Evaluation of corrosion behaviors for reactor pressure vessels/primary containment vessels in Fukushima Daiichi units 1–3 nuclear power plant

Fukushima Daiichi nuclear power plants (1F) were damaged by unprecedented severe accident in the Great East Japan Earthquake on 11 March 2011, and seawater has been injected as an emergency countermeasure for the core cooling. Although, the RPV and PCV were not supposed to be exposed to diluted seawater, they have been exposed to diluted seawater environment or high-moisture environment. Therefore, seawater corrosion has become an important issue. Immersion corrosion tests were performed for low-alloy steel of RPV material and carbon steel of PCV material in 1F cooling-water-simulated environment. As a result, the mass loss by corrosion was reduced with the decreasing temperature and chloride ion concentration. Moreover, the effects of nitrogen deaeration and Na₂WO₄ addition on corrosion protection were remarkable among the selected corrosion countermeasures. In addition, the integrity assessments of RPV and PCV were performed considering the reduction of plate thickness based on corrosion test data and the load condition based on earthquake response analysis results. It had been confirmed that primary stresses for RPV and PCV equipment satisfied with the allowable values until at least 15 years after the accident.     

Effects of gamma-ray irradiation on crevice corrosion repassivation potential of stainless steel in high temperature diluted simulated seawater

The crevice corrosion repassivation potentials (E_R,CREV) of type 304 stainless steel (304 SS) were measured in high temperature (373–553 K), diluted simulated seawater under gamma-ray irradiation, in order to confirm the effects of gamma-ray irradiation on the crevice corrosion behavior of a representative stainless steel in seawater. Overall, for high temperatures, the E_R,CREV values decreased with increasing chloride ion concentration, which was the same as the behavior observed under the non-irradiated condition. The E_R,CREV values measured under gamma-ray irradiation were the same or slightly higher than E_R,CREV values measured under the non-irradiated condition when the [Cl^?] was the same. Consequently, it was confirmed that the threshold potential of crevice corrosion of 304 SS for the gamma-ray irradiation of 1.8 kGy at least did not deteriorate compared with the non-irradiated condition. Under the conditions of this work (seawater composition, [Cl^?] range, dose rate, absorbed dose, flow rate, etc.), the crevice corrosion of 304 SS could be suppressed by maintaining the potential below the threshold potential which was determined approximately as ?0.3 V vs. SHE even for the irradiated condition at temperatures up to 553 K.     

Gamma-ray irradiation impact of humic substances on apparent formation constants with Cu(II)

Aqueous solution samples of humic acid and fulvic acid were irradiated with gamma-rays in the dose range of 0–500 kGy at two dose rates, 0.1 and 1 kGy/h. The brownish solutions discolored with 500 kGy irradiation indicating degradation by radiolysis, and the index of degree of humification (as the absorbance ratio at 400 nm and 600 nm) was studied using UV-Visible spectroscopy. Apparent formation constants of Cu(II) with humic substances (HSs) in 0.1 M NaClO₄ were determined at 298 K by potentiometric titration using Cu ion selective electrode (ISE), and the effect of gamma irradiation on the constants is herein discussed. To calculate formation constants, the acid dissociation constants of HSs were also measured by potentiometric titration and used as the degree of dissociation. Though the concentration of carboxylic groups decreased drastically with high radiation exposure, no significant change in apparent formation constants was found.     

低铜合金反应堆压力容器钢辐照脆化预测评估模型

反应堆压力容器（RPV）材料辐照脆化预测评估对保证核反应堆安全运行、预防重大灾难性事故的发生具有重要意义。通过深入了解RPV材料辐照损伤机理和分析国外较为成熟的RPV辐照脆化预测模型,揭示了国外有关压力容器辐照脆化预测模型对低铜RPV辐照脆化预测的不足及其原因。在此基础上,发展和建立了适用于低铜RPV辐照脆化趋势的预测模型CIAE-2009。利用辐照性能数据对CIAE-2009模型进行了验证。结果表明,CIAE-2009对低铜含量RPV材料辐照脆化趋势预测具有较高的准确性和可靠性。     

Gamma-rays irradiation effects on polysulfone at high temperature

The temperature dependence of the irradiation effects on polysulfone was studies by measuring the molecular weight, glass transition temperature, gel fraction and evolved gas. Polysulfone was irradiated with gamma-rays at room temperature, 100, 150, 180 and 210 °C. The change of molecular weight distribution and glass transition temperature showed occurrences of a main chain scission at room temperature and cross-linking at high temperature. The decrease of gel dose, the increases of gel fraction and total gas evolution with increasing temperature was observed. The evolution of CO, CO₂ and SO₂ gases increased at high temperature, while yield of evolved H₂ was independent of irradiation temperature. The probability of the cross-linking was clearly increased by irradiation at high temperature above 180 °C, though the chain scission was not changed very much.     

