This LER on duel plant trip in the mid 2016. Why do they have so much troubles with the important lines surrounding Millstone. The NRC should have got a violation over unreliable power lines.
Millstone once had three unit at their sites. Basically if two of three line tripped, the remaining lines would quickly lead to an overload. If the line would have tripped, it would lead to a loss of all power to the site and a hard trip scram to three plants. Now we only have two operating plants. Basically they had a circuit that would automatically reduce the load or trip plants such off site line load to 1650 MWes. The idea here was they would keep at least one plant operating to supply emergency power to the scammed plant. The NRC caught them in the dual plant special inspection they illegally removed this protection circuit because Millstone worried that if that circuit failed it would inappropriately scram a reactor.
1)Violation: Unreliable off site lines.
2) Violation: Because of the heavy interest removing the circuit...the NRC should have made sure Millstone had adequate training and procedure for the next trip of two Line
3) Violation: threat of a two line trip or warnings, should have powered down 1650 MWe before any trip.
4) Violation: I don't see any crew briefing when they first took over the shift or when the first line was taken down...study up on what we have to do if the second line trips in procedures and this is how we anticipate doing if it occurs.
5)Violation: Obviously something is wrong with simulator training. Is it modeled correctly and was there intense training on line trips and managing reactor in a emergency.
6) Not following boric acid procedures in a plant emergy
The NRC based on 2014 duel plant trip special should have followed up...make sure
DOMINION NUCLEAR CONNECTICUT, INC. MILLSTONE POWER STATION UNITS 2 AND 3 LICENSEE EVENT REPORT 2014-006-00 MILLSTONE POWER STATION DUAL UNIT REACTOR TRIP ON LOSS OF OFFSITE POWERHere is the new inspection. Boy, these guys got recently a lot of big LERs!!!
MILLSTONE POWER STATION – INTEGRATED INSPECTION REPORT 05000336/2017003 AND 05000423/2017003
Annual Sample: Unit 3 Rod Insertion Limit LO-LO Actuated During a Rapid Down Power to Support the Loss of Two Offsite Power Lines on August 14Violation: they lost control of power. It should have been a violation on Unit 3
a. Inspection Scope
The inspectors performed an in-depth review of Dominion’s cause evaluation and corrective actions associated with CR1068836 for an unplanned rapid power reduction on May 15, 2017. Specifically, the loss of two 345kV offsite power lines caused Unit 3 operators to rapidly reduce power from 1127 MWe to 900 MWe as required by Technical Requirements Manual 3.8.1, “Electrical Power Systems,” to prevent grid instability.
The inspectors assessed Dominion’s problem identification threshold, cause analyses, extent of condition reviews, compensatory actions, and the prioritization and timeliness of corrective actions to determine whether Dominion was appropriately identifying, characterizing, and correcting problems associated with this issue and whether the planned or completed corrective actions were appropriate.
b. Findings and Observations
No findings were identified.
On May 15, 2017, Millstone station experienced the loss of two 345kV offsite feeder lines and was directed by the grid operator to rapidly reduce station output power to 1725 MWe within 25 minutes. Millstone Unit 3 entered TRM under requirement 3.8.1, action B, which required reducing total station output to 1650 MWe within 30 minutes. Both units entered C OP-200.8, “Response to ISO New England / CONVEX Notifications and Alerts,” and coordinated the load reduction to achieve the required downpower. Unit 3 entered AOP 3575, “Rapid Power Reduction,” and commenced a power reduction at 3 percent/min from 1267 MWe to 900 MWe. Despite the fact that one offsite 345kV line was already out of service, Unit 2 and Unit 3 had not predetermined how much of the total power reduction would be shared by each unit if a second line was lost. Coordination of this effort took 10 minutes to complete which caused a delay in starting the power reduction which could have been performed concurrently, and resulted in a shorter time (20 minutes) to reach the rapid power reduction target. Upon entry into AOP 3575, the operators calculated and added an initial amount of boric acid that should be sufficient to complete the power reduction. However, a recent change to AOP 3575 directed the operators to use a value for boric acid reactivity effectiveness of 15 (gallons of boric acid)/(percent power) which was appropriate for beginning of life, but was non-conservative for end of life reactivity conditions. The correct value for end of life is approximately 18 gal/percent. The operators correctly followed AOP 3575 and computed the amount of boric acid to be added based on the 15 gal/percent as directed and thus under-estimated the amount of boric acid to be added to maintain the shutdown margin by approximately 20 percent. During the rapid power reduction, the control rods continuously inserted in automatic as designed. The operators slowed the power reduction rate from 3percent/min to 1 percent/min at 1650 but did not increase the boration rate or add more boric acid despite the fact that the control rods were approaching the rod insertion limit (RIL). Step 6.h of AOP-3575 requires the operators to monitor the rapid
downpower parameters and adjust (decrease) loading rate, boration time and flow rate, or rod position as necessary. Although the operators reduced the power reduction rate, this change would have little effect on the final control rod position and approach to RIL as the RCS temperature deviation (Tave – Tref) was +4°F and control rods were stepping in rapidly. As the control rods approached RIL, additional boric acid was required to be added to prevent exceeding the rod insertion limit which was a warning alarm for a pending loss of adequate shutdown margin.
At 1658, Unit 3 reached the required target of 900 MWe and the “RIL LO” alarm annunciated. The required action in AOP 3575, step 7.m, for this event is to “increase the boration flow rate”. Although the initial rapid boration had been completed and should have been sufficient, the procedure directs the operators to immediately restart the boration to prevent the RIL LO-LO alarm. At 1659, the RIL LO-LO annunciator alarmed. The operators responded at 1703 by rapidly borating until sufficient additional negative reactivity was added so the control rods could be withdrawn to clear the RIL alarm, which occurred at 1705. TS 3.1.3.6 requires the rods to be maintained above the RIL. The action statement is to either restore rods above the RIL setpoint or reduce power to clear the RIL setpoint within two hours. The operators entered TS 3.1.3.6 and restored the control rods above RIL within six minutes. Two minor performance deficiencies were noted during this inspection. The first involved procedure AOP 3575, which directed the operators to calculate a boric acid addition that should have been sufficient to complete the rapid downpower without control rods inserting below RIL alarms. However, the procedure assumed beginning of life conditions in the core. The core was operating at the end of life when the reactivity coefficients and power defect were different. These differences resulted in an insufficient amount of boric acid being calculated and added to the RCS. This procedural inadequacy was identified by the licensee in the apparent cause evaluation and was promptly corrected by a revision to AOP 3575.
A second minor performance deficiency was identified by the inspectors. The inspectors noted that operators did not adequately control the reactivity balance during the power reduction. AOP 3575, step 6.h requires the operators to monitor the rapid downpower parameters and adjust (decrease) loading rate, boration time and flow rate, or rod position as necessary. The operators reduced the power reduction rate but did not add additional boric acid as the control rods approached RIL alarm. Furthermore, steps 7.k, l and m, provided specific direction to immediately increase boration flow if the RIL LO alarm occurs during a power reduction that was requested by the grid operator. Contrary to this direction, the operators did not address the need to add additional boric acid to the RCS to properly control the reactivity balance during the rapid downpower until after the RIL LO-LO annunciator had alarmed. After the event, operators discussed this issue during the 4.0 crew debrief; however, the inspectors identified that this issue was not appropriately captured in the CAP and corrective actions associated with the event failed to address the operator performance issues concerning reactivity management. However, the inspectors noted that appropriate corrective actions were taken to address this issue through changes to AOP 3575 and through changes made to operator training, which were addressed with a systematic approach to training, during training cycle 17-03, June 20 through August 11, 2017.
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