Smarter solution

WHEN MOST NUCLEAR PLANTS STARTED operating around 40 years ago, plant water chemistry was monitored by technicians who drew water samples manually, then walked them back to the laboratory for analysis, trending, and recording. This occurred at regular intervals, ranging from every four to six hours to once a day to once a week, depending on the parameter or chemical being measured.

For the most part, it’s still done that way, with resources taking manual data readings at scheduled intervals. Conservatism is built into operational guidelines to help compensate for an incomplete picture of water chemistry.

This could be about to change with EPRI’s Smart Chemistry initiative. “We are on the verge of a new era in water chemistry,” says EPRI senior programme manager, Lisa Edwards.

“Through automation and smart analytics, we can provide better information with fewer resources and rethink our operational guidelines.”

After years of preparation, EPRI and its utility partners have built three skids, each about 4.5ft long and 1.5ft wide and capable of housing up to eight instruments for automated online measurement of various chemicals and parameters. The skids were installed at the Salem pressurised water reactor (PWR) in New Jersey this year, with trials planned at the Darlington PHWR in Canada and an Exelon-operated boiling-water reactor in 2019.

“We expect there to be cost-saving benefits from applying these online technologies if the maintenance requirements are found to be low enough,” says Dan Wells, EPRI nuclear fuels and chemistry programme manager. “That’s one of the main objectives of the trials – to determine the maintenance requirements.”

Wells explains that US utilities installed online water chemistry technologies including ion chromatography instruments some 10-15 years ago, but these were ultimately abandoned due to high maintenance requirements. And while online monitoring is already applied in and outside of the USA for PWR secondary side monitoring and some BWR monitoring, the new EPRI skids include some entirely new technologies. “From our research, we know that ion chromatography, ion selective and dissolved gas technologies have been applied in various plants for routine online monitoring throughout the world; whereas gaps remain, or questions exist around the online or continuous monitoring of corrosion product, coolant gamma isotopics, boron and alkali (other than sodium) technologies.”

Salem trials

Three skids have been placed into trial demonstrations at Salem over the past year. Each skid operates independently: one measures water streams from the reactor coolant system, one is for the steam generator blowdown system, and one is for the main feedwater system. On each skid, the water stream flows through a line with branches to each of the instruments. Additional equipment on the skid will capture and analyse the readings.

The steam generator blowdown skid started operating at Salem in late May. The skid includes ion chromatography, cation conductivity, specific conductivity, sodium, pH, reactive silica and microchip capillary electrophoresis (MCE) instruments.

The main feedwater skid was placed into operation at Salem in early July 2018. This skid includes online X-ray Fluorescence (XRF, primarily for Fe and Cu), online dissolved oxygen, hydrazine and turbidity instruments to monitor all required feedwater monitoring parameters.

Finally, a reactor coolant system skid was started up in early October 2018, and operated briefly until Salem 2’s scheduled refuelling outage later than month. The RCS skid includes inductively coupled plasma optical emission spectroscopy (ICP-OES), online ion chromatography, specific conductivity, hydrogen and oxygen, reactive silica, turbidity and inline sodium instruments (to measure lithium).

Online coolant gamma isotopic monitoring is not currently included in the skid, but is a highly desirable diagnostic parameter for many utilities that will be added in future, Wells explains. A sample handling system that allows for both continuous monitoring of the coolant and routine decay counting is being designed and planned for demonstration over the next 12 to 18 months.

Even for those plants who already apply a significant amount of online monitoring technology, instruments/ capabilities that are of interest include the online XRF instrument for Fe/Cu measurements and online ICP-OES, which has the potential to provide “significant improvements” in monitoring of boron concentration in the primary coolant.

Next steps

All three skids operated until Salem 2 begun its refuelling outage on 11 October, and trials will continue following the outage. Both the steam generator blowdown and main feedwater skids are expected to return to service to gather startup data before being sent to OPG’s Darlington plant in Canada for the second round of trials in early 2019. Meanwhile, the RCS skid is expected to operate for 12 weeks before being sent to a to-be-determined Exelon BWR plant in the first or second quarter of 2019.

Salem continued to take manual measurements alongside the trial skids. While EPRI is still analysing the data collected, it has already identified a few improvements for the next phase of testing or completion of the demonstration at Salem.

For example, there was some mismatch between online sample data and plant-collected manual data, which EPRI believes is related to particulate drop-out in the sample lines. EPRI is exploring various options for improvement, including changing the inner diameter of sample tubing within the instrument to increase flow velocity, as well as sample acidification.

More broadly, EPRI’s Smart Chemistry initiative has objectives beyond just deploying the instrument technologies. It is hoping to leverage the latest in data analytics, connectivity and diagnostic tools to help improve control margins and reduce operating costs.

Both Darlington and the potential Exelon BWR have already installed wireless systems that are planned for use in the second round for moving data from the skids to existing databases, says Wells. “This will also facilitate evaluation of advanced data analytics.”

Beyond this, EPRI is planning a full-scale demonstration and rollout of automated water chemistry for 2021. “We’re going to do a final demonstration in 2021, applying everything we have learned since this year’s demonstration—optimised instrumentation, improved analytics, and more effective operational guidelines,” says Joe McElrath, Smart Chemistry project manager.

“Ultimately taken together, these will improve asset protection, worker efficiency, reduce radiation exposure and provide an optimised monitoring programme,” adds Wells. “The technologies will provide the correct data and evaluations to making the right responses. This improves control margins and reduces operating costs.”  

Goals of Smart Chemistry

• Deployment of advanced detection technologies that remove the need for manual sampling of chemistry.
• Deployment of advanced data analytics to enhance chemistry control including improving predictive capabilities and understanding the relationships between chemistry and plant operation.
• Improvement of chemistry control guidance. More frequent data improves the understanding of chemistry at any giving point during operation, which allows for further optimisation of plant responses to chemistry observations.