Chemistry, Fuel & Radiation Protection

Utility Consulting: Effective water chemistry programs ensure fuel and material reliability and radiological performance objectives are achieved, while minimizing direct costs and impact to plant operations. DEI regularly assists utilities by providing objective and quantitative analysis to support optimization of water chemistry practices. In a recent example study, DEI assisted a US utility with the following:

• Standardization of fleet-wide PWR chemistry practices
• Optimization of zinc injection concentration to achieve dose rate reductions while minimizing risk of crud-induced power shift (CIPS)
• Identification of alternate, lower cost resin products demonstrated to be equivalent with regard to radiological performance and other technical metrics
• Optimization of shutdown cleanup practices including RCP run time in order to shorten outage schedule and minimize the risk of contamination events
• Identification of changes in demineralization and filtration practices to reduce radwaste volume and disposal costs

A key benefit of these studies is that DEI recommendations are supported not only by independent analysis, but also benchmarking against US and non-US operating experience.

Root Cause Investigation: When properly analyzed, water chemistry data can provide significant insights into factors contributing to elevated dose rates and radiation exposure to workers. Recently, a two-unit BWR site observed a divergence in chemistry and radiological performance between the two units and DEI provided an independent root cause investigation and assisted the utility in prioritizing corrective actions to resolve the issue. Key findings and results achieved as a result of DEI’s consulting study were as follows:

• Legacy crud already present on the fuel and within the reactor recirculation system was confirmed to account for >90% of the elevated Co-60 activity, with fresh cobalt from Stellite^TM surfaces being a minor contributor
• Costly and dose intensive efforts to remove/replace Stellite^TM containing components was deprioritized
• Recommended dose rate reduction activities were performed during the subsequent refueling outage, reducing plant dose rates by a factor of 10

DEI has continued to work with this utility to further optimize radiological performance and minimize recontamination during subsequent plant operation.

Independent Consulting: When a reactor is being exported, there are often gaps between technical information and justifications provided by the reactor supplier in the country of origin and that required by the regulator in the country of import. In a recent example project, DEI assisted an advanced reactor supplier with the general design assessment process for a foreign nuclear regulator. The following assistance and insights were provided:

• Comparison of the design and operational practices of the advanced reactor design to reactors currently operating globally, with a focus on chemistry, source term, and radiation field control experience and lessons learned
• Identification of design features, material selection choices and planned operational practices representing best available techniques, those differing from global practices but technically justifiable based on plant design differences, and those for which modified practices or material selections were recommended

DEI’s independent technical support was effective in justifying the advanced reactor design / operational practices to the local authorities and supporting regulatory acceptance of this advanced reactor design.

Impact Assessment: DEI was the principal investigator for EPRI report 3002005335, and regularly assists utilities both in developing effective water chemistry control strategies during extended outage periods and managing any startup chemistry excursions which occur after outages. In a recent project, DEI provided the following technical support when a CANDU unit experienced a sulfate excursion in steam generator (SG) blowdown during startup from an extended refurbishment outage.

• Identification of short, medium, and long term actions to bring sulfate back into specification while minimizing impact to plant materials
• Provision of a technical justification for continuing to operate, avoiding costly power reductions
• Demonstration that the sulfate originated from a sulfur source within the SGs (allowing for more focused corrective actions)
• Quantification of the risk of accelerated tubing degradation due to the sulfate excursion

Since return to power, this unit has continued to operate safely and reliably with no material degradation or performance issues attributable to the startup chemistry excursion.

Technical Evaluation & Experimental Validation: Foreign material can enter nuclear reactor systems during maintenance activities and as a result of component degradation. Recently, when plant operating experience highlighted high potential for an elastomeric component to degrade and enter the reactor system in a BWR plant design, DEI assisted a utility in evaluating the consequences of this event on plant integrity and performance. Specific assistance and insights provided by DEI in this study included.

• Identification of an alternate material that would decompose at operating temperatures, minimizing the risk of foreign material-induced fuel failures
• Analysis and testing of the alternate material to demonstrate functional equivalency and to confirm that decomposition of the alternate material was due to thermal effects alone, eliminating the need for costly irradiation testing or supplemental equivalency testing

The component was later replaced with the alternate material recommended by DEI and the component has performed reliably with no foreign material ingress to plant systems.