Effect of drying cracks on swelling and self-healing of bentonite-sand blocks used as engineered barriers for radioactive waste disposal

Experiments were conducted to evaluate the healing of drying cracks in air-dried bentonite-sand blocks after hydration and swelling in groundwater,providing justifications to simplify the protection of blocks prior to installation in a high-level radioactive waste repository.Synthetic groundwater was prepared to represent the geochemistry of Beishan groundwater,and was used to hydrate the blocks during the swelling pressure and swelling strain measurements,as Beishan is the most promising site for China's repository.Healing of the surface cracks was recorded by photography,and healing of the internal cracks was visualized by CT images and hydraulic conductivity of air-dried blocks.The results indicate that the maximum swelling pressure and swelling strain are primarily affected by the geochemistry of Beishan groundwater,but not affected by the drying cracks.The maximum swelling pressure and swelling strain of air-dried blocks are comparable to or even higher than the pressure and strain of fresh blocks.The maximum swelling pressure measured in strong(i.e.high ion strength)Beishan groundwater was 44%of the pressure measured in deionized(DI)water,and the maximum swelling strain was reduced to 23%of the strain measured in DI water.Nevertheless,the remained swelling of the blocks hydrated in strong Beishan groundwater was sufficient to heal the surface and internal drying cracks,as demonstrated by the pictures of surface cracks and CT images.The hydraulic conductivity of the air-dried block permeated with strong groundwater was comparable(3.7×higher)to the hydraulic conductivity of the fresh block,indicating the self-healing of drying cracks after hydration and swelling in groundwater.A simplified method of protecting the block with plastic wraps before installation is recommended,since the remained swelling of the block hydrated in Beishan groundwater is sufficient to heal the drying cracks.

Possibility of reaching the predicted center of the“island of stability”via the radioactive beam-induced fusion reactions

Based on the dinuclear system model,the synthesis of the predicted double-magic nuclei^(298)Fl and 304120 was investigated via neutron-rich radioactive beam-induced fusion reactions.The reaction^(58)Ca+^(244)Pu is predicted to be favorable for producing^(298)Fl with a maximal ER cross section of 0.301 pb.Investigations of the entrance channel effect reveal that the^(244)Pu target is more promising for synthesizing^(298)Fl than the neutron-rich targets^(248)Cm and^(249)Bk,because of the influence of the Coulomb barrier.For the synthesis of 304120,the maximal ER cross section of 0.046 fb emerges in the reaction^(58)V+^(249)Bk,indicating the need for further advancements in both experimental facilities and reaction mechanisms.

Application of radioactive iodine-125 microparticles in hepatocellular carcinoma with portal vein embolus

