铅冷行波堆堆芯物理设计及中子学特性分析

行波堆是一种先进的核能系统,可以通过堆内易裂变核素和可转换核素的优化布置,在寿期内能够保持易裂变核素的总量恒定从而维持堆芯有效增殖因子稳定。铅基材料作为冷却剂不仅具有优良的热工性能和化学安全特性,而且具有更低的中子慢化能力和更小的俘获截面,尤其是208Pb,因此采用208Pb冷却的行波堆具有更优的物理性能。本文提出了一种208Pb冷却的行波堆堆芯初步设计方案,并使用Super MC程序对方案进行计算和分析,其有效增殖因子(keff)在寿期内变化较小,稳态时为1.02左右,功率分布曲线随时间沿着轴向移动。其次,基于该堆芯设计方案,研究了不同点火区长度和富集度以及反射层材料对铅冷行波堆堆芯性能的影响。结果表明,点火区长度和富集度对铅冷行波堆稳态有效增殖因子无明显影响,但对功率分布影响较大;反射层材料对堆芯影响较大,208Pb作为反射层时,稳态时堆芯有效增殖因子最大,堆芯物理性能最佳。     

氟锂铍熔盐热中子散射效应对熔盐堆中子学性能的影响

氟锂铍(FLiBe)熔盐作为液态熔盐堆的冷却剂和载体盐，具有一定的慢化性能，其热中子散射数据影响熔盐堆的中子学性能，进而影响熔盐堆物理设计和安全运行。基于通用蒙特卡罗粒子输运程序分析了液态FLiBe熔盐的热中子散射数据对65 MW熔盐堆堆芯中子能谱、不同能谱下有效增殖因数k_eff、核素反应率、温度反应性系数等中子学性能的影响。研究结果表明：考虑FLiBe熔盐热散射效应，堆芯中子能谱变硬，导致²³⁵U裂变反应率和k_eff变小，燃料的温度反应性系数中多普勒系数减小0.28×10^-5 K^-1，而密度反应性系数几乎无变化。当堆芯由热谱转变为相对较快的中子能谱时，FLiBe熔盐热散射效应导致²³⁵U裂变率减少的变化量降低，k_eff的下降幅度从9.2×10^-4变为2×10^-4。因此，熔盐堆堆芯物理计算需开展FLiBe熔盐的热中子散射数据影响的量化。     

小型自然循环钠冷堆堆芯初步设计研究

提出了一种适用于分布式发电系统的小型自然循环钠冷堆AMTEC系统。通过对堆芯的临界计算和热工水力分析,研究了堆芯燃料装载量不变情况下,芯块半径、燃料棒长度和圈数对堆芯有效增殖因数k_eff、堆芯压降和传热的影响。同时分析了不同额外停堆裕量下,B₄C吸收层厚度和堆芯初始剩余反应性随燃料棒圈数的变化关系。计算结果表明：保持堆芯当量直径和冷却剂通道总截面积不变的情况下,减少燃料棒圈数和活性区长度不仅可增加k_eff,且能降低堆芯压降;为提高额外停堆裕量需增加吸收层厚度,但降低了堆芯初始剩余反应性,不利于电厂的经济性。     

长寿命小型自然循环铅基快堆燃料选型

针对铅基快堆长寿命、小型化、自然循环的设计目标，构建铅基快堆堆芯模型并开展燃料选型研究，选取U-Pu、Th-U循环燃料及氧化物、氮化物、碳化物、金属燃料，分析比较了不同燃料的物性参数、在不同能谱条件下的堆芯物理特性。结果表明：在偏软能谱中，Th基燃料堆芯增殖能力更强，反应性系数负值更大，热工安全裕量更大、裂变产物容留能力更强；PuN-ThN燃料堆芯燃耗特性最佳，可在较疏松栅格条件下获得较强增殖能力，减少燃料装载量，确保固有安全性，兼顾堆芯长寿命、小型化、自然循环设计要求；但堆芯有效缓发中子份额较小，不利于反应性控制。     

钠冷氧化物燃料快堆嬗变MA研究

研究了次量锕系核素(MA)在钠冷氧化物燃料快堆中嬗变的基本物理特性。结果表明,MA核素加入堆芯燃料中后对堆芯动态参数和反应性反馈会产生显著的影响,如:βeff会有所减小、多普勒负反馈会显著减弱以及钠空泡反应性正反馈会显著增强。添加MA所带来的收益是燃耗反应性损失减小,且一定量的MA被嬗变掉,同时MA裂变也有相应的能量产出。MA嬗变的本质在于MA的焚毁,MA的焚毁比消耗与其所占全堆的裂变份额(包括由其转换的238Pu的裂变)成正比,为此相同MA裂变份额下的堆芯安全参数成为MA嬗变快堆设计的关键点。研究表明,堆芯小型化能够有效地减小堆芯的钠空泡反应性正反馈,同时对MA的焚毁比消耗影响较小。     

