초록 ▼

○ 핵물질 선별기술 개발
- 트랙기법 및 방사선에 의한 핵물질 선별기술 개발
- 사찰시료 내 핵물질 분포측정 및 원소분석 기술 개발
- 우라늄 마이크로입자 제조 기술 개발
○ 극미량 핵물질 총량분석기술 개발
- 사찰시료 내 극미량 핵물질 화학처리기술 개발
- ng 이하급 우라늄 및 수 pg 급 플루토늄 총량 및 동위원소비 측정 연구
- 총량분석 시 우라늄 바탕값을 약 20 pg 수준으로 최소화
○ 사찰시료 내 핵물질에 대한 FT-TIMS 및 SIMS 입자분석 기술 개발
- 크기별 선택

○ 핵물질 선별기술 개발
- 트랙기법 및 방사선에 의한 핵물질 선별기술 개발
- 사찰시료 내 핵물질 분포측정 및 원소분석 기술 개발
- 우라늄 마이크로입자 제조 기술 개발
○ 극미량 핵물질 총량분석기술 개발
- 사찰시료 내 극미량 핵물질 화학처리기술 개발
- ng 이하급 우라늄 및 수 pg 급 플루토늄 총량 및 동위원소비 측정 연구
- 총량분석 시 우라늄 바탕값을 약 20 pg 수준으로 최소화
○ 사찰시료 내 핵물질에 대한 FT-TIMS 및 SIMS 입자분석 기술 개발
- 크기별 선택적 입자회수 기술 개발
- 미세 핵물질 함유 입자 취급기술 개발
- 수 μm 급 핵물질 함유 입자 동위원소 비 측정 실증
○ 사찰시료 분석기술의 국제적 인증 확보
- 품질경영체계 수립 및 QA/QC 문서 작성
- 총량분석 분야 IAEA-NWAL 가입 완료
- FT-TIMS에 의한 입자분석 분야 IAEA-NWAL 가입 추진 중

Abstract ▼

IV. Results of the Project

□ Development of screening techniques for nuclear materials in ultra trace levels

The correlation between the enrichment of U-235 and the size of the uranium particles, and the number of fission tracks and alpha tracks were acquired from the analysis of fissi

IV. Results of the Project

□ Development of screening techniques for nuclear materials in ultra trace levels

The correlation between the enrichment of U-235 and the size of the uranium particles, and the number of fission tracks and alpha tracks were acquired from the analysis of fission track and alpha track for uranium particles. It was possible to estimate the size of unknown uranium particles by using the linearity of the number of alpha tracks and the size of uranium particles. In addition, the enrichment of U-235 was estimated by the fission track technique. The elemental analysis technique for elements in environmental samples was developed by SEM-EDS and total X-ray reflection fluorescence(TXRF).

□ Development of chemical treatment techniques for nuclear materials at ultra trace levels

Decomposition methods of HNO₃ - H₂O₂ and HNO₃ - HF were used to extract U fraction in soil samples. The recovery of U with decomposition methods of HNO₃ - H₂O₂ was found to be 90.5% and the recovery of U with decomposition methods of HNO3 - HF was found to be 95.5%. The activity concentration of Pu-239, 240 in the IAEA reference soil sample with anion exchange method and extraction chromatographic method was very similar to the recommended value reported by the IAEA. While the activity concentration of Pu-239 and Pu-240 in the IAEA reference soil sample with TOPO solvent extraction method was found to be a little lower than the recommended value reported by the IAEA.
For determining very low levels of Pu and U in a swipe sample, an extraction chromatography method with a UTEVA column was developed in this study. The recoveries with the extraction chromatography method with a UTEVA column were found to be 94 ± 7% and 95 ± 5% for plutonium and uranium, respectively. The separation method of Pu and U isotopes with the UTEVA resin updated in this study makes it possible to be used for determining Pu and U isotopes in safeguard swipe samples with isotope dilution thermal ionization mass spectrometry (ID-TIMS).
In order to improve performance of chemical treatment process, cleaning protocols for containers used in chemical treatment were amended and the origins of uranium contaminations were investigated in each ste for entire processes. Also, all the chemical treatment process was peroformed in CLASS (Clean Laboratory for Analysis of Safeguard Samples) to reduce uranium backgrounds from experimental environments. By this manner, we decreased uranium background level three-fold down (60 pg to 20 pg).

