Kilopower空间堆掉落事故临界安全问题研究

美国Kilopower空间堆在掉落事故下的k_eff不满足我国现行空间堆掉落临界安全要求。该反应堆在掉落过程中，若反射层外围的B₄C脱落，则存在瞬发超临界的严重安全隐患。针对此问题，本文对反应堆方案进行调整，提出3种解决方案，各方案均可满足掉落临界安全要求。此外，为研究各方案的优劣，从尺寸、质量、物理和热工运行特性等方面对各方案进行综合比较，提出了最优建议方案。     

Sectored Compact Space Reactor (SCoRe) concepts with a supplementary lunar regolith reflector

Design concepts of the Sectored Compact Space Reactor for Small power (SCoRe-S) have been developed for the avoidance of single-point failures in reactor cooling and energy conversion and a wide range of thermal powers. These modular, fast neutron spectrum, lithium cooled reactors with 16.0 cm thick BeO radial reflector are designed for at least +$2.00 hot-clean excess reactivity, and with a sufficient reactivity shutdown margin. They employ ¹⁵⁷GdN additives in the UN fuel and a 0.10 mm thick coating of ¹⁵⁷Gd₂O₃ on the outer surface of the reactor vessel to ensure that the bare reactors, when submerged in wet sand and flooded with seawater following a launch abort accident, remain at least ?$1.00 subcritical. In addition to identifying the smallest SCoRe-S concept that satisfies the design reactivity requirements, the benefit of using a lunar regolith as a supplementary reflector to decrease the thickness of the BeO radial reflector and hence, the launch mass of the SCoRe-S concepts for a lunar outpost is investigated. Calculations performed using MCNP5 confirmed that SCoRe-S₇ with a 16 cm thick BeO reflector is the smallest to satisfy the stated reactivity requirements. Results also show that a lunar regolith reflector alone is inadequate for this reactor to achieve a critical state at the beginning of life. However, when the regolith is used in conjunction with a BeO reflector of a reduced thickness, this reactor not only becomes critical, but also satisfies the reactivity design requirements at a significantly reduced launch mass. Using a supplementary reflector of regolith decreases the thickness of the BeO reflector for the SCoRe-S₇ from 16 cm to 8.0 cm, and to 5.7 cm for the SCoRe-S₁₁ of the largest core. The resulting decreases in the launch mass of the SCoRe-S concepts are ～34% or 150–200 kg.     

CERMET-SNRE堆芯物理计算分析

核火箭发动机功率高、寿命长、比冲大,在执行深空探测和星际航行任务时具有不可替代的优势。小型化是核火箭发动机的一个重要趋势,基于此提出了一种使用钨基金属陶瓷燃料的小型核火箭发动机（CERMET-SNRE）堆芯方案,并采用蒙特卡罗程序（MCNP）进行了精确建模,计算了相关物理参数。计算分析结果表明：CERMET-SNRE堆芯能谱硬,燃耗浅,后备反应性足够,功率分布合理,控制鼓与安全棒价值足够,发射掉落事故下有效增殖因数小于0.98,堆芯方案合理,满足设计要求。     

Sensitivity analyses of the use of different reflector materials on the neutronics parameters of Tehran research reactor

In this paper, the effect of changes in neutron reflector type on neutronics parameters of Tehran research reactor is analyzed. In this study, at first, calculations for the HEU and LEU fuel configurations of the reactor core in which the light water is used as a neutron reflector in the core is done. Then, by using the reflectors such as graphite, beryllium and heavy water, changes on the neutronic parameters are examined. The results show that by altering the reflector, at HEU core configuration (compared with LEU), more changes appear in parameters such as neutron multiplication factor, average fast and thermal neutron flux, excess reactivity and shut down margin. Moreover, at LEU core configuration, changes are tangible specifically on parameters of cycle length and power peaking factor. In addition, the evaluated fuel temperature coefficient of reactivity is greater at HEU than LEU, while the temperature alteration of fuels represented greater influence on reactivity at LEU configuration.     

