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Optimization of the neutronics design of MNSRs
Progress in Nuclear Energy 52 (2010) 624e627
Contents lists available at ScienceDirect
Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene
Optimization of the neutronics design of MNSRs M. Albarhoum* Department of Nuclear Engineering, Atomic Energy Commission, P.O. Box 6091, Damascus, Syria
a b s t r a c t Keywords: MNSR Regulator IER Optimization Boron MOT
The small daily operation time of MNSRs and the consequent limited use of these reactors imply that their neutronics design should be improved. The optimization of the neutronics design is based on the optimization of all the neutronically influential components, the latest of which are the regulators. Both cadmium and stainless steel absorbers are substituted by boron. About 3.0 mm thickness of the Top Beryllium Reflector Shims are added to compensate for about 1 mk loss of initial excess reactivity caused by the now more efficient regulators. The new initial excess reactivity is about 4 mk. The daily operable time is extended to about 28.00 hrs, and much more samples (about ten times) can be irradiated daily. The neutronic characteristics of the optimized reactor are compared with those of the actual reactor. Advantages are listed, and savings are estimated. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction MNSRs are research reactors of the tank-in-pool type with highly enriched uranium fuel (w90 w/o U235). These reactors have been described many times elsewhere by their owners (AnimSampong et al., 2006; Jonah et al., 2006). These reactors have cores formed of about 350 fuel rods, with a surrounding beryllium reflector of about 10.00 cm thickness. The cold Initial Excess Reactivity (IER) is w4.0000 mk (Matos and Lell, 2005). This IER permits for these reactors to operate for only about 2.5 h/day at nominal power. This reactivity is consumed during reactor operation by moderator temperature rise and xenon poisoning. The limitation on the operable time leads to limitation in both the total number of samples that can be irradiated annually from one side, and the specific activity of the irradiated samples or produced short-lived radioisotopes from the other side. One solution would be to increase the daily operable time. This is because the flux depends mostly on the reactor power which is not allowed to increase for safety reasons. To increase the daily operable time more IER is needed, or alternatively minor consumption rates of the IER are required. The optimization of the control rod, the uranium load, and the reflector material (Albarhoum, 2004a,b) contributed a lot to the optimization of the neutronic design of MNSRs. The role of the regulators in the actual MNSRs is still considered marginal, and its improvement is necessary to support the role of the control rod, and to complete the neutronics design optimization of these reactors. * Tel.: þ963 11 2132580; fax: þ963 11 6112289. E-mail address: pscientifi[email protected] 0149-1970/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pnucene.2010.04.005
The quantity of Cd absorber which is used in a regulator is so small that the worth on one regulator is limited to about only 0.4 mk. More efficient regulators are suggested in this work. It would be also convenient to see what differences and advantages has the optimized reactor. This is done in the paper too. 2. Reactor modeling Calculations were performed using a detailed three-dimensional model implemented in the core calculation’s code CITATION (Fowler et al., 1971) coupled with the lattice cell code WIMSD4 (Askew et al., 1966), through the use of the BMAC system (Albarhoum, 2008). This system generates the cross sections for the problem automatically upon describing the problem (by the user) in a conventional input file. All reactor components were modeled for calculation including regulators tubes (Fig. 1, component No. 24). In Table 1 a summary comparison between calculated and measured data for the model used in BMAC is shown. Generally speaking, the model proves to be good enough to be used for the evaluation of the new regulators worths. In Table 2 the group constants for one regulator are shown while in Table 3 the average calculated neutron fluxes in some reactor components, before modification of the regulator, are reported for comparison. 3. Modification of the regulator and addition of the top beryllium reflector If cadmium and stainless steel are both substituted by boron in the regulators new group constants are obtained. Table 4 shows the
M. Albarhoum / Progress in Nuclear Energy 52 (2010) 624e627
625
Fig. 1. A schematic vertical cross section drawn by CITMOD (Albarhoum, 2001) of the modeled reactor showing some components of the Syrian MNSR.