BACKGROUND Radioactive iodine-125(125I)microparticle therapy is a new type of internal radiation therapy that has shown unique advantages in the treatment of malignant tumors,especially hepatocellular carcinoma.Patients with hepatocellular carcinoma frequently experience portal vein embolism,which exacerbates the difficulty and complexity of treatment.125I particles,used in local radiotherapy,can directly act on tumor tissue and reduce damage to surrounding healthy tissue.Through retrospective analysis,this study discussed the efficacy and safety of radioactive 125I particles in portal vein embolization patients with hepatocellular carcinoma in order to provide more powerful evidence supporting clinical treatment.AIM To investigate the effect of transcatheter arterial chemoembolization combined with portal vein 125I particle implantation in the treatment of primary liver cancer patients with portal vein tumor thrombus and its influence on liver function.METHODS The clinical data of 96 patients with primary liver cancer combined with portal vein tumor thrombus admitted to our hospital between January 2020 and December 2023 were retrospectively analyzed.Fifty-two patients received treatment with transcatheter arterial chemoembolization and implantation of 125I particles in the portal vein(combination group),while 44 patients received treatment with transcatheter arterial chemoembolization alone(control group).The therapeutic effects on tumor lesions,primary liver cancer,and portal vein tumor embolisms were compared between the two groups.Changes in relevant laboratory indexes before and after treatment were evaluated.The t test was used to compare the measurement data between the two groups,and the χ^(2) test was used to compare the counting data between groups.RESULTS The tumor lesion response rate in the combination group(59.62%vs 38.64%)and the response rate of patients with primary liver cancer complicated with portal vein tumor thrombus(80.77%vs 59.09%)were significantly greater than those in the control group(χ^(2)=4.196,5.421;P=0.041,0.020).At 8 wk after surgery,the serum alpha-fetoprotein,portal vein main diameter,and platelet of the combined group were significantly lower than those of the control group,and the serum alanine aminotransferase,aspartate aminotransferase,and total bilirubin were significantly greater than those of the control group(t=3.891,3.291,2.330,3.729,3.582,4.126;P<0.05).The serum aspartate aminotransferase,alanine aminotransferase,and total bilirubin levels of the two groups were significantly greater than those of the same group 8 wk after surgery(P<0.05),and the peripheral blood platelet,alphafetoprotein,and main portal vein diameter were significantly less than those of the same group before surgery(P<0.05).CONCLUSION In patients with primary liver cancer and a thrombus in the portal vein,transcatheter arterial chemoembolization plus portal vein 125I implantation is more effective than transcatheter arterial chemoembolization alone.However,during treatment it is crucial to pay attention to liver function injury caused by transcatheter arterial chemoembolization.

Clays in radioactive waste disposal

Clays and argillites are considered in some countries as possible host rocks for nuclear waste disposal at great depth.The use of compacted swelling clays as engineered barriers is also considered within the framework of the multi-barrier concept.In relation to these concepts,various research programs have been conducted to assess the thermo-hydro-mechanical properties of radioactive waste disposal at great depth.After introducing the concepts of waste isolation developed in Belgium,France and Switzerland,the paper describes the retention and transfer properties of engineered barriers made up of compacted swelling clays in relation to microstructure features.Some features of the thermo-mechanical behaviors of three possible geological barriers,namely Boom clay（Belgium）,Callovo-Oxfordian clay（France） and Opalinus clay（Switzerland）,are then described,including the retention and transfer properties,volume change behavior,shear strength and thermal aspects.

MANAGEMENT OF RADIOACTIVE WASTES IN CHINA

The policy and principles on management of radioactive wastes are stipulated.Cement solidification and bituminization unit has come into trial run. Solid radioactive waste is stored in tentative storage vault built in each of nuclear faCilities. Seventeen storages associated with applications of nuclear technology and radioisotopes have been built for provinces. Disposal of low and intermediate level radioactive wastes pursues the policy of 'regional disposal'. Four repositories have been planned to be built in northwest, southwest, south and east China respectively. A program for treatment and disposal of high level radioactive waste has been made.

The Beishan underground research laboratory for geological disposal of high-level radioactive waste in China:Planning, site selection,site characterization and in situ tests

With the rapid development of nuclear power in China, the disposal of high-level radioactive waste（HLW） has become an important issue for nuclear safety and environmental protection. Deep geological disposal is internationally accepted as a feasible and safe way to dispose of HLW, and underground research laboratories（URLs） play an important and multi-faceted role in the development of HLW repositories. This paper introduces the overall planning and the latest progress for China＇s URL. On the basis of the proposed strategy to build an area-specific URL in combination with a comprehensive evaluation of the site selection results obtained during the last 33 years, the Xinchang site in the Beishan area,located in Gansu Province of northwestern China, has been selected as the final site for China＇s first URL built in granite. In the process of characterizing the Xinchang URL site, a series of investigations,including borehole drilling,geological mapping, geophysical surveying,hydraulic testing and in situ stress measurements, has been conducted. The investigation results indicate that the geological,hydrogeological, engineering geological and geochemical conditions of the Xinchang site are very suitable for URL construction. Meanwhile, to validate and develop construction technologies for the Beishan URL, the Beishan exploration tunnel（BET）, which is a 50-m-deep facility in the Jiujing sub-area, has been constructed and several in situ tests, such as drill-and-blast tests, characterization of the excavation damaged zone（EDZ）, and long-term deformation monitoring of surrounding rocks, have been performed in the BET. The methodologies and technologies established in the BET will serve for URL construction.According to the achievements of the characterization of the URL site, a preliminary design of the URL with a maximum depth of 560 m is proposed and necessary in situ tests in the URL are planned.