Positron annihilation study and computational modeling of defect production in neutron-irradiated reactor pressure vessel steels

Positron annihilation spectroscopy (PAS) and a computer simulation were used to investigate a defect production in reactor pressure vessel (RPV) steels irradiated by neutrons. The RPV steels were irradiated at 250 °C in a high-flux advanced neutron application reactor. The PAS results showed that mainly single vacancies were created to a great extent as a result of a neutron irradiation. Formation of vacancies in the irradiated materials was also confirmed by a coincidence Doppler broadening measurement. For estimating the concentration of the point defects in the RPV steels, we applied computer simulation methods, including molecular dynamics (MD) simulation and point defect kinetics model calculation. MD simulations of displacement cascades in pure Fe were performed with a 4.7 keV primary knock-on atom to obtain the parameters related to displacement cascades. Then, we employed the point defect kinetics model to calculate the concentration of the point defects. By combining the positron trapping rate from the PAS measurement and the calculated vacancy concentrations, the trapping coefficient for the vacancies in the RPV steels was determined, which was about 0.97 × 10¹⁵ s⁻¹. The application of two techniques, PAS and computer simulation, provided complementary information on radiation-induced defect production.     

Mechanisms and kinetics of hydrogen yield from polymers by irradiation

Hydrogen yield from polyethylene by gamma-rays radiolysis was studied to understand the saturation phenomena of products with increase of dose in radiation resistance and also radiation processing of polymers. The hydrogen yield as a primary product was proportional with dose in the lower dose range and decreases gradually with dose above 10 kGy. The mechanism and kinetics were analyzed with a model of radiation protection effect by double bonds formed in polyethylene matrix during irradiation, that is, the double bond formed by primal irradiation reduces the hydrogen detachment from polyethylene molecules surrounding double bond by the following irradiation. By this analysis, one double bond covers about 800 methylene (–CH₂–) groups for the reduction of hydrogen detachment from polyethylene chains. When the 800 (–CH₂–) were concentrated in a sphere with a double bond at center, the radius was calculated to be 1.6 nm, where the radiation energy might be stabilized. G(H₂) was 4.0 for virgin polyethylene chains and was estimated to be 0.6–1 for the chains within the sphere.     

Small-angle neutron scattering study on the effect of hydrogen in irradiated reactor pressure vessel steels

Hydrogen uptake can enhance the neutron embrittlement of reactor pressure vessel (RPV) steels. This suggests that irradiation defects act as hydrogen traps. The evidence of hydrogen trapping was investigated using the small-angle neutron scattering (SANS) method on four RPV steels. The samples were examined in the unirradiated and irradiated states and both in the as-received condition and after hydrogen charging. Despite the low bulk content of hydrogen achieved after charging with low current densities, an enrichment of hydrogen in small microstructural defects could be identified. Preferential traps were microstructural defects in the size range of ≈ > 10 nm in the unirradiated and irradiated samples. However, the results do not show any evidence for hydrogen trapping in irradiation defects.     

TEM and PAS study of neutron irradiated VVER-type RPV steels

Conventional transmission electron microscopy and positron lifetime and Doppler broadening positron annihilation spectroscopy techniques have been used to investigate the radiation-induced microstructural changes in surveillance specimens of VVER-type reactor pressure vessel (RPV) steels, and RPV steels irradiated in the research reactor. Defects visible in transmission electron microscopy consist of black dots, dislocation loops and precipitates concentrated along the dislocation substructure. Their size and density depend on the neutron flux and fluence. The parallel set of thermally aged specimens, specimens recovery annealed after irradiation and specimens irradiated in a lower neutron flux was investigated too. No defects discernible in transmission electron microscopy were found after accelerated irradiation in the research reactor. In addition to visible defects, the small-volume vacancy clusters were identified by positron annihilation spectroscopy.     

PLA/POE-g-MAH共混材料的辐照效应研究

采用熔融共混的方法制备了PLA/POE-g-MAH/TAIC共混材料,并进行γ射线辐照.通过力学、凝胶和扫描电镜测试,研究了共混材料的辐照效应.结果表明,辐照可以对该体系进行界面原位增容,从而提高其力学性能.当重量配比为50/50/3的PLA/POE-g-MAH/TAIC共混材料在30kGy剂量下辐照时,其缺口冲击强度...     

