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ACADEMIA Letters
Confirmation of the radiological evaluation during
transport irradiated cobalt in open pool type reactor
Amr Abdelhady, Reactors Dept., Nuclear Research Center, Atomic Energy
Authority, Egypt
This study suggests an alternative path to transport the cobalt device after irradiation in
open-pool-type reactor from the reactor core to the cobalt cell. The cobalt transport process
in current path depends on using heavy shielded cask, 1500 Kg weight, under water surface
of spent fuel storage pool which may cause a missile impact of spent fuel accident (Falling
of heavy load into spent fuel storage pool). To avoid using the shielded cask, an alternative
path is suggested depending on transporting the cobalt device through the hot cells of the
reactor; the testing and the cobalt cells. The expected radiation dose rate rise associated with
the alternative transport path must be evaluated at positions which the worker will be found
during transport process. SCALE/MAVRIC sequence code was used to determine the dose
rate levels along the suggested transport path; over spent fuel storage pool water surface, and
around testing and cobalt cells. The calculated results show rise in radiation dose levels more
than the permissible dose rate limits around testing cell. Suggested procedures are presented
in this study to decrease the received dose by worker found around testing cell during transport
process.
1. Introduction
Cobalt-60 is an artificial isotope has a half-life of 5.3 years produced in nuclear reactors from
59Co by neutron absorption. In open pool type reactor of 22 MW power, the cobalt device is a fixed and in-core experiment irradiated for 455 days with average neutron flux of
Academia Letters, June 2021
©2021 by the author — Open Access — Distributed under CC BY 4.0
Corresponding Author: Amr Abdelhady, [email protected]
Citation: Abdelhady, A. (2021). Confirmation of the radiological evaluation during transport irradiated cobalt
in open pool type reactor. Academia Letters, Article 1172. https://doi.org/10.20935/AL1172.
1
1.4E14 n/cm2.s to reach the required activity suitable for medical and irradiation applications demands.
Transporting the cobalt device inside the reactor after irradiation is an important process and must
be planned and optimized previously to achieve better performances with keeping the best level of
radiological safety. The cobalt device is clamped in the reactor core which located at depth of 10 m
under the main pool water surface. After reaching the required activity (3.7E14 Bq), the device will be
removed from the core during reactor shutdown mode and transferred from main pool to auxiliary pool
(spent fuel storage pool) and then delivered to the cobalt cell for preparing to different applications.
The current transport path of the cobalt device is associated with risks during loading the device
into the shielded cask under pool water surface and so, an alternative path is proposed to avoid
using the shielded cask during transporting process [1]. Figure 1 shows the current and the
suggested paths for transporting the cobalt device.
The suggested path
The current path
Figure 1: the current and suggested paths.
The radiological doses associated with the alternative transport path were calculated to
assess the radiation dose that the worker would receive during cobalt device transporting process. MAVRIC [2] is the SCALE shielding sequence with automated variance reduction capabilities that was used to estimate the predicted radiation dose rates at positions that the worker
would locate during transport process; over the auxiliary pool surface, and around testing and
cobalt cells.
Academia Letters, June 2021
©2021 by the author — Open Access — Distributed under CC BY 4.0
Corresponding Author: Amr Abdelhady, [email protected]
Citation: Abdelhady, A. (2021). Confirmation of the radiological evaluation during transport irradiated cobalt
in open pool type reactor. Academia Letters, Article 1172. https://doi.org/10.20935/AL1172.
2
2. MAVRIC simulation
The calculations were presented using MCNP code in the paper published before and
so, the new calculation using SCALE.MAVRIC sequence will be presented in this
paper to confirm the previous calculations. The dose rate will be calculated in the same
positions that those calculated before using MCNP5 code; above the spent fuel storage
pool and around the testing cell. KENO-VI model was used to simulate the cobalt source
inside the storage pool and inside the testing cell as shown in figure 2.
b. around the testing cell
a. above the pool surface.
Figure 2: the KENO3D for the cobalt device inside the spent fuel storage pool
and inside the testing cell.
MAVRIC is the SCALE shielding sequence with automated variance reduction capabilities that is used [3]. The MAVRIC sequence employs the Denovo discrete ordinates code and
the Monaco fixed-source Monte Carlo radiation transport code [4].
Good statistical accuracy of the dose rate estimates within every geometry; above the pool
surface, and around the testing cell is obtained with the variance reduction method referred to
as forward weighted FW-CADIS [5]. This method requires both forward and adjoint discrete
ordinates calculations. The forward response is used as a weighting function to the source
for the adjoint discrete ordinates calculation to create larger adjoint source strength in the
geometry areas of low dose rate and smaller adjoint source strength in the geometry areas of
high dose rate [6].