长寿命小型自然循环铅基快堆燃料选型

针对铅基快堆长寿命、小型化、自然循环的设计目标,构建铅基快堆堆芯模型并开展燃料选型研究,选取U-Pu、Th-U循环燃料及氧化物、氮化物、碳化物、金属燃料,分析比较了不同燃料的物性参数、在不同能谱条件下的堆芯物理特性。结果表明:在偏软能谱中,Th基燃料堆芯增殖能力更强,反应性系数负值更大,热工安全裕量更大、裂变产物容留能力更强;PuN-ThN燃料堆芯燃耗特性最佳,可在较疏松栅格条件下获得较强增殖能力,减少燃料装载量,确保固有安全性,兼顾堆芯长寿命、小型化、自然循环设计要求;但堆芯有效缓发中子份额较小,不利于反应性控制。     

可增殖快谱超临界水冷堆物理初步设计计算

建立改进型快谱超临界水冷堆(SCFR-M)堆芯模型,探讨点火区燃料棒直径和增殖区水棒直径对堆芯转换比的影响,得到合理的燃料组件设计形式。设计并计算6种不同堆芯布置的反应堆增殖特性和空泡反应性,并分析燃料中235U和239Pu成分对堆芯转换比和空泡系数的影响,提高了转换比;研究燃料成分对堆芯转换比的影响。结果表明:减小氢原子数与重金属原子数之比(H/HM),增加堆芯增殖燃料组件数目并采用合理布置可满足堆芯负空泡反应系数,且可以提高堆芯转换比;降低燃料中Pu同位素质量分数可以使堆芯转换比大幅增加,同时使堆芯的空泡反应性系数负值更大;当点火燃料组件采用Pu同位素质量分数为20.8%的MOX燃料,增殖燃料组件采用0.2%富集度235U的贫铀燃料,6号设计方案可以使堆芯的初始转换比达到1.03128,且空泡反应性系数为负,初步达到超临界水冷快堆的增殖要求。进一步对堆芯的缓发中子有效份额、能谱、中子注量率、功率分布进行计算,分析研究增殖堆芯的物理特性。     

径向倒料式驻波堆堆芯概念设计

本工作在综合分析日本CANDLE堆和美国TerraPower公司设计的TP-1堆的基础上,提出沿径向倒料的驻波堆堆芯设计初步方案,通过高、低富集度组件在堆芯的混合布置展平功率,降低了堆芯的功率峰因子和组件的最大燃耗深度。通过倒换料,实现了增殖 燃耗波的传递。为能有效地利用行波堆增殖产生的易裂变核素,采用更换包壳的新技术,实现核燃料的持续利用。     

熔盐快堆Th-U燃料循环增殖性能分析

熔盐快堆是当前国际上关注的热点之一,本文基于堆芯结构双流体方案,即裂变熔盐燃料和增殖熔盐介质各自独立冷却循环,利用氟化或氯化熔盐中钍铀重金属盐高温下的高溶解度特性,获得熔盐快堆的高增殖。通过比较钍铀燃料循环熔盐快堆的三种可行性熔盐燃料方案(LiF+ThF_4+UF_4、NaF+ThF_4+UF_4和NaCl+ThCl_3+UCl_3),采用基于反应堆安全分析和设计的综合性模拟程序SCALE(Standardized Computer Analyses for Licensing Evaluation),计算了中子能谱、反应性温度系数,分析了增殖比BR(breeding ratio)受反应堆裂变区、增殖区和ZrC中子反射层的尺寸影响、熔盐中~6Li和~(35)Cl同位素丰度的影响,以及熔盐密度误差对BR计算值的准确性影响、易裂变核素随反应堆运行时间演化等。在钍铀燃料循环熔盐快堆中,通过优化处理得到三种熔盐燃料方案的增殖比BR约为1.2。     

超临界轻水冷却快堆的增殖比分析

本研究的目的是分析超临界压力轻水冷却快堆（SFPR）的增殖比和设计一个SFPR增殖堆芯。分析了堆芯参数对增殖比的敏感性。堆芯设计采用耦合的二维R-Z中子学和多通道热丁水力计算方法。对增殖比具有高敏感性的参数是燃料棒直径和空心柱状增殖燃料的冷却剂管直径。空心柱状燃料组件是指冷却剂在管内流动、燃料容纳在管外的“壳内管”燃料组件。为了增加重金属份额，考虑采用空心柱状增殖燃料。调换燃料和冷却剂的位置以增加空心柱状增殖燃料区内的重金属份额。带有棒状燃料增殖区的SFPR的增殖比为1．021，带空心柱状燃料增殖区的增殖比为1．034。当点火区和增殖区都由空心柱状燃料元件构成时，由于燃料体积份额高增殖比可达1．046。采用空心柱状燃料堆芯，反应堆功率也增加了。但即使点火区和增殖区都由棒状燃料组成，SCFR仍然可以是增殖堆。     

