Research Article Study of Thorium Fuel Cycles for Light Water...

Hindawi Publishing CorporationInternational Journal of Nuclear EnergyVolume 2013, Article ID 491898, 9 pageshttp://dx.doi.org/10.1155/2013/491898

Research ArticleStudy of Thorium Fuel Cycles for Light Water Reactor VBER-150

Daniel Evelio Milian Lorenzo,1 Daniel Milian Pérez,1 Lorena Pilar Rodríguez García,1

Jesús Salomón Llanes,1 Carlos Alberto Brayner de Oliveira Lira,2

Manuel Cadavid Rodríguez,3 and Carlos Rafael García Hernández1

1 Instituto Superior de Tecnologıas y Ciencias Aplicadas (InSTEC), Avenida Salvador Allende y Luaces, Quinta de Los Molinos,Plaza de la Revolucion, 10400 La Habana, Cuba

2Departamento de Energia Nuclear—UFPE, Cidade Universitaria, Avenida Professor Luiz Freire 1000 Recife, PE, Brazil3 Corporacion Nuclear Electrica Chile S. A., (CNE Chile), Latadia, Las Condes, 4250 Santiago, Chile

Correspondence should be addressed to Daniel Evelio Milian Lorenzo; [email protected]

Received 30 September 2013; Revised 11 November 2013; Accepted 12 November 2013

Academic Editor: Arkady Serikov

Copyright © 2013 Daniel Evelio Milian Lorenzo et al. This is an open access article distributed under the Creative CommonsAttribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work isproperly cited.

The main objective of this paper is to examine the use of thorium-based fuel cycle for the transportable reactors or transportablenuclear power plants (TNPP) VBER-150 concept, in particular the neutronic behavior. The thorium-based fuel cycles includedTh232+Pu239, Th232+U233, and Th232+U and the standard design fuel UOX. Parameters related to the neutronic behavior such asburnup, nuclear fuel breeding, MA stockpile, and Pu isotopes production (among others) were used to compare the fuel cycles.ThePu transmutation rate and accumulation of Pu with MA in the spent fuel were compared mutually and with an UOX open cycle.TheTh232+U233fuel cycle proved to be the best cycle for minimizing the production of Pu andMA.The neutronic calculations havebeen performed with the well-knownMCNPX computational code, which was verified for this type of fuel performing calculationof the IAEA benchmark announced by IAEA-TECDOC-1349.

1. Introduction

There is a growing interest in small reactors, and specificallyTNPP. These reactors could represent a solution for devel-oping countries with energy needs on islands, with remotelylocated areas without interconnected electricity grids orwithout the infrastructure required for land-based stationaryNPP. Various designs have been developed, but most of theTNPP are based on long-term experience acquired with shippropulsion reactors and with larger land-based stationaryreactors.

Depending on the host state requirements, the plant canbe operated by the supplier state or by an entity from thereceiving country. The host state can acquire a TNPP to ownwith all the consequences associated with the use of nuclearenergy. In other scenario, the supplier state has additionalresponsibilities that may include delivery and return of theTNPP and its operation if requested by the host state.All operations with the nuclear fuel are done at the zone of

responsibility of the supplier state. Anyway, to implementthis, it is necessary to design a reactor core with long oper-ation cycles without on-site reloading and shuffling of fuel,which ensures difficult access to the fuel during the entireperiod of the reactor installation operation including trans-portation. Some TNPP being considered today for export,but they are innovative concepts and need effort for thedemonstration of their viability [1].The use of thorium basedfuel cycle and the exclusion of on-site refueling providesthe solution to the nonproliferation problem; therefore, thiscategory of reactors is very attractive for energy supplies indeveloping countries.

