Yesterday, Diablo Canyon Nuclear Generating Station shut down after a leak was detected.
PLANT SHUTDOWN REQUIRED DUE TO RHR SYSTEM SOCKET WELD LEAK
“At 2158 PDT, plant personnel identified a through-wall leak in a Diablo Canyon Power Plant Unit 1 socket weld inside containment that provides a flow path to a relief valve that protects a common portion of both trains of the Residual heat Removal (RHR) system. The as-found condition did not comply with the requirements of equipment control guideline 7.6 and the ASME acceptance criteria. PG&E accordingly declared both Unit 1 trains of RHR inoperable and initiated plant shutdown at 2237 PDT in accordance with requirements of Technical Specification 3.0.3.
“PG&E will complete shutdown to Mode 4 and will perform repairs to restore compliance with ASME code requirements.”
The licensee notified the NRC Resident Inspector.
The Residual Heat Removal (RHR) system is a safety-related system relied on to remove decay heat from the reactor core during normal shutdown operations and in the event of an accident. Because the RHR system is safety-related, technical specifications are applied to the system to specify the limiting conditions the systems must meet in order for the plant to legally keep the air conditioning running in our homes. (I refer to this state of powering our homes as being “at power.” Is it hot in here?)
The RHR system can be inspected, tested, and worked on while the plant is at power because the RHR does not need to operate in order to make power. Per the plant’s Technical Specifications, in order for the plant to produce power to charge my greedy cell phone at least one “train” of RHR must be operable – meaning the RHR must still be able to perform it’s safety functions even if part if the system is not working or is taken down for maintenance. Because the part of the RHR that leaked was part of the system that is shared between “trains,” and the leaking crack meant that the system couldn’t meet its design code standards, the minimum conditions the plant had to meet to keep our lights on were not met and the plant operators began an orderly shutdown of the plant.
Many people don’t realize – or in the case of nuclear DIS-informers, won’t admit – that a nuclear plant is a very clean place. If you visit a nuclear plant, you’ll notice a lot of freaking noise, and shiny, clean, dry floors, clean equipment and bright lights. We don’t keep up the cleanliness to impress visitors. A clean plant is also a plant where it is easier to detect when something mechanical has failed.
Think of a used car. If you look under the hood, and there’s lots of crud and black stuff everywhere, does it make you feel all warm and fuzzy about the next 100k miles? I think not! If your car is filthy under the hood, you are much less likely to notice if something is starting to fail. (It’s pretty hard to notice miniscule ethylene glycol deposits on a leaky, black engine block.) The same logic applies to a nuclear plant. In a clean plant, little deposits of born crystal are easier to spot.
The leak was discovered during routine maintenance. Diablo Canyon plant personnel discovered boron deposits on the outside of the RHR piping (where it should never be) and knew it was not supposed to be there thanks, in part, to their plant cleanliness programs. Undoubtedly, a timeout was called to investigate why such cruddy deposits would be there. This is absolutely the right thing to do. Diablo Canyon personnel performed well by keeping the safety performance of their plant in the highest priority; and demonstrating the robust nuclear safety culture of their organization.
Politicians like Barbara Boxer (who was instrumental in delaying restart and ultimately shutting down San Onofre Nuclear Generating Station) may try to turn events like this into examples of nuclear plant failures. But in doing so, she does her constituents and all of us a disservice. Events such as the event at Diablo Canyon yesterday demonstrate how serious safety is to PG&E, to Diablo Canyon staff and to the nuclear industry.
Diablo Canyon personnel shut the plant down. Now they’ll repair the leak, study it’s root cause (how the leak happened), bring the plant back online (Turn the ac on, it’s hot in here!) and share their findings with the rest of the nuclear industry so that we can learn from it and prevent it happening again.
Keep up the good work guys.