PNP 2016-053, Supplement to License Amendment Request: Control Rod Drive Exercise Surveillance

Supplement to License Amendment Request: Control Rod Drive Exercise Surveillance

ML16252A351
Person / Time
Site:	Palisades
Issue date:	09/08/2016
From:	Arnone C Entergy Nuclear Operations
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
CAC MF8297, PNP 2016-053
Download: ML16252A351 (11)

Text

-===-Entergy Entergy Nuclear Operations, Inc.

Palisades Nuclear Plant 27780 Blue Star Memorial Highway Covert, MI 49043*9530 Tel 269 764 2000 Charles F. Arnone Site Vice President PNP 2016-053 September 8, 2016 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

SUBJECT:

Supplement to License Amendment Request: Control Rod Drive Exercise Surveillance (CAC No. MF8297)

Palisades Nuclear Plant Docket 50-255 Renewed Facility Operating License No. DPR-20

REFERENCES:

1. Entergy Nuclear Operations, Inc. letter to NRC, PNP 2016-049, License Amendment Request: Control Rod Drive Exercise Surveillance, dated August 22, 2016 (ADAMS Accession Number ML16235A195)

2. NRC letter to Entergy Nuclear Operations, Inc., Palisades Nuclear Plant

- Supplemental Information Needed for Acceptance of Requested Licensing Action Re: Control Rod Drive Exercise Surveillance (CAC No.

MF8297), dated August 29, 2016 (ADAMS Accession Number ML16238A030)

Dear Sir or Madam:

Entergy Nuclear Operations, Inc. (ENO) submitted a license amendment request (LAR) to the Nuclear Regulatory Commission (NRC) for approval to revise the requirements for performing a control rod drive exercise surveillance on control rod drive 13 for the remainder of cycle 25 (Reference 1). Subsequently, the NRC sent ENO a letter requesting supplemental information (Reference 2). ENO and the NRC held conference calls on August 24, 2016 and September 6, 2016 to clarify the requested supplemental information.

The attachment to this letter provides the requested supplemental information associated with the LAR.

Summary of Commitments This letter identifies no new commitments and no revisions to existing commitments.

PNP 2016-053 Page 2 of 2 I declare under penalty of perjury that the foregoing is true and accurate. Executed on September 8, 2016.

Sincerely, CFAljse

Attachment:

Supplement to License Amendment Request: Control Rod Drive Exercise Surveillance cc: Administrator, Region III, USNRC Project Manager, Palisades, USNRC Resident Inspector, Palisades, USNRC State of Michigan

ATTACHMENT PNP 2016-053 Supplement to License Amendment Request:

Control Rod Drive Exercise Surveillance By letter dated August 22, 2016 (ADAMS Accession Number ML16235A195), Entergy Nuclear Operations, Inc. (ENO) submitted a license amendment request (LAR) for Palisades Nuclear Plant (PNP). The LAR proposes to revise portions of the PNP Renewed Facility Operating License and Technical Specifications (TS) concerning the requirement for performing the TS control rod drive (CRD) exercising surveillance on CRD-13 for the remainder of cycle 25.

By letter dated August 29,2016 (ADAMS Accession No. ML16238A030), the Nuclear Regulatory Commission (NRC) requested supplemental information to enable the staff to complete its acceptance review of the LAR. The requested supplemental information is provided below.

NRC Information Request

1. Page 3 of Attachment 1 to the license amendment request (LAR) - Provide the basis and adequacy for the statement that the seal leakage from control rod drive (CRO)-13 will increase to the extent that continued operation to the planned refueling outage is unlikely.

ENO Response

1. The condition of a CRD seal is monitored with two parameters. The primary parameter, seal leak-off temperature, is measured to ascertain individual CRD seal conditions. As a seal degrades, it allows more primary coolant to pass by the sealing surface. The temperature of the primary coolant system fluid that has leaked by the seal faces is measured by a thermocouple at each CRD seal and is recorded as seal leak-off temperature. Seal leak-off temperature is trended over time for comparing individual seal temperatures for all 45 CRDs to assess individual seal performance. An increase in individual CRD seal leak-off temperature results in a corresponding rise in seal leak rate, indicating seal degradation. A control room recorder continuously collects seal leak-off temperature data and provides real-time information on the condition of the seals.