□ Development of isotopic measurement techniques for nuclear materials at ultra trace levels using thermal ionization mass spectrometry

The best condition to minimize the uranium background from rhenium filaments was determined as degassing with 3.5 A for 60 minutes. The minimized uranium background was approximately 0.5 fg, which is in a negligible level for the analysis of uranium in few pg levels. The optimized fixidation condition was determined as 1.8 A heating for 30 seconds.
Three correction methods was developed to improve the accuracy of U-234 and U-236 measurements. Among them, the correction technique based on a statistical method can be universally adopted to any samples although it requires huge volume of data base to deduce the correlation for statistics. The correction method was successfully verified by applying to uranium reference materials, U010 and IRMM-040a. The analytical accuracy and precision for the analysis of nuclear materials in ultra trace levels were enhanced by simultaneous isotopic analysis using multiple ion counters consisting of secondary electron multipliers (SEM) and compact discret dynode detectors(CDD)
The good agreements of the measurement of U005 with various amount from 10 pg to 1 ng, and the successful quantification using isotope dilution mass spectrometry using IRMM-040a showed that the TIMS measurement developed in KAERI can be applied to the isotopic analysis of nuclear materials in ultra trace levels.

□ Development of isotopic measurement techniques for nuclear materials at ultra trace levels using high resolution inductively coupled plasma spectrometry

Isotopic measurement with MC-ICP-MS is the most popular method for bulk analysis of swipe samples in IAEA-NWAL. Although introduction of MC-ICP-MS was delayed as expected due to lack of fund, the instrument was successfully set up in the second stage. Performance test have been achieved and various techniques with MC-ICP-MS have been also developed to maximize its performance. At first, analytical sensitivity was improved by 10 times after applying desolvator. Moreover, matrix effect in MC-ICP-MS was researched to improve the confidence of measurement. The advanced sample injection system associated with membrane desolvator (ARIDUS-II, Cetac., USA) was introduced in this experimental research. The detection limit was lowered by improving sensitivity of the ion signal of ultra trace uranium and plutonium. The advanced sample injection system is based on the concept that high temperature in membrane desolvator only evaporate the solvent in the sample and then exhaust them outside equipment, which results in enhancing the ionization degree of sample. It was identified that the advanced sample injection system have a better performance over 10 times than the conventional system in terms of signal sensitivity. The detection limit of uranium isotopes U-233 and U-238 was found to be 1.46 fg/ml, and 3.38 fg/ml. Analytic error attributed to plasma fluctuation was minimized by performing the simultaneous measurement of ultra trace uranium and plutonium isotope ratio using multi-collector system. Mass bias effect that the ion transmission efficiency depending on their mass was corrected by comparing the signal of standard having a similar concentration with the sample. U005 sample having a 100ppt (pg/ml) levels were used to measure the uranium isotope ratio. U010 as isotope standard was used for mass bias correction. It was found that the precision relative to the certified isotope ratio was clearly improved. The relative error for uranium isotope ratio U 234/238, U 235/238, U 236/238 were lowered from 2.10%, 1.71%, 1.92% to 0.35%, 0.097%, 0.56%, respectively. IRMM 290A1 sample having a 10ppq(fg/ml) levels were used to measure the plutonium isotope ratio. IRMM 290B1 sample as isotpoe standard was used for mass bias correction.
The relative error for Pu 239/242 was lowered from 8.72% to 0.22%.

□ Development of elemental techniques for nuclear particle analysis

The particle recovery system from environmental samples, consisting of a dry pump, a mass flow controller, and a filtering head was designed and set up. After then, about 50 % of recovery yield was acquired with 3.0 SLM. Improvement of recovery yield up to 80% is expected by additional studies on optimizing flow conditions and reducing particle loss by electrostatic force. The location of nuclear material particles among the numerous number of recovered particles was determined by applying the fission track technique or the SEM-EDS technique.
Particle handling techniques for FT-TIMS and SEM-TIMS were developed. For FT-TIMS, the particle handling requires a dissection technique using a micro knife, a pickup and loading technique using micro probes. Unfortunately this technique is needed skilled person. otherwise, additional work hours are required depending on skill levels To avoid these disadvantages, Laser Microdissection Device (LDM), leading to increase the efficiency of particle handling regardless of skill levels of individuals, was introduced. Moreover, SEM-TIMS, which does not require dissection technique during particle handling have been developted.
Isotopic measurement technique using TIMS was developed to determine the isotopic ratios of uranium contained in a micro particle, which can be applied to both of FT-TIMS and SEM-TIMS. Prior to the development of measurement technique for FT-TIMS, evaluation of uranium background from lexan films with various sizes was carried out, which showed negligible levels. Additional correction processes and adoption of a simultaneous measurement configuration using multi ion counters were required to ensure the measurement sensitivity for the micro particles with few micron sizes although mostly the same measurement techniques as the bulk analysis case can be applied. The good agreements of the measurement of the particles of uranium reference materials with the certified values showed that the TIMS measurement developed in KAERI can be applied to the particle analysis of nuclear materials.
Meanwhile, we have started the development of isotopic ratio measurement techniques of individual particles by SIMS, which can measure the isotopic ratios of secondary ions sputtered from the recovered particles under irradiation of primary oxygen ions. Although the accuracy and precision by SIMS is relatively less than that of FT-TIMS, this method widely used the cases required the analysis of many particles during the short period time due to simplified procedures. For developing related element techniques for establishing SIMS technique, impactor was introduced as the particle recovery technique. The recovery yields have been improved by applying visid grease on the surface of planchettes located inside impactor. Automated Particle Measurements (APM) technique of SIMS have been utilized to monitor the distribution maps of nuclear particles such as uranium among recovered particles, leading to enable selection of target nuclear element before measuring isotopic ratios. Finally, we were able to confirm that analysis technique by SIMS based on the developed element techiques in this study could be utilized as particle analysis of safeguards samples.

