Tailored Perovskite Waste Forms for Plutonium Trapping

Abstract

Perovskite ceramics have been extensively studied as host matrixes for radionuclide entrapment for nuclear waste disposal. As an expansion of these investigations, cerium, neodymium, and plutonium were incorporated into a perovskite phase, ACu 3 FeTi 3 O 12 (A = Nd, Ce, Pu), using sol−gel methods under oxidizing and reducing atmospheres. The targeted materials contained varying levels of Ce 3+ and Nd 3+ on the A site, yielding potential compositions of Nd 1−x Ce x Cu 3 FeTi 3 O 12 (x = 0, 0.1, 0.2, 0.3, 0.4, 0.8). However, interrogation of these materials shows that the maximum Ce 3+ loading is achieved near x ≈ 0.2. A single composition with plutonium was targeted, Nd 0.9 Pu 0.1 Cu 3 FeTi 3 O 12 , in order to properly model more realistic loading levels for a repositorydestined material. These compounds were characterized using powder X-ray diffraction with Rietveld refinements of the structures and by a variety of spectroscopic techniques. The data suggest that, in order to achieve Pu 3+ substitution onto the A sites in the Nd 0.9 Pu 0.1 Cu 3 FeTi 3 O 12 , a reducing atmosphere must be employed. Otherwise, the redox activity of plutonium results in substitution onto multiple sites in the material as well as the formation of secondary phases such as TiO 2 .

Radionuclides from Nature to Nature: Recent Progress in Immobilization of High Level Nuclear Wastes in SYNROC

“…广泛关注 [11][12][13][14][15] 点的不足, 可以提高对核素的包容量和普适性 [16] 。 目前我国在矿物相作为人造岩石固化体方面的 研究也取得了丰硕的成果。兰州大学李玉虹等 [17][18][19] [20][21] 采用加压/烧结的方法, 加入水铝英石, 得到 了稳定的 Cs 凝固产物; 并通过加压/烧结法, 添加 天然的水铝英石和丝光沸石得到稳定废铯吸附剂固 化体。笔者等 [22][23] 从合成、固溶量、微观结构、化 学耐久性等方面对锆石模拟固化 Nd 和 Ce 进行了系 统的研究; 卢喜瑞等 [24] 研究了 Gd 2 Zr 2 O 7 烧绿石固化 Ce、U 等锕系核素的耐辐照能力及其相关性质; 张 魁宝等 [25] 对钙钛锆石、独居石等进行了研究。中国 工程物理研究院 Zhang 等 [26] 研究了固化三价次锕系 Np(Sm)氟磷灰石型固溶体。此外, 中国原子能科学 研究院也研究了烧绿石、钙钛锆石、钛酸盐陶瓷等 陶瓷固化体 [27][28][29][30] [32] Fig. 4 Temperature gradient model of zircon interface by using microwave synthesis [32] 放电等离子烧结(Spark Plasma sintering, SPS)又 称为等离子辅助烧结(Plasma Activated), 是在粉末 颗粒间直接通入脉冲电流进行加热烧结, 具有加热 均匀、升温速度快、烧结温度低(比热压烧结可降低 100~200 ℃)、烧结时间短、生产效率高、致密度高 等特点。近年, 该方法在 SYNROC 固化体烧结方面 展现出良好的工程化前景。Wang 等 [34] 采用该方法 成功在 1600~1700 ℃, 80 MPa, 3 min 条件下, 在 Gd 2-x Nd x Zr 2-y Ce y O 7 (0≤x, y≤2.0)固化体中完成了 Nd 和 Ce 的共掺杂。 熔盐合成法(Molten salt synthesis, MSS)采用低 熔点的一种盐类或多种盐组成低熔点盐类体系作为 反应介质, 合成过程中出现液相, 反应物在熔盐中 有一定的溶解度, 加快了离子的扩散速率, 使得反 应在原子级进行。该法相对于常规固相法而言, 具 有制备方法简单, 不需要复杂的程序和危险的试剂, 能有效降低合成温度和反应时间, 制备的粉体化学 成分均匀、晶体形貌好、物相纯度高、熔盐可重复 使用等优点 [35] , 在 MAX [36] 、MXenes [37] 、二维层状 材料 [38] 、陶瓷固化体 [39][40] 等材料合成方面具有独特 优势。 Wu 等 [39] [48] 利用超高温烧结 技术, 直接在数秒内合成块体陶瓷材料, 大大提高 了材料的合成速度, 改善了材料质量, 见图 5。超高 温烧结技术的特点是温度分布均匀, 加热速度(10 3~ 10 4 ℃/min)和冷却速度(高达 10 4 ℃/min)超快, 并且 烧结温度高(高达 3000 ℃)。 超高的升温速率和超高 图 5 碳热冲击超高温快速烧结 [48] Fig.…”

Interaction of lanthanide and actinide with BaHfO3 perovskite: A case study with cerium and uranium

“…While a country like India adopts a closed fuel cycle approach for efficient utilization of its uranium reserves, resilient materials are still very much required for capturing radionuclides and their ultimate disposal in geological repositories. A wide range of materials encompassing cement, glasses, ceramics (pyrochlore and perovskite), and so forth, have been studied for the same 2 . The most widely explored nuclear waste host still remains borosilicate glass mainly due to its low cost, durability, ease of processing.…”

“…Among ceramics; ABO 3 type perovskite lattice with great structural flexibility 10 has shown several suitable features such as high tolerance to doping, excellent thermal/chemical/mechanical stability, and high resistance towards sintering of substituted metals which make them highly suitable candidates for nuclear waste hosts 11 . Because of the very high coordination number of the A site it can accommodate a large amount of ions with +1, +2, +3, and +4 ionic charge and there are several reports wherein perovskites have been used for immobilization of actinides 2,12–15 …”