杂质硼在高温气冷堆中的燃耗特性

在球床式高温气冷堆的堆芯和石墨反射层中,不可避免地含有少量杂质硼。硼杂质的存在及其燃耗会对反应堆的反应性产生影响。对于多次通过的球床堆芯,根据燃料元件的运行历史计算所有元件的硼燃耗,对于中子注量率差别较大的反射层,分区计算了硼燃耗。再采用微扰理论,计算燃耗过程中硼反应性价值的变化。计算结果表明,硼杂质燃耗很快,因此,硼杂质对反应性的影响降低很快。     

Reactivity control options of space nuclear reactors

This paper compares two ex-core control options of the gas-cooled Submersion Subcritical Safe Space (S^4) reactor with a fast neutrons energy spectrum: (a) rotating BeO drums with 120° thin segments of enriched B₄C in the BeO radial reflector; and (b) sliding segments in the BeO radial reflector. Investigated are the effects on the beginning-of-life (BOL) excess reactivity, reactivity depletion rate and operation life, and the spatial neutron flux distributions and fission power profiles in the core. Also investigated is the effect of reducing the thickness of the enriched B₄C segments in the control drums on the BOL excess reactivity, when one or two of the 6 drums are stuck in the shutdown position. Reducing the thickness of the B₄C segments from 0.5 mm to 0.238 mm, with one drums stuck in the shutdown position, increases BOL cold and hot-clean excess reactivity from +$1.71 and +$0.47 to +$2.38 and +$0.89, respectively. These reactivity values are almost identical to those of the reactor with one of the six reflector segments stuck open in the shutdown position. Results also showed that the control options made little difference in the reactor performance. The power peaking in the reactor core with sliding reflector segments is slightly lower and the spatial power profiles are relatively flatter. The operation life of the reactor with a sliding reflector segments control, when operating at a nominal thermal power of 471 kW, is only 22 full power days longer than with rotating drums control.     

空间锂冷概念快堆堆芯中子学特性研究

本文研究了一种空间锂冷概念快堆的堆芯中子学特性。反应堆燃料采用氮化铀,冷却剂采用⁷Li液态金属,主要结构材料采用W-25%Re。反应堆的控制靠反射层内的控制鼓来实现。建立了程序的计算模型,通过计算和分析,给出了堆芯的主要尺寸和物理参数,计算了堆芯的控制鼓价值、燃耗和功率分布。分析了堆芯中Re的谱移吸收特性和满功率运行7 a不需换料的性能,谱移吸收特性能确保反应堆在发射失败浸在水或湿沙中时处于次临界状态。     

Investigation of BeO as a reflector for the low power research reactor

Calculations of the fuel burnup, core excess reactivity, and the reactivity worths of the top beryllium shim plates for two reflector types (beryllium and beryllium oxide (BeO)) in the Miniature Neutron Source Reactor (MNSR) have been presented in this paper using the GETERA and MCNP4C codes. The results showed that the reactor infinity multiplication factors were 1.7030 and 1.6824, the core unadjusted excess reactivities were 31.9 and 5.0 mk, and the reactivity worths of the top beryllium shim plates were 22 and 19 mk for the BeO and Be reflectors respectively. Finally, using the beryllium oxide instead of the existing Be reflector in the MNSR reactor increased the core excess reactivity and reactor operation time.     

Parametric tests and measurements after shimming of a beryllium reflector in a miniature neutron source reactor (MNSR)

After 10 years operation of Pakistan research reactor-2 (PARR-2), a miniature neutron source reactor (MNSR), a beryllium reflector was added to compensate the loss of reactivity due to burn up of fuel. Beryllium shim plates have been placed at the top of the core in a tray provided for this purpose. The control rod was dismantled and withdrawn from the core and the reactor was made subcritical with cadmium shimming. To monitor the neutron population during this experiment, two additional neutron monitoring channels based on BF₃ were installed around the core. Measurement of important Parameters such as effective delayed neutron fraction, decay constant, excess reactivity, control rod worth, temperature coefficient of reactivity, thermal neutron flux, cadmium ratio was done after the addition of Be reflector. Increase in reactivity worth due to addition of Be shim was 1.0 mk.     

Optimization of the reflector design of the Syrian MNSR

The possibility of optimizing the dimensions and material of the miniature neutron source reactor of Syria was investigated based on a 3-D model of the reactor comprehensive of all reactor components. It was shown that the reflector can be optimized in terms of materials to have 10.00–11.50 mk of initial excess reactivity available at the start-up of the reactor if the side reflector material were substituted by the bottom reflector material. Otherwise if the initial excess reactivity of ～4.00 mk were to be maintained the saved material would be about 15.000 kg.     

