Solid state analogue meters for nuclear plants2 July 2020
Solid-state analogue meters could offer an alternative option for instrumentation and control upgrades. Otto Fest explains
CONTROL ROOMS FACE OBSOLESCENCE BECAUSE they use discontinued, 1960s-era analogue and 1980s-era digital panel meters. As manufacturers for these devices have dropped out of the market, replacement units are increasingly difficult to find. Some meters are only available as rebuilds from resellers and cost upwards of $20,000 each for Class 1E instruments, versus $200 for a commercial-grade replacement.
Security, personnel and cybersecurity requirements could increase the cost into the millions. Digitalisation of the instrumentation & control (I&C) room at the Oconee nuclear power plant in the USA cost $250 million and approvals by the US Nuclear Regulatory Commission took seven years.
As well as being obsolete, analogue meters are inefficient: inaccuracy, parallax, operator errors and stuck needles can all limit output and have an impact on plant profitability. In consideration of all expenses, modernisation can yield a low or no return on investment.
Scale of the problem
Most of the world’s operating reactors — around 350 — face decommissioning or plant life extension in the coming decades, as they are over 30 years old.
Most of these reactors use analogue meters — a technology developed in the 1890s, but the only option available when these plants were built. They were economical and easy to use and read. Does this technology still make economic and safety sense? Inaccuracies, operator parallax errors and unreliability have forced nuclear power plants to implement new safety protocols in their control rooms, which mean the plant operates below optimum efficiency. Can digital technology come to the rescue?
In the 1980s digitising main control rooms offered better accuracy, safety and hence profitability. The upgrade required a heavy investment in time and money, as the new digitals were not 100% compatible in form, fit or function with existing analogue signal-powered meters.
As existing plants consider digital upgrades, is history repeating itself? The flat touch-screens typically proposed are incompatible with existing I&C architecture, and too expensive for older plants with limited life expectancy. In addition, this approach requires years of planning, testing and regulatory approvals, and must comply with new cybersecurity regulations.
What options are available?
There are limited replacement options for obsolete analogue and digital meters in plants over 20 years old that can be installed as old ones fail, or ‘as required’.
There are no new 1980s Class 1E analogue and digital replacements, as the replacement market does not justify operating expenses of manufacturers.
Rebuilt replacements are expensive and hard to find, with a six months wait for delivery.
It takes 3-5 years to digitise the main control room with APC/SCADA and flatscreen monitors. The upgrade can cost over $200 million and it will take 2-4 years to receive NRC approvals. This is ideal — but unrealistic as it is only affordable in new installations.
A lower cost and faster turn-around option is available with a DAS; but this option still requires a new I&C room and wiring, takes 2-3 years to implement, and needs 2-3 years for NRC approval. The cost is estimated at $70 million including cybersecurity compliance.
Even the latest advances in digital meter technology do not comply with the Nuclear Energy Institute’s Cybersecurity Mandate (NEI 08-09). Otek offers a range of new technology meters that can be powered by the same two-wire signal that drives the analogue meter. They are compatible with a range of common analogue instruments. But as the I&C manager of one US nuclear power plant told Otek some plants cannot afford NTM Meters because of the high cost of implementing cybersecurity protection.
In response, Otek went back to the drawing board. The aim was to design a replacement meter with the following features:
- 100% solid state, with analogue and numerical coloured display and no processors.
- 100% signal and externally powered, with the same housings and wiring as obsolete meters.
- Fail safe ( eliminating ‘stuck needle’).
- Proof against obsolescence by using generic components likely to have more than 40 years availability.
- ‘One size fits all design’ to minimise expensive spares inventory.
- 101 segment bar (for 1% accuracy & resolution) and 4-1/2 digit display for 0.01% accuracy & resolution.
In my lab, I resuscitated a 2004 ‘all hardware’ project which had been abandoned in favour of a microprocessor-based design that was cybersecurity-exempt by design (see Figure 1). It was powered by the popular 4-20mA current loop and/ or AC/DCV, AC/DCA, AC/DCW & Hz. (like the obsolete analogue meters).
I used a pure white LED bar and a customised multicolour scale plate, per the customer’s needs, to replicate an RGB bar graph without processors (avoiding NEI08-09). This served two purposes: it mimics the ‘safe, caution and danger’ colour zones and it minimise inventory. The parasitic energy of the signal is used to power the SSAM; when the signal or power fails it notifies the user visually and via alarms.
The result is Class 1E (military specification): 100% hardware (no software); cybersecurity-exempt; powered by any AC or DC signal; and able to produce over 5mW of energy, with built-in adjustable alarm outputs (MOSFET, SSR or Reed Relays), 4-20mA output. It replaces obsolete analogue or digital meters at a fraction of the cost of rebuilt meters.
The SSAM continues to generate interest among nuclear I&C managers, and Otek hopes to deploy it in the US nuclear fleet in the next two years. It offers an alternative route for I&C managers in complying with the mandates of NEI 08-09. Under NEI 08-09 the SSAM can be used in commercial and safety-related applications within a nuclear power plant.
The SAAM and NTM series is available in industrial, commercial, and Class 1E grades and Otek is a 10CFR50 Appendix B, Part 21 manufacturer.
Author information: Otto Fest is President and founder of Otek Corporation