Buildup Of Radiation Fields Research Articles

Effect of anions on formation of ferrite coatings on carbon steel by hydrothermal method

The major concerns in Primary Heat Transport circuits of water cooled nuclear power plants are corrosion of structural materials and radiation field buildup on out-of-core surfaces due to accumulation of activated corrosion products. To address these concerns, hot conditioning and metal ion passivation are employed, which lead to the formation of protective magnetite coating on structural alloys like carbon steel. In this study, investigations were undertaken to modify the magnetite/ferrite films hydrothermally in the presence of zinc (Zn2+) and nickel (Ni2+) ions by using different salts of these ions containing anions such as acetate, nitrate and sulphate. Mixed ferrite coatings containing Zn2+ and Ni2+ ions were developed on carbon steel in lithiated water in presence of these anions at 250 °C by hydrothermal method and subsequently characterized by grazing incidence-X-ray diffraction for phase identification and scanning electron microscopy for surface morphology. The effects of these anions were studied by comparing the corrosion resistance properties of ferrite coated carbon steel specimens. The corrosion properties were studied in lithium hydroxide medium at ambient temperature by electrochemical techniques and the results of the investigation are discussed in this paper.

Evaluation of elevated temperature process for the decontamination of stainless steel 304LN surface

Abstract Deposition of activated corrosion products on out-of-core surfaces and ensuing radiation field build-up in nuclear reactors calls for remedial measures like decontamination to minimize exposure of service personnel carrying out routine maintenance jobs. Decontamination of stainless steel structural materials in nuclear power plants pose challenges due to the inherent difficulty in dissolving chromium containing oxides like ferrites or chromites. Stainless steel, SS 304LN, is the proposed structural material for the main heat transport system of Indian Advanced Heavy Water Reactors (AHWRs) and it is important to be equipped with an effective decontamination process to mitigate the radiation field build-up in AHWRs. This paper discusses the studies to develop an elevated temperature (ET) decontamination process for SS304LN surface. Oxide covered SS304LN specimens were prepared under simulated AHWR coolant chemistry conditions. The oxide film formed on the specimen surface was Ni and Cr substituted single phase ferrite spinel. The oxide film could be completely dissolved from the SS304LN surface in the nitrilotriacetic acid (NTA) based ET process at 180 °C in a single step with an acceptable and low corrosion rate of 7.7 × 10−3 μm/h. The efficiency of the ET process was compared with the known NTA based conventional low temperature dilute chemical decontamination process and a multi-step, multi-cycle process comprising of alternate oxidation and reduction processes. The ET process proved to be more effective and apt for decontamination of SS304LN surface.

Corrosion product deposits on boiling-water reactor cladding: Experimental and theoretical investigation of magnetic properties

Recent Eddy current investigations on the cladding of nuclear fuel pins have shown that the apparent oxide layers are falsified due to unexpected magnetic properties of corrosion product deposits. Analyses by Scanning Electron Microscopy (SEM) or Electron Probe Micro Analysis (EPMA) demonstrated that the deposit layer consists of complex 3-d element oxides (Ni, Mn, Fe) along with Zn, since the reactor operates with a Zn addition procedure to reduce buildup of radiation fields on the recirculation system surfaces. The oxides crystallise in ferritic spinel structures. These spinels are well-known for their magnetic behaviour. Since non-magnetic zinc ferrite (ZnFe 2O 4) may become magnetic when doped with even small amounts of Ni and/or Mn, their occurrence in the deposit layer has been analyzed. The magnetic permeability of zinc ferrite, trevorite and jacobsite and their solid solutions are estimated by magnetic moment additivity. From the void history examination, the low elevation sample (810 mm) did not face significant boiling during the irradiation cycles suggesting growth of ( Mn 0.09 2 + Zn 0.75 2 + Fe 0.29 3 + ) [ ( Fe 1.71 3 + Mn 0.03 2 + Ni 0.13 2 + ) O 4 ] crystals with theoretical value of the magnetic permeability for the averaged heterogeneous CRUD layer of 9.5 ± 3. Meanwhile, ( Mn 0.16 2 + Zn 0.55 2 + Fe 0.29 3 + ) [ ( Fe 1.71 3 + Mn 0.04 2 + Ni 0.25 2 + ) O 4 ] crystallizes at the mid elevation (1810 mm) with theoretical magnetic permeability for the CRUD layer of 4.2 ± 1.5 at the investigated azimuthal location. These theoretical data are compared with the magnetic permeability of the corrosion product deposited layers gained from reactor pool side Eddy current (EC) analyses (9.0 ± 1.0 for low and 3.5 ± 1.0 for high elevation). The calculated thicknesses and magnetic permeability values of the deposition layers (estimated by MAGNACROX multifrequency EC method) match together with these estimated using an “ion magnetic moment additivity” model.

Corrosion product measurements at Sizewell B PWR

Corrosion product concentrations and surface activities have been measured during hot functional tests and cycles I to 4 at Sizewell B, in a programme aimed at understanding corrosion product behaviour and radiation field build-up. The results are discussed in terms of primary coolant chemistry, sample line effects, passivation, radiation fields and, for shutdown and start-up, the origins of the corrosion products released into the primary coolant.

Effects of hydrogen water chemistry on radiation field buildup in BWRs

A number of boiling water reactor (BWR) plants worldwide are currently operating under hydrogen water chemistry (HWC). In some reactors, when switching from normal water chemistry (NWC) to HWC, an increase in the recirculation piping dose rates has been observed. Understanding the key factors which affect the dose rate increase is the subject of our current investigation. Laboratory experiments have been conducted under control chemistry conditions to examine the rates of 60Co deposition and the characteristic of oxide films formed on stainless steel surfaces. The activity buildup data obtained from two operating BWRs are carefully reviewed and discussed in this paper. Based on both laboratory and reactor data, a plausible mechanism of enhanced activity buildup under HWC conditions is hypothesized.

The Passivation Effects of Magnesium Ion on PHWR Primary Heat Transfer System Structural Materials.

Zinc ion injection passivation technique is being used in BWRs in order to reduce the radiation field build-up around the reactor coolant system. In the case of PWRs and PHWRs, the chemistry of the primary coolant system and the materials of construction are different from those of BWRs. In the present paper, the results of studies on the effect of magnesium ion in modifying the oxide layers formed under PHWR chemistry conditions are reported. The experiments carried out at room temperature and at 265°C are described. Electron spectroscopy for chemical analysis (ESCA) of the materials autoclaved at 265°C in magnesium containing solution has also been reported.

Suppression of Radiation Buildup on Stainless Steel in a Boiling Water Reactor

Abstract Deposition of radioactive corrosion products, such as Co-60, causes radiation field buildup in boiling water reactors (BWR) plants. In this study, deposition kinetics of Co-60 and elemental cobalt ions on stainless steels (SSs) and the effects of pre-oxidation on the suppression were evaluated in actual reactor water and laboratory autoclaves. Cobalt ions are incorporated as divalent cobalt oxides such as cobalt ferrite at the oxide/metal interface through corrosion. Therefore, a protective oxide film, which is preformed under suitable circumstances such as high temperature water with a certain amount of dissolved oxygen, can suppress the deposition. The oxide film containing aluminum has greater protectiveness.

Wear and neutron activition of positioning pins in the Millstone-2 reactor

Wear and Co 60 activity were measured on three positioning pins discharged from the Millstone-2 reactor. These data were used to explicitly calculate the inventory of Co 60 released from the full complement of 26 positioning pins. Activated Co 60 is the isotope primarily responsible for the buildup of radiation fields on out-of-core surfaces. The data show positioning pin wear was a significant source of activity in this reactor.