group constants for the new regulator. The macroscopic absorption is higher now. This causes the new regulator to be more efficient for the control of the reactor from one side, but it causes the IER of the reactor to decrease from the other side. The new IER will be 2.8846 mk only. Since the IER is now only about 2.8846 mk, to have about 4.0000 mk as prescribed by regulations (CIAE, 1993), some top reflector pieces should be added. The addition of two pieces of 1.50 mm thickness each increases the IER to 3.9285 mk. In this case the main reactor parameters will be that shown in Table 5. The new group constants of the components of Table 3 are shown in Table 6. 4. Results and discussion Tables 4e6 show the results obtained by modifying the regulators absorbing material. The reactor parameters shown in Table 5 indicate that the addition of 3 mm of top beryllium thickness brings about 1.04 mk IER to the reactor such a way that the IER is now 3.9285 mk. By comparing the values of the same parameters in
Table 1 Computed and measured (CIAE, 1993) values for some reactor parameters for the Syrian MNSR before modification of the regulators. Item Initial excess reactivity (mk) Effective control rod worth (mk) Reactivity regulator worth (mk) Total reactivity flooding effect of internal irradiation sites (mk) Total reactivity flooding effect of external irradiation sites (mk) Shut down margin (mk) Effective shut down margin (mk) Maximum operable time (min)
Calc. value
Meas. value
Exp. error (%)
3.9840 7.8900 0.4000 2.2380
3.9400 7.0000 0.4100 1.9500
1 1 1 e
1.0400
1.0000
3.9060 0.628 428.00
3.0600 0.1100 e
e 2 2 e
both the old and new configuration of the reactor the following will be seen: 1. The shut down margin increases to 3.5415 mk (from 3.9060 mk), which means less safety during the normal daily operation of the reactor (9.33%). 2. The effective worth of the control rod decreases from 7.89 to 7.4700 mk which means that the control rod has become less efficient too (5.32%). 3. The effective shut down margin (which is the shut down margin minus reactivity flooding effect of internal irradiation sites minus reactivity flooding effect of external irradiation sites) decreases to 0.3894 (38%) although the reactor is still safe. The reactor looses anyway in terms of neutronic safety. The reactor gains in terms of Maximum Operable Time (MOT). The maximum operable time for the reactor before regulator modification has been estimated earlier (Albarhoum, 2004a,b) to be about 428.00 min. Since the new available IER is now ¼ 3.9285 þ 4 * 0.8405 z 7.4413 mk (regulators are supposed to be withdrawn during operation), assuming that the same method is adopted to estimate the MOT, the new MOT would be found to be 1494 min (349%). The reactor MOT now is three and half times the old one. This result (being the MOT greater than 24.00 h) does not mean that the reactor can be operated permanently (everyday for many
Table 2 Calculated group constants for the four neutronic groups for a generic regulator before its modification. Group constants
Group 1
Group 2
Group 3
Group 4
Diffusion 2.02655 1.01562 0.624627 0.501994 Absorption 5.13227 102 4.37380 104 4.13005 101 7.54058 102
626
M. Albarhoum / Progress in Nuclear Energy 52 (2010) 624e627
Table 3 Average calculated neutron flux in some reactor components before the optimization of the regulators. Reactor component
Group 1
Group 2
Group 3
Group 4
Fuel circle No. 1 Fuel circle No. 8 Fuel circle No. 10 Beryllium annulus Inner irradiation sites Outer irradiation sites Reactor vessel Bottom beryllium Regulator
1.12895 1012 8.56135 1011 6.78828 1011 1.87166 1011 1.97559 1011 2.34542 1010 5.65458 108 2.38872 1011 1.66751 1010
1.02789 1012 8.29830 1011 7.29188 1011 3.09399 1011 3.33022 1011 4.80062 1010 7.05521 109 3.41272 1011 3.32321 1010
1.12491 1012 9.18301 1011 8.23667 1011 4.23064 1011 4.83339 1011 9.89125 1010 1.51679 109 4.28052 1011 7.40968 1010
1.06233 1012 8.52315 1011 8.94452 1011 8.60392 1011 1.00437 1012 4.75096 1011 1.28777 1010 9.26924 1011 1.27636 1011
Table 7 A comparison between final optimized configuration of the Syrian MNSR and the original configuration.