Thorium based fuel cycles are very attractive for pro-ducing long-term nuclear energy with low radiotoxicitywaste [2, 3]. Additionally, thorium fuel cycles could be donethrough the incineration of weapon grade plutonium (WPu)or civilian plutonium [4, 5]. Compared to the U238-Pu239fuel cycle, Th232-U233 cycle produces less quantity of pluto-nium and minor actinides (MA: Np, Am, Cm), minimizing

2 International Journal of Nuclear Energy

Table 1: 𝐾inf as function of burnup.

Burnup, GWd/T Russian Federation Japan Republic of Korea India Israel MCNPX ver. 2.6e0 1.1890 1.1987 1.1864 1.2076 1.1956 1.19775 ± 0.000470.5 1.1569 1.1670 1.1551 1.1736 1.1643 1.16734 ± 0.0004820 1.0298 1.0521 1.0303 1.0372 1.0290 1.05898 ± 0.0004740 0.9147 0.9527 0.9167 0.9104 0.9119 0.95610 ± 0.0004160 0.8315 0.8657 0.8310 0.8294 0.8314 0.86561 ± 0.00038

Figure 1: PWR fuel assembly model in MCNPX.

0 10 20 30 40 50 60

0.8

0.9

1.0

1.1

1.2

Burnup (GWd/T)

MCNPX ver. 2.6eRussian FederationJapan

Republic of KoreaIndiaIsrael

Kin

f

Figure 2: Comparison of 𝐾inf as function of burnup.

the radiotoxicity associated with spent fuel. Consequently,the production of radioactive waste in a thorium fuel cycleis lower than that in the U-Pu cycle used in traditional lightwater reactors (LWRs) [6].

The main objective of this paper is to examine the use ofthorium based fuel cycle for the TNPP VBER-150 concept,in particular the neutronic behavior. The thorium based

Table 2: Main parameters of the TNPP VBER-150 concept.

Parameter ValueThermal power (MWt) 350Electrical power (MWe) 110Core height (m) 2.2Core diameter (m) 2.42Core volume (m3) 9.02Coolant and moderator H2ONumber of fuel assembly 85Type of fuel assembly Same as VVER-1000Power density (MW/m3) 39Fuel mass (tons) 22.3

fuel cycles included Th232+Pu239, Th232+U233, Th232+U, andthe standard design fuel UOX. Parameters related to theneutronic behavior such as burnup, nuclear fuel breeding,MA stockpile, and Pu isotopes production (among others)were used to compare the fuel cycles. The thorium based fuelcycle was examined through computer simulations.

The neutronic calculations have been performed withthe MCNPX version 2.6e code [7]. Unfortunately there isinsufficient data of VVER reactors with fuel containingthorium to validate the MCNPX code version 2.6e code. Toreach this goal and considering the scope of this paper weperformed calculation of the IAEA benchmark announcedby IAEA-TECDOC-1349 for a simplified model of a PWRassembly with a plutonium-thorium fuel composition [8].Similar approach was proposed in [9]. The results obtainedfrom MCNPX version 2.6e code are in good agreement withthe results of other participants of this benchmark and thediscrepancies can be caused by the use of various methodsand nuclear database. The results of benchmark calculationsratified that MCNPX code version 2.6e with available libraryin XSDIR, ENDF/B VI.2, is adequate for studies of thoriumbased fuel cycles.

Three different models of VVER-1000 assemblies weredesigned for the MCNPX calculations with the purpose ofselecting the model more suitable for the present study. Toreach this goal the neutronic behavior of the reactor duringthe burnup and cycle duration for the three models wasstudied.