Effect of gamma irradiation on a polymer electrolyte: Variation in crystallinity, viscosity and ion-conductivity with dose

PEO(1 − x)NH₄ClO₄(x) samples with x = 0.18 are irradiated with gamma doses varying up to 50 kGy. DSC and XRD studies indicate, in general, a decrease in crystallinity with dose. Measurement of viscosity of aqueous solutions of the irradiated samples at the same concentration, shows that there is overall chain scission on irradiation, though there is evidence of some cross-linking also at higher doses. This is corroborated by FTIR measurements. The ion-conductivity shows a strong increase for irradiation dose 35 kGy. This suggests that there is a possibility of improving polymer electrolyte properties on gamma irradiation.     

堆内捕集器对压力容器中子辐照影响分析

严重事故下为实现堆内熔融物滞留,可采用堆内捕集器(IVCC)的策略。捕集器属压力容器的一部分,属不可更换设备,需长期在堆内受中子辐照。本文通过对典型压水堆压力容器模型和带IVCC的压力容器模型的比较,发现IVCC不会改变压力容器内快中子通量,不会对压力容器的辐照造成影响。且IVCC使得压力容器的热中子通量明显减小,降低了压力容器的整体辐照水平。这说明IVCC对压力容器的辐照性能不会产生不利影响,反而有助于防止压力容器的老化。     

Reactor pressure vessel design of the high temperature engineering test reactor

The reactor pressure vessel (RPV) of the HTTR is 5.5 m (inside diameter), 13.2 m (inside height), and 122 mm (shell thickness). The RPV contains core components, reactor internals, reactivity control system, etc.2 1/4Cr–1Mo steel is chosen as the material for RPV. The temperature reaches about 400 °C at normal operation. The fluence of the RPV is estimated to be less than 1 × 10¹⁷ n/cm² (E > 1 MeV) and so irradiation embrittlement is negligible, but temper embrittlement is not negligible. For the purpose of reducing embrittlement, content of some elements must be limited in the 2 1/4Cr–1Mo steel for the RPV; embrittlement parameters, J-factor and are used.In this paper, design and structure of the RPV are reviewed first. Fabrication procedure of the RPV and its special feature are described. Material data on the 2 1/4Cr–1Mo steel manufactured for the RPV, especially the embrittlement parameters, J-factor and , and nil-ductility transition temperatures, T_NDT, by drop weight tests, are shown. In-service inspection and results of R&Ds are also described.     

Neutron induced damage in reactor pressure vessel steel: An X-ray absorption fine structure study

The radiation damage produced in reactor pressure vessel (RPV) steels during neutron irradiation is a long-standing problem of considerable practical interest. In this study, an extended X-ray absorption fine structure (EXAFS) spectroscopy has been applied at Cu, Ni and Mn K-edges to systematically investigate neutron induced radiation damage to the metal-site bcc structure of RPV steels, irradiated with neutrons in the fluence range from 0.85 to 5.0 × 10¹⁹ cm⁻². An overall similarity of Cu, Ni and Mn atomic environment in the iron matrix is observed. The radial distribution functions (RDFs), derived from EXAFS data have been found to evolve continuously as a function of neutron fluence describing the atomic-scale structural modifications in RPVs by neutron irradiations. From the pristine data, long range order beyond the first- and second-shell is apparent in the RDF spectra. In the irradiated specimens, all near-neighbour peaks are greatly reduced in magnitude, typical of damaged material. Prolonged annealing leads annihilation of point defects to give rise to an increase in the coordination numbers of near-neighbour atomic shells approaching values close to that of non-irradiated material, but does not suppress the formation of nano-sized Cu and/or Ni-rich-precipitates. Total amount of radiation damage under a given irradiation condition has been determined. The average structural parameters estimated from the EXAFS data are presented and discussed.     

Microstructural aspects of neutron embrittlement of reactor pressure vessel steels - A view from positron annihilation spectroscopy

A comprehensive review of positron annihilation studies of Cr---Mo---V reactor pressure vessel (RPV) steels (Soviet type 15Kh2MFA) in unirradiated and neutron irradiated states is presented. The influences of lattice defects, impurity atom distribution, irradiation temperature, flux and fluence of fast neutrons on positron annihilation parameters, especially during isochronal annealing, are discussed in terms of the positron trapping model. In contrast to the literature, where irradiation-enhanced Cu precipitates and solute coated microvoids are thought to be major defect types responsible for strengthening and hence embrittling of RPV steels, we suggest irradiation-induced precipitates, i.e. probably carbides, to play this role. Possibilities to probe this model are suggested.     