High-level radioactive waste disposal in China: update 2010

For geological disposal of high-level radioactive waste （HLW）, the Chinese policy is that the spent nuclear fuel （SNF） should be reprocessed first, followed by vitrification and final disposal. The preliminary repository concept is a shaft-tunnel model, located in saturated zones in granite, while the final waste form for disposal is vitrified high-level radioactive waste. In 2006, the government published a long-term research and development （R＆D） plan for geological disposal of high-level radioactive waste. The program consists of three steps： （1） laboratory studies and site selection for a HLW repository （2006-2020）; （2） underground in-situ tests （2021-2040）; and （3） repository construction （2041-2050） followed by operation. With the support of China Atomic Energy Authority, comprehensive studies are underway and some progresses are made. The site characterization, including deep borehole drilling, has been performed at the most potential Beishan site in Gansu Province, Northwestern China. The data from geological and hydrogeological investigations, in-situ stress and permeability measurements of rock mass are presented in this paper. Engineered barrier studies are concentrated on the Gaomiaozi bentonite. A mock-up facility, which is used to study the thermo-hydro-mechano-chemical （THMC） properties of the bentonite, is under construction. Several projects on mechanical properties of Beishan granite are also underway. The key scientific challenges faced with HLW disposal are also discussed.

An experimental study of preventing and treating acute radioactive enteritis with human umbilical cord mesenchymal stem cells

Objective:To test the curative effect of human umbilical cord-derived mesenchymal stem cells on rat acute radioactive enteritis and thus in provide clinical therapeutic basis for radiation sickness.Methods:Human umbilical cord-derived mesenchymal stem cells were cultivated in vitro and the model of acute radioactive enteritis of rats was established.Then,the umbilical cord mesenchymal stem cells were injected into the rats via tail vein.Visual and histopathiological changes of the experimental rats were observed.Results:After the injection,the rats in the prevention group and treatment group had remarkably better survival status than those in the control group.The histological observations revealed that the former also had better intestinal mucosa structure,more regenerative cells and stronger proliferation activity than the latter.Conclusions:Human umbilical cord-derived mesenchymal stem cells have a definite therapeutic effect on acute radioactive enteritis in rats.

Efficient Separation of Ar and Kr from Environmental Samples for Trace Radioactive Noble Gas Detection

Radioactive noble-gas isotopes, SSKr （half-life tl/2=10.8 y）, 39Ar （tl/2=269 y）, and SlKr （t1/2-229,000 y）, are ideal tracers and can be detected by atom trap trace analysis （ATTA）, a laser-based technique, from environmental samples like air and groundwater. Prior to ATTA measurements, it is necessary to efficiently extract krypton and argon gases from samples. Using a combination of cryogenic distillation, titanium chemical reaction and gas chromatography, we demonstrate that we can recover both krypton and argon gases from 1-10 L ＂air-like＂ samples with yields in excess of 90% and 98%, respectively, which meet well the requirements for ATTA measurements. A group of testing samples are analyzed to verify the performance of the system, including two groundwater samples obtained from north China plain.

