Plutonium utilization in a small modular molten-salt reactor based on a batch fuel reprocessing scheme

A molten salt reactor(MSR)has outstanding features considering the application of thorium fuel,inherent safety,sustainability,and resistance to proliferation.However,fissile material^(233)U is significantly rare at the current stage,thus it is difficult for MSR to achieve a pure thorium-uranium fuel cycle.Therefore,using plutonium or enriched uranium as the initial fuel for MSR is more practical.In this study,we aim to verify the feasibility of a small modular MSR that utilizes plutonium as the starting fuel(SM-MSR-Pu),and highlight its advantages and disadvantages.First,the structural design and fuel management scheme of the SM-MSR-Pu were presented.Second,the neutronic characteristics,such as the graphite-irradiation lifetime,burn-up performance,and coefficient of temperature reactivity were calculated to analyze the physical characteristics of the SM-MSR-Pu.The results indicate that plutonium is a feasible and advantageous starting fuel for a SM-MSR;however,there are certain shortcomings that need to be solved.In a 250 MWth SM-MSR-Pu,approximately 288.64 kg^(233)U of plutonium with a purity of greater than 90% is produced while 978.00 kg is burned every ten years.The temperature reactivity coefficient decreases from -4.0 to -6.5 pcm K^(-1) over the 50-year operating time,which ensures a long-term safe operation.However,the amount of plutonium and accumulation of minor actinides(MAs)would increase as the burn-up time increases,and the annual production and purity of^(233)U will decrease.To achieve an optimal burn-up performance,setting the entire operation time to 30 years is advisable.Regardless,more than 3600 kg of plutonium eventually accumulate in the core.Further research is required to effectively utilize this accumulated plutonium.

Analysis of burnup performance and temperature coefficient for a small modular molten‑salt reactor started with plutonium

In a thorium-based molten salt reactor(TMSR),it is difficult to achieve the pure 232Th–^(233)U fuel cycle without sufficient^(233)U fuel supply.Therefore,the original molten salt reactor was designed to use enriched uranium or plutonium as the starting fuel.By exploiting plutonium as the starting fuel and thorium as the fertile fuel,the high-purity^(233)U produced can be separated from the spent fuel by fluorination volatilization.Therefore,the molten salt reactor started with plutonium can be designed as a^(233)U breeder with the burning plutonium extracted from a pressurized water reactor(PWR).Combining these advantages,the study of the physical properties of plutonium-activated salt reactors is attractive.This study mainly focused on the burnup performance and temperature reactivity coefficient of a small modular molten-salt reactor started with plutonium(SM-MSR-Pu).The neutron spectra,^(233)U production,plutonium incineration,minor actinide(MA)residues,and temperature reactivity coefficients for different fuel salt volume fractions(VF)and hexagon pitch(P)sizes were calculated to analyze the burnup behavior in the SM-SMR-Pu.Based on the comparative analysis results of the burn-up calculation,a lower VF and larger P size are more beneficial for improving the burnup performance.However,from a passive safety perspective,a higher fuel volume fraction and smaller hexagon pitch size are necessary to achieve a deep negative feedback coefficient.Therefore,an excellent burnup performance and a deep negative temperature feedback coefficient are incompatible,and the optimal design range is relatively narrow in the optimized design of an SM-MSR-Pu.In a comprehensive consideration,P=20 cm and VF=20%are considered to be relatively balanced design parameters.Based on the fuel off-line batching scheme,a 250 MWth SM-MSR-Pu can produce approximately 29.83 kg of ^(233)U,incinerate 98.29 kg of plutonium,and accumulate 14.70 kg of MAs per year,and the temperature reactivity coefficient can always be lower than−4.0pcm/K.

