富烧绿石人造岩石和锆英石固化模拟锕系废物研究

【作者】 杨建文；

【导师】 罗上庚； 汪德熙；

【作者基本信息】 中国原子能科学研究院 ， 核燃料循环与材料， 2000， 博士

【摘要】 本研究以从高放废液中分离产生的锕系废物为研究对象，采用国际上研究较少的烧绿石为包容锕系核素的主体矿相，系统地进行了富饶绿石人造岩石固化体固化锕系废物的研究，证实了烧绿石具有优越的性能，是包容锕系核素的合适矿相。并初步进行了以天然锆英石为原料制备包容锕系废物锆英石固化体的研究，阐明了此种新的工艺路线的可行性。 研究中以钕（Nd）和铀(U）分别模拟三价和四价锕系核素，设计了包容量为32～50wt％的富烧绿石人造岩石固化体配方，采用的矿相组合为 85wt%烧绿石，5wt％碱硬锰矿和 10wt％的金红石。测试表明，所制备的固化体具有很好的物理性能，高的体积密度(＞5．1g／cm~3),高的硬度(≥947kg/mm~2）和较少的气孔(＜2 ％）。 采用PCT、MCC-l和本研究建立的模拟地质处置条件浸泡方法对固化体的抗浸出性能进行了测试，其质量和元素归一化浸出率均低于或等于富钙钛锆石人造岩石固化体和Synroc-C的浸出率，并且固化体表面所受的侵蚀极小，其主要元素的浸出深度小于100nm，地质介质的存在会加剧固化体中元素（Ti，U）的浸出，但固化体表面仍无明显侵蚀，说明固化体具有较好的抗浸出性能。 利用扫描电镜(SEM）和国际上尚没有应用于人造岩石固化体研究的正电子湮灭技术（PAT）以及国际上新开展的放射热分析（ETA）对固化体的浸出表面进行了研究，结果表明浸出后固化体表面有Ti-o膜形成，使固化体表面致密，Ti-o膜和极耐浸出的钛氧网络结构的共同作用可阻止固化体进一步的侵蚀。浸出机理的研究表明固化体中元素的浸出是一个多因素共同作用的复杂过程，并给出了固化体中主要元素的浸出模型。 采用 XRD、SEM/MDS和 TEM/EDS对实际制备固化体的矿相组合、微观结构、元素分布和矿相化学组成进行了分析。研究结果表明，固 互 ＋回原于 学研究耽俗士研玩止学位论又化体中矿相组合基本上与设计目标一致，烧绿石为主要矿相。在本研究的制备条件下，固化体固相反应较完全、矿相结合致密、孔隙较少，矿相晶粒较小（＜lpm厂 晶相发育较好，结合紧密，晶界极窄。但存在少量包容很少废物离子的团聚体（乏 100 p m入 造成废物离子的不均匀分布．基体中主要由两种不同化学组成的烧绿石组成，存在少量非设计目标相（晶质铀矿和钛铀矿人 团聚体主要由两种不同化学组成的金红石相组成，还存在少量的碱硬锰矿，低包容量时还存在钙钛铝石。通过对矿相化学组成的分析，得出了实际固化体中基体烧绿石相和相对含量较高的金红石和晶质铀矿的化学式，对烧绿石相确定了其离子取代和价态补偿的规律。 利用我院串列粒子加速器，在国内率先开展了重离子辐照模拟固化体a衰变自辐照损伤对固化体的抗辐照性能的研究，结果表明，富烧绿石固化体具有较好的耐辐照性能。X射线衍射（XA13）和透射电镜选区电子衍射（TEM／SAED）分析得到基体烧绿石相的蜕晶质剂量为0．sdpa，比钙钛铝石（．3～0．4dpal高。PAT分析表明重离子辐照的造成的缺陷主要为大的空位团缺陷，蜕晶质后辐照仍使缺陷增加。io和PAT对辐照后样品的退火研究表明，缺陷可在一定程度上得到修复，烧绿石相在900’C之前可恢复其晶体结构，但固化体中辐照所造成的缺陷在1200℃仍没有完全恢复。 对包容模拟铡系元素的铬英石固化体的初步研究表明，以天然铬英石为原料，采用人造岩石的制备工艺，通过固相反应使废物离子包容于桔英石矿相的方案是可行的，所制备的铅英石固化体具有较好的抗浸出性能和耐辐照性能。但是在制备中由于铬英石原料颗粒较大，影响了固相反应的进行，造成固化体的密度较低、孔隙多，这问题今后可以通过降低原料颗粒的尺度和改进制备工艺条件来解决。更多还原