The second monitoring parameter, seal leak rate, is used to identify seal degradation. Seal leakage from each individual CRD is collected in a common leak header and routed to a small accumulator where it can be measured to give a combined quantitative leak rate for all of the CRDs. Figure 1 depicts the system configuration. Seal leak rate can be correlated to a particular CRD seal by examining the seal leak-off temperature data for the CRD seals.

PNP operating experience has shown that performing the CRD exercise surveillance required by TS Surveillance Requirement (SR) 3.1.4.3 has the potential to negatively impact the leak tightness of CRD seals. Historically, ENO has observed that a temporary slight increase in seal leak-off temperature with a corresponding minor increase in seal leak rate may occur following the exercise surveillance. However, the parameters typically return to pretest values following testing. When the parameters do not return to pretest values after testing, the higher leak-off temperatures and leak rates are normally indicative of a degraded seal. As the seal further degrades, seal leakage often escalates rapidly, eventually resulting in an unplanned plant shutdown to repair the seal.

Page 1 of 6

ATTACHMENT PNP 2016-053 Supplement to License Amendment Request:

Control Rod Drive Exercise Surveillance During the exercise surveillance, the movement of CRDs may cause scouring of the seal faces due to foreign material, and repositioning of the seal faces (due to rotation from CRD movement). These effects may create new leak paths across the seal faces. These new leak paths result in increased seal leak rates and correlating higher leak-off temperatures.

Performance of the CRD exercise surveillance during July 2016 resulted in increases in CRD-13 leak-off temperature and seal leak rates that have not returned to their pretest values following testing.

To date, the post-test leak rate for CRD-13 this cycle has closely tracked the leak rate for CRD-22 observed in 2009 and 2010 (see Figures 2 and 3). As discussed in the LAR, following the 2009 refueling outage, CRD-22 exhibited increasing seal leak rates, leading ENO to submit a LAR on March 31, 2010 to suspend the exercise surveillance of CRD-22 for the remainder of the cycle. At the time of the LAR, the CRD-22 leak rate had been measured at 400 ml/min following the most recent performance of the surveillance. The request was approved by the NRC on June 2, 2010 in Amendment Number 239.

Subsequent to approval of the license amendment request, without further CRD-22 movement, CRD-22 seal leak rate escalated and the reactor was shut down in June 2010 to replace the CRD-22 seals.

Figure 2 projects future CRD-13 leak rates with and without the remaining two required exercise surveillances. Projected CRD-13 seal leak rates with the remaining required exercise surveillances is based on the performance of CRD-22 in 2010.

Projected CRD-13 seal leak rates without further surveillances is based on the current trend of CRD-13 seal leak rates and historical data. For example, in the spring of 2003, CRD-19 exhibited increased leak-off temperature, indicating seal degradation. The exercise surveillance of CRD-19 was suspended for a year, and the elevated CRD-19 leak-off temperature and leak rate remained within limits throughout this period.

With continued performance of the exercise surveillance during this cycle, the CRD-13 leak rate is projected to exceed the operational decision making issue (ODMI) implementation action plan leak rate limit of 1200 ml/min and will likely require a plant shutdown to repair the degraded CRD seals.

Without further performance of the exercise surveillance during this cycle, CRD-13 is projected to remain below the ODMI implementation action plan leak rate limit until the plant starts the spring 2017 refueling outage.