Effect of reprocessing on neutrons of a molten chloride salt fast reactor

Due to their unique features,such as the inherent safety,simplified fuel cycle,and continuous on-line reprocessing,molten salt reactors(MSRs)are regarded as one of the six reference reactors in the Generation IV International Forum(GEN-IV).Molten chloride salt fast reactors(MCFRs)are a type of MSR.Compared to molten fluoride salt reactors(MFSRs),MCFRs have a higher solubility of heavy metal atoms,a harder neutron spectrum,lower accumulation of fission products(FPs),and better breeding and transmutation performance.Thus,MCFRs have been recognized as a type of MSR with great prospects for future development.However,as the most important feature for MSRs,the effect of different reprocessing modes on MCFRs must be researched in depth.As such,this study investigated the effect of different isotopes,especially FPs,on the neutronic performance of an MCFR,such as its breeding performance.Furthermore,the characteristics of the different reprocessing modes and MCFR rates were analyzed in terms of safety,radioactivity level,neutron economy,and breeding capacity.In the end,a reprocessing method suitable for MCFRs was determined through calculation and analysis,which provides a reference for the further research of MCFRs.

Effects of feeding untreated, pasteurized and acidified waste milk and bunk tank milk on the performance, serum metabolic profiles, immunity, and intestinal development in Holstein calves

Background: The present experiment was performed to assess the effects of different sources of milk on the growth performance, serum metabolism, immunity, and intestinal development of calves. Eighty-four Holstein male neonatal calves were assigned to one of the following four treatment groups: those that received bunk tank milk(BTM), untreated waste milk(UWM), pasteurized waste milk(PWM), and acidified waste milk(AWM) for 21 d.Results: Calves in the BTM and AWM groups consumed more starter(P < 0.05) than those in the UWM group.Average daily gain in the UWM group was the highest(P < 0.05). Calves exhibited the highest(P < 0.05) serum total protein, albumin, total cholesterol, high density lipoprotein, triglycerides, growth hormone, immunoglobulin(Ig) A and Ig M concentrations in the UWM group, highest malondialdehyde and tumor necrosis factor-α in the PWM group(P < 0.05), and highest glutathione peroxidase and Ig G in the BTM group(P < 0.05). The jejunum and ileum of the calves in all treatments presented a slight inflammatory response. The jejunal inflammation scores were higher(P < 0.05) in the UWM and AWM groups than the BTM group; the ileal inflammation scores increased more(P < 0.05) in the AWM group than the BTM group. Jejunal immunohistochemical scores(IHS) were higher(P < 0.05) in the PWM and AWM groups than the BTM group. Compared to the other three groups, calves feeding on BTM had lower(P < 0.05) ileal IHS. Jejunal interleukin(IL)-1β, IL-8, and IL-10 mRNA expression in the UWM group was the highest(P < 0.05). Calves fed AWM increased(P < 0.05) mRNA expression of IL-8 and toll like receptor 4(TLR-4) in the jejunum and IL-8, IL-1β, IL-6, IL-8, and IL-10 in the mesenteric lymph nodes.Conclusions: Overall, bunk tank milk is the best choice for calf raising compared to waste milk. The efficiency of feeding pasteurized and acidified waste milk are comparable, and the acidification of waste milk is an acceptable labor-saving and diarrhea-preventing feed for young calves.

Influences of ^7Li enrichment on Th-U fuel breeding for an Improved Molten Salt Fast Reactor(IMSFR)

The molten salt fast reactor(MSFR) shows great promise with high breeding ratio(BR),large negative temperature coefficient of reactivity,high thermal-electric conversion efficiency,inherent safety,and online reprocessing.Based on an improved MSFR optimized by adding axial fertile salt and a graphite reflector,the influences of ~7Li enrichment on Th-U breeding are investigated,aiming to provide a feasible selection for the molten salt with high fissile breeding and a relatively low technology requirement for ~7Li concentration.With the self-developed molten salt reactor reprocessing sequence based on SCALE6.1,the burn-up calculations with online reprocessing are carried out.Parameters are explored including BR,^(233)U production,double time(DT),spectrum,~6Li inventory,neutron absorption,and the tritium production.The results show that the Li enrichment of 99.95% is appropriate in the fast fission reactor.In this case,BR above 1.10 can be achieved for a long time,corresponding to the ^(233)U production of130 kg per year and DT of 36 years.After 80 years' operation,the tritium production for 99.5% is only about 7kg,and there is no obvious increase compared to that for 99.9995%.

