The spent fuel was radioactivity. Its matrix was complicated and the content of tin was low. So measurement of tin in spent fuel was difficult. 121 Sn and 126Sn in spent nuclear fuel element were determined by isotope dilution-thermal ionization mass spectrometry(ID-TIMS) using natural standard tin solution as spike. The sample loading techniques of silica gel-tin-phosphate was employed. Ionization filaments heating rate and temperature holding time was optimized. Thirteen signals are collected by retarding potential quadrupole (RPQ), which effectively eliminating isobaric interferences of Te,Sb and CaPO3+ . The content and isotopic abundance of ng/g level of Sn is obtained. The mass concentration of 121 Sn and 126Sn in spent fuel are 5. 5 ng/g and 230. 5 ng/g, measurement uncertainty are 4.2% and 1. 4%(k = 2), respectively.%乏燃料样品基体复杂、具有放射性,裂变产物锡含量低,难以准确测定.本研究以天然锡(Sn)标准溶液为稀释剂,采用同位素稀释-热电离质谱法测定乏燃料元件中121Sn和126Sn裂变产物的含量.热电离质谱测量时采用硅胶-锡-磷酸涂样,优化选择电离带升温速率和温度保持时间,利用阻滞电位四极杆(RPQ)跳峰对13个质量数信号进行数据采集,有效扣除了Te、Sb、CaPO3+多个同量异位素的干扰,获得了ng/g级Sn的含量及同位素丰度测量数据.乏燃料元件中121Sn和126Sn的质量浓度分别为5.5、230.5 ng/g,测量不确定度分别为4.2％和1.4％(k=2).
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