The leak rate from the CRD-13 seal was measured at 32.2 mVmin following the most recent exercise surveillance. This leak rate is lower than the leak rate of 400 ml/min for CRD-22 following the exercise surveillance in February of 2010, as documented in the LAR for CRD-22. However, later in 2010, CRD-22 leak rate escalated quickly and resulted in an unplanned plant shutdown to replace the CRD-22 seals. If the exercise surveillance had been suspended earlier in the operating cycle, when CRD-22 leak rate was lower, an unplanned plant shutdown may have been avoided. By submitting the LAR for CRD-13 at this time, with the current CRD-13 seal leak rate, ENO expects to prevent an unplanned plant shutdown to repair the degraded seals.

Page 2 of 6

ATTACHMENT PNP 2016-053 Supplement to License Amendment Request:

Control Rod Drive Exercise Surveillance NRC Information Request

2. Page 7 of Attachment 1 to the LAR - Discuss any operational procedures that exist for operating the "rod rundown" feature, and address the effect on the Updated Final Safety Analysis Report, Chapter 14, transient and accident analyses of operating the "rod rundown" feature.

ENO Response

2. The control rod rundown feature for the shutdown and regulating rods is initiated by a reactor trip through electrical relays connected in parallel with the control rod drive mechanism (CRDM) clutches. Since this is an electronic automatic feature initiated by a reactor trip, there are no operational procedures to perform this action.

PNP does not credit the automatic CRDM rod rundown feature to mitigate postulated Final Safety Analysis Report (FSAR) Chapter 14 safety analyses. Therefore, operation of the rundown feature has no effect on the FSAR Chapter 14 safety analyses.

The rod rundown feature was described in the LAR to highlight that, in the unlikely event that a control rod would not insert as designed due to gravity when released by its clutch, a back-up feature would, by mechanical force, insert the control rod. This is a backup feature because the FSAR Chapter 14 safety analyses assume failure of one full-length control rod to fully insert into the core, with the remainder of the rods fully inserting by gravity as designed.

NRC Information Request

3. Page 13 of Attachment 1 to the LAR - Provide the basis and adequacy for the 2 gal/on per minute (gpm) seal leakage limit for manual plant shutdown.

ENO Response

3. The CRD seal leakage collection system, depicted in Figure 1, collects the combined leakage from all 45 CRDs into a small accumulator. Leakage from individual CRDs is distinguishable by increased CRD leak-off temperature, as discussed above in the response to NRC Information Request Question 1. Individual CRD seal leak-off temperatures are available for review and trending on a recorder in the control room .

The 2 gpm CRD seal leak rate limit is a station abnormal operating procedure (AOP) value that requires a plant shutdown when exceeded. This value has not changed since initial PNP operation and is associated with the capacity of the CRD leakage collection system.

When the CRD seal leak rate approaches 2 gpm, two phase flow (liquid and vapor/steam) typically exits the leakage accumulator, hampering CRD seal leak rate measurements.

Without the ability to accurately measure leakage, all CRD seal leakage would be quantified as "unidentified leakage," and, as such, would exceed the TS primary coolant system operational leakage limit of 1 gpm for unidentified leakage, which requires an immediate plant shutdown.

Page 3 of 6

ATTACHMENT PNP 2016-053 Supplement to License Amendment Aequest:

Control Aod Drive Exercise Surveillance PNP has implemented an ODMI implementation action plan that conservatively limits seal leak rate to 1200 mVmin (about 0.317 gpm) for CAD-13. This limit is based on historical degraded CAD seal leak rates that have resulted in a plant shutdown to repair. Previous plant experience indicates that when the CAD seal leak rate reaches approximately 1200 ml/min, steam cutting across the seal face will accelerate the rise in leak rate such that the procedural requirement of 2 gpm will most likely be challenged in the near future.

Therefore, initiating a plant shutdown at approximately 1200 ml/min allows time to prepare the station operating crews (e.g., staffing, pre-job briefings, just-in-time training) to conduct an orderly plant shutdown versus the AOP-required immediate plant shutdown when the 2 gpm leak rate limit is exceeded.

NRC Information Request

4. Page 14 of Attachment 1 to the LAR - Provide industry and/or plant data that demonstrate the following:

a. eRDs with seal leakage are trippable on a reactor trip signal including a discussion of the associated seal leakage rate (up to 2 gpm) for the applicable eROs; and

b. eROs declared "immovable" (with and without seal leakage) are trippable.