径向步进倒料行波堆的数值研究

行波堆是一种可实现自持增殖-燃耗的新概念快堆,它可直接使用天然铀、贫铀、钍等可转换核材料,实现非常高的燃料利用率。基于行波堆的原理,提出了具有现实应用价值的径向步进倒料行波堆的概念,并将其与典型钠冷快堆的设计相结合,采用数值方法对由外而内的径向步进行波堆二维渐近稳态特性进行了研究。计算结果表明:渐近keff随倒料循环周期近似抛物线分布,而渐近燃耗随倒料循环周期线性增长,满足临界条件的倒料循环周期中最大燃耗可达38%;堆芯功率峰随着倒料循环周期的增长,从燃料卸出区(堆芯中心)向燃料导入区(堆芯外围)移动,功率峰值逐渐降低,在高燃耗情况下,靠近堆芯中心的轴向功率分布呈M形。     

行波堆堆芯方案设计研究

本文对行波堆燃料组件、堆芯中子学和热工水力方案进行了设计优化,分析了行波堆堆芯方案的主要性能参数。结果表明,优化后的堆芯方案具有明显的增殖焚烧特性,堆芯最大线功率小于500 W/cm,峰值燃耗水平低于30%,燃料中心最高温度低于熔点。该设计方案一方面充分兼顾了现实工艺水平,另一方面实现了行波堆的基本特点。该方案的设计优化指出了典型行波堆设计的初步方向。     

Feasible Region of Design Parameters for Water Cooled Thorium Breeder Reactor

The performances of a light water cooled thorium breeder reactor have been investigated. A feasible region of fresh fuel enrichment and moderator to fuel ratio (MFR) is found to satisfy the constrains of criticality, breeding, and negative void coefficient for several burnups of discharged fuel. The equilibrium fuel cycle burnup calculation has been performed which is coupled with the cell calculation. The MFR is changed to investigate its effect to the breeding capability and void reactivity coefficient profile for different average discharged burnups. For moderated cases, the conversion ratio (CR) decreases with increasing burnup and MFR. The ratio of fissile inventory in equilibrium core to the initial fissile loading (FIR) has the maximum value at certain burnups depending on the MFR and its value increases with the decreasing MFR. Considering to the breeding capability of the reactor, for burnups of equal to 30 GWd/t or higher, the MFR ≤ 0.3 is needed. For the larger MFR and lower burnups, the void reactivity coefficient becomes more negative with an increasing void fraction. The most negative value of the void reactivity coefficient is obtained at MFR = 0:3.     

双面慢化环形燃料反应堆物理实验

环形燃料零功率反应堆是首个双面慢化环形燃料作为核燃料的反应堆。本文采用周期法、落棒法获取环形燃料零功率反应堆的临界参数、控制棒价值、元件价值、含Gd元件的反应性效应等关键参数,对环形燃料零功率反应堆的物理性能进行实验研究,验证环形燃料反应堆堆芯物理设计计算程序。结果表明：根据外推过程确定堆芯临界装载环形燃料元件96根,实心燃料元件172根,此时k_eff为1.000 40,堆芯调节棒价值为-247.5 pcm,安全棒价值为-1 358.4 pcm;元件价值与理论值平均偏差为1.3 pcm,含Gd元件反应性效应与理论值平均相对偏差为8.8%。本文结果为环形燃料的工程化设计程序提供关键数据支撑。     

Preliminary study on feasibility of large and small water cooled thorium breeder reactor in equilibrium states

Fuel breeding is one of the essential performances for a self-sustaining reactor system which can maintains the fuel sustainability while the reactor produces energy and consumes the fissile materials during operation. Thorium cycle shows some advantageous on higher breeding characteristics in thermal neutron spectrum region as shown in the Shippingport reactor and molten salt breeder reactor (MSBR) project. In the present study, the feasibility of large and small water cooled thorium breeder reactors is investigated under equilibrium conditions where the reactors are fueled by ²³³U–Th oxide and they adopts light water coolant as moderator. The key properties such as required enrichment, breeding capability, and initial fissile inventory are evaluated. The conversion ratio and fissile inventory ratio (FIR) are used for evaluating breeding performance. The results show the feasibility of breeding for small and large reactors. The breeding performance increases with increasing power output and lower power density. The small reactor may achieve the breeding condition when the fuel pellets' power density of about 22.5 W/cm³ and burnup of about 20 GWd/t.     

