BWR Decommissioning General Information and Experiences

(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.


Consequences of Power Uprating

A relatively high percentage of all operating LWRs in the world have implemented or are considering some kind of increase of the power (power uprate). This Report provides a worldwide review of power uprates. Water chemistry and radiology experiences of power uprates are presented separated on BWRs and PWRs. Key issues are identified and discussed and available options to assure maintained or improved conditions at power uprates are presented.


Corrosion Product Generation, Activity Transport and Dose Rate Mitigation in Water Cooled Nuclear Reactors

This report discusses in detail, the steps involved in, generation of corrosion products including colloid formation, activation on fuel, transport through the coolant, deposition on surfaces including zeta potential effects, release from surfaces and removal of activated corrosion products in light water reactors. The report also discusses activity transport that will include basic steps involved and models used.


CRUD in PWR/VVER and BWR Primary Circuits

The objective of this report is to provide members with the basic understanding of the mechanisms involved and their relationship to material performance and activity buildup. Content of the report is outlined below.

  • Fuel cladding failures due to accelerated corrosion
  • Axial Offset Anomaly (AOA)
  • Pressure drop problems especially in CANDU-plants and VVER units
  • Build-up of out-of-core radiation fields
  • Shutdown extensions due to high activity releases (Coolant clean-up)
  • Increased generation of radioactive waste
  • Interference with inspection necessities


CRUD in PWR/VVER Coolant Volume II – Control of CRUD in the PWR/VVER Coolant and Mitigation Tools

All materials used in nuclear power plants, as bare material (steels and alloys), are not stable in the reactor water and dissolve by corrosion. They are protected by passive oxide layers formed by the corrosion attack of the water to the metal surface under operating conditions. However, to some small extent these oxide layers dissolve in the reactor coolant and are transported as corrosion products (called also CRUD) to the reactor core. There they deposit on the fuel assemblies and are activated. The deposition of the crud on fuel assemblies and their release to the coolant highly influences the core and plant performance with respect to fuel cladding integrity and radiation fields.

The purpose of the Volume II of this Report, in LCC11, is to describe the tools and their application to adequately control the coolant crud in order to improve the fuel and out-core radiation performance. This information can support the plant chemists to establish strategies of applying the mitigating tools for crud control to achieve their plant specific goals. The information given in this Report is also valuable for fuel vendors and plant fuel engineers to evaluate the possible ways of improving the fuel performance. In a similar way, this information helps the Regulators at properly examining the relative importance of various CRUD Control Mitigating Tools to ensuring an improved fuel performance for safe operation. 
The associated Volume I containing: Mechanism of Sources, Transportation in Coolant, Fuel Deposition and Radiation Build-up, was published within the LCC10 Programme.


CRUD in PWR/VVER Coolant. Volume I – Sources, Transportation in Coolant, Fuel Deposition and Radiation Build-Up

Crud in PWR/VVER Coolant. Volume I – Sources, Transportation in Coolant, Fuel Deposition and Radiation Build-up (LCC10 STR) The topic is covered in two separate volumes. Volume I which is provided within the LCC10 Programme, and Volume II which will be provided in the LCC11 Programme. This document, Volume I covers the following topics:

  • Introduction
  • Sources of CRUD
  • CRUD Transportation in PWR/VVER Coolant
  • Crud Deposition in the Core
  • Crud Release from Core and Radiation Build-up Mechanism
  • Summary Volume II will contain information on Control of CRUD in the PWR/VVER Coolant and Mitigation Tools


Decontamination and Steam Generator Chemical Cleaning

The objective of this Report is to help the reader to gain a basic understanding of the mechanisms involved in the Decontamination and the Steam Generator Chemical Cleaning Processes. The processes described do not only deal with the basic description but also with application considerations. A second approach to Decontamination is a chronology of the plant applications which range from components to subsystem and full system Decontamination.


Deposit Formation on Fuel Cladding in PWR Primary Systems

Formation of deposits on Pressurised Water Reactor (PWR) fuel cladding has been an inherent problem in these systems since their inception and remains a problem to-date. The report provides: 1) a brief history of fuel crud in PWR systems, 2) mechanisms for material release, transport and deposition in the core and the influence by material choice, coolant chemistry and core design 3) discussions of what occurs within fuel crud that may affect its deposition rate, its effect on core neutronics and possible impact on clad corrosion leading to failure. Finally, a discussion is given summarizing our current understanding and where future work is required to further this knowledge.


Effect of Zink in BWR and PWR/VVER on Activity Build-Up, IGSCC and Fuel Performance

This Report gives a comprehensive understanding of the zinc chemistry mechanism and information on how Zinc Chemistry in BWR and PWR plants was introduced in the plants and explains the results achieved. This information is useful not only for utilities that are intending to apply Zinc Chemistry in the near future in their plants and for selecting strategies for adding zinc; but also for those utilities that are already applying Zinc Chemistry in order to optimize their strategy based on international experience. It will also be useful for Manufacturers and Regulators.