The US Nuclear Regulatory Commission will begin a special inspection at Progress Energy’s Brunswick-2 unit in North Carolina after the utility said Friday the reactor pressure vessel’s lid was not adequately tightened when it restarted earlier this week.

Most of us are also paying close attention to the events at Brunswick Nuclear Power Plant, and today I talked with a former nuclear engineer  Chris Harris about the recent developments.

Background:

The unit shut Wednesday morning after the reactor leaked. An investigation showed the inadequately tightened reactor vessel head was a potentially “significant” safety issue, Progress said in a report filed Friday with the NRC.

Workers seeking the source of the leak found that at least 10 of the 64 bolts that secure the reactor vessel head to the pressure vessel were not fully tightened, Progress spokesman Ryan Mosier said in an email Friday.

The company is reviewing what happened and whether any components were damaged, Mosier said.

The unit had been in a maintenance outage, was in the process of restarting and was operating at 7% power when workers discovered the leak in the reactor coolant system, Progress said in an event report filed Wednesday with NRC. When the leak exceeded 10 gal/minute, the unit was shut, Progress said.

The Brunswick Nuclear Plant has two boiling-water reactors that generate 1,875 megawatts of electricity. Each of the Brunswick reactors is refueled once every 24 months, usually in the spring when the demand for electricity is relatively low.

At the Brunswick Plant, 1 million gallons of water per minute are pumped from the Cape Fear River where it passes through the plant’s cooling system and then drops approximately  15 feet to the head of the outflow canal.

Description in Detail:

Refueling procedures are elaborate and well documented procedures, and one of the biggest questions is why the proper procedures were not followed, or were carried out incorrectly.

The bolts need to be tensioned in a specific Torque Pattern, which generally includes multiple passes.  Refueling procedures require a crew of  at least 6 engineers, and additional Quality Control inspectors.

The Tensioning Tool is inspected and maintained, and is also part of the QC checklist.  This is not a simple situation where someone didn’t torque down the bolts correctly, as multiple personnel would have had to check and confirm the status prior to restart.

In fact, according to Progress Energy’s 35 day outage schedule, the reassembly and reactor test are the 9th, and 10th steps of the process, and one can’t help but wonder why this was not detected before the reactor was re-pressurized.

[quote]

Dr Corcoran is the President of the Nuclear Safety Review Concepts Corporation, a company providing oversight, assessment, and investigation services to the high hazard industries. In this capacity he has served various U. S. Department of Energy (DOE) sites, the U. S. Nuclear Regulatory Commission (NRC), nuclear power plants, fossil power plants, construction companies, power supply companies, and other high hazard industry entities.

Dr Corcoran shared his thoughts in the comments, and readers should also look at his other research in root cause and lessons learned.  One of these presentations,

Recent Experience in Organizational Learning from Adverse Events in High Hazard Industry, can be found here.

Dr Corcoran: “The overarching question that needs banner visibility is:

What were the earlier, better, cheaper, safer, more risk-informed, more regulation compliant, more safety culture supportive….ways that the problem and/or its harmful factors could have been detected?”

[/quote]

Chris had some very good questions regarding the Brunswick event, that I felt were worth sharing.

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1. What testing was performed to determine that the RPV Head was Tensioned properly?
2. What caused the improper Tensioning ? Procedure, Skill of the Craft? Aggressive Schedule?
3. What are the Acceptance Criteria in the procedure for a properly tensioned head”
4. How do you know that you meet the Acceptance Criteria?

[/quote]

Not only are the procedures and QC process in question, but the event also impacts operations and reliability of reactor components.  Chris highlighted a few questions that he felt were critical to ensure safe restart and operation.

[quote]

1. Could there have been Foreign Material on the RPV Head Flange?
2. What damage to surrounding equipment in the Drywell was sustained by the Steam/Water Leak?
3. What is the condition of the Refueling Seal, now that it has been sprayed with Steamy/Hot Water?
4. Did Hot/Steamy water find its way on the Outside of the Containment such that Corrosion in the future will be a problem?
5. Did the steam leakage affect the Reactor Vessel Head Studs and their Threaded Holes (in the Reactor Vessel Flange) such that they will fail at a future date?

[/quote]

At this point, Progress Energy is keeping fairly quiet about the specifics, and initially only revealed information of a “possible leak at the top of the reactor vessel”.  Monday morning should prove eventful not only for the Utility, but also for regulators.

The NRC has an opportunity to handle this event in a more effective manner then the North Anna restart debacle. (Only 1 reactor was able to restart)  But after recent actions (or lack thereof) taken by the NRC, we will have to wait and see, and are unable to take press releases meant to make us feel safe, rather then describing and outlining “safe”.

Related articles

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• Tags: BWR, Drywell, Editorials, ENENews, Fukushima Daiichi, Japan, Nuclear, Nuclear Fuel, Nuclear Reactor, Nuclear Regulatory Commission, Nuclear Safety, Radioactive, Reactor 2, Reactor 4, Reactor Coolant System, Reactor Pressure Vessel, Safety Issues, Strontium, TEPCO