2. The Reactor

The TNPP VBER-150 concept is a two-loop modification ofthe VBER-300 reactor installation [10]. This nuclear reactor

International Journal of Nuclear Energy 3

0 20 40 60

0.96

0.98

1.00

Burnup (GWd/ton)

Relat

ive c

once

ntra

tion

MCNPX Th232 Japan Th232

Russia Th232 Korea Th232

(a)

0 20 40 60Burnup (GWd/ton)

0.0

0.5

1.0

MCNPX Russia

Japan Korea

Relat

ive c

once

ntra

tion

Pu239 Pu239

Pu239Pu239

(b)

0.4

0.6

0.8

1.0

MCNPX Russia

Japan Korea

Relat

ive c

once

ntra

tion

0 20 40 60Burnup (GWd/ton)

Pu241

Pu241 Pu241

Pu241

(c)

Figure 3: (a) Comparison of relative concentrations of Th232. (b) Comparison of relative concentrations of Pu239. (c) Comparison of relativeconcentrations of Pu241.

is a small sized loop type pressurized water reactor withouton-site refueling for a floatingNPPwith cogeneration option.Thenuclear fuel developed for theVVER reactorswill be usedfor the VBER-150. Refueling, radioactive waste managementand repairs could then be provided offsite, in special mainte-nance centers. Absence of on-site refueling ensures difficultaccess to the fuel during the entire period of the reactorinstallation operation including transportation. This TNPPconcept is based on a successful multidecade experiencein the production and operation of marine propulsion inthe Russian Federation. Along with the VVER-type powerreactors, the modular shipboard pressurized water reactorsrepresent the most developed reactor technology; it is wellexamined and proven by successful operation. The total

operating life of VVER-type reactors exceeded 1500 reactor-years, and over this period there were no events with theradiation-significant consequences. The operating experi-ence of shipboard reactors exceeds 6000 reactor-years [11, 12].

3. Computer Code Description

The neutronic calculations have been performed with theMCNPX version 2.6e code with the available library inXSDIR, ENDF/B VI.2, on a standard personal computer withIntel(R) Core(TM) i3-2328M CPU of 2.20GHz and 4GBRAM. MCNPX code is based on the Monte Carlo methodand incorporates new possibilities used in the present study,


Table 3: Main results for the TNPP VBER-150 concept assembly models.

Parameter Model Figure 5(a) Model Figure 5(b) Model Figure 5(c)Initial 𝐾eff 1.18813 ± 0.00022 1.21255 ± 0.00021 1.22083 ± 0.00022Full power days (FPD) 1160 1178 1200Discharge burnup (GWd/T) 17.27 17.46 18.03

Table 4: Results for the considered fuel cycles.

Parameter Fuel cyclesTh232-Pu239 Th232-U233 Th232-U UOX

Discharge burnup (GWd/T) 26.29 39.06 18.03 31.30Full power days (FPD) 1750 2600 1200 2083

Figure 4: TNPP VBER-150 concept model in MCNPX.

such as depletion/burnup capability based on CINDER90,which works with a 63-energy-group structure. Cross-sections for these 63 groups are condensed using a genericspectrum. CINDER90 utilizes decay and energy integratedreaction-rate probabilities along with fission yield informa-tion to calculate the temporal nuclide buildup and depletion.The library of data in CINDER90, residing in the CIN-DER.dat library file, includes isotope decay and interactionprobability data for 3400 isotopes, including ∼30 fission yieldsets and yield data for 1325 fission products.

The neutronics analysis performed in this work is thefollowing:

(1) Calculate the IAEA benchmark announced by IAEA-TECDOC-1349. Compare the reactor physics param-eters: 𝐾inf and fuel composition as a function ofburnup, in a simplifiedmodel of a PWRassemblywitha Plutonium-Thorium fuel composition.

(2) Calculate parameters related to the neutronic behav-ior as burnup and cycle duration for the three differentmodels of VVER-1000 assemblies designed for theMCNPX calculations with the purpose of selectingthe model more suitable for the present study.

Table 5: Reactor’s BC for the fuel cycles studied.

Cycle BCTh232+Pu239 0.50Th232+U233 0.51Th232+U 0.55UOX 0.70

(3) Calculate parameters related to the neutronic behav-ior such as burnup, nuclear fuel breeding, MA stock-pile, and Pu isotopes production (among others), forthe TNPP VBER-150 concept.

