China
Africa
Explore chapters and articles related to this topic
Bioremediation Current Status, Prospects and Challenges
Published in Amitava Rakshit, Manoj Parihar, Binoy Sarkar, Harikesh B. Singh, Leonardo Fernandes Fraceto, Bioremediation Science From Theory to Practice, 2021
Ruby Patel, Anandkumar Naorem, Kaushik Batabyal, Sidhu Murmu
Neptunium, an alpha-emitting transuranic radionuclide, is of great concern because of its long half-life (2.14 × 106 years), high radio-toxicity, and relatively high solubility as Np (V) under toxic conditions. In comparison, Np (IV) species dominate under-reducing conditions and can be removed from the solution by hydrolysis and a reaction with the surfaces (Dozol and Hagemann 1993, Kaszuba and Runde 1999). Low Np uptakes (10 mg g-1 dry weight) were reported with Pseudomonas aeruginosa, Streptomyces viridochromogenes, Scenedesmus obliquus, and Micrococcus luteus (Strandberg and Arnold 1988). Songkasiri and coworkers suggested that Pseudomonasfluorescens can biosorb significant quantities of Np, removing 85 percent Np (V) from the solution at pH 7 (Songkasiri 2002). Neptunyl species (NpO2+) can also be biologically reduced to insoluble Np (IV) under anaerobic conditions (Lloyd et al. 2000, Rittmann et al. 2002). Shewenella putrefaciens reduced Np (V) to Np (IV), which was then precipitated from solution as Np (IV) phosphate in the presence of a Citrobacter species with high phosphatase activity. Desulfovibrio desulfuricans have also been reported to reduce Np (V) into Np (IV).
Dendrimer-Based Hybrid Nanomaterials for Water Remediation: Adsorption of Inorganic Contaminants
Published in Surender Kumar Sharma, Nanohybrids in Environmental & Biomedical Applications, 2019
Herlys Viltres, Oscar F. Odio, Edilso Reguera
Much of the research work in the field of nuclear waste management is still centered on the separation/preconcentration of several isotopes of uranium (U) (Alijani et al., 2015, Sengupta et al., 2016), thorium (Th) (Chen et al., 2007, Sengupta et al., 2016), plutonium (Pu) (Gupta et al., 2016, Kumar et al., 2016), and cesium (Cs) (Thammawong et al., 2013) due to their great importance in nuclear applications and to the irreversible damage that they provoke in living organisms (Taylor, 1989). An important alpha-emitting long-lived radionuclide is 237Np (neptunium), which requires proper mitigation steps in the case of nuclear fallout since exposure can induce bone, lung, and liver cancers. The separation of these elements requires special conditions that will be discussed in section 12.3.3.
Managing High-Level Radioactive Wastes
Published in Roland Pusch, Raymond N. Yong, Masashi Nakano, Geologic Disposal of High-Level Radioactive Waste, 2018
Roland Pusch, Raymond N. Yong, Masashi Nakano
High-level radioactive wastes (HLWs) include both spent nuclear fuel and various highly radioactive materials such as transuranic (TRU) radionuclides obtained in the reprocessing of spent nuclear fuel. Transuranic wastes, which are solid radioactive elements obtained from the irradiation of uranium and thorium in the reactors, contain isotopes that have atomic numbers higher than uranium. They include such isotopes as 239Pu (plutonium), 243Am (americium), and 237Np (neptunium), with half-lives of 24.1 × 103, 7.38 × 103, and 2.14 × 106 years, respectively.
Uranium-based TRU multi-recycling with thermal neutron HTGR to reduce environmental burden and threat of nuclear proliferation
Published in Journal of Nuclear Science and Technology, 2018
Yuji Fukaya, Minoru Goto, Hirofumi Ohashi, Xing Yan, Tetsuo Nishihara, Yasuhiro Tsubata, Tatsuro Matsumura
Second, potential toxicity is often used to show the effect of nuclear transmutation. Potential toxicity is defined as the total dose in the event of intake of whole radioactive nuclides. In Japan, the policy of geological disposal of HLW was criticized by the Science Council of Japan (SCJ), which was selected by Japan Atomic Energy Committee as a third-party source of opinion about HLW disposal. The opinions of the SCJ were distilled in a report entitled ‘Issues concerning HLW Disposal (Reply)’ [4] in 2012. This report caused a fad of fearing potential toxicity among the public. An expert committee of Atomic Energy Society in Japan criticized this public tendency in their report [5]. In their report, the expert committee emphasized that potential toxicity cannot be the index directly to assess safety, and the safety of geological disposal should be assessed based on public dose. In addition, they stated their own view that the safety of geological disposal tends to be assessed by potential toxicity in recent times because this indicator is intuitive. Potential toxicity has been recognized in public without depending on reasonability. However, not all MAs are problematic from the potential toxicity perspective. Figure 1 shows the potential toxicity of each element included in the spent fuels (SFs) of light water reactor (LWR). The toxicity of SFs should be lower than that of natural uranium used to fabricate the fuel. From the viewpoint of potential toxicity, neptunium, which accounts for approximately half the MAs, is not problematic in the first place.
