side fuel elements, the water beyond the width of the meat and the water channels surrounding the fuel element. In a diffusion calculation, a fuel element will be represented by three zones, the central zone is a homogenization of the meat, cladding and the cooling and the lateral zones are identical to each other and are formed by a homogenous mixture of aluminum and water. The nuclear constants for beryllium elements, aluminum elements, blanking elements, absorber tail plates and the water as a reflector have been obtained using different macro-cell models.

The fission product activities were calculated using ORIGEN-S code from the SCALE-4.4a system [5], considering an irradiation at constant thermal neutron flux, 1.0×1014 n cm-2 s-1, and an irradiation time of 3 days for a target containing 8 gm of uranium 19.75% enriched. The 99Mo activity in curie as a function of time is shown in Figure 3.

The irradiation time has a large impact on specific activity. All the molybdenum isotopes from 95Mo to 100Mo are produced from fission and they continue to build up, making the 99Mo Ci content per gram of molybdenum material decrease with increased irradiation time. A determination of the specific activity of the 99Mo must consider the fission products which are stable isotopes of molybdenum (97Mo, 98Mo and 100Mo).

The results of the ORIGEN-S [5] calculations during the irradiation period are presented in the Table 2 and Figure 4, where Asp is the specific activity of 99Mo in Ci per mg of Mo. At end-of-irradiation (72 hrs), the activity of 99Mo is 203 Ci, that is 25.38 Ci 99Mo per gram of 19.75% enriched uranium irradiated, the 99Mo yield after 10 hrs of decay in pool is 183 Ci the specific activity of 99Mo is 103.00 Ci per milligram of molybdenum (97Mo, 98Mo, 99Mo and 100Mo),

Figure 3. 99Mo activity for 8 grams of 19.75% enriched uranium, an irradiation time of 3

days and Φth = 1.0×1014 n cm-2 s-1

Table 2.Activity of 99Mo and Specific

Activity of 99Mo, Asp, Ci per mg of Mo (97Mo, 98Mo, 99Mo and

100Mo) for Different Irradiation Times

ti, [h]

99Mo, [Ci]

Asp [Ci/mg Mo]

12 34.20 215,2616 45.21 211.1624 67.23 208,5032 89.90 203.8936 101.29 205,5840 112.81 202.6748 134.84 200.65

the total activity of the actinides is 450 Ci/g U and the total activity of the fission products is 3904 Ci/g U.

At the end of the irradiation, the LEU foil target will be allowed to decay in the reactor pool for a period of 6 hours minimum. Prior to reactor start up, the irradiated target will be removed from the reactor pool and transported to the hot cell for disassembly. Allowing the target to decay in the reactor pool for 6 hours will reduce the end-of-irradiation total fission product activity in 85.37%. [6]

3. ConclusionsThe neutronic calculations were performed supposing that the target

would be introduced in the cell 6-1 position of the reactor grid in the removable beryllium reflector, the present maximum neutron flux position of Tajoura reactor. In this case, the mean neutron thermal flux is 1.0×1014 n cm-

2 s-1 and the power generated in the target is 7.6 KW.The fission product activities have been calculated using ORIGEN-S

code from the SCALE-4.4a system, considering an irradiation at constant thermal neutron flux, 1.0×1014 n cm-2 s-1, for a target containing 8 gm of uranium 19.75% enriched, taking into account different irradiation and decay times.

The irradiation time has a large impact on specific activity. All the molybdenum isotopes from 95Mo to 100Mo are produced from fission and they continue to build up, making the 99Mo Ci content per gram of molybdenum material decrease with increased irradiation time. A determination of the specific activity of the 99Mo must consider the fission products which are stable isotopes of molybdenum (97Mo, 98Mo and 100Mo).

AcknowledgmentThe authors wish to express their thanks to Dr. Faisel Abotweirat (Head

of Reactor Department) for supporting this work and Dr Charlie Allen (Missouri University Research Reactor (MURR), Columbia Research Reactor, and University of Missouri) for his helping during the Origen results for 8 g LEU foil

4. References

1. KNOW-HOW DOCUMENTATIONS: "Tajoura Nuclear Research Design", Building 1, Design Features of the Control Rod Arrangement in the

Table 3.Activity of 99Mo and Total Activity of

Fission Products, ATfp, in Ci/g U after 72 hours

of Irradiation and Different Decay

Timestd, [h]

99Mo, [Ci]

ATfp [Ci/mg Mo]

0 203.12 3904.001 201.72 1852.872 200.46 1060.703 199.24 753.934 198.04 635.145 196.86 589.136 195.71 571.327 194.59 564.428 193.49 561.759 192.42 560.71

10 191.36 560.31

Figure 4. 99Mo Specific activity as a

function of Decay Time.

Reactor Ensuring Replacement with the Fuel Charge Pattern in the Core, 622-1-KH-151 (9), 1979.

2. Bsebsu, F. M.:”IRT- 4M Fuel Assembly Design and Calculation

Parameters”, Technical Report, REWRDC: R-CU2-01-2005, Tajoura

(Tripoli) Libya, 2005.01.31

3. Charlie Allen, Technical Drawing of LEU Target Assembly, Email massage,

2007.

4. Eduardo A. Villarino, MTR_PC V3.0, Neutronic, Thermal Hydraulic and

Shielding Calculations on PC, INVAP SE, Argentina, 2001.

5. Charlie Allen, ORIGEN Code Results for 8 g LEU foil, Email massage, 2007.

6. Jorge Medel, Fission Mo-99 Production by the Irradiation of a LEU Metallic Uranium Foil at RECH-1 Reactor, Chilean Nuclear Energy Commission, Santiago, Chile, January, 2007