O-rings in Pressurized Water Reactor
One of the many uses of boiler feed pumps is as part of a Pressurized Water Reactor (PWR) system in nuclear power plants.
In a PWR, the primary coolant (superheated water) is pumped under high pressure to the reactor core. The heated water then transfers thermal energy to a steam generator. Due to the combination of extreme temperature, pressure and chemical environments, an FFKM was used in a series of mechanical seals employed in the operation of boiler feed pumps for PWRs.
Boiler Feed Pump
The temperature and pressure of these pumps are typically 200 °C and 3.5 MPa, with rapid gas decompression in some cases. Media is boiler feed water with dissolved oxygen, ammonia sodium salts and hydrazine. Since the O-rings are mounted in a mechanical seal in pumps connected to the boiler in the secondary unit (i.e., outside of the reactor containment structure), no radiation is present.
The incumbent FFKM O-rings previously used showed signs of thermal and chemical degradation, as well as mechanical degradation. Cracks on the inside of the O-rings indicated that there was high probability that the damage occurred at the time of a rapid gas decompression event, when the pump was switched off. The life time of the seal was less than the required 18 months the customer had specified.
The customer tested and specified DuPont™ Kalrez® 0090 parts. Kalrez® 0090 parts offer an excellent combination of chemical, rapid gas decompression (RGD) resistance, and high temperature resistance up to 250 °C for O-ring applications in mechanical seals under these conditions. The use of Kalrez® 0090 parts and components can extend the MTBR (Mean Time Between Repair) of the pumps and reduce leakage which can translate into reduced maintenance costs and increased safety. The customer has replaced all seals that were due for maintenance with Kalrez® 0090.
Kalrez® parts last longer and seal more effectively than other elastomers due to their exceptional heat resistance. Even after long-term exposure up to 327°C, they retain elasticity and recovery properties better than other high temperature elastomers.