Finding obsolete equipment and parts for Candu reactors

30 November 2001

Nuclear utilities are finding it increasingly difficult to procure spare parts from the original equipment manufacturers. Obsolescence, OEMs ceasing to be in business due to lack of ongoing demand, the costs of maintaining nuclear vendor qualifications with the associated documentation burden and changing regulatory requirements are key contributing factors to these difficulties. By S Azeez, G Mizuno and P Tume

Demand for items in the traditional supply chain naturally arises from plant maintenance programmes. In the early years of the nuclear industry, this demand was easily met, because the approved vendors list was well defined, and plant owners could easily ensure that items met the quality assurance standards for safe plant operation. However, over time, the approved vendors list has become more difficult to maintain for a variety of reasons. It has been estimated that over 60% of nuclear qualified manufacturers have left the market or have dropped their nuclear programmes.

Contrary to the traditional definition of obsolescence, where an item is out-moded or no longer used, nuclear supply obsolescence refers to in-place equipment that is still needed, but is unavailable or no longer supplied by the OEM. Even if an alternative item is found, it is a significant challenge to ensure that the item meets the original specifications. It can be very expensive when such costs are amortised over a relatively small number of spares. Compounding this problem is the fact that an individual station's localised practices such as designation of equipment and spares makes the procurement process cumbersome and labour intensive. For example, identical equipment, if designated differently, can make the exchange of such parts between identical stations difficult in cases of emergencies or for pooling of spares. The lack of replacement parts is an everyday issue facing operating plants and may negatively affect station performance if its timely availability is difficult. As time progresses, these issues will increase in severity unless they are dealt with before they become emergencies. To a large extent, these difficulties can be overcome by having a central organisation play a key role in developing a common basis to identify parts, defining the attributes of each spare part and providing easy access to such inventory lists.

The advent of on-line inventories gives operators electronic access to a virtual spare parts store, enabling stations to order items, request customisation of off-the-shelf items and considerably speed up the procurement process.

Furthermore, based on statistical surveys of operating plant needs, an inventory of high usage spares can be developed from which spare parts can be ordered directly using Internet-based systems to access these items, review their specifications and request any customisation that may be required. All necessary documentation can also be viewed remotely and requested on-line. Such a system, linked with established proven techniques such as the 'min/max' and 'just-in-time' procurement will yield significant cost benefits by optimising inventory management.

AECL has undertaken a strategic initiative to provide spare part assurance to the Candu reactors. These initiatives focus on resolving obsolescence problems, providing a centralised resource for rapid and cost effective purchase of spare parts, and inventory balancing problems.

Solutions by design, test or build

Finding replacements for obsolete items is dependent upon several factors, including the age of the operating plants and the size of the new plant build programme. There are 20 Candu plants in operation worldwide, and two are under construction. It is difficult to convince manufacturers to supply the small orders typically needed by operating plants.

As the original designer of the Candu reactors, AECL has integrated its operations to provide a cost-effective service. In the event that a component is no longer available through traditional sources, AECL has:

• Supported replacement of obsolete equipment with upgraded technology or alternative sources.

• Provided commercial grade nuclear upgrade and reverse engineering as needed.

• Facilitated exchange of common and surplus spares among Candu plants.

• Conducted studies for parts substitutes.

• Sourced replacement parts using Internet services.

Alternative sources of supply

Several replacement parts solutions were needed during the fuelling machine manufacturing for Qinshan in China and Wolsong reactors in South Korea.

Nuclear upgrades

Under a comprehensive quality assurance programme, AECL has offered nuclear upgrades and/or commercial grade dedication services for both materials and components. Examples of these include:

• Barton pressure transmitters. In this case, it was required that the supplier would provide a transmitter that was registered with the Jurisdictional Authority prior to use. After a year of unsuccessful attempts to register the item, the project schedule was under threat. AECL worked with the supplier to upgrade the commercial quality transmitters to the requirements of ASME Section III, class 3.

• 10" flow nozzle. This was needed for a class 3 installation. AECL upgraded both the material and the design.

• Weed pressure transmitters. These required a stress analysis and upgrading to meet the requirements of ASME Section III, class 3.

• 2" gate and ball valves. The combined cost and delivery of these items as nuclear class was unacceptable. The work performed included hardness testing, chemical and physical analysis, ultrasonic inspection for minimum wall thickness, dimensional inspection and preparation of all documentation. This information was certified and submitted to both the regulatory (Canadian Nuclear Safety Commission) and the jurisdictional authority (Technical Standards and Safety Authority) for approval and acceptance.