选择性硒掺杂提高NiFe2O4/NiOOH异质结电催化析氧性能

氢能具有能量密度高、清洁无污染等优势,被认为是理想的能源,受到越来越多的关注.利用太阳能和风能等可再生能源电解水制氢是一种极具发展前景的可以规模化获取清洁氢气的能源技术,其挑战在于如何降低电能消耗并实现稳定地高速电解制氢.由于电解水阳极析氧反应(OER)涉及四电子转移,动力学过程缓慢,是电解水过程的决速步骤.因此,开发高效、廉价、稳定的OER电催化剂对于推动电解水制氢的应用至关重要.硫族化合物具有良好的导电性,对OER中间体表现出适宜的吸附/脱附能力,是一类高活性的析氧电催化剂.但在析氧反应中硫族化合物会不可避免地发生氧化,导致其结构坍塌,使其性能发生大幅衰减.NiOOH被认为是Ni(OH)2、NiSe和NiS等镍基电催化剂析氧过程中的真实催化活性位点,在析氧反应过程中表现出优异的稳定性.因此,结合硫族化合物的高催化活性和羟基氧化物的高稳定性,将有望获得高效稳定的析氧电催化剂.本文提出了一种选择性硒掺杂的策略,实现了不锈钢基底上NiFe2O4/NiOOH异质结的选择性硒掺杂,获得了硒掺杂浓度可调的NiFe2O4-xSex/NiOOH异质结电催化剂,大幅提升了其电催化析氧性能.采用X射线衍射技术、拉曼光谱、扫描电镜和透射电镜技术等对NiFe2O4/NiOOH异质结的结构、形貌和组分进行了表征.利用X射线光电子能谱和透射电镜的能量色散光谱仪对硒掺杂产物的元素组成和分布进行了分析.结果表明,硒元素仅掺杂到NiFe2O4纳米颗粒中,而NiOOH纳米片骨架保持不变,保证了催化剂在析氧过程的稳定性.NiFe2O4-xSex/NiOOH异质结电极在1 M KOH溶液中表现出较好的析氧性能,达到10和500 mA cm^(−2)电流密度所需要的过电位分别仅为153和259 mV,塔菲尔斜率为22.2 mV dec^(−1).更重要的是,NiFe2O4-xSex/NiOOH电催化剂的电化学性能稳定性,计时电流测试表明,在10~400 mA cm^(−2)电流密度下可稳定工作.稳定性测试表明,催化剂在100 mA cm^(−2)的电流密度下可稳定工作至少300 h.电催化过程研究表明,选择性硒掺杂提高了界面间电荷输运能力,改善了电极表面的浸润性,优化了活性位点的电子结构,从而大幅提高催化剂的电催化性能.密度泛函理论计算结果表明,硒掺杂会导致NiFe2O4表面晶格发生畸变,显著改善了反应中间体的吸附过程,因此明显降低了析氧反应决速步骤的能垒.本研究结果将为未来探索高效和稳定的电催化剂提供新的研究思路.

Changes in feed intake, nutrient digestion, plasma metabolites, and oxidative stress parameters in dairy cows with subacute ruminal acidosis and its regulation with pelleted beet pulp