The control parameters in the MCNPX calculations arethe following:

Source size per cycle: 2000Initial guess for𝐾-infinite: 1.0Number of settle cycles: 50Total cycles to run: 1000Total histories: 2,000,000.

4. Benchmark

The coordinated research project (CRP) “Potential of Tho-rium Based Fuel Cycles to Constrain Plutonium and toReduce Long-term Waste Toxicity” examined different fuelcycle options in which plutonium can be recycled with tho-rium to incinerate the burner. The potential of the thorium-matrix was examined through computer simulations. Threebenchmark tasks for different reactor concepts were per-formed in order to compare the effect of different methodsand databases applied in the countries participating in theCRP. The agreement of the benchmark results generally wasvery satisfying [8].

The objective in this part of the present work wasperforming calculation of the IAEA benchmark announcedby IAEA-TECDOC-1349 to verify that MCNPX code ver-sion 2.6e with available library in XSDIR, ENDF/B VI.2,is adequate for studies of thorium based fuel cycles. Weperformed calculation of the second benchmark. Five coun-tries participated in this benchmark using its own methods


Fuel element with thorium oxide

(a)

Fuel elementwith UOX

(b)

(c)

Figure 5: (a) and (b) TNPP VBER-150 concept advance fuel assembly model in MCNPX. (c) TNPP VBER-150 concept fuel assembly modelin MCNPX.

0 500 1000 1500 2000 2500 3000

1.0

1.1

1.2

1.3

1.4

1.5

Time (days)

UOXTh232-U

Th232-U233

Th232-Pu

Keff

Figure 6: 𝐾eff evolution for the fuel cycles studied.

and computer codes as well as its specific database: India,Israel, Japan, Republic of Korea, and Russian Federation.The benchmark was designed to compare assembly-levelcalculation methods, by defining a 2D lattice simulating atypical PWR fuel assembly.

The benchmark consists of a simplified model of a PWRassembly with a Plutonium-Thorium fuel composition. Themodel includes a 17 × 17 array of fuel rods, with 25 water holepositions without assembly casing and guide tubes (Figure 1).Burnup calculations were carried out with a constant specificpower of 37.7 MW/t (initial heavy metal). Dimensions ofthe assembly and the material compositions of the fuel (5%PuO2+ 95%ThO

2), cladding (natural zirconium), and mod-

erator (light water with 500 ppm concentration of naturalboron) can be found in [8].

We compared the results of criticality and fuel compo-sition as a function of burnup (burnup range from 0 to60GWd/t)with those obtained by the participants of theCRP.Table 1 and Figure 2 show the evolution of the multiplicationfactor during the burnup. Figures 3(a), 3(b), and 3(c) show


0 200 400 600 800 1000 1200 1400 1600 1800Time (days)

Mas

s (gr

)

1.2 × 106

1.0 × 106

8.0 × 105

6.0 × 105

4.0 × 105

2.0 × 105

0.0

Pu239

U233

(a)

0 200 400 600 800 1000 1200 1400 1600 1800Time (days)

Mas

s (gr

)

2.5 × 104

5.0 × 104

7.5 × 104

1.0 × 105

1.3 × 105

1.5 × 105

0.0

Pu240

Pu241

Pu238

(b)

Figure 7: (a) Mass depletion of the fissile isotopes (Pu239 and U233). (b) Plutonium isotopes variation in the reactor (Pu238, Pu240, and Pu241).

0 500 1000 1500 2000 2500Time (days)

Mas

s (gr

)

1.2 × 106

1.0 × 106

8.0 × 105

6.0 × 105

4.0 × 105

2.0 × 105

0.0

U233

Figure 8: Mass depletion of the fissile isotope (U233).

the relative concentration of Th232, Pu239, and Pu241 duringthe burnup. The results obtained from MCNPX version2.6e code are in good agreement with the results of otherparticipants of this benchmark and the discrepancies foundcorrespond to those reported in [8]. These discrepanciescan be caused by the use of various methods and nucleardatabase. Benchmark calculations performed contribute tothe verification ofMCNPX code for studies of thorium cyclesin PWR and at the same time demonstrates the ability of theteam in it use for burnup calculations.