Academia Letters, June 2021
©2021 by the author — Open Access — Distributed under CC BY 4.0
Corresponding Author: Amr Abdelhady, [email protected]
Citation: Abdelhady, A. (2021). Confirmation of the radiological evaluation during transport irradiated cobalt
in open pool type reactor. Academia Letters, Article 1172. https://doi.org/10.20935/AL1172.
3
3. The results and discussion
The cobalt source inside the pool surface
ICRU-57 conversion factor ((Sv/h)/ (photon flux p/cm2.s)) [7] was used in the model to
determine the dose rate. The dose rate mapping around the cobalt device, in figure 3, shows
that the dose rate in the region above the pool surface would be lower than the permissible
limit (10 µSv/h)[8] for cobalt device that located under the pool surface with 230 cm. The
corresponding uncertainties would be lower than 0.1. So, this depth is sufficient to
transporting the cobalt device under the pool surface with the optimum radiological safety
condition
Figure 3: dose rate mapping (left) around the cobalt device in the spent fuel storage pool
and its corresponding uncertainties (right).
The cobalt source inside the testing cell
The dose rate mapping around the cobalt device inside and outside the testing cell is presented. The dose rate map shows, in figure 4, that the dose rate, in the position that the
operator located during the transport process, would be higher than the permissible limit
(10 µSv/h) [8] and then some suggestions would be presented, as discussed in the original
paper [1], to decreasethe accumulated dose that received by the operator.
Academia Letters, June 2021
©2021 by the author — Open Access — Distributed under CC BY 4.0
Corresponding Author: Amr Abdelhady, [email protected]
Citation: Abdelhady, A. (2021). Confirmation of the radiological evaluation during transport irradiated cobalt
in open pool type reactor. Academia Letters, Article 1172. https://doi.org/10.20935/AL1172.
4
Horizontal cross section
Vertical cross section
Figure 4: the dose rate mapping (left) around the cobalt device in and outside the testing cell and its
corresponding uncertainties (right).
Academia Letters, June 2021
©2021 by the author — Open Access — Distributed under CC BY 4.0
Corresponding Author: Amr Abdelhady, [email protected]
Citation: Abdelhady, A. (2021). Confirmation of the radiological evaluation during transport irradiated cobalt
in open pool type reactor. Academia Letters, Article 1172. https://doi.org/10.20935/AL1172.
5
Conclusion
The radiation dose calculations during transporting the cobalt device from the core to the
cobalt cell were done using MAVRIC code. Along the cobalt transport path, the dose rate
was calculated at two certain points: above the storage pool and around the testing cell. The
results show a good agreement with the dose calculated using MCNP5 code in reference [1].
Consequently, the recommendations, that were mentioned in reference [1] during the
transportprocess, were confirmed.
References.
1. Amr Abdelhady, Radiological Evaluation of an Alternative Path to Transport Cobalt
Device after Irradiation in Open Pool Type Reactor, Journal of Scientific and Engineering Research, 2018, 5(5):78-85, ISSN: 2394-2630.
2. Scale: A Comprehensive Modeling and Simulation Suite for Nuclear Safety Analysis
and Design, ORNL/TM-2005/39 Version 6.1, June 2011.
3. D. E. PEPLOW, “Monte Carlo Shielding Analysis Capabilities with MAVRIC,” Nucl.
Technol. 174(2), 289– 313 (2011).
4. T. M. EVANS, A. S. STAFFORD, R. N. SLAYBAUGH, and K. T. CLARNO, “Denovo: A New Three Dimensional Parallel Discrete Ordinates Code in SCALE,” Nucl.
Technol. 71(2), 171–200 (2010).
5. J. C. WAGNER and A. HAGHIGHAT, “Automatic Variance Reduction of Monte Carlo
Shielding Calculations Using the Discrete Ordinates Adjoint Function,” Nucl. Sci. Eng.
128, 186–208 (1998).
6. J. C. WAGNER, D. E. PEPLOW, and S. W. MOSHER, “FW-CADIS Method for Global
and Regional Variance Reduction of Monte Carlo Radiation Transport Calculations,”
Nucl. Sci. Eng. 176(1), 37–57 (2014).
7. International Commission on Radiation Units and Measurements, Conversion Coefficients for Use in Radiological Protection against External Radiation, ICRU Report 57,
(ICRU, Bethesda, 1998).
8. ICRP (International Commission on Radiation Protection) (1991), Recommendations
of the International Commission on Radiation Protection, Pergamon Press, Oxford,
England, ICRP Publication 60.
Academia Letters, June 2021
©2021 by the author — Open Access — Distributed under CC BY 4.0
Corresponding Author: Amr Abdelhady, [email protected]
Citation: Abdelhady, A. (2021). Confirmation of the radiological evaluation during transport irradiated cobalt
in open pool type reactor. Academia Letters, Article 1172. https://doi.org/10.20935/AL1172.
6