The objectives of this study were to 1） determine the variation of nutrient digestion, plasma metabolites and oxidative stress parameters triggered by induced subacute ruminal acidosis （SARA）; and 2） evaluate the ability of pelleted beet pulp （BP） as a replacement for ground corn to alleviate SARA. Eight Holstein-Friesian cows were fed four diets during four successive17 day periods： 1） total mixed ration （TMR） containing 0% finely ground wheat （FGW） （WO）; 2） TMR containing 10% FGW （W10）; 3） TMR containing 20% FGW （W20）; and 4） TMR containing 10% BP as a replacement for 10% ground corn （BP10）. The SARA induction protocol reduced the mean ruminal pH from 6.37 to 5.94, and the minimum ruminal pH decreased from 5.99 to 5.41 from baseline to challenge period. Mean ruminal pH increased from 5.94 to 6.05, and minimum daily ruminal pH increased from 5.41 to 5.63, when BP was substituted for corn. The apparent digestibility of nutrients was not affected by the dietary treatments, except that the digestibility of neutral detergent fibre （NDF） and acid detergent fibre （ADF） was reduced in cows fed the W20 diet compared with cows fed the W0 and W10 diets, and cows fed the BP10 diet had higher NDF and ADF digestibility than the cows fed the W20 diet. Cows fed the W20 diet had a lower plasma concentration of 13-hydroxybutyrate （BHBA）, non-esterified fatty acids （NEFA）, cholesterol, triglyceride, and total antioxidative capacity （TAC）, and a higher plasma concentration of glucose, insulin, malonaldehyde （MDA）, super oxygen dehydrogenises （SOD）, and glutathione peroxidase （GSH-Px） than cows fed the W0 diet. Substitution of BP for corn increased concentrations of plasma BHBA and TAC, but decreased concentrations of plasma MDA. Our results indicate that reduction of fibre digestion; the concomitant increase of plasma glucose and insulin; the decrease of plasma BHBA, NEFA, cholesterol, and triglyceride; and changes of plasma oxidative stress parameters are highly related to SARA induced by W20 diets. These variables may be alternative candidates for SARA diagnosis. We also suggest that the substitution of BP for corn could reduce the risk of SARA, increase fibre digestion, and improve the antioxidant status in dairy cows.

Deactivation mechanism of beta-zeolite catalyst for synthesis of cumene by benzene alkylation with isopropanol

The alkylation of benzene with isopropanol over beta-zeolite is a more cost-effective solution to cumene production. During the benzene alkylation cycles, the cumene selectivity slowly increased, while the benzene conversion presented the sharp decrease due to catalyst deactivation. The deactivation mechanism of betazeolite catalyst was investigated by characterizing the fresh and used catalysts. The XRD, SEM and TEM results show that the crystalline and particle size of the beta-zeolite catalyst almost remained stable during the alkylation cycles. The drop in catalytic activity and benzene conversion could be explained by the TG, BET,NH_3-TPD and GC–MS results. The organic matters mainly consisted of ethylbenzene, p-xylene and 1-ethyl-3-(1-methyl) benzene produced in the benzene alkylation deposited in the catalyst, which strongly reduced the specific surface area of beta-zeolite catalyst. Moreover, during the reaction cycles, the amount of acidity also significantly decreased. As a result, the catalyst deactivation occurred. To maintain the catalytic performance,the catalyst regeneration was carried out by using ethanol rinse and calcination. The deactivated catalyst could be effectively regenerated by the calcination method and the good catalytic performance was obtained.

Impact of photoneutrons on reactivity measurements for TMSR-SF1

The solid-fueled thorium molten salt reactor(TMSR-SF1) is a 10 MW_(th) test reactor design to be deployed in 5-10 years by the TMSR group.Its design combines coated particle fuel and molten FLiBe coolant for great intrinsic safety features and economic advantages.Due to a large amount of beryllium in the coolant salt,photoneutrons are produced by(y,n) reaction,hence the increasing fraction of effective delayed neutrons in the core by the photoneutrons originating from the long-lived fission products.Some of the delayed photoneutron groups are of long lifetime,so a direct effect is resulted in the transient process and reactivity measurement.To study the impact of photoneutrons for TMSR-SF1,the effective photoneutron fraction is estimated using k-ratio method and performed by the Monte Carlo code(MCNP5) with ENDF/B-Ⅶ cross sections.Based on the coupled neutronphoton point kinetics equations,influence of the photoneutrons is analyzed.The results show that the impact of photoneutrons is not negligible in reactivity measurement.Without considering photoneutrons in on-line reactivity measurement based on inverse point kinetics can result in overestimation of the positive reactivity and underestimation of the negative reactivity.The photoneutrons also lead to more waiting time for the doubling time measurement.Since the photoneutron precursors take extremely long time to achieve equilibrium,a "steady" power operation may not directly imply a "real" criticality.

