Thanks for visiting my website. I am a Professional Engineer in a Consultant in nuclear business. I am experienced in solving Obsolescence issues and implementation of Nuclear Digitalization and difficult I&C problems. For obsolescence resolution, sometimes digitalization is an answer. On the other hand digital technology becomes obsolete sooner than its analog counterpart. Currently, “Nuclear Promise” defines the goal of current Nuclear Management that the nuclear business needs to be more competitive by adopting various cost saving strategies. Digitalization is one of the options to make nuclear business more competitive in comparison to other energy sources of supply.

Nuclear Digitalization

Digitalization has a few aspects that affect the nuclear plant design, operation, maintenance, data monitoring etc.  It also poses certain concerns, such as Regulatory compliance, Software Qualification, Cyber Security, implementation cost etc.

Benefits of Digitalization are well known.  It increases plant efficiency, automatic configuration management, helps condition based maintenance, improved reliability, paperless infrastructure procedures, walk down and instant communications among the stakeholders which further enhances nuclear performance.

Current CEO’s of Nuclear Utilities have taken a pledge to reduce nuclear operating costs and have adopted a program, called: "Nuclear Promise & quot;

(Ref # 1).  Some of the aspects of Nuclear Promise: Improve Efficiency of the Nuclear Plants; Target focus areas to reduce operating costs. Industry has the target to reduce nuclear operating costs by 30%. Cost reduction is contributed by overall nuclear plant Safety, equipment reliability and efficiency improvements Nuclear Digitalization at CANDU Stations.

CANDU reactors have adopted reactor controls digitally since 1971.  Major applications of digital reactor controls were achieved during start up of Pickering A (Ontario Hydro, Toronto, Canada).

Digital implementations included complex control logic for large control programs such as: Steam Generator Level Control, Reactor control, Primary heat transport system ressure and inventory control. These controls are Category 2 type;

(Ref 2) controls and have less significant consequences in comparison to Category 1 type functions, such as Reactor shutdown system, ECIS and Containment functions. Here is the timeline.

1971 – Pickering ‘A’ introduced the Digital Control Computer that controlled all critical functions of the reactor. These were mostly Category 2 functions.

1. 1985- Microprocessor based system was introduced for ECIS (Emergency Coolant Injection System) conditioning signal and addition of Reactor Dump Trip for Pickering A Reactor SDS system. These were category 1 functions and the technology worked perfectly ever since.

2. 1989- Powerhouse Emergency Venting (safety Related application) due to steam break in the turbine building. The use of microprocessor based system was needed due complex timing requirements. The application was successfully implemented meeting the safety requirements.

1992 Development of Digital Trip Meter funding was approved by Ontario Hydro Management. The project was initiated to address a unique human factor issue. The reactor high temperature trip margin (3.5 deg C) could not be accurately interpreted in an analog meter and hence the operator could trip the reactor inadvertently (due to inadequate interpretation of analog meters) even when the process does not require a reactor tripping. A business case was developed that projected savings of $20 million dollar due to prevention of spurious trips, operation closer to trip set point (increased efficiency) and a more reliable hardware.

Digital Trip meter development provided an opportunity for the trial run of newly developed Software Standards by OPG (formerly Ontario Hydro) and Candu Energy (formerly AECL). This initiative received full endorsement of CNSC (Canadian Nuclear Safety. With successful development of Category 1 application software in accordance with the new software quality standard, the CNSC allowed OPG to rewrite Darlington SDS1 and SDS2 software.

Darlington trip computer software development (late eighties) faced licensing challenges and development of new Software Engineering Standards was needed. Digital Trip Meter provided the opportunity for trial run of newly developed Software Engineering Quality standards.  These software development standards require processes to follow rigorous verification, hazard analysis, testing and reliability. Darlington SDS1 and SDS2 software rewrite was completed around 1995.

1997- Analog controller replacement by Digital Controllers using ABB 5000 series micro DCI platform. Several peripheral modifications were made to manufacture's original design to make the new controllers selected for Pickering A applications. The new design was adopted for replacement of all controllers in other CANDU Stations.  It should be noted that the new controllers had optical isolation for all input output circuits and an EPROM was used for loading application specific data.  Also the wiring for the new controllers was configured such a way that replacement digital controller was plug and play type while maintaining the existing enclosures.

This design strategy saved significant amount of installation, commissioning and maintenance costs. Some controllers required software qualifications for Category 2 applications.

2007- DCCs used by CANDU Stations were obsolete as the original company stopped manufacturing the hardware. CANDU Owners Group (COG) purchased a company (SSCI) which manufactured the similar hardware.  A contract was set up with a L3 Mapps for life cycle management on behalf of 8 utilities and coordinated by COG. The process is running successfully for the last 10 years without any difficulties.

Challenges Regulation, Software Qualification and Obsolescence.

 Regulation
Pre-developed software was used for Pickering A ECIS conditioning signal and dump arrest trip and Power House Emergency Venting. CNSC did not have much concern on software quality (due to new introduction in nuclear business) in 1980s.

CNSC endorsed Digital Trip Meter software development process prior to Darlington SDS1 and SDS2 software rewrite.
Darlington SDS1 and SDS2 software rewrite was needed due to lack of reviewability and mapping of various software elements translated to the requirements.

3. Use of software in the US jurisdiction is very difficult for safety critical application;

 Software Qualification Standards:
It was not well defined in the 1970s or 80s. The standards developed by IEEE were not very helpful Software Engineering Standards were developed by Ontario Hydro, AECL, to address the deficiencies identified in first version of Darlington SDS1 and SDS2 software. A well developed standard may not eliminate software related errors.  Digital Trip Meter software development followed Category 1 standards in early 1990s, still had 4 errors, which would not have affected the safety functions and hence left alone.

 Obsolescence:
Life cycle for Digital technology has a much shorter  than analog hardware as the developers continue to improvement the product, which makes the current design obsolete much sooner.  Digital Obsolescence is more difficult to solve than analog hardware obsolescence, unless mitigating actions are considered at the time of software and hardware design. A well developed strategy will provide a better “Life Cycle” of the product, as currently being followed for DCC replacements in various CANDU Stations.

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