γ辐照联合H_2O_2处理污泥滤液的研究

采用60 Coγ射线辐照处理污泥滤液,通过对比处理前后化学需氧量(COD)、紫外可见吸光度和浑浊度的变化,研究了辐照处理中初始pH、初始H2O2浓度和吸收剂量对污泥滤液处理效果的影响。结果表明:在相同吸收剂量和初始H2O2浓度条件下,酸性条件更利于CODCr的降低;γ辐照联合H2O2处理存在显著协同效应,吸收剂量为18.75kGy、初始H2O2浓度为2mmol/L时,污泥滤液CODcr去除率达70.4%,浑浊度下降94.9%。     

国产反应堆压力容器的辐照脆化行为及预测

反应堆压力容器（RPV）是保障核电站运行安全性、经济性的核心构件。对RPV的完整性评估而言辐照脆化是必须面对的问题。我国已开发了第三代设计寿命为60 a的核电站。当达到寿期末时,辐照脆化的行为是未知的,这给国产RPV的辐照脆化预测带来了困难。为研究高注量下的辐照脆化行为,对A508-3钢的材料力学性能试样进行辐照考验,辐照温度为(288±8) ℃,中子注量水平达到反应堆压力容器60 a寿期末的辐照水平1×10²⁰ cm^-2;开展拉伸、冲击和断裂韧性试验,分析辐照脆化行为,在EONY模型基础上,提出针对国产RPV钢的改进的辐照脆化模型。模型的有效性被试验数据证实,其可准确预测国内A508-3材料的辐照脆化趋势。     

Characterization of neutron-irradiated ferritic model alloys and a RPV steel from combined APT, SANS, TEM and PAS analyses

Understanding the behavior of reactor pressure vessel (RPV) steels under irradiation is a mandatory task that has to be elucidated in order to be able to operate safely a nuclear power plant or to extend its lifetime. To build up predictive tools, a substantial experimental data base is needed at the nanometre scale to extract quantitative information on neutron-irradiated materials and to validate the theoretical models. To reach this experimental goal, ferritic model alloys and French RPV steel were neutron irradiated in a test reactor at an irradiation flux of 9 × 10¹⁷ nm⁻² s, doses from 0.18 to 1.3 × 10²⁴ nm⁻² and 300 °C. The main goal of this paper is to report the characterization of the radiation-induced microstructural change in the materials by using the state-of-the-art of characterization techniques available in Europe at the nanometre scale. Possibilities, limitations and complementarities of the techniques to each other are highlighted.     

FTIR and DSC studies on gamma irradiated P(VdF-HFP) fluoropolymers applied to dosimetry

Radiation effects on semicrystalline poly(fluorovinylidene-co-hexafluoropropylene) copolymer [P(VdF-HFP)] induced by high-energy irradiation were investigated. Films with 150 μm thickness were irradiated with gamma doses ranging from 1.0 kGy to 3.0 MGy. Fourier transform infrared (FTIR) spectroscopy was used to follow the radio-induction of new molecular bonds. Differential scanning calorimetry (DSC) was employed to study the crystalline degradation of the irradiated samples. P(VdF-HFP) copolymers have fluorinated monomers [-CF₂-CF-CF₃-] randomly added to the [-CH₂-CF₂-] main chain of PVdF homopolymer. In this case, the [-CF₃-] molecular bonds are branched to the main chain. There is an increasing interest about the effect of high gamma radiation dose on the P(VdF-HFP) radiolysis, once it could enhance some of their already known interesting properties such as biomedical applications and electrostrictive transducers/actuators. FTIR spectroscopic data revealed two optical absorption bands at 1730 and 1754 cm⁻¹ whose intensities are unambiguously related to gamma delivered dose ranging from 0.0 to 1000 kGy. Fading analysis has demonstrated no loss of signal until 11 months after irradiation. DSC and XRD data revealed a continuous decrease in both the melting latent heat and crystalline dimensions for doses ranging from 250 to 3000 kGy. Because of the low fading and the linear behavior with respect to delivered gamma doses of the absorption band at 1754 cm⁻¹, P(VdF-HFP) copolymers are good candidates for being explored for high gamma dose dosimetry application.     

6 MeV electron irradiation effects on electrical properties of Al/TiO2/n-Si MOS capacitors

The irradiation effects of 6 MeV electrons on the electrical properties of Al/TiO₂/n-Si metal-oxide-semiconductor capacitors have been investigated. Nine Al/TiO₂/n-Si capacitors were fabricated using radio frequency magnetron sputtering and divided into three groups. Groups were irradiated with 6 MeV electrons at 10, 20, and 30 kGy doses, respectively, keeping the dose rate ∼1 kGy/min. The variations in the capacitance-voltage and leakage current-voltage characteristics, in addition to the electrical parameters, such as conductance (G/ω), flat-band voltage, interface trap density and the surface charge density with electron dose were studied. The Poole-Frenkel coefficient of the MOS capacitors was determined from current-voltage characteristics. Possible mechanisms for the enhanced leakage current in the electron irradiated MOS capacitors are discussed.