基于新的残差沙漏网络的人脸对齐

针对传统沙漏网络每一层使用单一感受野来提取特征,缺乏对关键点整体和局部关联信息描述的问题,提出了新的残差沙漏网络(NRHG)方法。该方法通过增加新的卷积分支来增加网络的感受野以更好地提取到不同尺度下的特征信息,同时新的感受野增加了网络对整体信息的描述;针对网络不同层相应调整新增卷积分支感受野大小来平衡feature map分辨率和感受野之间的关系,在更好地保留从局部到整体的结构化信息的同时,突出了网络对局部细节特征信息的描述。最后沙漏网络之间采用中间监督,对每一个沙漏网络输出的结果都进行loss计算,以避免网络深度造成梯度消失的问题。通过在300W、IBUG、COFW数据集上大量的实验证明了该方法的有效性,并且实验结果优于传统的沙漏网络。

Study on neutronics design of ordered-pebble-bed fluoride-salt- cooled high-temperature experimental reactor

This paper presents a neutronics design of a 10 MW ordered-pebble-bed fluoride-salt-cooled high-temperature experimental reactor. Through delicate layout, a core with ordered arranged pebble bed can be formed,which can keep core stability and meet the space requirements for thermal hydraulics and neutronics measurements.Overall, objectives of the core include inherent safety and sufficient excess reactivity providing 120 effective full power days for experiments. Considering the requirements above, the reactive control system is designed to consist of 16 control rods distributed in the graphite reflector. Combining the large control rods worth about 18000–20000 pcm, molten salt drain supplementary means(-6980 to -3651 pcm) and negative temperature coefficient(-6.32 to -3.80 pcm/K) feedback of the whole core, the reactor can realize sufficient shutdown margin and safety under steady state. Besides, some main physical properties, such as reactivity control, neutron spectrum and flux, power density distribution, and reactivity coefficient,have been calculated and analyzed in this study. In addition, some special problems in molten salt coolant are also considered, including ~6Li depletion and tritium production.

Effect of 37Cl enrichment on neutrons in a molten chloride salt fast reactor

A molten chloride salt fast reactor(MCFR)is well suited to fuel breeding and the transmutation of transuranium(TRU)elements owing to its advantageous features of fast neutron spectrum and high TRU solubility.However,the neutron absorption cross section of 35Cl is approximately 1000 times greater than for 37Cl,which has a significant impact on the neutron physical characteristics of a MCFR.Based on an automatic online refueling and reprocessing procedure,the influences of 37Cl enrichment on neutron economy,breeding performance,and the production of harmful nuclides were analyzed.Results show that 37Cl enrichment strongly influences the neutron properties of a MCFR.With natural chlorine,233U breeding cannot be achieved and the yields of S and 36Cl are very high.Increasing the 37Cl enrichment to 97%brings a clear improvement in its neutronics property,making it almost equal to that corresponding to 100%enrichment.Moreover,when 37Cl is enriched to 99%,its neutronics parameters are almost the same as for 100%enrichment.Considering the enrichment cost and the neutron properties,a 37Cl enrichment of 97%is recommended.Achieving an optimal neutronics performance requires 99%37Cl enrichment.

Numerical study of the dynamic characteristics of a single-layer graphite core in a thorium molten salt reactor

A reactor core in a thorium molten salt reactor uses graphite as a moderator and reflector. The graphite core is a multi-layered arrangement of graphite bricks that are loosely connected to each other using a system of keys and dowels. Consequently, the graphite core is a type of discrete stack structure with highly nonlinear dynamic behavior. Hence, it is important to investigate the dynamic characteristics of the graphite core. In this study, a threedimensional single-layer graphite core model, which is a part of the thorium molten salt reactor side reflector structure, was analyzed using the explicit method in ABAQUS 2016 to study the core dynamic behavior when subjected to different excitations. The design parameters,such as the diameter of the dowel, the gap between key and keyway and the bypass flow gap between two adjacent bricks, were also considered in this model. To reduce excessive demands on available computational resources considering the effect of molten salt, the spring–dashpot model was applied to model the interaction forces between the molten salt and graphite bricks. Numerical simulation results show that the effect of molten salt is a reduction inthe peak maximal principal stress, and a larger gap between two bricks is beneficial to maintain the integrity of the graphite core under earthquake loading. The results obtained by the simulation can be used as a reference for future designs of a molten salt graphite core.

