• The Journal of the Acoustical Society of Korea
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• v.16 no.5
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• pp.83-91
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• 1997

A reactor vibration monitoring has been performed using neutron noise obtained from excore detectors for the safety operation, Traditionally, the spectral estimator based on Fourier analysis has been widely used in the noise analysis of the reactor system. If the bias is too severe, the resolution would not be adequate for a given application. One major motivation for the current interests in the parametric approach to spectral estimation is the apparent higher resolution achievable with these modern techniques. In considering an unbias, a consistency, an efficency, and a minimum lower bound of the statictic estimation, an AR model is appropriate for noise spectral estimation with sharp peaks but not deep valley. In order to select an appropriate model order, the lag value of autocorrleaton function is applied. Burg method to trace the vibration mode of RPV internal is the most sucuessful.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.3
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• pp.307-312
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• 2001

Ultrasonic signals from Charpy impact test specimen have been analyzed in order to evaluate the integrity of reactor pressure vessel. Base and weld metal that were extracted from reactor vessel doting plant outages according to the schedule of the surveillance test required by the related regulations have been used and the ultrasonic test parameters including velocity, attenuation, etc. showed a close correlations with the amount of neutron irradiation for base metal, relatively homogeneous materials. This result showed certain possibility where a nondestructive method could be used to predict the fluence of the Irradiation due to neutron in nuclear reactor vessel materials.

• Nuclear Engineering and Technology
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• v.4 no.2
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• pp.116-131
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• 1972

A fast neutron time-of-flight spectrometer has been constructed with suitable choice of target thickness and proton bombarding energy in Li$^{7}$ (p, n) Be$^{7}$ nuclear reaction for a continuous keV spectrum of neutrons at 0 degree in 1-nsec pulse from a Van do Graaff and a time-pick-up fast neutron detector assembled with a 5 mm-thick 92% enriched B$^{10}$ slab and four heavily shielded 4＂$\times$3＂ NaI scintillation detectors. Energy resolution of this spectrometer is better than 0.3% at 50 keV and the signal-to-background ratio is also improved. Total cross section measurements of several separated single isotopes have been carried out with this spectrometer and analyzed by Rmaxtrix multi-level computer code. The spin values and resonance parameters of each individual resonances are given.

• Journal of KSNVE
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• v.10 no.1
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• pp.129-137
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• 2000

This paper presents the vibration characteristics of reactor internals of Ulchin-1 nuclear power plant, which are identified by using the conventional and the phase separated spectral analysis of the pressure vessel acceleration and ex-core neutron signals. These identified vibration characteristics show excellent agreement with those of Tricastin-1 nuclear power plant that is the prototype of Ulchin-1. And the trend of ex-core neutron signals has been observed during one reactor cycle. These results can be used as basic data for fault diagnosis of reactor internals.

• Proceedings of the Korean Nuclear Society Conference
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• 1997.05b
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• pp.365-372
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• 1997

이 연구의 목적은 밀도측정 및 수분함량측정용 RI 계기의 개발에 있다. 방사성동위원소를 이용하여 성토시공의 현장다짐 밀도 및 수분함량 측정에 이용되곤 있는 RI 계기는 중성자 검출부분, 감마선 검출부분, 고전압 공급부분, 마이크로 컴퓨터 부분으로 크게 나눌 수 있다. 감마선을 검출하는 G-M 검출기는 그 특징으로 인해 방사선검출 전기회로가 간단하다. 그러나 열중성자를 검출하는 He-3 검출기는 검출기에서 발생하는 신호원이 매우 작아서 검출회로의 상호 간섭으로 인한 전기적 잡음이 발생한다 이 잡음을 제거하는 것이 He-3 중성자 검출기로 열중성자를 검출하는데 중요한 문제이다. 본 연구에서 제작하는 RI 계기는 원자력법에서 제한하는 방사능 이하를 (100$\mu$Ci 의 밀봉선원) 사용하므로 종래의 RI 계기에 비해 방사선의 검출수가 줄어든다. 이에 따라 검출기의 개수를 늘려서 방사선을 검출해야 한다. 또한 본 연구에서는 He-3검출기의 검출 스펙트럼을 분석하여 적정한 방사선 검출 측정영역을 결정하였다.

• Nuclear Engineering and Technology
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• v.27 no.6
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• pp.911-917
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• 1995

