US debut for Westinghouse fuel pool monitor

The commissioning of a system enabling remote monitoring of the used fuel pool level at Watts Bar has marked the first use of the Westinghouse technology at a US nuclear power plant. The system has already been deployed at some European plants.

Westinghouse has completed installation of its spent fuel pool instrumentation system (SFPIS) at Tennessee Valley Authority's Watts Bar plant and, following successful testing, it has now been declared operational.

Westinghouse said its SFPIS "provides plant operators a way to monitor the water level in the pool to verify that the used fuel remains covered by water and appropriately cooled."

The system uses primary and back-up guided wave radar sensors, both permanently installed. Each measuring device consists of a flexible stainless-steel cable probe, suspended into the used fuel pool, with the tip of the probe sitting just above the fuel racks.

The electronics for the sensor are mounted in an adjacent room so that the instrument is not subjected to the radiation and high temperatures that could result from loss of water in the pool. The sensor electronics module is connected to a battery-backed uninterruptible power supply and a transmitter, which sends readings of the pool water level to a remote location. Two such independent systems would be installed at each fuel pool, the first as a primary and the second as a back-up.

Westinghouse senior vice president for automation and field services David Howell said, "This is one of the first Westinghouse post-Fukushima modifications to be installed and be operational at a US nuclear power plant."

The company has contracts to supply more than 90 used fuel instrumentation systems in the USA. These systems are at various stages of installation and testing. The system has already been supplied to a number of European plants. It has also been incorporated into the design of the AP1000.

Post- Fukushima requirement

In March 2012, in response to the accident at the Fukushima Daiichi plant a year earlier, the US Nuclear Regulatory Commission (NRC) ordered all US utilities to install "a reliable means of remotely monitoring wide-range spent fuel pool levels." This, it said, will "support effective prioritization of event mitigation and recovery actions in the event of a beyond-design-basis external event."

The used fuel pool level instrumentation at US plants is typically narrow range and, therefore, only capable of monitoring normal and slightly off-normal conditions. According to the NRC, "beyond-design-basis external events could challenge the ability of existing instrumentation to provide emergency responders with reliable information on the condition of spent fuel pools."

Researched and written
by World Nuclear News