Refurbishing a contaminated nuclear casing13 January 2021
With increasing pressure in the nuclear industry to reduce overall costs, innovation can mitigate maintenance costs. Faisal Salman explains how creative thinking and reverse engineering helped with refurbishment of a contaminated nuclear casing
CREATIVE APPROACHES THAT EXTEND BEYOND original designs, standard tools, and traditional engineering practices can cut costs and improve the reliability of pumping equipment.
In one example, the casing of a charging pump at a European nuclear plant had been over-pressurised and had to be refurbished. Not only was the pump service radioactive, the casing was found to be twisted. Its internal components no longer properly fit into the casing, and the machined surfaces were out of alignment.
The original equipment manufacturer (OEM) of the pump said that they could not repair the casing and that the only option was to purchase a new one. The plant engineers approached Hydro, Inc, a global aftermarket pump service provider, for assistance in finding a spare casing. When no spare was found, Hydro initiated a more detailed discussion with the plant about refurbishing the casing.
Hydro’s team inspected the pump, the casing, and the internal element and explored all possible options. It was able to find an inventive solution by machining the casing in its contaminated state and developing creative methods to guarantee a proper fit-up when the casing repair was completed.
Instead of buying a new pump, the service provider was able to repair the casing at lower cost and reduce downtime.
The nuclear plant had ordered a new casing. However, the long lead time from the OEM added additional risk because the plant was running without a backup.
When Hydro suggested exploring options for repairing the casing it had a 3D scan of the casing, but Hydro needed a more detailed approach to guarantee a successful repair. The initial step was to examine the equipment first-hand with precision tools, shims and precision straightedge to measure flatness and geometry. A Hydro inspector visited the plant and conducted a thorough inspection of the internal element and casing. With a complete report of the geometric data, Hydro’s engineering team determined that the casing could be repaired.
The casing was contaminated with radioactive material, which presented an additional challenge. Because the pump had a unique configuration, it could not be free released.
The size of the casing and the machining requirements meant the work had to be done at a facility with a large machine tool. Hydro talked to three major contaminated pump service facilities (hot shops), but these facilities do not usually have the proper tooling to meet the provider’s precision standards for managing the contamination and for the repairs. Fortunately, Hydro had the necessary machine tool.
Precision equipment and hot shop operation was integral to the success of the repair as Hydro had to be certain that the casing and internal element would fit perfectly at the plant in Europe. To accomplish the repair a Radioactive Material License was transferred to Hydro’s facility. The area was fenced-in so the entire workspace would be protected. Workers were subject to hazmat conditions and wore proper personal protective equipment. Four technicians were trained with an emergency set-up.
A licensed certified health physics project manager was on site to oversee the entire project and ensure protection from contamination.
The casing was sent to a nuclear contamination service provider for as-found radiation and some initial decontamination and then to Hydro’s facility to perform the repairs. The nuclear plant sent its pump specialist, QA specialist and lead machinist to oversee the repair.
It took two 12-hour shifts of machining for six days to successfully repair the casing.
An interesting part of this complex project was the verification of the final machining dimensions and the quality of the machining to make sure the rotor would fit into the casing. Hydro’s engineering team did not want to take any chances that the rotor would not fit properly in the casing when it was returned to the nuclear plant, so they developed an approach to verify these critical dimensions in the casing. During the initial inspection at the nuclear plant, the team measured the relevant components of the rotor so they could create mock-up wear rings (the stationary components that support the rotor in the casing). If the mock-up rings matched exactly, then the rings could be manufactured to ensure the repaired casing would fit properly.
The precision mock-up rings were used to measure concentricity and to ensure that the rotor would fit properly in the casing when assembled. The precision mock-up rings were manufactured by Hydro.
Hydro had all proper protection of the machine tools, and trained four machinists and inspectors for the radioactive work environment. This was done under emergency conditions and in parallel with other tasks to save time. The casing was machined successfully in six days, on time, and the entire project, from receipt of the pump in the US to its return took only two weeks.
Hydro performed a final cleaning and passivation check to ensure there were no iron contaminants in the newly repaired casing. With negative results, Hydro was able to ship the casing back to Europe. The customer was impressed with the innovative approach and with the management of the many details in this unique project scope. The creative approach saved the nuclear plant time and money, while also reducing its risk.
Because of the unique aspects of the project scope, close coordination and project management were significant for the complex variables. Among these, the pump is a Safety-Related ASME-N Stamp pump, which requires stringent and specific compliance rules.
Author details: Faisal Salman is Director of nuclear services at HydroAire