로듐 자기 기전력형 중성자 계측기는 단위 중성자당 발생되는 전류 신호가 매우 커 계측성이 우수하나 연소율이 빨라 자주 교체해야 하므로 재장전 기간 연장 및 새로운 로듐계측기 구입 등의 문제점이 있다. 75% 연소에 해당하는 제5핵 연료 주기 기간 동안 영광 3, 4호기와 같은 C-E 원자로에 사용되고 있는 로듐 자기 기전력형 중성자 계측기의 연소 거동이 C-E에 의해서 연구되었다. 약 제3핵연료주기까지 분석한C-E의 초창기 연구에서는 중성자 방사화율 개념에 근거하여 약 66%연소시점까지 로듐계측기 연소특성곡선은 선형적임이 밝혀진 바 있다. ［l, 2］ 그 후 C-E의 연구에 의하면 약 75% 연소에 해당하는 제5핵연료 주기까지도 로듐계측기 연소 특성 곡선은 선형적임이 밝혀졌다. 그 결과로 C-E형 원자력발전소에서 사용되는 로듐 노내계측기의 수명을 약 60%연소에서 66%연소 시점까지 연장시킬 수 있게 되었다. ［3］이 정도의 계측기 수명 연장은 약 반년의 원자로 운전 기간에 해당되며 차기 핵연료주기에서 많은 로듐 노내계측기를 계속 사용할 수 있게 한다. 특히 영광 3, 4호기가 12개월 핵연료 주기에서 18개월 핵연료 주기로 재장전 전략을 바꿀 경우 로듐 노내계측기의 수명 이 연장되지 않으면 계측기 교체가 빈번해 질 것으로 사료되어 로듐 수명 연장과 관련된 기술 특히 C-E 및 B&W의 로듐 노내계측기 연소도 특성곡선 불확실도 평가 및 출력 측정 계통 오차 분석 기술을 소개하고자 한다. 영광3, 4호기에서 사용중인 로듐 노내계측기 수명을 현재 연소도 기준 66%내로 한정하고 있는데 C-E 및 B&W의 로듐 노내계측기연소 특성에 관한 연구 내용을 분석한 결과 노내계측기 수명을 연소도가 66%를 초과하는 계측기가 있어도 전체적으로 불확실도가 안전한계를 넘지 않으면 노내상주가 가능한 것으로 평가되었다.

• Proceedings of the KIEE Conference
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• 2005.10b
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• pp.439-441
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• 2005

A kernel regression filter with adaptive bandwidth is developed and successfully applied to digital reactivity meter for neutron signal measurement in nuclear reactors. The purpose of this work is not only reduction of the measurement noise but also the edge preservation of the reactivity signal. The performance of the filtering algorithm is demonstrated comparing with well known smoothing methods of conventional low-pass and bilateral filters. The developed method gives satisfactory filtering performance and edge preservation capability.

• Journal of Radiation Protection and Research
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• v.39 no.1
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• pp.21-29
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• 2014

A new cold neutron triple-axis spectrometer (Cold-TAS) was recently constructed at the 30 MWth research reactor, HANARO. The spectrometer, which is composed of neutron optical components and radiation shield, required a redesign of the segmented monochromator shield due to the lack of adequate support of its weight. To shed some weight, lowering the height of the segmented shield was suggested while adding more radiation shield to the top cover of the monochromator chamber. To investigate the radiological effect of such change, we performed MCNPX simulations of a few different configurations of the Cold-TAS monochromator shield and obtained neutron and photon intensities at 5 reference points just outside the shield. Reducing the 35% of the height of the segmented shield and locating lead 10 cm from the bottom of the top cover made of polyethylene was shown to perform just as well as the original configuration as radiation shield excepting gamma flux at two points. Using gamma map by MCNPX, it was checked that is distribution of gamma. Increased flux had direction to the top and it had longer distance from top of segmented shield. However, because of reducing the 35% of the height, height of dissipated gamma was lower than original geometry. Reducing the 35% of the height of the segmented shield and locating lead 10cm from the bottom of the top cover was selected. After changing geometry, radiation dose was measured by TLD for confirming tester's safety at any condition. Neutron(0.21 ${\mu}Svhr^{-1}$) and gamma(3.69 ${\mu}Svhr^{-1}$) radiation dose were satisfied standard(6.25 ${\mu}Svhr^{-1}$).

• Journal of Advanced Navigation Technology
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• v.23 no.6
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• pp.554-560
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• 2019

Excore Nuclear Flux Monitoring System in Nuclear Power Plant monitors continuous reactor power up to maximum 200%. The monitoring method, however, has to be different depending on the reactor power level. Because the logarithmic pulse signals must be counted and processed exactly due to large uncertainty if their levels are low, on the other hand, they must be processed through statistical methodolgies if theirs are high to get exact monitoring values, in point of thermal degradation view. Therefore, we developed thermal degradation input signal selection circuit to transfer low level reactor power monitoring circuit to high level reactor power circuit at rated value in this paper. We proved their validities through testing them using real data used in nuclear power plant and analyzed their results. And, These methods will be used to measure the neutron level of excore nuclear flux monitoring system in nuclear power plant.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1998.04a
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• pp.582-589
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• 1998

This paper presents the analysis results of ex-core and in-core neutron noise, acceleration signals and pressure fluctuation measured at Ulchin Nuclear Unit 1 & 2 to identify and monitor the reactor internals vibration including fuel motion. A phase separation algorithm developed by authors was applied to the neutron noises to clearly identify the reactor internals vibratory motion. The beam mode frequency of the core support barrel was identified to be 8Hz and the shell mode to be 20Hz. The first frequency of the fuel assembly was also found to be 3Hz, while first two acoustic frequencies of the primary coolant system were 6 and 17.5Hz. By monitoring and analyzing these frequencies periodically, it is possible to diagnose the operating condition of reactor internals and to provide an early detection of faults for the predictive maintenance.