A U.S. BWR utility contracted with Structural Integrity (SI) to review their current reinspection guidance documents relative to those contained in the BWRVIP inspection guidelines, the purpose of which was two-fold:
Are current reinspection guidelines compliant with industry requirements?
Are there components where reinspection intervals could possibly be extended?
for Bottom Tubesheet Filter/Demineralizers Initial Installation and Performance at Browns Ferry Nuclear StatioThe Browns Ferry Nuclear Station (BFNS) intends to implement an extended power uprate (EPU) at all three units beginning in 2018 for Unit 3 and Unit 1, and in 2019 for Unit 2. EPU implementation will increase the total thermal power of each unit by 494 MWth resulting in a total uprate of 20% from the originally licensed thermal power of 3293 MWth.
Each BFNS unit is currently designed with ten bottom tubesheet condensate filter/demineralizers (CF/Ds) in the condensate treatment system that require an application of a powdered resin precoat to perform the function of demineralization. The precoat material is applied as an overlay on top of vertical filter septa. The filter septa have an inner pleated area, and with a precoat overlay, perform the function of demineralization as well as particulate iron removal. In the absence of circulating water leakage into the condenser, the primary function of the CF/Ds is to remove particulate iron that collects in the condenser hotwell. The iron source is from the corrosion of carbon steel piping and components in contact with main steam and heater drain systems.
Nuclear plant workers accrue most of their radiation exposure during refueling outages, when many plant systems are opened for corrective and preventive maintenance. The total refueling outage radiation exposure can be 100-200 person-Rem at a typical Boiling Water Reactor (BWR), and 30-100 person-Rem at a typical Pressurized Water Reactor (PWR). Accrued refueling outage radiation exposure values can be significantly greater than these values depending upon radiation fields, outage work scope, and emergent work. Outage radiation exposure is one metric used by a plant to determine outage success and by industry regulators in assessing the overall performance of a plant. Plants with high personnel radiation exposure tend to be those plants with more equipment problems and more unscheduled shutdowns; consequently, they may be subjected to increased regulatory oversight.
Radiation source term assessments are performed to understand the causes of high collective radiation exposure and to help plants evaluate their strategies for source term reduction. This involves understanding how a plant’s material choices and chemistry and operational history influence the radiation fields that develop in the plant systems. Consequently, a source term evaluation is very plant-specific, but can help a plant identify which strategies may be most effective for their specific situation.
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