ENO Response 4.a. PNP operating experience shows that control rods have been successfully tripped with seal leak rates above the 1200 mVmin ODMI implementation action plan limit. While leak-rates greater than this limit create additional operating burdens to the plant (e.g., cleaning of boric acid when repairing the seal, operator temperature exposure during seal leak rate measurements, implementation of additional monitoring to ensure that exponential seal degradation does not reach the 2 gpm limit), initiating a controlled plant shutdown at this value prior to reaching the procedure limit of 2 gpm minimizes these burdens. Moreover, when CAD seal leak rates reach approximately 1200 ml/min, CAD leak-off temperature may be high, causing steam cutting across the seal face which accelerates the rise in the leak rate.

The following chart of recent leak rate history shows that the plant has been shut down after seal leak rates have increased beyond 1200 mVmin. In all of these cases, the reactor was successfully tripped with all rods being fully inserted by gravity. In plant history, seal leakage has never affected the ability to fully insert a control rod by graVity.

Page 4 of 6

ATTACHMENT PNP 2016-053 Supplement to License Amendment Request:

Control Rod Drive Exercise Surveillance Date of CRD Leak CRD Leak Rate Date of Plant Shutdown*

Rate Measurement (mllmin) 8/5/2008 2182 8/5/2008 2117/2009 1290 2/17/2009 6/24/2010 1650 6/24/2010 1/512012 800 1/5/2012

• Plant shutdown included tripping control rods with seal leakage from a fully withdrawn position.

As discussed in the LAR, CRO seal leakage does not increase the likelihood of a control rod becoming untrippable. The factors that ensure that a control rod will not become untrippable due to a CRO seal leak also prevent a CRO seal leak from affecting the insertion time of a control rod dropped by gravity. See LAR Attachment 1, Section 4.0,

Technical Analysis," subsection "Effects of Continued CRO-13 Seal Leakage," for additional information.

The above discussion is supported by plant operational experience, which shows that CRO seal leakage does not affect control rod drop times. For example, for each of the plant shutdowns listed above, there were no discernable differences observed between the drop times of the control rod with the leaking seal and the drop times of the control rods without seal leakage.

4.b. TS Limiting Condition for Operation (LCO) 3.1.4, "Control Rod Alignment," Condition 3.1.4 0, allows for one full-length control rod to be declared immovable, but trippable. The required action for this condition is to restore the affected control rod to operable status prior to entering Mode 2, following the next Mode 3 entry.

As discussed in the LAR, the TS Bases for Condition 3.1.4.0 states that Condition 0 is entered whenever it is discovered that a single full-length control rod cannot be moved by its operator, yet the control rod is still capable of being tripped. The inability to move a full-length control rod by its operator may be indicative of a systemic failure (other than trippability) that could potentially affect other rods.

Under the proposed amendment, CRO-13 would be declared immovable but trippable and Condition 0 would be entered. Condition 0 would be entered administratively because the exercise surveillance required by TS SR 3.1.4.3 would not have been performed. The CRO would continue to be movable and fully capable of tripping.

Control rod drop timing testing (surveillance test RO-22) is performed each refueling outage after reactor reassembly, prior to reactor criticality. This testing ensures that the CROs are trippable within their accident analysis times of 2.5 seconds. CRO-13 successfully completed its drop timing test this cycle, providing confidence that it will successfully insert into the reactor core when tripped. Note that, although RO-22 was performed at the beginning of the cycle when CRO-13 did not exhibit increased seal leakage, seal leak rates Page 5 of 6

ATTACHMENT PNP 2016-053 Supplement to license Amendment Request:

Control Rod Drive Exercise Surveillance have no adverse impact on CRD drop time, as discussed in the ENO response to NRC Information Request Question 4.a above, As discussed in the LAR, CRD-13 has been moved 725 inches during this operating cycle, including RO-22 drop time testing, providing added confidence that service-induced binding is not occurring. Therefore, suspending further CRD-13 exercise surveillances during this cycle, which would preclude additional CRD movement of approximately 24 inches (two exercise surveillances), would provide minimal added confidence that CRD-13 remains trippable.