Table 4 The new group constants for one regulator in MNSRs after its modification. Group constants
Group 1
Group 2
Group 3
Group 4
Diffusion Absorption
1.66568 8.87891 102
0.25386 0.29130
0.11012 2.11747
0.05234 3.51450 102
Item Initial excess reactivity (mk) Effective control rod worth (mk) Total reactivity regulators worth (4 0.8405 mk) Total potentially available excess reactivity (after addition of beryllium, and withdrawal of the regulators, mk) Shut down margin (mk) Total uranium-235 load in the core (g) Maximum operable time (min)
Table 5 Computed values for some reactor parameters after the modification of the regulators. Item
Calc. value
Initial excess reactivity (mk) Reactivity regulator worth (mk) Effective control rod worth (mk) Total reactivity flooding effect of internal irradiation sites (mk) Total reactivity flooding effect of external irradiation sites (mk) Shut down margin (mk) Effective shut down margin (mk)
3.9285 0.8405 7.4700 2.2323 0.9198 3.5415 0.3894
years) because the xenon may not reach the equilibrium during this period (27e29 hrs are required for xenon to saturate), and the reactor will be stopped shortly after to allow for the xenon to decay to the acceptable levels that permit to the reactor to re-start-up. The reactor will re-start-up only after the xenon has decayed. The xenon decays normally within hours. The reactor will work for this time intermittently. The core flux distributions before and after modification of the regulator are presented in Tables 3 and 6, respectively. It is evident that the two distributions are substantially the same in the inner and outer irradiation sites at least. Major differences are encountered in the regulator itself (which now is more absorbing). In this way the reactor can irradiate samples at the same flux operating for much longer time, and can be also shut down safely. No additional operational procedures are required here because no modifications to the original procedures have been brought.
Optimized reactor 3.9285 9.7851 3.3620 8.000
3.5415 909.010 1733.00
Actual reactor 3.9400 7.0000 1.2000 No addition
3.0600 999.856 428.00
Even in the case of an accident in which all the ten Irradiation Sites (IS) are flooded with reactor water simultaneously, which brings about 3.1521 additional mk to the initial excess reactivity the reactor cannot go critical since the shut down margin is still negative; in this case it is about 3.5415 þ 3.1521 ¼ 0.3894 mk. This margin will be sufficient to keep the reactor sub-critical since uncertainties in measured parameters are limited to 1e2%. Taking into consideration the results of the other works done for the optimization of the other components of the reactor (Albarhoum, 2004a,b) it comes out that more top reflector material should be added and more IER would be available (about 8.0000 mk) even if less U-235 would be in the core which results from the optimization of the uranium load in the core. With 8 mk IER the reactor is near to be prompt critical (the delayed fraction of neutrons for MNSR is about 8.05 mk), but it is still not. The final optimized configuration of the reactor is that shown in Table 7. The MOT is now even greater (about 1733 min). The reactor will work for about 28.00 h continuously. Since the xenon saturation occurs in about this time the reactor may happen to work permanently. The operation costs will decrease significantly since the capacity to irradiate samples will be about 5 times that of the actual reactor.
Table 6 Average calculated neutron flux in some reactor components after modification of the regulators. Reactor component
Group 1
Group 2
Group 3
Group 4
Fuel circle No. 1 Fuel circle No. 8 Fuel circle No. 10 Beryllium annulus Inner irradiation sites Outer irradiation sites Reactor vessel Bottom Beryllium Regulator
1.13007 1012 8.56623 1011 6.79131 1011 1.87280 1011 1.97332 1011 2.27527 1010 4.92124 108 2.38377 1011 0.98927 1010
1.02906 1012 8.30401 1011 7.29594 1011 3.08733 1011 3.32284 1011 4.59345 1010 0.56872 109 3.40561 1011 1.01437 1010
1.12624 1012 9.18765 1011 8.23521 1011 4.17549 1011 4.79664 1011 9.22155 1010 1.15539 109 4.26976 1011 0.18652 1010
1.06341 1012 8.52281 1011 8.92937 1011 8.54480 1011 9.94196 1011 4.80983 1011 1.11303 1010 9.22535 1011 2.31589 107
M. Albarhoum / Progress in Nuclear Energy 52 (2010) 624e627
627
5. Conclusions
References
The neutronics design of MNSRs can be optimized in terms of the regulators worth after other components had been optimized in other works. The optimization of a MNSR leads to a different reactor which has;