□ Verification of the developed techniques for bulk analysis

Isotopic analysis of soil samples and ground water samples was performed to verify the bulk analysis techniques developed in KAERI. In case of soil samples, chemical treatment and separation processes were required, while no pretreatment is necessary for the analysis of ground water samples due to the low matrix interference of TIMS. The isotopic ratios of uranium contained in soil samples and ground water samples agreed with the ratios of natural uranium. The amount of uranium in ground water was determined to be lower than the regulatory levels for drinking water.
KAERI participated the NUSIMEP-7 program to verify the elemental technique developed in KAERI for particle analysis. The particle screening, handling, and isotopic measurement techniques for SEM-TIMS was utilized. The measurement results agreed well with the certified values opened with closing the program. The draft report of IRMM showed that the SEM-TIMS of KAERI reaches the international level compared with the measurement results of the other participants including IAEA-NWAL.

□ Establishment of sputtered neutral mass spectrometer for analysis of isobaric elements

To establish SNMS, three wavelength tunable Titanium:Sapphire lasers, a Nd:YAG pump laser with high repetition rate, a gold liquid metal ion gun and a TOF-MS were introduced and installed in CLASS (Clean Laboratory for Analysis of Safeguard Samples). The laser system meets the range of wavelength corresponding to three-step ionization energy required for the selective ionization of uranium and plutonium. The gold liquid metal ion gun generates pulsed ion beam synchronizing with the pulsed laser beam and provides high yield of secondary ions and neutrals. The TOF-MS is a user-friendly system which enables quick measurement, and also satisfies all the requirements for this research. After the installment, each instrument was tested for its performance and we confirmed that all the instruments qualify specifications initially set by KAERI and manufacturers.

□ Establishment of quality management system for the analysis of nuclear materials in ultra trace levels

To set up quality management system for the analysis of nuclear materials in ultra trace levels, based on the guide book published by International Organization for Standardization, system of quality document was established as well as quality manual and operation procedures were finished. Also, based on the ISO/IEC 17025, KS Q ISO/IEC 17025, general requirements for the competence of testing and calibration laboratories and quality documents published by IAEA and JAEA system of document for quality management was established.

□ Process for joining IAEA-NWAL

KAERI, as an official candidate for IAEA-NWAL, is planing to complete join IAEA-NWAL in bulk analysis and particle analysis using both of FT-TIMS and SIMS by 2014. As the bulk analysis ability of KAERI reaches the international levels and the quality management system was well established, the test samples for IAEA-NWAL were received from IAEA for analysis. The analysis were completed for result reporting in 60 days complying the IAEA's request. According to the IAEA's review, most analytical results was satisfactory, while part of the results required corrective actions. KAERI is performing the proper corrective actions to meet the requirement of IAEA for NWAL. In Nov. of 2012, KAERI had fulfilled the IAEA inspection. In Dec. of 2012, KAERI was informed the successful qualification of the bulk analytical ability by meeting the all the requirement of IAEA for NWAL.
KAERI had conducted the validation of the bulk analytical ability using TIMS after the completion of the construction of CLASS (Clean Laboratory for Analysis of Safeguard Samples) and the moving of analytical equipments and instruments, which was approved by IAEA in Feb. of 2014. The qualification process of the bulk analytical ability using MC-ICP-MS has been being performed. In addition, the first test of FT-TIMS particle analysis for qualifcation of NWAL was completed in 2014.

□ Preparation of uranium micro particle

Mesoporous silica microspheres with 3~10nm of uniform mesopores and 60~70 μm in average particle size were acquired by using surfactant template method. To avoid particle aggregations, a cationic surfactant, CTAB(cetyltrimethylammonium bromide), was used to prepare the polydisperse mesoporous silica microspheres in the particle size range of 1~100 μm. Then, the silica microspheres was post-treated by using electro-formed Ni sieve to prepare the monodisperse microspheres with 10 μm and 50 μm in size, respectively. Silica-uranium composites were also prepared by using organic ligands for the uniform distribution of uranium element in silica base material. According to the characterizations using a variety of analytical instruments such as thermo-gravimetric analyser, elemental analyser, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, inductively coupled plasma atomic emission spectrometry, nuclear track analysis, etc, the uniform silica-uranium composites were successfully prepared. Additionally, a mass production process was developed with 20L-sized reactor within 1 hour of synthesis time.