Exelon PowerLabs’ Parts Quality Initiative (PQI) is a Nuclear Energy Institute (NEI) award-winning program that uses Operating Experience to improve nuclear power plant performance. The PQI program is a continuous learning program that proactively tests spare parts critical to nuclear safety and reliability. PQI testing ensures each component will perform its critical function once installed.

The goal of the PQI program is to identify poor quality parts caused by manufacturing defects or other factors prior to inventorying or installation. Since 2006, Exelon PowerLabs has collected manufacturer and model-based failure rate data on more than 70,000 PQI tested components. This data empowers PQI customers to identify trends and flag high-failure rate components for PQI testing. Once PQI tested, deficient parts are identified earlier, which significantly reduces plant expenses and improves schedule adherence. PQI facilitates timely warranty replacement of deficient parts, as opposed to the traditional method in which parts are placed in inventory and either fail during installation or prematurely after installation requiring unplanned replacement.


Exelon Powerlabs develops dynamic testing templates based on failure analysis as well as additional Operating Experience to ensure all possible known failure modes are evaluated. Customers send their high-failure rate critical parts to Exelon PowerLabs for PQI testing based on maintenance strategy demand or replenishment of critical spares. One customer sent seven pressure regulators to be tested against the known failure modes and added additional plant–mandated acceptance criteria to the PQI standard testing procedure. These regulators were to be installed in a valve that performs a critical function for the nuclear power plant.
PQI Standard Testing Procedure

The standard PQI testing template tests the regulators for the following critical functionality:

  • Leakage
  • Function
  • Input/Output
  • Output Lock Up
  • Repeatability

However, the testing templates are constantly evolving as new failure modes are identified through Exelon Powerlabs’ failure analysis and external Operating Experience. These testing templates are continuously updated to reflect the new information.

Pressure Regulator PQI Testing Results

Each pressure regulator would need to pass all functional tests to pass the PQI testing.

The first PQI test that was initiated was the leakage test. Exelon PowerLabs’ team applied air pressure for a set time on each regulator to ensure there was no leakage. As a result, all seven regulators passed the leakage test.
The next test performed on the regulators was the function test, which ensures the regulator can function throughout its full range based on set air pressures. The functionality test determined all seven regulators passed.
During input/output testing, the regulator’s output is set to various pressures corresponding to 50% of its output range. Pressure is then reduced and then increased a few times until it reaches the pressure determined by the testing template to ensure the regulator maintains within 0.4 psi of its determined output. After testing the regulators input/output, once again all seven passed.

Identifying the Failures

Proving functionality during normal plant conditions ensures the regulators can perform their required functions during normal operations. However, the regulators also must perform their transient functions during a disruption. Exelon PowerLabs performs a series of tests by disrupting the pressure to ensure repeatability and output lock up test measures the flow’s stabilization. Once the valve regulator is closed, it should stabilize and remain at set pressure for a period of time. Among the components tested, technicians found three regulators failed this test due to continuous pressure drift from original set pressure.
When parts fail PQI testing, the true value of the PQI program is realized. These deficient parts are returned and replaced with new quality parts that do pass PQI testing, and the plant avoids introducing a new vulnerability.

And Then There Was One

Apart from the PQI standard testing procedures, an overshoot on pressurization test was performed on the last qualifying parts that had not yet failed based on the customer’s request for additional plant-mandated acceptance criteria. The overshoot on pressurization test measures the regulators’ pressurization at 120% of rated valued and to verify pressure does not exceed this percentage on the output. Since the regulators were to be installed in a critical application, it is crucial they perform at the required pressurization.
Finally, a pulse test was performed on the remaining four regulators. In this test, a large pulse of air is applied into the input of the regulators to ensure it would be dampened so the pulse will not carry through the regulator to the rupture disc, also known as an emergency safety disc. If the pulse goes through the regulator and blows the disc, it can cause an unplanned plant transient.
Of the four regulators tested, only one passed this test. The PQI testing confirmed only one of the seven regulators purchased meet plant specifications for the application. The three regulators that failed the over pressurization test can still be used in the plant since they passed the other PQI testing standards and qualified as functional parts. However, these three regulators, cannot be used in the application originally intended.

PQI Savings Unfolded

Out of the seven regulators purchased, six failed Exelon PowerLabs’ PQI testing as well as the additional customer-imposed testing requirements. The PQI program helped prevent unplanned plant transients that could have affected nuclear safety and plant reliability. The PQI program worked as designed and stopped inadequate parts from not only entering inventory but most importantly, it kept deficient parts from being installed in the plant. The six regulators were returned to the supplier to be exchanged for new quality parts. The replacement parts were then PQI tested prior to plant receipt and successful installation.

Exelon PowerLabs’ PQI program is a dynamic program constantly adapting as new parts are tested, and new failure modes are identified. With hundreds of parts tested daily, Exelon PowerLabs continuously updates its OneLab PQI database so customers can zero in on problematic parts and easily avoid component failures. As a growing community, PQI continues to inform customers on how to better manage inventory to a higher level of quality.