Silicon detector array for radioactive beam experiments at HIRFL-RIBLL

A new and innovative detector system based on a silicon strip detector dedicated to the study of the reaction induced by lighter radioactive beams is described herein.The detector system consists of five sets of three types of telescopes,which are successfully used to measure the angular distributions of both elastic scattering and breakup simultaneously, on the Radioactive Ion Beam Line in Lanzhou at Heavy Ion Research Facility in Lanzhou. This silicon detector array is used to measure the elastic scattering angular distributions of ^(11) Be on a ^(208) Pb target at E_(lab) = 140 and 209 MeV. A comparison of the Monte Carlo simulations with the experimental results shows a reasonable consistency.

Design and development of large-scale in-situ PRACLAY heater test and horizontal high-level radioactive waste disposal gallery seal test in Belgian HADES

In Belgium,the Boom clay was selected as a potential host formation for the disposal of high-level radioactive waste（HLW）.To demonstrate the suitability of Boom clay for bearing thermal load induced by the HLW,a large-scale in-situ heater test,called PRACLAY heater test,will be conducted in the underground research laboratory（URL） in Mol.Owing to the limitations of the test（a short period of time compared with that considered in a real repository,different boundary conditions,etc.）,the test is designed to simulate,in a conservative way,the most critical state and phenomena that could occur in the host rock.The PRACLAY gallery was excavated at the end of 2007;the heating phase will begin in 2010 and will last for at least 10 years.The PRACLAY gallery itself leaves an opportunity to study the possibilities of sealing a disposal drift in Boom clay and testing the feasibility of hydraulic cut-off of any preferential pathway to the main access gallery through the excavation damage zone（EDZ） and the lining with a seal in a horizontal drift（horizontal seal）.Indeed,this is a generic problem for all deep geological disposal facilities for HLW.An annular seal made of compacted swelling bentonite will be installed in the front of the heated part of the PRACLAY gallery for these purposes.This paper provides detailed considerations on the thermo-hydro-mechanical（THM） boundary conditions for the design of the PRACLAY heater test and the seal test with the support of numerical calculations.It is believed that these important items considered in the PRACLAY heater test design also constitute key issues for the repository design.The outcome of the PRACLAY heater test will be an important milestone for the Belgian repository design.

Main outcomes from in situ thermo-hydro-mechanical experiments programme to demonstrate feasibility of radioactive high-level waste disposal in the Callovo-Oxfordian claystone

In the context of radioactive waste disposal,an underground research laboratory(URL)is a facility in which experiments are conducted to demonstrate the feasibility of constructing and operating a radioactive waste disposal facility within a geological formation.The Meuse/Haute-Marne URL is a sitespecific facility planned to study the feasibility of a radioactive waste disposal in the Callovo-Oxfordian(COx)claystone.The thermo-hydro-mechanical(THM)behaviour of the host rock is significant for the design of the underground nuclear waste disposal facility and for its long-term safety.The French National Radioactive Waste Management Agency(Andra)has begun a research programme aiming to demonstrate the relevancy of the French high-level waste(HLW)concept.This paper presents the programme implemented from small-scale(small diameter)boreholes to full-scale demonstration experiments to study the THM effects of the thermal transient on the COx claystone and the strategy implemented in this new programme to demonstrate and optimise current disposal facility components for HLW.It shows that the French high-level waste concept is feasible and working in the COx claystone.It also exhibits that,as for other plastic clay or claystone,heating-induced pore pressure increases and that the THM behaviour is anisotropic.

Primary research on neoplasm needle track implantation metastasis after radioactive seeds implantation and preventive measures