5. Models and Fuel Cycles Studied

In this paper three thorium-based fuel cycles are presentedand compared:

(i) Th232+4.7%U233, in this cycle one fissile isotopemainly sustain the criticality of the reactor: U233,which represents a certain percent of the fresh fuel,

and the U233 produced by transmutation of fertileTh232.

(ii) Th232+4.7%Pu239, in this cycle two fissile isotopesmainly sustain the criticality of the reactor: Pu239,which represents a certain percent of the fresh fuel,and the U233 produced by transmutation of fertileTh232.

(iii) 40%Th232+60%U238 enriched at the 7.83% in U235,in this cycle three fissile isotopes mainly sustain thecriticality of the reactor: U235, which represents acertain percent of the fresh Uranium, U233, which isproduced by transmutation of fertileTh232, and Pu239,which is produced by transmutation of fertile U238.

Table 2 summarizes some of the main parameters of theTNPP VBER-150 concept in whole-core refueling mode usedin the MCNPX calculation; detailed information about thisreactor model (Figure 4) can be found in [13].

Three models of VVER-1000 assemblies were designed.The first one and second (Figures 5(a) and 5(b)) are anadvanced VVER-1000 assembly with two different fuel ele-ment types. The thorium oxide fuel is placed into dark pinsand the rest are fresh UOX pins. The third one, (Figure 5(c))is the VVER-1000 assembly with one type of fuel pins; thisassembly presents a homogeneous fuel distribution; in thethree models the thorium oxide percent, enrichment, andU235 mass are the same.

The neutronic behavior of the reactor was studied asfor burnup and cycle duration for the three models ofdistribution of the fuel element in the fuel assembly. As isshown in Table 3, the multiplicative properties are higherin the third model (fuel homogeneous distribution in theassembly), as well as the cycle duration in FPD; therefore,the burnup is relatively the highest. For this reason anyposterior study presented in this paper will be made with thehomogeneous model of fuel distribution.


0 200 400 600 800 1000 1200Time (days)

Mas

s (gr

)1.1 × 10

6

9.0 × 105

7.2 × 105

5.4 × 105

3.6 × 105

1.8 × 105

0.0

Pu239

U233

U235

(a)

0 200 400 600 800 1000 1200Time (days)

Mas

s (gr

)

1.3 × 104

1.1 × 104

8.8 × 103

6.6 × 103

4.4 × 103

2.2 × 105

0.0

Pu240

Pu241

Pu242

Pu238

(b)

Figure 9: (a) Mass depletion of the fissile isotopes (U235, U233, and Pu239). (b) Plutonium isotopes variation in the reactor (Pu238, Pu240, Pu241,and Pu242).

500 1000 1500 20000Time (days)

Mas

s (gr

)

1.2 × 106

1.0 × 106

8.0 × 105

6.0 × 105

4.0 × 105

2.0 × 105

0.0

Pu239

U235

(a)

0 500 1000 1500 2000Time (days)

3.6 × 104

3.0 × 104

2.4 × 104

1.8 × 104

1.2 × 104

6.0 × 103

0.0

Mas

s (gr

)

Pu240

Pu241

Pu242

Pu238

(b)

Figure 10: (a) Mass depletion of the fissile isotopes (U235 and Pu239). (b) Plutonium isotopes variation in the reactor (Pu238, Pu240, Pu241 andPu242).

6. Results

Thereactor behavior using the three-thorium-based fuels andthe basic UOX cycles was modeled. The fuel burnup in thereactor was calculated using (1). The results of the dischargeburnup, fuel cycle duration and 𝐾eff evolution can be seen inTable 4 and Figure 6:

Fuel burnup (GWd/ton) =Power (GW) ⋅ Time (days)

Fuel mass (ton).

