When it comes to nuclear power, no margin for error
 |
| "We're safe, guys. It's not a wind turbine" |
The Union of Concerned Scientists, a highly respected non-profit research organization, released a report, “Living on Borrowed Time,” on Tuesday, February 28 that tallied serious incidents at America
Not counting the 50+ year old nuclear research reactor 12 miles away at URI’s Bay Campus, the two nearest commercial nuclear power plants to Charlestown are Millstone, on the western outskirts of New London, CT only 20 miles upwind to the west, and the Pilgrim power station in Plymouth, MA. Pilgrim is 68 miles northeast of Partridge Run in Charlestown
Last year, both Millstone and Pilgrim suffered what the Union of Concerned Scientists describe as “near misses” which are significant safety-related events that could have led to catastrophic results. The report lists one such near miss at Millstone and two at Pilgrim (one is a classified security issue).
While it’s wonderful news that each “near miss” turned out to be just that, and no one was hurt, it is NOT good news that there were three serious “events” at the power plants closest to us in 2011, and that doesn’t count the accident at URI where a student intern was exposed to excess levels of radiation.
In January, I wrote about negative findings in the federal Nuclear Regulatory Commission’s audit at Millstone. and about the NRC’s notice of violation issued to URI.
During Charlestown’s long debate about wind energy – ending with Charlestown’s virtual ban on all wind energy – much attention was paid to largely discredited health risk claims attached to wind energy, while little attention was given to these real threats well within striking range of our town.
Here is the summary table from the UCS report, followed by the detail from their study on the Millstone power plant near New London
NUCLEAR NEAR-MISSES IN 2011
| ||
Reactor & Location
|
Owner
|
Highlights
|
Millstone Unit 2
|
Dominion
|
Despite a dry run of an infrequently performed test on the control room simulator and other precautionary measures, errors during the actual test produced an unexpected and uncontrolled increase in the reactor’s power level.
|
Pilgrim
|
Entergy
|
Security problems prompted the NRC to conduct a special inspection. Details of the problems, their causes, and their fixes are not publicly available.
|
Pilgrim
|
Entergy
|
When restarting the reactor after a refueling outage, workers overreacted to indications that the water inside the reactor was heating up too rapidly, and lost control of the reactor. The plant’s safety systems automatically kicked in to shut down the reactor.
|
MILLSTONE UNIT 2, CT (verbatim account from the UCS report)
The Near-Miss
The NRC sent an SIT to the site after a test procedure led to an unplanned and uncontrolled increase in the reactor’s power level. The SIT identified two violations involving workers not following procedures and failing to properly control the reactor’s power level as a result.
 |
| Millstone - 20 miles from Charlestown |
Operators in the control room of the Unit 2 pressurized water reactor (PWR) at Millstone reduced the power level from 100 percent to 88 percent on February 12, 2011, to perform a quarterly test of control valves for the main turbine. Because operating crews work in rotating shifts, this group had not conducted the test for many months. The crew took several steps to prepare for this infrequent operation and guard against any mistakes.
For example, the crew reported to the training center at Millstone on February 10, to review test procedures and perform them on a full-scale control room simulator. To prevent error, a peer checker guided each operator as he or she manipulated switches on a control panel, to ensure that the operator turned the correct switches at the correct time in the correct direction.
Workers must maintain a constant steam flow to hold the reactor’s power level steady during testing. The heat produced by the reactor is transferred to the steam generators, so they can make the steam that flows to the turbine. The steam generators are the balancing point. If testing changed the steam flow, it would upset the balance and change the reactor’s power level.
The key to the test involved balancing opposing effects in the reactor. Thus, during the simulated test, operators first reduced the reactor’s power level from 100 percent to 88 percent. An inherent result was the buildup of xenon, a fission byproduct, which further decreased the power level. To maintain a constant power level, the operators diluted the boron concentration in the reactor cooling water, offsetting the xenon effect.
To further ensure proper balance, the operators opened one of the turbine bypass valves (labeled BPV). The open bypass valve allowed steam to detour around the turbine control valves and the turbine, and flow directly into the condenser, to maintain a constant flow.
When the operators performed the practice test on the control room simulator, they successfully maintained a constant steam flow.
Two days later, the freshly prepared operators reported to the real Unit 2 control room for a repeat performance. The crew leader conducted a briefing to review the test procedures and revisit each individual’s responsibilities. The operators then reduced the reactor’s power level to 88 percent, as planned and practiced. They then diluted the boron concentration and opened the turbine bypass valve, as they had done on the simulator just two days earlier.
However, when testing the first control valve, an operator turned the dial for the remaining three control valves in the wrong direction. That operator’s peer checker mistakenly believed the operator had turned the dial in the correct direction. The control room supervisor, who was watching the test, also mistakenly thought the operator had turned the dial in the correct direction. However, because it was actually turned in the wrong direction, it upset the steam flow balance. The operator immediately saw that the reactor was losing balance, but turned the dial improperly three more times—further upsetting the balance.
The turbine bypass valve—which operators had opened in case they lost balance between the closing and opening control valves—closed fully about a minute later, in a futile attempt to restore the balance. The crew leader noticed that the bypass valve had closed and directed an operator to reopen it about 45 second later, but it automatically reclosed within 6 seconds.
The imbalance caused more steam to flow into the main turbine, and the pressure—which all the balancing measures were supposed to hold constant—rose 10 percent. In a PWR, increasing the steam flow causes the reactor’s power level to rise. Three minutes after the test began, the power level stabilized at 96 percent—8 percent higher than before the test.
The operators reduced the reactor’s power level back down to 88 percent and successfully completed testing of the turbine control valve about an hour later (NRC 2011q).
NRC Sanctions
The SIT identified two violations of regulatory requirements associated with the ROP’s initiating events cornerstone:
• Failure by operators to implement written procedures delineating responsibilities for controlling power output from the reactor core.
• Failure by operators to implement written procedures for testing the turbine valves, producing an unplanned increase in the reactor’s power level from 88 percent to 96 percent.
