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Key Issues in Plant Chemistry and Corrosion in BWRs – 2018

Annual Reports Presenting Key Results Published During 18 Months, BWR Chemistry, Coolant Chemistry & Corrosion

(LCC14)

The second report summarising the BWR related papers and various other subjects is designed to provide updated information with the author’s critique and analysis for the benefit of the LCC customers. The report is expected to be a comprehensive summary document incorporating the latest information on BWR water chemistry and decommissioning that would benefit the operators and regulators, and those who have not been able to attend the NPC 2018 Conference.

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Key Emerging Issues and Recent Progress Related to Structural Materials Degradation

Annual Reports Presenting Key Results Published During 18 Months, Degradation of Different Types of Structural Materials, Structural Material Degradation

(LCC14 AR)

During operation, the materials used for the construction of components react with light water reactor environment and cause component degradation, including cracking at welds and piping. Such degradation is due to irradiation, corrosion, fatigue, and other damage mechanisms, and has remained a severe operational challenge for utilities. Details on such degradation are regularly reported and published in scientific journals and at utility workshops and conferences. Foremost in the latter category are those organised since 1983 by NACE, TMS, ANS and CNS in the Environmental Degradation of Water Reactor Materials.
The Annual Report will contain highlights from the 18th International Conference on Environmental Degradation of Materials in Nuclear Power Systems Water Reactors, which was held in Portland, Oregon in August 2017. It will cover PWRs, VVERs, CANDUs and BWRs.

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The Effect of Hydrogen and Hydrides on the Integrity of Zirconium Alloy Components: Hydride Reorientation

Fuel Material, Properties of Hydrides and Impact on Fuel In-Reactor Performance

Hydride orientation has an important effect on fracture toughness of hydride-containing zirconium alloys because hydrides form as approximately linear arrays of platelet-shaped microscopic precipitates with habits on or near the basal planes of the α–Zr matrix in which they form.

This Stand Alone Report (SAR) addresses a key aspect of the issues raised in the foregoing by providing a comprehensive, self-contained and up-to-date review and analyses of the results of studies carried out on the conditions governing hydride orientation in zirconium alloy pressure and fuel cladding tubes used in nuclear reactors. The report combines a detailed theoretical and experimental overview of this subject with the author’s own analyses of these results. These analyses make use of theoretical advances documented in the author’s 2012 book dealing with the effects of hydrogen and hydrides on the integrity of zirconium alloy components. In the author’s 2012 book, emphasis is placed on delayed hydride cracking, which is a localised failure mechanism.

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Use of Film Forming Amines (FFA) in Nuclear Power Plants for Lay-up and Power Operation

Annual Reports Presenting Key Results Published During 18 Months, Coolant Chemistry & Corrosion, PWR/VVER Chemistry

(LCC13 AR)
This report presents a new corrosion inhibitor based on film forming amines (FFA), which are often referred to as fatty amines or polyamines. FFA can form a mono-molecular hydrophobic film or layer adsorbed on the metal surfaces, that constitutes a homogeneous protective barrier against corrosion by its water-repellent behaviour. FFA belongs to chemical substances of the class of oligo alkylamino fatty amines, the simplest one being the well-known Octadecylamine (ODA). Due to the volatility of the film forming amine, the whole steam water cycle can be protected. The high affinity to surfaces can lead to a slow removal of surface deposits such as loose magnetite and impurities. FFA’s are successfully used as water treatment additives for several decades, in steam water cycles of the VVER type in Eastern Germany and Russia with positive treatment results.

For several years, AREVA has very successfully applied this treatment using a specific procedure in several PWR plants. The purposes are to control the corrosion product transport into steam generators during power operation and for long time lay-up of whole steam water cycle without using hydrazine. Even in a BWR plant this FFA treatment was applied in several parts of steam water cycle with success. This report explains the mechanism of the FFA chemistry treatment and summarises the published information regarding the application results achieved in western nuclear plants.

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The Underestimated Role of the Oxygen on RCS Component Failures

Annual Reports Presenting Key Results Published During 18 Months, Coolant Chemistry & Corrosion, PWR/VVER Chemistry

(LCC13 AR)

PWR chemists may claim that there is no oxygen in the Reactor Cooling System because hydrogen injection suppresses the oxidising species generated by radiolysis. This is why, at EDF, the RCS has no oxygen monitoring. In fact, this assessment is true only if free flowing conditions are considered. The RCS contains many flow-restricted or occluded zones where some chemistry deviations can occur, one being the presence of oxygen.

