Thermochemical Study of Hardening Cement Mixtures Which Contained Simulated Radioactive Waste

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Physical Chemistry Communications, Volume 3 Issue 2, October 2016 www.bacpl.org/j/pcc

Thermochemical Study of Hardening Cement Mixtures Which Contained Simulated Radioactive Waste P.V. Kozlov1, O.M. Slyunchev1, K.V. Kirʹyanov2, I. V. Myalkin2, A.V. Knyazev*2 Federal State Unitary Enterprise Mayak Production Association, str. Lenina, 31, 456780, Ozersk, Russia

1

N.I. Lobachevsky State university of Nizhni Novgorod , Gagarin Prospekt 23/2,603950, Nizhni Novgorod, Russia

2

*2

knyazevav@gmail.com (A. Knyazev)

Abstract Heat generation of cement mixtures of various compositions was measured with the calorimetric method during hardening of solutions, which simulated liquid medium‐level wastes (MLW) from the radiochemical plant and distillation residues obtained from evaporation of Nuclear Power Plant (NPP) liquid radioactive wastes. Thermal capacity was determined and heat generation was calculated for the processes of hydration and solidification of cement mixtures. Impact of dry mixture and solution compositions on heat generation was determined, as well as that of the solution‐cement ratio. A scaled‐up experiment was carried out to solidify a 4 m3 block of compound using the developed cement mixture with reduced heat generation. It was found that at hardening, the temperature in the specimen didn’t exceed 57ºС. This fact confirmed the efficiency of the measures undertaken to decrease heating up of the compound in the course of hardening. Applicability of the cementation technology was considered in relation to NPP distillation residues with subsequent storage of the obtained compound in pour‐ type compartments. It was demonstrated that the developed dry mixture compositions ensured compliance of the cement compound with the respective process and regulation requirements during NPP distillation residues hardening. Results of the study will help verify and, if necessary, adjust the mathematical model used in preliminary calculations to describe the process of storage compartment heating. It will allow developing a safe mode of filling compartments of the storage facility with the cement compound containing solidified MLW. Keywords Medium‐level Waste; Cementation; Specific Heat Generation; Heating; Calorimetric Studies

Introduction Cementation is the primary way for hardening distillation residues resulted from evaporation of NPP liquid medium‐level and low‐level wastes. It can be explained by a relative simplicity of practical realization of cementation and by a satisfactory quality of the produced cement compound [1]. Mayak PA intends to use the cementation technology to solidify liquid medium‐level waste (MLW) from the radiochemical plant. A storage facility of pour ‐ type is planned to be used at the cementation complex now under construction at the Mayak PA to locate the cement compound with solidified radioactive wastes. It will be a surface construction consisting of 100 reinforced concrete compartments to be filled with cement grout. A compartment (5m L x 5m W x 11m H) will contain about 260 m3 of solidified waste. Annually, it is planned to fill 4 ‐ 6 such compartments with a total volume of up to 1600 m3. Filling compartments with the cement mixture will be performed successively so that to ensure optimum temperature conditions in the storage facility. When the operating life (20‐50 years) of the MLW cementation complex comes to an end, all equipment and easily detachable building structures located above the storage facility will be dismantled, while remaining auxiliary rooms, openings, corridors and other voids will be filled with cement. The storage facility will be isolated and then transferred to a category of repository. Despite obvious advantages of the pour ‐ type storage facilities, there are numerous specific requirements imposed upon the given technology:

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