(1)

The results obtained for basic cycle of UOX are similaras those reported in [13] for this reactor; results obtained for

thorium cycles support the use of thorium as fuel for thisreactor. However, it is necessary to go deeper in safety studiesregarding the thermomechanical behavior of the nuclear fueland others.

The mass variation of the fissile isotopes and plutoniumisotopes in the reactor as a function of time are shown inFigures 7(a) and 7(b) forTh232-Pu239 cycle, Figure 8 forTh232-U233 cycle, Figures 9(a) and 9(b) for Th232-U, cycle andFigures 10(a) and 10(b) for UOX cycle.

Figure 7(a) shows an important Pu239 decrease withrespect to the loaded mass and it can be seen that the massof U233 isotope presents a quasilinear growth. Figure 7(b)shows that plutonium isotopes grow in all cases except in


200 600 1000 1400 1800 2200Time (days)

Th232-UTh232-

UOX

8.0 × 103

6.0 × 103

4.0 × 103

2.0 × 103

0.0

Mas

s (gr

)

Pu239

Figure 11: Np237 mass variation for the Th232-Pu239, Th232-U, andUOX cycles.

Pu238. Figure 8 shows a light depletion of fissile isotope U233,product of the new U233 obtained from transmutation ofTh232 isotope. In Th232+U233 cycle plutonium isotopes arenot produced in the reactor. Figure 9(a) shows U235 decreasewith respect to the loaded mass and it can be seen that themass ofU233 andPu239 isotopes presents a quasilinear growth.Figure 9(b) shows that plutonium isotopes grow in all casesexcept in Pu238 and Pu242; in these two cases the plutoniummasses presents a quasilinear growth. Figure 10(a) showsU235decrease with respect to the loaded mass and it can be seenthat the mass of Pu239 isotope tends to reach a constantvalue. Figure 10(b) shows that plutonium isotopes growth inall cases except in Pu238 and Pu242 in these two cases theplutonium masses presents a quasilinear growth. In all casesthe fertile isotopes U238 and Th232 do not show importantrelative variation with burnup.

Table 5 presented the results of calculation of the fuelbreeding coefficient (BC) values for the fuel cycles studiedusing similar approach proposed in [14].The greater BC valueis obtained for UOX cycle; however, important BC valueswere obtained for thorium cycles too; in these cases the finalmass of fissile fuel left in the spent fuel is greater than UOXcycle. This is due to the quasilinear increase of the U233 massin Th232-Pu239 cycle and Th232-U cycle (Figures 7(a) and9(a)) and the quasilinear decrease of the U233 mass in Th232-U233 (Figure 8), while the mass of Pu239 is almost depleted inTh232-Pu239 cycle and the mass of U235 is consumed in a 40%inTh232-U cycle.

Figure 11 shows the mass variations of the minor actinideisotope Np237 in the reactor as a function of time for Th232-Pu239 cycle, Th232-U cycle, and UOX cycle.

Minor actinide which accumulates more is Np237; itis produced by neutron capture of U236 and subsequentbeta disintegration of U237. Figure 11 shows an increase inthe accumulation rate of this isotope in Th232-U cycle andUOX cycle, in Th232-Pu239 cycle Np237 mass is negligible.

In the Th232-U233 cycle insignificant masses of minoractinides isotopes are produced in the reactor.

7. Conclusions

Theprimary objective of this paper contribute to the neutron-ics analysis of the TNPP VBER-150 core, innovative conceptcurrently in development.