Critical neutron heating in the control drums of a dual purpose thermionic space reactor for power and propulsion

The critical neutron heating in the reflector control drums is investigated for a fast incore thermionic space craft reactor for power and nuclear propulsion. The reactor is fueled with uranium carbide (UC) and controlled with the help of rotating B₄C drums imbedded into the beryllium reflector. While the neutron heating in the drums would not require a cooling mechanism in the power phase, the heat generation during the thrust phase obliges cooling for a nuclear thermal thrust around F = 5000 N by a specific impulse of 670 s⁻¹ at an hydrogen exit temperature around 1900°K. With a beryllium reflector without extra cooling measures, thermal thrust must be kept F < 2500 N to relieve the thermal load in the reflector. On the other hand, a reflector made of BeO may withstand a thermal load for a nuclear thermal thrust of F = 5000 N. The neutronic analysis has been conducted in S₁₆-P₃ and S₈-P₃ approximation with the help of one- and two-dimensional neutron transport codes ANISN and DORT, respectively. A reactor control with boronated reflector drums (drum diameter = 14 cm) at the outer periphery of the radial reflector of 16 cm thickness would make possible reactivity changes of Δk_{eff = 13.55%}—amply sufficient for a fast reactor—without a significant distortion of the fission power profile during all phases of the space mission. Calculations are conducted for a reactor with a core radius of 22 cm and core height of 35 cm leading to power levels around 50 kW_el.     

微型中子源堆低浓化堆芯的探讨

通过对２３５Ｕ富集度为１９．９％的ＵＯ２和Ｕ３Ｓｉ２－Ａｌ的弥散体２种燃料进行物理计算，从中筛选出了优化的堆芯方案，并对其静态物理参数，诸如有效倍增因子、绝对中子通量密度、上铍反射层反应性价值、反应性温度系数、控制棒价值等进行了计算。     

Conceptual design of a small nuclear reactor for large-diameter NTD-Si using short PWR fuel assemblies

A design of a small nuclear reactor for a large-diameter NTD-Si using a conventional Pressurized Water Reactors (PWR) full-length assembly was proposed in previous works. The height of the full-length assembly was 400 cm, and the overall size of the reactor and reflector around the core became large. In addition, the irradiation channel became very long, making handling of the Si ingots in the channel more difficult. The use of a short PWR fuel assembly, with a height of 100 cm, was considered in the current work. With the shorter assembly, the design of the reactor became compact and more practical. Gd₂O₃ and control rods were used to suppress excess reactivity. Criticality, neutron transport, and core burn-up calculations were performed using the MVP/GMVP II code and MVP-BURN code. Steady-state single-channel thermal hydraulic analyses were also performed. The calculation results showed that the reactor could be critical over 1200 days, and that heat removal from core was possible under 1 atm operating pressure. Large-diameter ingot up to 20 cm in height could be doped with sufficient uniformity. The reactor semiconductor production rate was estimated, and varied between 48 tons/year and 70 tons/year for the 50 Ω cm target resistivity depending on the position of the control rod.     

Preliminary design study of the ultra long life fast reactor

A preliminary design study of the ultra long life fast reactor has been performed. In the present study, a parametric survey was carried out for three regioned spherical reactors with metallic fuels. Changes of multiplication factor, conversion ratio, and peak power density during burnup were analyzed. The calculation results showed that 40 years reactor life time without refueling can be achieved by choosing appropriate values for the initial plutonium enrichment, fuel volume fraction, and size of each corresponding region. For this design the maximum excess reactivity can be reduced to a few percent by shifting the position of the power peak from the outer to the inner region of the core along burnup. Especially, dividing core and blanket into two regions, respectively, and adjusting parameters of each region reduced the excess reactivity during burnup to below 0.2%Δk.     

