Analysis Andcalculation Of Nucritical Safety In Waste Water Treatment System Of A Uranium Enrichment Plant

During the construction process of commercial uranium enrichment and centrifugal engineering in China,the design institute conducted nuclear criticality safety analysis and calculation of key processes and equipment in the process system during the safety analysis and evaluation process of the design stage.However,the critical safety of the product container cleaning and uranium-containing waste liquid treatment system is simply analyzed,and no system analysis and calculations are performed.In recent years,a uranium enrichment plant has also carried out several renovations to the wastewater treatment process system.The wastewater treatment process has changed greatly compared with the original design,and it is necessary to analyze and calculate the nuclear criticality safety system again.Based on the operational data of a uranium enrichment plant uranium wastewater treatment system from 2010 to 2012,this paper conducted a critical safety analysis of critical process vessel cleaning,wastewater storage,ion exchange adsorption,concentration and sodium salt precipitation system.The Keff(effective proliferative factor)of key equipment for wastewater storage was calculated by Monte Carlo(MCNP)critical safety calculation software.The key equipment for wastewater storage was K-2 storage tank,G-9MA liquid lifter and F6/1 liquid lifter.The critical calculation results(Keff)were 0.07467,0.07233 and 0.07054 under the condition of oil concentration of 10g/L full volume,which verified that the wastewater treatment system was under the existing concentration control limit(uranium concentration less than 10g/L).Reliable subcritical state.Through analysis and calculation,the following conclusions and recommendations are drawn:(一)Under normal production conditions,the safe operating limit of uranium concentration in a uranium enrichment plant containing uranium wastewater treatment system is less than 10g/L,which is much lower than the subcritical safety limit of 261g/L.Container cleaning and wastewater treatment systems are subcritical.Safe state and a large safety margin.(二)Under extreme conditions,uranium concentration may exceed the safe operating limit during vessel cleaning and ion exchange adsorption and leaching,but it is also far below the subcritical safety limit.It can reduce the residual amount of product containers and strengthen the uranium content.The monitoring of uranium concentration in the equipment and the uranium balance calculation ensure that the uranium concentration and total amount in the equipment are less than the safe operation limit,and the critical safety reliability is improved.(三)To ensure nuclear criticality safety,reliable theoretical calculations must be used in addition to safety analysis.It is recommended that in the future work,a comprehensive critical safety calculation of the wastewater treatment system and equipment operation and transformation process of a uranium enrichment plant should be carried out by introducing corresponding critical safety calculation software and models to ensure the absolute safety of the nuclear facilities.(四)It is recommended to modify the operating limit of the wastewater treatment system(critical safety part)in the ten-year operation evaluation of the 1A project,so that the operational limit and the four-phase introduction of centrifugal engineering are unified to apply to the daily safety standard management of similar uranium enrichment plants.