Liquid–Liquid Extraction and Supported Liquid Membrane Transport of Neptunium(IV) Across a Flat-Sheet Supported Liquid Membrane Containing a TREN-DGA Derivative
Published in Solvent Extraction and Ion Exchange, 2022
Bholanath Mahanty, Prasanta K. Mohapatra, Andrea Leoncini, Jurriaan Huskens, Willem Verboom
Neptunium is an important element in the group of actinide elements and is produced as an activation product in nuclear reactors. 237Np is used as a target for the production of 238Pu, which has found application as a power source in the thermoelectric generator in the space program due to its high heat output.[1] The quantity of 237Np (t1/2: 2.14 × 106 yr) in the spent fuel of Pressurized Heavy Water Reactor (PHWR) origin with a burn up of about 6700 MWD/Te (megawatt-day per tonne) is approximately 25 g per tone of the fuel discharged and the quantity may be higher with high burn up fuels.[2] Hence, it is very important to separate this long-lived isotope from the spent fuel not only for its subsequent use to produce 238Pu but also to get rid of the long-term radiotoxicity and health hazards arising out of this isotope.[3] Neptunium can be present in the spent fuel dissolver solution in different oxidation states (+4, +5, +6) and during the PUREX (Plutonium Uranium Redox Extraction) process it gets distributed among the organic and aqueous phases because of the different extractability of its different ionic species.[4–6] The +4 and +6 oxidation states of neptunium are extractable by the PUREX organic phase, while the +5 state is weakly extractable. Generally, more than 40% of neptunium stays in the aqueous raffinate, while around 60% neptunium goes to the TBP (tri-n-butyl phosphate) phase during the first cycle of the PUREX process.[7]The chemistry of neptunium in nitric acid medium is quite complicated due to its complex redox reactions.[8–12] Therefore, it is very important to adjust the neptunium oxidation state in the nitric acid solution to the extractable (+4, +6) or weakly extractable (+5) oxidation state to route it to the organic phase or to the aqueous phase, respectively. Neptunium can exist in different oxidation states (+4, +5 and +6) in 3 M HNO3 due to the close proximation of the reduction potentials of different oxidation state couples of neptunium.[13,14] By using stronger reducing agent, such as the mixture of ferrous sulfamate and hydroxyl amine hydrochloride it can be possible to reduce +6 and +5 oxidation states of neptunium in dilute nitric acid to the +4 oxidation state[2,15] and therefore, can be extracted in the organic phase containing suitable extractant. Similarly, using a suitable complexing agent, the extracted Np(IV) can also be stripped to the aqueous solution.
Selective Separation of Neptunium from an Acidic Feed Containing a Mixture of Actinides Using Dialkylamides
Published in Solvent Extraction and Ion Exchange, 2020
Bholanath Mahanty, Arunasis Bhattacharyya, Avinash S. Kanekar, P.K. Mohapatra
N,N-Dialkyl substituted monoamides have been studied extensively for the separation of hexa- and tetravalent actinide ions in various streams at the back end of the nuclear fuel cycle and are proposed as an alternative to tri-n-butyl phosphate (TBP) due to their complete incinerability and innocuous nature of their degradation products.[1]N,N-Di-n-hexyl octanamide (DHOA, Fig. 1(a)) was evaluated as an alternative to TBP for the co-processing or separation of uranium and plutonium from the dissolver solution in a Plutonium Uranium Reduction EXtraction PUREX type process. N,N-di-2-ethylhexyl isobutyramide (D2EHIBA, Fig. 1(b)), on the other hand, showed a promising behavior of high selectivity for the hexavalent actinides over the tetravalent ones.[2] This property of D2EHIBA has been exploited for the separation of U(VI) and Th(IV) from a simulated thorium-based spent-fuel dissolver solution.[3] This amide molecule was also proposed for the separation of Pu(IV) from the U(VI) stream in the ARTIST process by the Japanese researchers.[4] In the uranium extraction (UREX) process developed in the USA, the extraction of the tetravalent actinides Pu(IV) and Np(IV) is, however, suppressed during the extraction of uranium and technetium by addition of acetohydroxamic acid (AHA) in the aqueous phase at 1 M HNO3.[5] AHA, however, is inefficient under the PUREX conditions (3–4 M HNO3) because of its acid-catalyzed hydrolysis. N,N-Dimethyl-3-oxa glutaramic acid (DMOGA) was also evaluated as an aqueous complexant for the tetravalent actinides for the selective extraction of U(VI) under the PUREX conditions.[6] Pathak et al. have extensively studied the extraction behavior of various hexavalent (U(VI), Pu(VI)) and tetravalent (Th(IV), Np(IV), Pu(IV)) actinide ions using D2EHIBA and found that it has a potential to separate the hexa- and the tetravalent actinide ions.[7,8] Neptunium is one of the most important activation products present in the spent nuclear fuel. 237Neptunium, in particular, is one of the longest-lived radionuclides formed in the nuclear reactor with a half-life of 2.14 × 106 years resulting in long-term radiotoxicity and health hazard of the nuclear waste.[9] It, therefore, has to be isolated from the rest of the shorter-lived elements present in the spent nuclear fuel for the safe management of the radioactive wastes. 237Np is a very useful isotope required for the production of Pu-238, which can find application as a power source in the thermoelectric generator in the space program with very high heat output.[10] 237Np is, therefore, a resource to be recovered from the radioactive wastes.