Albarhoum, M., 2001. CITOPP, CITMOD, CITWI (CITATION Output Processing Programs). IAEA 1385-1. NEA Data Bank. Albarhoum, M., 2004a. Extending the operable time of the Syrian MNSR. Annals of Nuclear Energy 31 (18), 2201e2207. Albarhoum, M., 2004b. Optimization of MNSR Design. Final Report on Scientific Research. Atomic Energy Commission of Syria (AECS). AECS-NE\FRSR 306. Albarhoum, M., 2008. Automation of the modeling and some neutronic calculations of the Syrian miniature neutron source reactors. Annals of Nuclear Energy 35 (9), 1760e1763. Anim-Sampong, S., Maakuu, B.T., Akaho, E.H.K., Andam, A., Liaw, J.J.R., Matos, J.E., 2006. Progress in the neutronic core conversion (HEU-LEU). Analysis on Ghana Research Reactor-1. In: Proceedings of the 2006 RERTR Conference, Cape Town, South Africa, Oct. 29eNov. 2. Askew, J.R., Fayers, F.J., Kemshell, P.B., 1966. A general description of lattice code WIMSD. Journal of the British Nuclear Energy Society 5, 564. CIAE, 1993. Safety Analysis Report (SAR) for the Syrian Miniature Neutron Source Reactor, China. Fowler, T.B., Vondy, D.R., Cunningham, G.W., 1971. Nuclear Reactor Core Analysis Code: CITATION. ORNL-TM-2496, Rev. 2, July. Jonah, S.A., Liaw, J.R., Olson, A., Matos, J.E., 2006. Criticality calculations and transient analysis of the Nigeria MNSR (NIRR-1) for conversion to LEU. In: Proceedings of the 2006 RERTR Conference, Cape Town, South Africa, Oct. 29eNov. 2. Matos, J.E., Lell, R.M., 2005. Feasibility study of potential LEU fuels for a generic MNSR reactor. In: Proceedings of the 2005 RERTR Conference, Boston, USA, Nov. 6e10.
1. 2. 3. 4.
a more efficient regulator (110%), a more efficient control rod (w40%), less U235 loaded in the core (10%), a much longer MOT (a permanently working reactor) which means about 5 times more samples irradiated in these reactors annually.
No special precautions are implied to the operation of the reactor.
Acknowledgment The author thanks Professor I. Othman, Director General of the Atomic Energy Commission of Syria, for his encouragement and continued support.
Contents lists available at ScienceDirect
Progress in Nuclear Energy journal homepage: www.elsevier.com/locate/pnucene
Optimization of the neutronics design of MNSRs M. Albarhoum* Department of Nuclear Engineering, Atomic Energy Commission, P.O. Box 6091, Damascus, Syria
a b s t r a c t Keywords: MNSR Regulator IER Optimization Boron MOT
The small daily operation time of MNSRs and the consequent limited use of these reactors imply that their neutronics design should be improved. The optimization of the neutronics design is based on the optimization of all the neutronically influential components, the latest of which are the regulators. Both cadmium and stainless steel absorbers are substituted by boron. About 3.0 mm thickness of the Top Beryllium Reflector Shims are added to compensate for about 1 mk loss of initial excess reactivity caused by the now more efficient regulators. The new initial excess reactivity is about 4 mk. The daily operable time is extended to about 28.00 hrs, and much more samples (about ten times) can be irradiated daily. The neutronic characteristics of the optimized reactor are compared with those of the actual reactor. Advantages are listed, and savings are estimated. Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction MNSRs are research reactors of the tank-in-pool type with highly enriched uranium fuel (w90 w/o U235). These reactors have been described many times elsewhere by their owners (AnimSampong et al., 2006; Jonah et al., 2006). These reactors have cores formed of about 350 fuel rods, with a surrounding beryllium reflector of about 10.00 cm thickness. The cold Initial Excess Reactivity (IER) is w4.0000 mk (Matos and Lell, 2005). This IER permits for these reactors to operate for only about 2.5 h/day at nominal power. This reactivity is consumed during reactor operation by moderator temperature rise and xenon poisoning. The limitation on the operable time leads to limitation in both the total number of samples that can be irradiated annually from one side, and the specific activity of the irradiated samples or produced short-lived radioisotopes from the other side. One solution would be to increase the daily operable time. This is because the flux depends mostly on the reactor power which is not allowed to increase for safety reasons. To increase the daily operable time more IER is needed, or alternatively minor consumption rates of the IER are required. The optimization of the control rod, the uranium load, and the reflector material (Albarhoum, 2004a,b) contributed a lot to the optimization of the neutronic design of MNSRs. The role of the regulators in the actual MNSRs is still considered marginal, and its improvement is necessary to support the role of the control rod, and to complete the neutronics design optimization of these reactors. * Tel.: þ963 11 2132580; fax: þ963 11 6112289. E-mail address: pscientifi[email protected] 0149-1970/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.pnucene.2010.04.005