The main objective of this paper is to examine the use ofthorium based fuel cycle for the TNPP VBER-150 concept,in particular the neutronic behavior. The thorium basedfuel cycles included Th232+Pu239, Th232+U233, Th232+U, andthe standard design fuel UOX. The Th232+U233 fuel cycleproved to be the best cycle for minimizing the productionof Pu and MA in the TNPP VBER-150 concept. Also, it wasdemonstrated that a relatively low percent of fissile isotopesin the fuel mixture (4.7%) is sufficient to design the reactorcore with long operation cycles. Further studies are neededto confirm these results and contribute to developmentand demonstration of their technical, safety, and economicviability.

The neutronic calculations have been performed withthe MCNPX version 2.6e code. Three different models ofVVER-1000 assemblies were designed for the calculationswith the purpose of selecting the model more suitable forthe present study. Unfortunately there is insufficient dataof VVER reactors with fuel containing thorium to validatethe MCNPX code version 2.6e code. To reach this goal andconsidering the scope of this paper we performed calculationof the IAEA benchmark announced by IAEA-TECDOC-1349for a simplified model of a PWR assembly with a plutonium-Thorium fuel compositionThe results of benchmark calcula-tions ratified that MCNPX code version 2.6e with availablelibrary in XSDIR, ENDF/B VI.2, is adequate for studies ofthorium based fuel cycles.

Acknowledgment

Daniel Evelio Milian Lorenzo and Carlos Rafael GarcıaHernandez, project researchers CAPES-MES 114/11 “Estudode sistemas nucleares avancados com combustıvel TRISOpara a transmutacao de rejeitos de longa vida e producaode hidrogenio com tecnologias de temperatura muito alta,”thank CAPES (Coordenacao de Aperfeicoamento de Pessoalde Nivel Superior) of Education Ministry of Brazil for thefinancial support for this work.

References

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[3] International Atomic EnergyAgency,Role ofThorium to Supple-ment Fuel Cycles of Future Nuclear Energy Systems, IAEA, 2012.

[4] International Atomic Energy Agency, Thorium Fuel Cycle—Potential Benefits and Challenges, IAEA, 2005.


[5] International Atomic Energy Agency,Thorium Fuel Utilization:Options and Trends, IAEA, 2002.

[6] C. R. G. Hernandez, A. M. Oliva, L. G. Fajardo, J. A. R. Garcıa,and J. P. Curbelo, “Uranium-thorium fuel cycle in a veryhigh temperature hybrid system,” in Proceedings of the Interna-tional Conference on Mathematics and Computational MethodsApplied to Nuclear Science and Engineering, Brasılia, Brazil, 2011.

[7] The MCNPX Team, MCNPX User’s Manual 2.5.0, LA-CP-05-0369, Los Alamos National Laboratory, 2005.

[8] International Atomic Energy Agency, Potential of ThoriumBased Fuel Cycles to Constrain Plutonium andReduce Long LivedWaste Toxicity, IAEA, 2003.

[9] J. Breza, P. Darılek, and V. Necas, “Study of thorium advancedfuel cycle utilization in light water reactor VVER-440,” Annalsof Nuclear Energy, vol. 37, no. 5, pp. 685–690, 2010.

[10] International Atomic Energy Agency, Status of Innovative Smalland Medium Sized Reactor Designs, IAEA, 2006.

[11] “Safety assurance of NPP with VVER,” Recommendationsof the 8th International Scientific and Technical Conference,Podolsk, Russia, May 2013, http://www.gidropress.podolsk.ru/files/mntk2013/mntk2013-final.pdf.

[12] L. N. Andreeva-Andrievskaya and V. P. Kuznetsov, “Trans-portable nuclear power facilities in the INPRO InternationalProject,” Atomic Energy, vol. 111, no. 5, pp. 1–4, 2012.

[13] International Atomic Energy Agency, Status of Small ReactorDesigns without On-Site Refueling, IAEA, 2007.

[14] C. Garcıa, J. Rosales, L. Garcıa et al., “Evaluation of uraniumthorium and plutonium thorium fuel cycles in a very hightemperature hybrid system,” Progress in Nuclear Energy, vol. 66,pp. 61–72, 2013.

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