Typically, nuclear upgrade entails either the 'upward' qualification of components from non-nuclear to nuclear grade, or 'upgrade' the nuclear class from a lower to higher grade in conformance with the applicable regulatory and jurisdictional requirements. Dedication of a commercial grade item requires that the item not be subject to design or specification requirements that are unique to nuclear facilities, that it is used in applications other than nuclear facilities, and it is to be ordered from the manufacturer on the basis of specifications set forth in the manufacturer's published product description.

The dedication process involves specifying the critical characteristics for the safety related, non-pressure boundary application, following a process to ensure the item meets the requirements and complies with any additional requirements of the jurisdictional authority, including registration.

Reverse and re-engineering

Where items are no longer available in the marketplace, AECL has carried out reverse-engineering services to develop a replacement item that is based on a component that is similar to the obsolete original item in the station. In addition, AECL has provided re-engineering services as a method of improving the original design above what is available in the current marketplace. Examples of such reverse or re-engineering include:

• Paper tape emulators for Bruce A. These resulted from reverse engineering of the reader/punch units of the original configuration. The redesign replaces the obsolete, mechanical relay-type technology with digital I/C floppy drive based units.

• Airlock valves for Darlington. AECL re-engineered the valves so that the final replacement product could be registered as nuclear class, and incorporated upgraded elastomer seals to improve the item's performance. The work included redesign, manufacturing, inspection, extensive performance and acceptance testing, and registering the item with the TSSA.

• Pickering B fuel transfer mechanism pump cover/pedestal. The original pump pedestals were made of cast iron and developed cracks during the course of routine operation. The CNSC dictated that the replacement cover/pedestals must meet nuclear class 3 requirements. AECL re-engineered the pedestals using ASME code material, manufactured, inspected, tested and registered the item with the TSSA.

Candu utility resource centre

A general problem across the Candu industry is the lack of a centralised resource centre with the tools to connect technically qualified people and information relating to procurement issues. The direct benefits of this type of a centre result in development of parts equivalencies, a source of generic parts supply and reduced duplication in services.

Furthermore, such a centre must provide access to a steady resource of pooled expertise to address common obsolescence problems.

AECL is developing web-based technologies to facilitate electronic exchange of information. The objective is to provide convenient access to information by users around the clock. Currently, there are two AECL initiatives for the web technology: a centralised information repository with links to an on-line spare parts warehouse; and pooled inventory management.

Centralised information - an e-commerce backbone

Effective materials management involves activities ranging from materials planning to investment recovery. Most of these activities depend on readily available and accurate materials information. Sharing of product specifications and other inventory information among operating stations has been difficult due to a variety of reasons such as the use of utility specific materials management systems that are not cross-compatible. The Internet and advances in e-commerce have overcome many of the technical barriers against information sharing.

On-line directory

Since December 1999, AECL has been a subscriber to the on-line directory called RAPID (Readily Accessible Parts Information Directory), which is a common database of inventories accessible through the Internet. The members include power utilities, other industries and their suppliers. The directory facilitates the buying and selling of parts between the stations and their suppliers, and among the stations themselves. This service relies upon the purchaser to ensure they understand the full engineering-related implications from purchasing the product. In using this facility, AECL assesses the engineering equivalency of the available items from the database against the requirements, performs reconciliation of code items from various standards when needed, and upgrades as necessary.

Inventory recovery operations

There are several options available to recover some of the investment tied up in inventory. As part of the inventory initiative, AECL is currently working with Candu utilities to create plant life maintenance programmes that allow the client to optimise maintenance activities using techniques such as reliability centred maintenance. As an outcome of this process, the utility can better specify parts demand, which in turn can lead to minimised inventory investment and warehousing. This service is supported by inventory brokerage and pooling of low frequency of use, high-cost assets.

Inventory brokerage

Stations can realise major cost savings by having a common inventory broker who facilitates the bulk purchasing and exchange of common, specialised spare parts among the stations. The cost savings would be realised through the centralised information resource to reduce procurement engineering labour hours, improved material availability and disposal of surplus inventory through sales to other utilities.

Inventory pooling

In addition to brokerage, AECL has the capability to create and maintain an inter-utility pool of high cost, low frequency of usage critical items. This inventory may be physically relocated to one or more key warehouses, or may be virtually stored. In both cases, the inventory can be Internet-ready to allow real-time client access.

Depending on individual items and their interchangeability, it will be possible for utilities to not have to carry such costly items individually in their inventory. As long as the location and delivery arrangements are known and planned for, significant reductions can be made in the size of the inventory pool with associated lowering of carrying costs.

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