The quantity of Cd absorber which is used in a regulator is so small that the worth on one regulator is limited to about only 0.4 mk. More efficient regulators are suggested in this work. It would be also convenient to see what differences and advantages has the optimized reactor. This is done in the paper too. 2. Reactor modeling Calculations were performed using a detailed three-dimensional model implemented in the core calculation’s code CITATION (Fowler et al., 1971) coupled with the lattice cell code WIMSD4 (Askew et al., 1966), through the use of the BMAC system (Albarhoum, 2008). This system generates the cross sections for the problem automatically upon describing the problem (by the user) in a conventional input file. All reactor components were modeled for calculation including regulators tubes (Fig. 1, component No. 24). In Table 1 a summary comparison between calculated and measured data for the model used in BMAC is shown. Generally speaking, the model proves to be good enough to be used for the evaluation of the new regulators worths. In Table 2 the group constants for one regulator are shown while in Table 3 the average calculated neutron fluxes in some reactor components, before modification of the regulator, are reported for comparison. 3. Modification of the regulator and addition of the top beryllium reflector If cadmium and stainless steel are both substituted by boron in the regulators new group constants are obtained. Table 4 shows the
M. Albarhoum / Progress in Nuclear Energy 52 (2010) 624e627
625
Fig. 1. A schematic vertical cross section drawn by CITMOD (Albarhoum, 2001) of the modeled reactor showing some components of the Syrian MNSR.
group constants for the new regulator. The macroscopic absorption is higher now. This causes the new regulator to be more efficient for the control of the reactor from one side, but it causes the IER of the reactor to decrease from the other side. The new IER will be 2.8846 mk only. Since the IER is now only about 2.8846 mk, to have about 4.0000 mk as prescribed by regulations (CIAE, 1993), some top reflector pieces should be added. The addition of two pieces of 1.50 mm thickness each increases the IER to 3.9285 mk. In this case the main reactor parameters will be that shown in Table 5. The new group constants of the components of Table 3 are shown in Table 6. 4. Results and discussion Tables 4e6 show the results obtained by modifying the regulators absorbing material. The reactor parameters shown in Table 5 indicate that the addition of 3 mm of top beryllium thickness brings about 1.04 mk IER to the reactor such a way that the IER is now 3.9285 mk. By comparing the values of the same parameters in
Table 1 Computed and measured (CIAE, 1993) values for some reactor parameters for the Syrian MNSR before modification of the regulators. Item Initial excess reactivity (mk) Effective control rod worth (mk) Reactivity regulator worth (mk) Total reactivity flooding effect of internal irradiation sites (mk) Total reactivity flooding effect of external irradiation sites (mk) Shut down margin (mk) Effective shut down margin (mk) Maximum operable time (min)
Calc. value
Meas. value
Exp. error (%)
3.9840 7.8900 0.4000 2.2380
3.9400 7.0000 0.4100 1.9500
1 1 1 e
1.0400
1.0000
3.9060 0.628 428.00
3.0600 0.1100 e
e 2 2 e
both the old and new configuration of the reactor the following will be seen: 1. The shut down margin increases to 3.5415 mk (from 3.9060 mk), which means less safety during the normal daily operation of the reactor (9.33%). 2. The effective worth of the control rod decreases from 7.89 to 7.4700 mk which means that the control rod has become less efficient too (5.32%). 3. The effective shut down margin (which is the shut down margin minus reactivity flooding effect of internal irradiation sites minus reactivity flooding effect of external irradiation sites) decreases to 0.3894 (38%) although the reactor is still safe. The reactor looses anyway in terms of neutronic safety. The reactor gains in terms of Maximum Operable Time (MOT). The maximum operable time for the reactor before regulator modification has been estimated earlier (Albarhoum, 2004a,b) to be about 428.00 min. Since the new available IER is now ¼ 3.9285 þ 4 * 0.8405 z 7.4413 mk (regulators are supposed to be withdrawn during operation), assuming that the same method is adopted to estimate the MOT, the new MOT would be found to be 1494 min (349%). The reactor MOT now is three and half times the old one. This result (being the MOT greater than 24.00 h) does not mean that the reactor can be operated permanently (everyday for many