Objective:To observe the possibility of neoplasm needle track implantation after radioactive seeds implantation and seek preventive measures to avoid it.Methods:Superficial tissue of 250 seeding needle cores and 250 stylophores employed in neoplasm radioactive seeds implantation was smeared on slides to search for tumor cells.All patients received chemotherapy or endocrine therapy after operations.Ultrasound B-mode or computer tomography(CT)was performed at 10th day,30th day,60th day,and 180th day post operation to detect neoplasm implantation metastasis through needle tracks. Results:Positive cells were found on 13 of 250(5.20%)cores,and 7 of 250(2.80%)stylophores.The difference was not sta- tistically significant(P>0.05).The positive cells frequency of needles those traversed distance less than 3 cm in normal tissue was 6.19%(13/210),while the frequency of the others those traversed longer distance in normal tissue was 2.41%(7/290). The positive cells frequency of needles traversing different distances in normal tissues is significantly different(P<0.05).No neoplasm was detected through needle tracks by ultrasound B-mode or CT in 180 days after operation.Conclusion:Tumor cells could ablate into the needle track during radioactive seed implantation.Some preventive measures,such as optimization of pre-operation and intra-operation treatment plan,chemotherapy or endocrine therapy after operation,may be beneficial to avoid the implantation metastasis of neoplasm in seeding needle tracks.

Radioactive 125I seed implantation for pancreatic cancer with unexpected liver metastasis:A preliminary experience with 26 patients

BACKGROUND Preoperative diagnosis rate of pancreatic cancer has increased year by year.The prognosis of pancreatic cancer patients with unexpected liver metastasis found by intraoperative exploration is very poor,and there is no effective and unified treatment strategy.AIM To evaluate the therapeutic effect of radioactive 125I seed implantation for pancreatic cancer patients with unexpected liver metastasis.METHODS The demographics and perioperative outcomes of patients who underwent 125I seed implantation to treat pancreatic cancer with unexpected liver metastasis between January 1,2017 and June 1,2019 were retrospectively analyzed.During the operation,125I seeds were implanted into the pancreatic tumor under the guidance of intraoperative ultrasound,with a spacing of 1.5 cm and a row spacing of 1.5 cm.For patients with obstructive jaundice and digestive tract obstruction,choledochojejunostomy and gastroenterostomy were performed simultaneously.After operation,the patients were divided into a non-chemotherapy group and a chemotherapy group that received gemcitabine combined with albumin-bound paclitaxel treatment.RESULTS Preoperative imaging evaluation of all patients in this study showed that the tumor was resectable without liver metastasis.There were 26 patients in this study,including 18 males and 8 females,aged 60.5±9.7 years.The most common tumor site was the pancreatic head(17,65.4%),followed by the pancreatic neck and body(6,23.2%)and pancreatic tail(3,11.4%).Fourteen patients(53.8%)underwent palliative surgery and postoperative pain relief occurred in 22 patients(84.6%).The estimated blood loss in operation was 148.3±282.1 mL and one patient received blood transfusion.The postoperative hospital stay was 7.6±2.8 d.One patient had biliary fistula,one had pancreatic fistula,and all recovered after conservative treatment.After operation,7 patients received chemotherapy and 19 did not.The 1-year survival rate was significantly higher in patients who received chemotherapy than in those who did not(68.6%vs 15.8%,P=0.012).The mean overall survival of patients in the chemotherapy group and non-chemotherapy group was 16.3 mo and 10 mo,respectively(χ2=7.083,P=0.008).CONCLUSION Radioactive 125I seed implantation combined with postoperative chemotherapy can prolong the survival time and relieve pain of pancreatic cancer patients with unexpected liver metastasis.

Production of p-rich nuclei with Z = 20-25 based on radioactive ion beams

Within the framework of isospin-dependent Boltzmann-Langevin model,the production cross sections of proton-rich nuclei with Z=20-25 are investigated.According to the reaction results for different isospin of projectiles^(48)Ni,^(49)Ni,and^(50)Ni,proton-rich fragments tend to be more easily produced in reactions with the protonrich projectile^(48)Ni.The production cross sections of the unknown nuclei in the vicinity of the projectile are sensitive to incident energy.It is observed that incident energy of 345 MeV/u is appropriate for producing proton-rich nuclei with Z=20-25.In projectile fragmentation reactions based on the radioactive ion beam of48Ni at 345MeV/u,several unknown proton-rich nuclei near the proton drip line are generated in the simulations.All these new nuclei are near-projectile elements near Z=28.The production cross sections of the new nuclei^(34)Ca,37,38Sc,^(38)Ti,^(40,41,42)V,^(40,41)Cr,and^(42,43,44,45)Mn are in the range of 10-2-102mb.Hence,projectile fragmentation of radioactive ion beams of Ni is a potential method for generating new proton-rich nuclei with Z=20-25.

