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Extrabudgetary Programme on Safety Aspects of Long Term Operation of Water Moderated Reactors (SALTO)

Welcome to the web pages of the IAEA's Extrabudgetary Programme on Safety Aspects of Long Term Operation (LTO) of Water Moderated Reactors. The Agency established the Programme in May 2003, and it was concluded at the end of 2006.


The number of Member States giving high priority to the long term operation of existing nuclear power plants is increasing. Decisions on long term operation (LTO) involve the consideration of a number of factors. While many of these decisions concern economic viability, all are grounded in the premise of maintaining plant safety.

The IAEA developed comprehensive generic guidance on how to manage the safety aspects of physical ageing in the 1990’s.

It was recognized, however, that internationally agreed-upon, comprehensive guidance was needed to assist regulators and operators in dealing with the unique challenges associated with the LTO.

In response, the IAEA initiated this Extrabudgetary Programme on Safety Aspects of Long Term Operation of Water Moderated Reactors (Programme). The Programme’s objectives are to assist those Member States considering LTO of water moderated reactors in how best to reconcile the related processes and practices; how to establish a general LTO framework; and finally, it provides a forum in which Member States can freely exchange information.


The Programme is focused on developing the general framework needed to effectively pursue LTO. In particular, the following outcomes are anticipated:

Reviewing existing national approaches, practices and experience that need to be considered during LTO decision-making;
Developing guidance for regulators on the identification of the applicable safety criteria and on the establishment of guidelines for plant operators’ LTO licensing submittals; and
Providing guidance for plant operators on the processes and practices needed to support safe LTO.


The Programme Steering Committee (SC), composed of senior representatives from the participating Member States, guides the Programme efforts implemented through 4 Working Groups (WG) dedicated to:

  • WG 1 on General LTO Framework;
  • WG 2 on Mechanical Components and Materials;
  • WG 3 on Electrical Components and I&C; and
  • WG 4 on Structural Components and Structures.

SC Members WG1 Members WG2 Members WG3 Members WG4 Members

Working Group 1 deals with the general aspects of long term operation and identifies necessary pre-conditions and scoping criteria for Working Groups 2, 3, and 4. The Working Groups 2, 3, and 4 evaluate information for those structures, systems and components that are within the scope of long term operation.

The Working Groups conduct their work in four tasks in line with the Programme’s internal documents:

  • Collect available information on long term operation;
  • Review and compare the information collected, identify common elements and differences;
  • Reconcile the differences, identify future challenges and open issues;
  • Develop a Final Working Group Report.

Almost 100 experts from 13 MS and the European Commission participate directly in the Programme activities.

The Programme Final Report, which should provide information related to the required safety level of plants and how to maintain it during long term operation, should also provide information on generic tools to support the identification of safety criteria and practices at the national level applicable to LTO. The Programme Final Report is expected to be available before the end of 2006.

The Programme Final Meeting, to be held in Vienna, Austria, September 2006, will serve as the conclusion of the extrabudgetary programme.

From 2007 onwards, the IAEA regular budgetary programme on Engineering Safety for Long Term Operation of Nuclear Power Plants will continue this effort, which includes peer review service, safety standards, coordinated research, knowledge management and advisory group on LTO & Ageing Management.

Key components

The LTO of a nuclear power plant involves consideration of a number of factors to ensure plant safety during LTO operation. The Steering Committee agreed to use the IAEA Safety Guide on Periodic Safety Review of Nuclear Power Plants (PSR) as a reference to define the common terms associated with plant safety. The Safety Guide introduces the concept of 14 safety factors (and a number of associated elements), covering the whole scope of overall plant safety.

The scope of activities of this Programme does not cover all the safety factors/elements listed in the Safety Guide. Each WG identifies those safety factors and elements, for which information needs to be collected, reviewed, and reconciled to meet the WG objectives as specified in Working Group Workplan.

SALTO Key components

The Steering Committee also recognized the essential role of two other processes, the design basis management and configuration management. The interaction of design basis management, periodic safety review (or current licensing basis), configuration management, etc. are the key elements and preconditions for successful LTO.

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| Last update: Tuesday, 09 December, 2014.