Characterization of Mechanical Strengths for Simulated High-Level Waste Forms
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CHARACTERIZATION OF MECHANICAL STRENGTHS FOR SIMULATED HIGH-LEVEL WASTE FORMS Hiroshi Igarashi and Takeshi Takahashi Power Reactor & Nuclear Fuel Development Corp.(PNC) 4-33 ,Muramatsu, Tokai-mura,Ibarakl,319-11,JAPAN ABSTRACT Waste forms have been developed and characterized at PNC (Power Reactor and Nuclear Fuel Development Corporation)to immobilize high-level liquid waste generated from the reprocessing of nuclear spent fuel. Mechanical strength tests were excecuted on simulated solidified highlevel waste forms which were borosilicate glass and diopside glass-ceramic. Commercial glass was tested for comparison. Measured strengths were three -point bending strength,uniaxial compressive strength,impact strength by falling weight method,and Vickers hardness. Fracture toughness and fracture surface energy were also measured by both notch-beam and indentation technique. The results show that mechanical strengths of waste glass form are similar and that the glass ceramic form has the higher fracture toughness.
INTRODUCTION Waste forms should be as consolidated and monolithic as possible when they are subjected to static or impact force during handling,transportation ,storage and the processes in the repository [1]. Fracturing of waste forms increases their surface areas which are potentially relevant to leaching. Various methods can be applied for the evaluation of mechanical strength of waste forms. Bending and compressive tests are applicable to brittle materials. Vickers hardness test is also used as a simple method,although the mechanism of indentation has not been established for glass [2]. The fracture mechanics approach has been applied to evaluate the mechanical properties of waste forms [3]. Measuring or estimating fracture toughness by Vickers indentation has been widely applied for more than a decade. This fracture toughness estimation technique was published by Evance and Charles[4]. The indentation test was applied to estimate the fracture toughness of simulated nuclear waste forms (5]. Impact tests were conducted on waste forms and the size distribution of crushed matrial was analyzed to evaluate the amount of respirable fines[6]. The increase of surface area,however, has not been directly measured on the crushed sample in many cases,but estimated from the size distribution. In this paper,the mechanical strengths of waste forms are summarized for several types of tests. Several test methods were applied to our waste forms and the results are reported and discussed. SIMULATED SOLIDIFIED WASTE FORMS Mechanical strength tests were excecuted on five glasses and one glass -ceramic which have been developed at PNC. Commercial glass (Pyrex No.7740) was also tested to compare the strengths of waste forms with those of commercial glass. Indentation test was performed with a commercial soda-lime -silicate glass(wt%, 71.4 S10 2 , 13.7 Na2 O, 7.1 CaO, 1.4 A12 0 3 and others), because the crack was not visible for Pyrex. The compositions of waste forms are listed in Table I. The reference glass in this test is P0545
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