DTI and pathological changes in a rabbit model of radiation injury to the spinal cord after ^(125)I radioactive seed implantation

Excessive radiation exposure may lead to edema of the spinal cord and deterioration of the nervous system. Magnetic resonance imaging can be used to judge and assess the extent of edema and to evaluate pathological changes and thus may be used for the evaluation of spinal cord injuries caused by radiation therapy. Radioactive ^125I seeds to irradiate 90% of the spinal cord tissue at doses of 40–100 Gy （D90） were implanted in rabbits at T10 to induce radiation injury, and we evaluated their safety for use in the spinal cord. Diffusion tensor imaging showed that with increased D90, the apparent diffusion coefficient and fractional anisotropy values were increased. Moreover, pathological damage of neurons and microvessels in the gray matter and white matter was aggravated. At 2 months after implantation, obvious pathological injury was visible in the spinal cords of each group. Magnetic resonance diffusion tensor imaging revealed the radiation injury to the spinal cord, and we quantified the degree of spinal cord injury through apparent diffusion coefficient and fractional anisotropy.

Implications of safety requirements for the treatment of THMC processes in geological disposal systems for radioactive waste

The mission of nuclear safety authorities in national radioactive waste disposal programmes is to ensure that people and the environment are protected against the hazards of ionising radiations emitted by the waste.It implies the establishment of safety requirements and the oversight of the activities of the waste management organisation in charge of implementing the programme.In Belgium,the safety requirements for geological disposal rest on the following principles:defence-in-depth,demonstrability and the radiation protection principles elaborated by the International Commission on Radiological Protection(ICRP).Applying these principles requires notably an appropriate identification and characterisation of the processes upon which the safety functions fulfilled by the disposal system rely and of the processes that may affect the system performance.Therefore,research and development(R&D)on safety-relevant thermo-hydro-mechanical-chemical(THMC)issues is important to build confidence in the safety assessment.This paper points out the key THMC processes that might influence radionuclide transport in a disposal system and its surrounding environment,considering the dynamic nature of these processes.Their nature and significance are expected to change according to prevailing internal and external conditions,which evolve from the repository construction phase to the whole heatingecooling cycle of decaying waste after closure.As these processes have a potential impact on safety,it is essential to identify and to understand them properly when developing a disposal concept to ensure compliance with relevant safety requirements.In particular,the investigation of THMC processes is needed to manage uncertainties.This includes the identification and characterisation of uncertainties as well as for the understanding of their safety-relevance.R&D may also be necessary to reduce uncertainties of which the magnitude does not allow demonstrating the safety of the disposal system.

To explore the curative effect of CT-guided Iodine-125 radioactive seed implantation in the treatment of stage Ⅳprimary hepatocellular carcinoma

