Process Simulation And Test On 100-ton Ductile Iron Container For Spent Nuclear Fuel

With the rapid development of nuclear power,there was a huge and rapidly growing demand for spent nuclear fuel storage and transportation containers.Compared with other materials of storage and transportation containers,ductile cast iron spent nuclear fuel containers had a complete body structure,excel lent radiation shielding performance,obvious economy and other advantages.The 100-ton ductile cast iron spent nuclear fuel container has been studied in this project that had a wall thickness of 520mm and a weight of about 130t.The characteristics of container is long solidification time,severe segregation,and large tendency of shrinkage and dispersed shrinkage,meaning that the production technology of ductile cast iron spent nuclear fuel containers is difficult.In this project,by simulating the casting process of 100-ton ductile iron spent nuclear fuel container,designing 45°fan-shaped test block and measuring its solidification temperature field,dissecting the 45° fan-shaped test block and analyzing its micro-structure and properties,the conclusion is as follows:(1)The sand casting process had a solidification time of up to 50.64h,which obviously can not meet the requirements of ductile iron spent nuclear fuel containers;Although the sand and chill casting process had accelerated the solidification speed of container castings,the solidification time was still up to 25.88h,which was also not suitable for the process requirements of ductile iron spent nuclear fuel containers;Using the permanent mould process,the solidification time of the ductile iron spent nuclear fuel container was shortened to 3.49h,and the number and distribution of defects were also the least,so it was determined that the ductile iron spent nuclear fuel container used the permanent mould casting process;(2)Using the self-developed 16-channel temperature measurement system,the temperature field and mold temperature curve of the 45°fan-shape test block were successfully measured;The simulation results were basically consistent with the actual temperature measurement results(The error is about 2%).The current simulation software could be used to optimize the casting process of heavy-section ductile iron spent nuclear fuel containers;(3)In the 45° test block experiment,the final solidification position was the inner 1/4 place,not the center of the test block,and the weakness of impact property appeared in the inner 1/4 place.the study also found that the solidification temperature of the heavy-section ductile iron was not 1147 ℃,but a range of 1080℃～1147℃;(4)In the experimental study of the 45° test block,through a series of quality control measures,the maximum solidification time of the 45° test block has been controlled in 3.42 hours,the Spheroidization rate≥85%,the number of graphite nodule≥50/mm2,and the matrix structure is full ferrite,tensile strength≥371 MPa,yield strength≥233MPa,elongation≥19.5%,-40℃ impact toughness≥5.4J/cm2,all meet the requirements of ductile iron spent nuclear fuel containers,It showed that the properties index of ductile iron spent nuclear fuel containers abroad can be achieved under present domestic technical conditions;(5)The number of graphite nodule has little effect on the conventional mechanical properties such as yield strength,tensile strength,elongation,etc;but has a great effect on the impact property,especially the property of low-temperature at-40℃;In addition to measures such as optimizing raw materials,strictly controlling the content of trace elements,proper spheroidizing treatment and inoculation treatment,measures should also be taken to further accelerate the cooling rate of the casting to solidify it within 3.5 hours to ensure the number of graphite nodule≥50/mm2;(6)After optimizing the casting process of the ductile iron spent nuclear fuel container,The casting process of 300mm permanent mould and 300mm chill was adapted at the body part of the ductile iron spent nuclear fuel container,and 450mm permanent mould and 450mm chill iron process was utilized at the top hot spot part.Such process can not only ensure the solidification of the ductile iron spent nuclear fuel container in 3.5h,but also coordinate the solidification temperature field of the body part and the hot spot to ensure the consistency of the micro-structure and mechanical properties of the ductile iron spent nuclear fuel container.(7)The results of temperature measurement and anatomical analysis of the 45° test blocks has been applied to the optimization of the casting process and scheme design of the 100-ton ductile iron spent nuclear fuel container,and some good results has been achieved,There are more solidification hat in the actual production process of 100-ton ductile iron spent nuclear fuel containers,the solidification conditions of which are more complicated.To ensure that the obtained volume index of 100-ton ductile iron spent nuclear fuel containers meet the requirements of foreign containers,lots of research should be done.