Table 2 Calculated group constants for the four neutronic groups for a generic regulator before its modification. Group constants
Group 1
Group 2
Group 3
Group 4
Diffusion 2.02655 1.01562 0.624627 0.501994 Absorption 5.13227 102 4.37380 104 4.13005 101 7.54058 102
626
M. Albarhoum / Progress in Nuclear Energy 52 (2010) 624e627
Table 3 Average calculated neutron flux in some reactor components before the optimization of the regulators. Reactor component
Group 1
Group 2
Group 3
Group 4
Fuel circle No. 1 Fuel circle No. 8 Fuel circle No. 10 Beryllium annulus Inner irradiation sites Outer irradiation sites Reactor vessel Bottom beryllium Regulator
1.12895 1012 8.56135 1011 6.78828 1011 1.87166 1011 1.97559 1011 2.34542 1010 5.65458 108 2.38872 1011 1.66751 1010
1.02789 1012 8.29830 1011 7.29188 1011 3.09399 1011 3.33022 1011 4.80062 1010 7.05521 109 3.41272 1011 3.32321 1010
1.12491 1012 9.18301 1011 8.23667 1011 4.23064 1011 4.83339 1011 9.89125 1010 1.51679 109 4.28052 1011 7.40968 1010
1.06233 1012 8.52315 1011 8.94452 1011 8.60392 1011 1.00437 1012 4.75096 1011 1.28777 1010 9.26924 1011 1.27636 1011
Table 7 A comparison between final optimized configuration of the Syrian MNSR and the original configuration.
Table 4 The new group constants for one regulator in MNSRs after its modification. Group constants
Group 1
Group 2
Group 3
Group 4
Diffusion Absorption
1.66568 8.87891 102
0.25386 0.29130
0.11012 2.11747
0.05234 3.51450 102
Item Initial excess reactivity (mk) Effective control rod worth (mk) Total reactivity regulators worth (4 0.8405 mk) Total potentially available excess reactivity (after addition of beryllium, and withdrawal of the regulators, mk) Shut down margin (mk) Total uranium-235 load in the core (g) Maximum operable time (min)
Table 5 Computed values for some reactor parameters after the modification of the regulators. Item
Calc. value
Initial excess reactivity (mk) Reactivity regulator worth (mk) Effective control rod worth (mk) Total reactivity flooding effect of internal irradiation sites (mk) Total reactivity flooding effect of external irradiation sites (mk) Shut down margin (mk) Effective shut down margin (mk)
3.9285 0.8405 7.4700 2.2323 0.9198 3.5415 0.3894
years) because the xenon may not reach the equilibrium during this period (27e29 hrs are required for xenon to saturate), and the reactor will be stopped shortly after to allow for the xenon to decay to the acceptable levels that permit to the reactor to re-start-up. The reactor will re-start-up only after the xenon has decayed. The xenon decays normally within hours. The reactor will work for this time intermittently. The core flux distributions before and after modification of the regulator are presented in Tables 3 and 6, respectively. It is evident that the two distributions are substantially the same in the inner and outer irradiation sites at least. Major differences are encountered in the regulator itself (which now is more absorbing). In this way the reactor can irradiate samples at the same flux operating for much longer time, and can be also shut down safely. No additional operational procedures are required here because no modifications to the original procedures have been brought.
Optimized reactor 3.9285 9.7851 3.3620 8.000
3.5415 909.010 1733.00
Actual reactor 3.9400 7.0000 1.2000 No addition
3.0600 999.856 428.00
Even in the case of an accident in which all the ten Irradiation Sites (IS) are flooded with reactor water simultaneously, which brings about 3.1521 additional mk to the initial excess reactivity the reactor cannot go critical since the shut down margin is still negative; in this case it is about 3.5415 þ 3.1521 ¼ 0.3894 mk. This margin will be sufficient to keep the reactor sub-critical since uncertainties in measured parameters are limited to 1e2%. Taking into consideration the results of the other works done for the optimization of the other components of the reactor (Albarhoum, 2004a,b) it comes out that more top reflector material should be added and more IER would be available (about 8.0000 mk) even if less U-235 would be in the core which results from the optimization of the uranium load in the core. With 8 mk IER the reactor is near to be prompt critical (the delayed fraction of neutrons for MNSR is about 8.05 mk), but it is still not. The final optimized configuration of the reactor is that shown in Table 7. The MOT is now even greater (about 1733 min). The reactor will work for about 28.00 h continuously. Since the xenon saturation occurs in about this time the reactor may happen to work permanently. The operation costs will decrease significantly since the capacity to irradiate samples will be about 5 times that of the actual reactor.
