There has been a recent flurry of activity in building 11 on the Alden campus. Various types of materials used in the nuclear industry to insulate steam piping are being prepared in large vats for introduction into one of two large test flumes. Wooden scaffolding with stairs lead up to the tops of the flumes, where observations can be made and material can be added for the tests. Inside the tanks, debris-laden water flows to screen modules designed to keep the insulation material out and let the water pass freely to the pumps. To the casual onlooker the testing may seem superfluous; for Alden and its clients, however, it is critical to ensuring the safety of hundreds of thousands of people who happen to live near nuclear power plants. This testing simulates the unlikely event of a loss of coolant accident or “LOCA”.
The testing described above is a single step in a larger process which addresses the adequacy of Pressurized Water Reactor (PWR) emergency core cooling sump screen sizes at each of the 59 PWR nuclear plants in the United States. Generic Safety Issue 191 (GSI-191) was created by the Nuclear Regulatory Commission to address potential safety issues associated with loss of cooling water (LOCA) events at nuclear power plants. GSI-191 requires all PWR operators in the United States to evaluate the ability of the existing emergency sump screens (located in the reactor core sump) to block debris from entering pump inlets while not exceeding required head loss limits. This is to ensure that a plant’s cooling water system will not fail during the unlikely event of an accident. If a steam line ruptures and the resulting blast wave scatters debris throughout the containment building, that debris may become trapped against the sump screens and impair the ability of the cooling water to flow to the pump suction inlets. It is critical that this cooling water is able to pass unimpeded to the core in order to prevent a meltdown. So figuring out how to keep those screens clear is very serious business.
As Vice President Stuart Cain recently explained, the large flume setup in Building 11 accurately reproduces the water’s approach flow velocities, and also the transport characteristics of the problem-causing debris. The test setup reproduces key real-world conditions, including flow rates up to 3 cfs, elevated pool temperature, and prototypical water depths. Testing usually requires 8 to 12 hours to complete and may be repeated for different accident scenarios at each individual plant. The water is also sampled downstream of the strainer to determine the bypass fraction, and to gain an understanding of what kinds of materials make it through the screen and to the core.
While it is costly to replace these screens, it is imperative that adequate cooling water be passed through the reactor core in the unlikely event of a LOCA. These same concerns are being addressed world-wide, and Alden is becoming an integral part in assuring that all of these systems perform as intended.