Objectives: To explore the clinical efficacy and survival of CT-guided Iodine-125 radioactive seed implantation in the treatment of stage Ⅳ primary hepatocellular carcinoma.Methods: A retrospective study of 62 patients with primary hepatocellular carcinoma in our hospital from January2017 to December 2018 [60 males, 2 females, age(52.76 ± 10.82) years old], All patients were implanted with Iodine-125 radioactive seeds under CT guidance, followed up regularly after operation to observe the clinical efficacy, including comparison of changes in cancer size before and after treatment, tumor marker AFP, and improvement in complications such as abdominal pain and ascites. Follow-up 3–36 months to assess patient survival.Results: Among the 62 patients, 3 months after Iodine-125 radioactive seed implantation, 5 cases(8.1%) had complete remission of cancer, 33 cases(53.2%) had partial remission, 12 cases(19.4%) had stable lesions, and 12 cases(19.4%) had disease progression. The effective rate was 61.3%. The tumor volume(31.44 ± 14.51 cm3) was significantly smaller than before(50.96 ± 30.13 cm3)(t=5.303, p < 0.05). The tumor marker AFP(69.28 ±50.99) ug/L of 3 months after implantation was significantly lower than that before treatment(90.63 ± 68.58)ug/L(t=3.702, P < 0.05). The average survival time of Iodine-125 seed implantation for stageⅣhepatocellular carcinoma is 11.47 ± 0.85 months, and the median survival time is 9 months. The survival time of the group with better pathological differentiation(grade Ⅰ+ⅡⅠ) was significantly better than that of the group with poor differentiation(grade Ⅲ+Ⅳ)(x2=6.869 p < 0.05). Among the 38 patients with different degrees of abdominal pain,22 patients improved better than before;15 of 28 patients with different degrees of ascites were better than before. All patients had no serious complications related to treatment.Conclusions: Iodine-125 radioactive seed implantation therapy can safely and effectively treat hepatocellular carcinoma, and relieve the clinical symptoms of abdominal pain and ascites.

Experimental study on the physico-mechanical properties of Tamusu mudstone — A potential host rock for high-level radioactive waste in Inner Mongolia of China

Tamusu mudstone, located in Bayin Gobi Basin in Inner Mongolia of China, has been selected as a potential host rock for high-level radioactive waste(HLW) disposal in China. A series of tests has been carried out, including X-ray diffraction(XRD) tests, scanning electron microscopy(SEM) tests, disintegration tests, permeability tests and triaxial compression tests, to estimate the physico-mechanical properties of Tamusu mudstone in this work. The mineral composition of Tamusu mudstone was analyzed and it was considered as a stable rock due to its low disintegration rate, i.e. approximately 0.11%after several wet/dry cycles. Based on the results of permeability test, it was found that Tamusu mudstone has a low permeability, with the magnitude of about 10—20m^(2). The low permeability makes the mudstone well prevent nuclide migration and diffusion, and might be influenced by temperature.The triaxial tests show that Tamusu mudstone is a stiff mudstone with high compressive strength, which means that the excavation disturbed zone would be smaller compared to other types of mudstone due to construction and operation of HLW repositories. Finally, the properties of Tamusu mudstone were compared with those of Opalinus clay, Callovo-Oxfordian(COx) argillite, and Boom clay to further discuss the possibility of using Tamusu mudstone as a potential nuclear waste disposal medium.

Rock Mass Characteristics in Beishan,A Preselected Area for China's High-Level Radioactive Waste Disposal

Geological and hydrological characteristics, joint geometric features, rock physical and mechanical properties and rock mass quality are studied in the Beishan area, preselected for China5 s high-level radioactive waste(HLW) disposal engineering. A comprehensive survey method is developed to study joint geometric features in the outcrop and samples from borehole BS06 into the Xinchang rock mass were tested. The optimal joint sets are determined by rose diagrams and equal-area lower hemisphere plots of joint poles. Results show that: 1) the distribution of joint occurrence obeys a normal distribution, while the distribution of joint spacing obeys a negative exponential distribution; 2) concentric circular and tangent circular sampling windows are applied to study the trace length and the trace midpoint density. Results indicate that tangent circular sampling window is more stable and reasonable; 3) Beishan granite shows high density, low porosity and high strength based on many laboratory tests and the physical properties and mechanical properties are closely related; and4) a synthesis index, Joint Structure Rating(JSR), is applied to evaluate the quality of rock mass. Through the research results of rock mass characteristics, the Xinchang rock mass in the Beishan preselected area has the favorable conditions for China's HLW disposal repository site.