Study on Key Factors of 252Cf Production in Super High Flux Reactor
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摘要: 252Cf核素是反应堆启动和中子活化分析等领域的重要材料，开展252Cf辐照生产方法研究意义重大。252Cf质量数大、转换链长、生产难度大，本文基于铅冷快中子超高通量研究堆重点开展252Cf辐照生产关键技术研究。根据252Cf生产方法的难点，建立高精度核数据库和靶件长寿期模拟计算方法，开展靶件结构及材料设计、中子能谱及中子注量率等关键因素研究。252Cf靶件辐照计算表明，252Cf虽然转换率低，但在辐照靶件结构、中子能谱及中子注量率方面可进行优化设计，从而提高252Cf生产效率；提出通过共振屏蔽优化中子局部能谱的方法，减少核素裂变消耗，从而提高252Cf生产效率。本文阐明252Cf生产机理和关键因素影响规律，并给出辐照生产252Cf的设计论证方向。Abstract: 252Cf is widely used in reactor startup and neutron activation analysis, and it is of great significance to carry out research on irradiation production technology. Production of 252Cf is not easy because of its huge nucleon number and long nuclide transmutation chain. Based on the lead-cooled fast neutron super high flux research reactor, this paper focuses on the key technologies of its irradiation production. According to the difficulty of 252Cf production, a precise nuclide databank and longtime burnup calculating procedure of nuclide production targets are established, and the key factors such as target structure and material design, neutron energy spectrum and neutron flux density are studied. The irradiation calculation of 252Cf target shows that although 252Cf has a low transmutation productivity, it can be improved with appropriate designs of 252Cf target, neutron energy spectrum and neutron flux density, thus improving the production efficiency of 252Cf. A method of optimizing neutron local energy spectrum through resonance shielding is proposed to reduce fission consumption of nuclides, thus improving the production efficiency of 252Cf. This paper expounds the production mechanism of 252Cf and the influence law of key factors, and gives the demonstration direction of 252Cf irradiation production technology design.
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Key words:
- Nuclide production /
- Super high flux reactor /
- 252Cf /
- Resonance shielding
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图 3 核素辐照靶件长寿期模拟程序计算流程图
Figure 3. Longtime Burnup Calculating Flow Chart of Nuclide Production Targets
图 4 不同材料靶件252Cf产量随辐照时间的关系
Figure 4. 252Cf Production of Different Nuclide Production Targets vs. Irradiation Time
图 5 238U靶件主要超铀核素产量随辐照时间的关系
Figure 5. Main Transuranic Nuclide Production of 238U Target vs. Irradiation Time
图 6 252Cf 产量随243Am靶件高度的变化关系
Figure 6. 252Cf Production of 243Am Target vs. Target Height
图 7 243Am、244Cm、245Cm与249Bk的反应截面
Figure 7. (n,γ) Cross Sections of 243Am, 244Cm, 245Cm and 249Bk
图 8 243Am生成252Cf过程中主要核素的总裂变俘获比
Figure 8. Fission per (n,γ) Capture of Main Nuclides from 243Am to 252Cf
图 9 不同慢化能谱下252Cf产量与辐照时间的关系
Figure 9. 252Cf Production with Different Neutron Spectrums vs. Irradiation Time
图 10 245Cm、247Cm及251Cf的裂变俘获比
Figure 10. Fission per (n,γ) Capture of 245Cm, 247Cm and 251Cf
图 12 不同中子注量率水平下243Am靶材252Cf产量
Figure 12. 252Cf Production of 243Am Target with Different Neutron Flux
表 1 244Cm到252Cf核素的损耗源
Table 1. Main Reactions of Nuclide Transmutation from 244Cm to 252Cf
核素 损耗源 244Cm 俘获反应：85%；裂变反应：15% 245Cm 俘获反应：13%；裂变反应：87% 246Cm 俘获反应：83%；裂变反应：17% 247Cm 俘获反应：34%；裂变反应：66% 248Cm 俘获反应：93%；裂变反应：7% 249Cm 半衰期64 min，接近100%经β衰变成249Bk 249Bk 半衰期330 d，1%经β衰变成249Cf，99%俘获生成250Bk 250Bk 半衰期3.2 h，约94%经β衰变成250Cf 249Cf 俘获反应：23%；裂变反应：77% 250Cf 俘获反应：96%；α衰变反应和裂变反应：4% 251Cf 俘获反应：37%；α衰变反应和裂变反应：63% 252Cf 半衰期2.6 a，α衰变反应：3%；自发裂变反应：97% 注：基于接近压水堆中子能谱评估结果 
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表 2 Cm靶件初始核素损耗比较
Table 2. Initial Irradiated Nuclides loss of Cm Targets
核素 核素消耗量/g 消耗量相对变化/% 纯Cm靶件 加入177Hf的Cm靶件 244Cm 0.99 0.91 −8.1 246Cm 0.35 0.34 −2.9 248Cm 0.34 0.34 0
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表 3 Cm靶件主要锕系核素产量比较
Table 3. Important Actinium Nuclide Production of Cm Targets
核素 核素产量/mg 产量相对变化/% 纯Cm靶件 加入177Hf的Cm靶件 245Cm 47.0 50.0 6.4 247Cm 178.1 187.8 5.4 249Bk 27.9 30.0 7.3 251Cf 5.0 6.9 38.4 252Cf 93.0 92.0 −1.1
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