Preferred Engineering’s Best Practices for Jet Pump Plugs

The jet pump plug is an essential tool used in the maintenance of Boiling Water Reactors (BWRs) in nuclear power plants. The jet pump system involves driving water through a nozzle to create a high-velocity jet, which in turn induces a lower pressure that draws additional water along with it, effectively mixing and circulating the water.

Jet pump plugs are used to isolate a jet pump or a section of the jet pump from the rest of the reactor coolant system to facilitate plant maintenance or inspections. By inserting a plug, maintenance personnel can safely work on the recirculation system in parallel with other activities, saving time and dose.

Preferred Engineering’s extensive experience with jet pump plugs in the nuclear power industry has allowed us to develop a number of best practices. Here are the few of the standards we’ve established in recent applications.

Continuous Rope

We continue to have good results with the continuous rope/large removal hook method for installing and removing the JPPs with both 5-nozzle and single nozzle plugs.

Air Challenge Station

The air challenge station provides assurance of the leak-tight integrity of the installed JPP, and it reveals any leakage issues with the jet pump transition pieces. By monitoring the sizes of bubbles coming from the jet pump transition joint, the nuclear plant can forecast the in-leakage and plan for handling excess flow to complete valve work.

Along with making installation easier, the air challenge has eliminated the need to obtain some of the more difficult camera shots.

Pressure Equalization

It is essential that the pressure (Delta P) across the plugs is 0 psi before plug removal. We assure zero pressure by filling the loop with demineralized water from below and observing the air in the jet pump loop vent through the JPP vent lines.

We recommend that the ends of the JPP vent lines be temporarily submerged in the cavity water for this operation. Bubbles will be observed when air is being vented and will stop when all air is removed from the jet pump loop. When the venting stops and a steady stream of water is observed from the vent lines, the plugs may be removed.

Preventative Maintenance

The 5-nozzle seal screws are not run to a hard stop and are retained with thread locker. Over tightening the screws deforms the seal. Personnel performing the TIC inspections on 5-nozzle JPPs need to keep this in mind.

When exercising and lubricating the mechanism, the plug hooks should be left in the fully retracted position ready for installation. This positioning should be verified just before the plugs enter the water to save time at the nozzle elevation.

Preferred Engineering has been designing and supplying jet pump plugs for the nuclear industry since 1983. We have continuously improved the design and have supplied JPPs to more than 16 nuclear power plants, with hundreds of successful installations. Our JPP is designed as an electropolished stainless steel weldment with a hard coated aluminum body specially designed to seal the jet pump mixer nozzle.

To learn more about the many benefits of Preferred Engineering’s Jet Pup Plugs and other products for nuclear power plants, Contact Us today.

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