Therefore, based on the above, a control rod that is declared immovable under TS LCO 3.1.4 will continue to be trippable, without or without seal leakage.

See the END response to NRC Information Request Question 4.a above for additional information.

NRC Information Request

5. Provide information regarding the use of high seal temperature to manually trip the reactor, if applicable to this LAR, and the adequacy of the seal temperature trip point.

ENO Response

5. PNP does not have a requirement to shut down the plant due to high CRD leak-off temperature. PNP has an ODMI implementation action plan in place that requires operators to enter containment and measure CRD seal leak rate if CRD-13 seal leak-off temperature reaches 212°F. Accurate CRD leak rate measurements at leak-off temperatures greater than 212°F would not be achievable due to boiling. In addition, temperatures greater than 212°F can cause steam cutting across the seal face and accelerate the CRD seal leak rate. Follow-up actions are based on the results of the leak rate measurement and are not dependent on CRD leak-off temperature.

Figures Figure 1 - Control Rod Drive (CRD) Seal Collection System Figure 2 - CRD-13 Actual and Postulated Seal Leak Rates Figure 3 - CRD-22 Actual and Postulated Seal Leak Rates Page 6 of 6

Figure 1 Control Rod Drive (CRD) Seal Collection System r - - - - - - - - - - - - - - - CRD-1 I~

I * ~

I

• I I

r - - - - - - - - - - - - - - - - CRD-12 0

• 0 I

I ~VAPOR , SEAL I

CONTROL ROOM I I

CRD-13 TEMP ~

' . ..,.... :J.';

RECORDER

ELEMENT CRD-13 LEAK OFF I-I f-f- - .....J SEALING SURFACE ALL 45 CRD r SEAL LEAK OFF _ _ _ _ .1 r-1--,

TEMPERATURES CLEAR SIGHT DISPLAYED ltl [-

1- --.., GLASS I

I PCS L.....- CRD DRIVE SHAFT I

I PRESSURE ALL 45 CRD LEAK L - - - - - - - - - - - - - - - CRD-14 0 (! ACCUMULATOR I

I I

~---------------CRD-15 0 , [:-1----1-.

I

• I

• I I * ------'""'--

L _______________ CRD-45 0 I:'

LEAK OFF FROM ALL 45 CRDs MEASURED Page 1 of 1

Figure 2 CRD-13 Actual and Projected Seal Leak Rates I

1600 ...-......-- Refuel Date

-e-Projected Seal Leak Rate with Testing Spring 2017

.. ..... Total Seal Leak Off 1400 -'---=.,- - - -

~ Projected Seal Leak Rate Without Testing

.& Elercise Test

~ I ~ ~

1000 C

"e

.5-

==

0 800

..lI:

III QI iii QI 600 400 8/29/2016 ~

200 I *1 §A .,/'

0 10/23/2015 1/31/2016 5/10/2016 8/18/2016 11/26/2016 3/6/2017 6/14/2017 00 00 00 00 00 00 0 q- q- q- q- q- q- 0 LI'l q- IV) N .-t 0I 0I I I I I I l- I- l- I- l- I- I-Page 1 of 1

Figure 3 CRD-22 Actual and Projected Seal Leak Rates 1600

-+-Actual Seal leak Rate Plant Shutdown 1400

• Exercise Test 6/24/2010 I~

" ' -Projected Seal leak Rate With One less Exercise Test 1200

-°e s::

1000 E

t:

0

~

ns 800 CII ns CII VI 600 400 200 Refuel Date 1/

8/3/2010

°T-S43 T-443 T-343 T-243 T-143 T-43 T-O Days to the Refuelng Outage in (T-ddd)

Page 1 of 1