【Abstract】 Pyrochlore as a host phase in synroc for separated actinides fromHLW was systematically studied. Six different formulae with actinidewaste loading 32-50wt% of pyrochlore-rich synroc samples werefabricated and evaluated. The results indicated that pyrochlore is thesuitable host phase for actinides with satisfied properties. Thepreliminary study on zircon waste form for actinide wastes which wasfabricated by using natural zircon as the precursor material was alsocarried out in this study the feasibility of this method wasdemonstrated.For the study of pyrochlore-rich synroc waste forms, neodymium(Nd) and uranium (U) were used as the simulants for trivalent andtetravalent actinides, the designed phase assemblage was 85wt%pyrochlore, 5wt% hollandite and l0wt% rutile. The fabricatedpyrochlore-rich synroc samples had good physical properties with highdensity (>5.1g/cm~3) and Vickers hardness (≥947kg/mm~2), and fewporosities (<2 %). The PCT, MCC-1 and simulated geological leachingtest results showed that the samples were highly durable, with mass lossand elemental nominalized leach rates lower than or equal tozirconolite-rich synroc and synroc-C. The corrosion to the samplesurface was negligible with the matrix elements leaching depth lowerthan 100nm, the leaching of the elements (Ti, U) was enhanced by thegeological media (granite, clay etc.), but there was also no significantcorrosion effects on the sample surfaces. The scanning electronmicroscopy (SEM), positron annihilation technology (PAT) andemanation thermal analysis (ETA) study indicated that amorphous Ti-Omembrane was formed on the surface of the leached samPles, with thehighly leach resistance matrix Ti net they can retard the furthercorrosion to the samPles. The leaching mechanism of elements werevery comPlicated with many influence factrs, the leaching models ofthe main elements were also given in this stUdyThe heaVy ion irradiation technique was used in this study tosimulate the Q -decay self irradiation damage in the waste forms. ThestUdy of radiation effects on pyrochlore-rich synroc samPle showed thatthe saInPle was highly irradiation resiStance, the amorphous dOse fOrmatrix Pyrochlore Phase was 0.5dPa, Which is higher than thezirconolite (0.3~0.4dPa). PAT analyses indicated tha the defects in thesamPles produced by heaVy ion irrallation wer mainly large voids. X-ray dihoeter (XRD) and PAT fOr annalation study of the fullyamorphous samPle showed that the pyrochlore Phase could recover itScrystal StrUCtUr before 900’C, and the defects produced by irradiationwere nOt fully recovered even by annalation at l200C.W, SEWS and transmission electron microscOPy withenergy disPersive sPectrOmeter (TEM/EDS) were used to study thephase assemblage, microStrUctUr, element patitioning and phasechemical comPosition of the pyrochlore-rich synroc samPles. TheresultS showed tha the fabricated saInPles wer highly densified withfew porosity, the phase crystas were finely developed with narrowcrysta bOUnedes. The Pyrochlore phase was the main phase of thesamPles in accordance with the original design. Due tO theinhomogeneity of the fabrication process, ther were few agglomethes(<100 ll m) distributed among the matrix, the agglomer8tes mainlyconsisted of two ldnds of rutile, and a small quantity of hOllandite andzirconolite(low waste loading).There were mainly two kinds ofpyrochlore phase existed in matrix, few unexPeCtCd phases such asuraninite and brannerite also existed in matrix. The chemical formula ofthe phases (Pyrochlore, rutile and uraninite.) were determined by theanalysis of the phase elemental comPositiOn, the ion subStitution andcharge comPensaton rules wer also discussed.The preliminny study on zircon waste form fabricated by usingnatural zircon as Precursor material indicated tha this idea is feasible.The zircon waste form with high leach resistance and irradiatonresistance proPertes was fabri更多还原