This report aims to keep the plant chemists alert regarding oxygen tracking, ingress, venting, scavenging, monitoring. It also shows some examples of field failures that occurred because oxygen presence was not anticipated in the environment. This report helps plant engineers understand why they should stay alert regarding oxygen control. The report shows there are several ways to limit oxygen ingress or to scavenge oxygen in the RCS. The oxygen specification may seem stringent, however the failures presented in this report support a non-deviation application of the RCS oxygen specification.

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Strategic Plans for Primary and Secondary Water Chemistry Programmes

Annual Reports Presenting Key Results Published During 18 Months, Coolant Chemistry & Corrosion, PWR/VVER Chemistry

(LCC13 AR)

The U.S. requirements for a Strategic Water Chemistry Plan, despite the additional work for plants, has been a benefit to U.S. nuclear utilities. The reasons for this are that it requires plants to consider the balance of plant components and their chemistry considerations to the overall integrity of the steam generator integrity, primary system pressure boundary and the fuel cladding integrity. This not to imply that either U.S. utilities or non-U.S. utilities would not consider these issues in developing their own water chemistry plans. However, these voluntary commitments by the U.S. nuclear utilities has probably reduced the regulatory requirements imposed by the NRC, although this is not known for certain.

This document explains the Objective and Optimisation Methodology of this Strategic Water Chemistry Plan. For the Primary Coolant, it includes the Parameters Impacting or not the Pressure Boundary or Fuel Cladding Integrity. For the Secondary System, it includes the key elements and the components susceptibility and reliability. The report is of benefit to those non-U.S. utilities in developing their own water chemistry programs, both primary and secondary side.

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BWR Decommissioning General Information and Experiences

Coolant Chemistry & Corrosion, Decomissioning

(LCC13 AR)

Many BWR nuclear power plants have begun decommissioning activities recently after a period of 30 to 40 years, with the final goal of obtaining license termination and getting the property released based on the regulator’s decommissioning regulations and guidelines. The power plants use a variety of strategies for dismantling systems, structures, and components, waste management, and deciding on the future use of the site. Typical activities include safely decommissioning of the plant, minimising radioactive waste generation, fuel removal and storage, license termination and getting the site restored and released. In the US, it is expected that decommissioning will be completed within a period of 60 years.

During decommissioning, plant sites typically use one of three approaches, Immediate Dismantling (DCON), Safe Enclosure (SAFSTOR) or Entombment (ENTOMB). Each approach has its benefits and disadvantages although most plants have used the SAFSTOR approach. The report summarises the publicly available BWR decommissioning general information and experiences with salient features and practices employed in the decommissioning activity including potential costs involved.

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EPRI LWRs Material Reliability 2016 Conference

Annual Reports Presenting Key Results Published During 18 Months, Degradation of Different Types of Structural Materials, Structural Material Degradation

(LCC13 AR)

For many years, EPRI has organised conferences on light water reactors materials reliability. Given there was neither Environmental Degradation nor Fontevraud conferences in 2016, EPRI took the opportunity of providing this conference in 2016. During days 2 to 4, 104 slides were presented in 3 parallel sessions, which covered 18 topics on a whole range of concerns of LWRs.

This ANT report is a summary of some of the most important slides, with little text added. The report contains a summary and a chapter dedicated to the relevance of some results presented for the Industry. This conference brings up-to-date information regarding the latest research, plant experiences, analyses, planning and solutions for increased materials reliability in BWR and PWR components. The report is of interest for engineers in charge of expertise, materials, chemistry, non-destructive testing, fracture mechanics, corrosion, irradiation effects, degradation mitigation, and modelling.

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Covering the Zr Related Results Published During 2016-2017

Annual Reports Presenting Key Results Published During 18 Months, Fuel Material

(ZIRAT22/IZNA17 AR)

The overall objective of the ZIRAT Programme is to enable the nuclear utilities and laboratories to:

  • Gain increased understanding of material behaviour related to successful core options for the back end of the fuel cycle.

The objective is met through review and evaluation of the most recent data on zirconium alloys, identification of the most important new information, and discussion of its significance in relation to fuel performance now and in the future. Included in the review are topics on materials research and development, fabrication, component design and in-reactor performance.

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Dimensional Instability and Irradiation Growth of Zirconium Alloys

Dimensional Changes of Fuel Assemblies/Channels and Components, Fuel Material

(ZIRAT22/IZNA17 STR)

In this STR review, aimed specifically at irradiation growth, addressed are conditions of direct interest to LWRs and CANDUs, including information that has mechanistic implications. Irradiation creep was covered earlier by ZIRAT14 Special Topic Report: In-reactor Creep of Zirconium Alloys, authored by Ron Adamson, Friedrich Garzarolli and Charles Patterson, 2009.

The STR addresses all data deemed relevant to understanding irradiation growth, including a broad review of growth mechanisms, and a summary of practical effects of growth on component performance.

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