ROCK MASS QUALITY ASSESSMENT OF BOREHOLE NRG01 IN BAYANNUORIGONG ALXA BASED ON BQ-SYSTEM

High level radioactive waste is the inevitable product of nuclear power development. The whole world has paid more attention to the safety disposal of the waste so as to maintain the sustainable development of nuclear power. At present,deep geological disposal has become a recognized permanent disposal method of high level radioactive waste,and surrounding rock mass quality assessment is the key to the selection of high-level waste disposal repository. Alxa is a pre-selected area for high-level radioactive waste disposal in China. Based on BQ-system,the rock mass quality of Bayannuorigong borehole NRG01 in Alxa region was assessed. BQ-system is a comprehensive rock mass quality assessment method,which take the rock mass hardness and integrity into consideration. The borehole data of NRG01 is rich. The evalution parameters of BQ-system were obtained by different methods and techniques such as core logging,wave velocity logging,hydrofracturing in situ stress measurement,rock ultrasonic wave velocity measurement and uniaxial compression test. The BQ value was calculated using those parameters. Then,according to the effects of ground water,weak structural surface and initial crustal stress,the BQ value was modified. The modifiedBQ value was used to classify the quality of rockmass into five categories. Result shows that the rock mass quality of borehole NRG01 is good,about 90%rock belong to Ⅰ and Ⅱ category,the rock mas range of 410~500 m can be regarded as the target rock for the construction of the repository. The qualitive conclusion of BQ-system was compared with that by RQD index. RQD index is simple and straightforward which is the most commonly used indicator for rock mass quality assessment. Comparison result showed that two methods have good coherence. However,BQ-system take more factors into consideration,therefore it is more comprehensive and refined. Evaluation results can provide reference for siting the repository of high-radioactive waste disposal and the the selection of the target rock.