星球表面用核反应堆临界安全分析

核反应堆电源具有寿命长、可全天候工作等特点,可作为星球表面及其他深空探测任务的电源。针对星球表面用核反应堆电源在发射过程中重返地面的临界安全问题,提出了星球表面用核反应堆的临界安全分析要求、分析假设与模型,并对反应堆临界安全特性及采取的临界安全措施进行了计算分析。计算结果表明,不同假设掉落环境下的星球表面用核反应堆的有效增殖因数均小于0.98,满足临界安全要求。反应堆通过采用Mo-14%Re合金结构材料、设置相对较厚的堆芯反射层以及在反射层包壳和堆芯外围涂覆Gd₂O₃涂层等措施有利于确保反应堆在事故时处于次临界状态。     

Design concept of self-contained low power reactor master for heat supply

This paper demonstrates technical features and conceptual scheme of innovative self-contained low power reactor MASTER for heat supply. Neutron-physical and thermo-hydraulic characteristics of this reactor are analyzed. The possibility of power self-control and minimization of reactivity swing during fuel burnup are considered.     

空间核反应堆本体参数最优化研究

空间技术是具有重大潜在前景的技术,对国家的科学、国防、政治、经济具有重要意义。为了满足空间条件及发射条件的要求,并使空间核反应堆经济性最大化,对空间核反应堆本体的结构设计方案和参数最优化进行了研究。在调研多种国外空间核反应堆方案设计的基础上,提出了空间核反应堆堆型与堆本体结构设计方案。建立了堆本体数学模型,将设计最优化的工程学问题转化为求解非线性整数优化的数学问题,采用编写Matlab程序语言的方法,利用数学软件求解了最优化问题,在理论上得到了所建立模型的最优化参数设计并探讨了旋转控制鼓数量变化与堆芯燃料半径变化对堆本体总质量的影响。堆本体总质量较初始模型下降了14.3%,为今后完成更进一步的空间核反应堆设计提供了参考。     

The laboratory investigation of the experimental nuclear reactor VVR-S

Results are given in this paper of the laboratory investigation of the characteristics of the experimental reactor VVR-S undertaken with the aim of studying the neutron and physical parameters which are the most important for putting the reactor into operation and for its exploitation. As the result of the experimental work carried out, the critical mass and the maximum and operating fuel charges were found, the compensating capacity of the control and emergency rods was determined, the influence of the various factors (variation in the temperature of the water in the active zone, variations in the properties of the reflector, etc.) on the reactivity was studied, the distributions of neutron density with height and along the radius of the active zone were measured, and the operating time of the control rods was obtained.In conclusion the authors express their gratitude to T. N. Zubarev for discussion of the results and to O. I. Liubimtsev and I. V. Koptev for help in the work.     

Burnable poison for reactivity management in a very high temperature reactor

A physics study has been performed to find the optimal application of burnable poison (BP) for an excess reactivity management in a 600 MWth block-type very high temperature reactor (VHTR). Six potential BP materials (B, Gd, Er, Eu, Sm, Dy) were evaluated for an equilibrium cycle in terms of the major core performance parameters such as the burnup reactivity swing, discharge burnup, fuel and moderator temperature coefficients, and fuel temperature. In addition to the conventional 6-hole BP loading in a fuel block, a 12-hole BP application was also considered in order to accelerate the depletion rate of the BPs. The self-shielding effect of the BP was optimized for a successful management of the excess reactivity by changing the effective diameter of the BP region. Additionally, a mixed BP application of Gd and Er was proposed to make better use of the two BP materials in terms of the reactivity swing and the core temperature coefficients. It has been demonstrated that the burnup reactivity swing over a long cycle period can be reduced from ∼15,000 pcm to 3000–5000 pcm with only a small reduction of the discharge fuel burnup.     

Benchmark analysis of SPERT IV reactor

Benchmark calculations have been performed for SPERT IV D-12/25 core. Experimental data of the core was provided by International Atomic Energy Agency (IAEA). Combination of WIMS/D4 and CITATION codes has been used for performing the neutronic analysis of the reactor. Lattice calculations have been performed through WIMS/D4 while 3-dimensional reactor core has been modeled in CITATION. Ten energy groups were considered for these calculations. Energy wise microscopic cross-sections were generated for fuel, control absorber, control follower, guide tube, grid plate, reflector and structural regions separately of the core using WIMS/D4. Thermal neutron flux profiles at different axial and radial locations of the core were evaluated. Critical position of the control rods, excess reactivity, shut down margin, control rod worth, reactivity feed back coefficients and kinetic parameters of the core were estimated. Reasonable agreement has been found between experimentally determined and the calculated parameters.