Study on dynamic characteristics of fission products in 2 MW molten salt reactor

In this study,a numerical flow model of the fission products(FPs)in the primary loop system of a molten salt reactor(MSR)was established and solved using Mathematica 7.0.The simulation results were compared with those of the ORIGEN-S program in the static burnup mode,and the deviation was found to be less than 10%,which indicates that the results are in good agreement.Furthermore,the FPs distribution in the primary loop system under normal operating conditions of the 2 MW MSR was quantitatively analyzed.In addition,the distribution phenomenon of the FPs under different flow rate conditions was studied.At the end of life,the FPs activity in the core region(including active region,and upper and lower plenum regions)accounted for 77.3%,and that in the hot leg #1,main pump,hot leg #2,heat exchanger,and cold leg region accounted for 1.2%,16.15%,0.99%,2.5%,and 1.9%,respectively,of the total FPs in the primary loop under normal operating conditions.The proportion of FPs in the core decreased with the increase in flow rate in the range of 2.24-22,400 cm^3 s^-1.The established analytical method and conclusions of this study can provide an important basis for radiation safety design of the primary loop,radioactive source management design,thermal-hydraulic safety analysis,and radiochemical analysis of FPs of 2 MW MSRs.

Avoiding sealing failure of flanged connection for tubes made of dissimilar materials subjected to elevated temperature

Carbonic composite materials and ceramics appear to be excellent structural materials for parts subjected to very high temperatures in molten salt reactors(MSRs), in which the reactor core outlet temperature is normally above 700℃. Because of the high temperature,there are major challenges in the sealing of flanged connections for tubes made of alloys and nonmetallic materials. In this study, an improved method for sealing bolted flange connections for tubes made of dissimilar materials at high temperature is analyzed. The study focuses on the compensation mechanism for the difference in thermal expansion between the bolts and the flanges. An angle is introduced for the sealing surface in the flanged connection to provide effective sealing. The arctangent of the angle is the ratio of the thickness between the theoretical core of the sealing surface and the outside end face of the flange to the distances between the axis of the flanged joint and the theoretical core of the sealing surface of the flange; the sealing surface of the flange, which is made of the same material as the fastening assemblies, faces the fastening assemblies. To ensure effective sealing, the frictional coefficient between the two sealing surfaces should not exceed the tangent of the angle. This result does not agree well with the solution given by previous researchers. Further, in the modified flanged connection, the compression of each bolt in the clamped condition is increased to maintain the compaction force unchanged without increasing the number of bolts on the flanged joint.

Research on the effect of the heavy nuclei amount on the temperature reactivity coefficient in a small modular molten salt reactor

Small modular thorium-based graphite-moderated molten salt reactors (smTMSRs), which combine the advantages of small modular reactors and molten salt reactors, are regarded as a wise development path to speed deployment time. In a smTMSR, low enriched uranium and thorium fuels are used in once-through mode, which makes a marked difference in their neutronic properties compared with the case when a conventional molten salt breeder reactor is used. This study investigated the temperature reactivity coefficient (TRC) in a smTMSR, which is mainly affected by the molten salt volume fraction (VF) and the heavy nuclei concentration in the fuel salt (HN). The fourfactor formula method and the reaction rate method were used to indicate the reasons for the TRC change, including the fuel density effect, the fuel Doppler effect, and the graphite thermal scattering effect. The results indicate that only the fuel density has a positive effect on the TRC in the undermoderated region. Thermal scattering from both salt and graphite has a significant negative influence on the TRC in the overmoderated region. The maximal effective multiplication factor, which shows the highest fuel utilization, is located at 10% VF and 12 mol% HN and is still located in the negative TRC region. In addition, on increasing the heavy nuclei amount from 2 mol% HN to 12 mol% HN (VF = 10%), the total TRC undergoes an obvious change from - 11 to - 3 pcm/K, which implies that the change in the HN caused by the fuel feed online should be small to avoid potential trouble in the reactivity control scheme.