铅冷快堆嬗变次锕系核素对安全性的影响研究

铅冷快堆可用于对乏燃料中部分次锕系（MA）核素进行后处理,为研究MA核素的添加是否会影响反应堆安全性能,本文设计了3种MA核素添加方式,分析研究了MA核素在铅冷快堆中嬗变对堆芯临界性能、堆芯寿期和燃料温度系数的影响。结果表明,MA核素的添加会对堆芯临界性能产生影响,使堆芯初始临界性能下降;镀层和混合燃料添加方式对铅冷快堆的寿期有明显的延长,嬗变棒添加方式根据添加位置不同对堆芯寿期的影响不同;MA核素的添加会引起燃料温度系数的改变,但燃料温度系数始终为负。本文提出的3种添加方式均可行,但是嬗变棒添加方式需要注意嬗变棒位置对堆芯寿期的影响,不建议采用较为集中的嬗变棒分布方式。      

Uranium-based TRU multi-recycling with thermal neutron HTGR to reduce environmental burden and threat of nuclear proliferation

To reduce environmental burden and threat of nuclear proliferation, multi-recycling fuel cycle with high temperature gas-cooled reactor has been investigated. Those problems are solved by incinerating trans-uranium (TRU) nuclides, which is composed of plutonium and minor actinoid, and there is concept to realize TRU incineration by multi-recycling with fast breeder reactor. In this study, multi-recycling is realized even with a thermal reactor by feeding fissile uranium from outside of the fuel cycle instead of breeding fissile nuclide. In this fuel cycle, recovered uranium and natural uranium are enriched and mixed with recovered TRU to fabricate fresh fuels.

The fuel cycle was designed for a gas turbine high temperature reactor (GTHTR300). Reprocessing is assumed as existing reprocessing with four-group partitioning technology.

As a result, the TRU nuclides excluding neptunium can be recycled by the proposed cycle. The duration of potential toxicity decaying to natural uranium level can be reduced to approximately 300 years, and the footprint of repository for high-level waste can be reduced by 99.7% compared with the standard case. Surplus plutonium is not generated by this cycle. Moreover, incineration of TRU from light water reactor cycle can be performed in this cycle.     

Variations in Neutronic Characteristics Accompanying Burnup in a Large Fast Breeder

Burnup calculations based on one-dimensional slab model approximation have been performed to determine the variations occurring in the neutronic characteristics of a pancake-shaped 1,000 MWe sodium-cooled fast breeder when operated under a specified refueling scheme.

The fissile plutonium enrichment [fiss.Pu/(Pu+U)] of the initially loaded fuel is 18.0%. It proves from the present calculations that the partial replacement of spent fuel according to the specified scheme requires use of fresh fuel containing 21.6% fissile plutonium in order to prevent the decline of reactivity with progress of refueling cycles. The above enrichment of the replacement fuel will assure equilibrium of the neutronic characteristics after about 5 years of operation. Thus, unless the refueling charges are provided with fissile plutonium enrichment higher than that of the initially loaded fuel, the state of the reactor will soon fall below criticality.

When the refueling cycle is repeated with fuel of the above specified enrichment, the breeding ratio will decline with progress of operation, from 1.24 in the initial state to 1.14 in the equilibrium state.

At the same time, both sodium void effect and Doppler coefficient will tend toward more unfavorable values, the former from ?0.083Δk/k% to ?0.068Δk/k% (calculated for cases of complete sodium removal from core), and the latter from ?0.0075T-dk/dT to ?0.0051T-dkldT (with sodium). Thus, reactor safety is foreseen to be gradually encroached as the operation progresses.     

Impact of Resonance Treatment on Minor Actinide Incineration in a D–T Thorium Fusion Concept

Resonance treatments have an essential role to reliable neutronic calculations with different neutronic parameters. In this study presents the effect of resonance treatment and various tritium breeder materials on the incineration of the nitride fuels containing minor actinide mixed thoria in the Deuterium–Tritium fusion driven hybrid reactor as time dependent. Neutron transport calculations under resonance treatment and without resonance treatment are performed by using XSDRNPM/SCALE 5 codes. The impact of resonance treatments and various tritium breeder materials on tritium breeding, energy multiplication, total fission rate (∑_f), cumulative fissile fuel enrichment, fissile fuel breeding, average burn up values are comparatively investigated. It is observed that the neutronic results affect from both resonance treatment and the tritium breeder materials as time dependent.