Table 6 Average calculated neutron flux in some reactor components after modification of the regulators. Reactor component
Group 1
Group 2
Group 3
Group 4
Fuel circle No. 1 Fuel circle No. 8 Fuel circle No. 10 Beryllium annulus Inner irradiation sites Outer irradiation sites Reactor vessel Bottom Beryllium Regulator
1.13007 1012 8.56623 1011 6.79131 1011 1.87280 1011 1.97332 1011 2.27527 1010 4.92124 108 2.38377 1011 0.98927 1010
1.02906 1012 8.30401 1011 7.29594 1011 3.08733 1011 3.32284 1011 4.59345 1010 0.56872 109 3.40561 1011 1.01437 1010
1.12624 1012 9.18765 1011 8.23521 1011 4.17549 1011 4.79664 1011 9.22155 1010 1.15539 109 4.26976 1011 0.18652 1010
1.06341 1012 8.52281 1011 8.92937 1011 8.54480 1011 9.94196 1011 4.80983 1011 1.11303 1010 9.22535 1011 2.31589 107
M. Albarhoum / Progress in Nuclear Energy 52 (2010) 624e627
627
5. Conclusions
References
The neutronics design of MNSRs can be optimized in terms of the regulators worth after other components had been optimized in other works. The optimization of a MNSR leads to a different reactor which has;
Albarhoum, M., 2001. CITOPP, CITMOD, CITWI (CITATION Output Processing Programs). IAEA 1385-1. NEA Data Bank. Albarhoum, M., 2004a. Extending the operable time of the Syrian MNSR. Annals of Nuclear Energy 31 (18), 2201e2207. Albarhoum, M., 2004b. Optimization of MNSR Design. Final Report on Scientific Research. Atomic Energy Commission of Syria (AECS). AECS-NE\FRSR 306. Albarhoum, M., 2008. Automation of the modeling and some neutronic calculations of the Syrian miniature neutron source reactors. Annals of Nuclear Energy 35 (9), 1760e1763. Anim-Sampong, S., Maakuu, B.T., Akaho, E.H.K., Andam, A., Liaw, J.J.R., Matos, J.E., 2006. Progress in the neutronic core conversion (HEU-LEU). Analysis on Ghana Research Reactor-1. In: Proceedings of the 2006 RERTR Conference, Cape Town, South Africa, Oct. 29eNov. 2. Askew, J.R., Fayers, F.J., Kemshell, P.B., 1966. A general description of lattice code WIMSD. Journal of the British Nuclear Energy Society 5, 564. CIAE, 1993. Safety Analysis Report (SAR) for the Syrian Miniature Neutron Source Reactor, China. Fowler, T.B., Vondy, D.R., Cunningham, G.W., 1971. Nuclear Reactor Core Analysis Code: CITATION. ORNL-TM-2496, Rev. 2, July. Jonah, S.A., Liaw, J.R., Olson, A., Matos, J.E., 2006. Criticality calculations and transient analysis of the Nigeria MNSR (NIRR-1) for conversion to LEU. In: Proceedings of the 2006 RERTR Conference, Cape Town, South Africa, Oct. 29eNov. 2. Matos, J.E., Lell, R.M., 2005. Feasibility study of potential LEU fuels for a generic MNSR reactor. In: Proceedings of the 2005 RERTR Conference, Boston, USA, Nov. 6e10.
1. 2. 3. 4.
a more efficient regulator (110%), a more efficient control rod (w40%), less U235 loaded in the core (10%), a much longer MOT (a permanently working reactor) which means about 5 times more samples irradiated in these reactors annually.
No special precautions are implied to the operation of the reactor.
Acknowledgment The author thanks Professor I. Othman, Director General of the Atomic Energy Commission of Syria, for his encouragement and continued support.