Th–U cycle performance analysis based on molten chloride salt and molten fluoride salt fast reactors

The recent development of molten salt fast reactors has generated a renewed interest in them. As compared to traditional solid fuel fast neutron systems, it has many unique advantages, e.g., lower fissile inventory,no initial criticality reserve, waste reduction, and a simplified fuel cycle. It has been recognized as an ideal reactor for achieving a closed Th–U cycle. Based on the carrier salt, molten salt fast reactors could be divided into either a molten chloride salt fast reactor(MCFR) or a molten fluoride salt fast reactor(MFFR);to compare their Th–U cycle performance, the neutronic parameters in a breeding and burning(B&B) transition scenario were studied based on similar core geometry and power. The results demonstrated that the required reprocessing rate for an MCFR to achieve self-breeding was lower than that of an MFFR.Moreover, the breeding capability of an MCFR was better than that of an MFFR;at a reprocessing rate of 40 L/day,using LEU and Pu as start-up fissile materials, the doubling time(DT) of an MFFR and MCFR were 88.0 years and 48.0 years, and 16.5 years and 16.2 years, respectively.Besides, an MCFR has lower radio-toxicity due to lower buildup of fission products(FPs) and transuranium(TRU),while an MFFR has a larger, delayed neutron fraction with smaller changes during the entire operation.

Application of global variance reduction method to calculate a high-resolution fast neutron flux distribution for TMSR-SF1

The solid fuel thorium molten salt reactor(TMSR-SF1) is a 10-MWth fluoride-cooled pebble bed reactor. As a new reactor concept, one of the major limiting factors to reactor lifetime is radiation-induced material damage. The fast neutron flux(E > 0.1 MeV) can be used to assess possible radiation damage. Hence, a method for calculating high-resolution fast neutron flux distribution of the full-scale TMSR-SF1 reactor is required. In this study,a two-step subsection approach based on MCNP5 involving a global variance reduction method, referred to as forward-weighted consistent adjoint-driven importance sampling, was implemented to provide fast neutron flux distribution throughout the TMSR-SF1 facility. In addition,instead of using the general source specification cards, the user-provided SOURCE subroutine in MCNP5 source code was employed to implement a source biasing technique specialized for TMSR-SF1. In contrast to the one-step analog approach, the two-step subsection approach eliminates zero-scored mesh tally cells and obtains tally results with extremely uniform and low relative uncertainties.Furthermore, the maximum fast neutron fluxes of the main components in TMSR-SF1 are provided, which can be used for radiation damage assessment of the structural materials.

Neutronics analysis for MSR cell with different fuel salt channel geometries

The neutronic properties of molten salt reactors(MSRs)differ from those of traditional solid fuel reactors owing to their nuclear fuel particularity.Based on the Monte-Carlo N particle transport code,the effects of the size and shape of the fuel salt channel on the neutron physics of an MSR cell are investigated systematically in this study.The results show that the infinite multiplication factor(k?)first increases and then decreases with the change in the graphite cell size under certain fuel volume fraction(FVF)conditions.For the same FVF and average chord length,when the average chord length is relatively small,the k?values for different fuel salt channel shapes agree well.When the average chord length is relatively large,the k?values for different fuel salt channel shapes differ significantly.In addition,some examples of practical applications of this study are presented,including cell selection for the core and thermal expansion displacement analysis of the cell.

Neutronics physics analysis of a large fluoride-salt-cooled solidfuel fast reactor with Th-based fuel

Fast reactors based on thorium fuel have enhanced inherent safety. Fluoride salt performs well as a coolant in high-temperature nuclear systems. In this paper,we present a reference core for a large fluoride-salt-cooled solid-fuel fast reactor(LSFR) using thorium–uranium fuel cycle. Neutronics physics of the LSFR reference core is investigated with 2D and 3D in-core fuel management strategy. The design parameters analyzed include the fuel volume fraction, power density level and continuous removal of fission products with 3D fuel shuffling that obtains better equilibrium core performance than 2D shuffling. A self-sustained core is achieved for all cases,and the core of 60% fuel volume fraction at 50 MW/m^3 power density is of the best breeding performance(average breeding ratio 1.134). The LSFR core based on thorium fuel is advantageous in its high discharge burn-up of 20–30% fissions per initial heavy metal atom, small reactivity swing over the whole lifetime(to simplify the reactivity control system), the negative reactivity temperature coefficient(intrinsically safe for all cases) and accepted cladding peak radiation damage. The LSFR reactor is a good alternative option for the deployment of a self-sustained thorium-based nuclear system.