United States Nuclear Regulatory Commission - Protecting People and the Environment

ACCESSION #:  9501230060
                       LICENSEE EVENT REPORT (LER)

FACILITY NAME:  Perry Nuclear Power Plant, Unit 1         PAGE: 1 OF 9

DOCKET NUMBER:  05000440

TITLE:  Slow Control Rod Scram Insertion Times Result in
        Technical Specification Violation

EVENT DATE:  12/12/94   LER #:  94-023-00   REPORT DATE:  01/11/95

OTHER FACILITIES INVOLVED:  N/A                     DOCKET NO:  05000

OPERATING MODE:  1   POWER LEVEL:  80

THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR
SECTION:
50.73(a)(2)(i)

LICENSEE CONTACT FOR THIS LER:
NAME:  Charles R. Elberfeld, Compliance
       Engineer                             TELEPHONE:  (216) 280-5264

COMPONENT FAILURE DESCRIPTION:
CAUSE: X    SYSTEM:  AA   COMPONENT:  PSV  MANUFACTURER:  A610
REPORTABLE NPRDS:  Yes

SUPPLEMENTAL REPORT EXPECTED:  NO

ABSTRACT:

On December 11, 1994, at 2045, during Technical Specification (TS)
Surveillance testing of control rod scram insertion times, TS Limiting
Condition for Operation (LCO) 3.1.3.2 ACTION c.1 was entered due to the
number of "slow" control rods exceeding twenty percent of a ten percent
sample.  Enforcement discretion was requested from the NRC and granted.
On December 12, 1994, at 0845, the TS LCO ACTION was exceeded when the
plant was not placed into HOT SHUTDOWN condition.

The cause of this event is attributed to degradation of the batch 314
Viton seating material located in the disk holder sub-assembly used in
some of the Scram Solenoid Pilot Valves (SSPVs) replaced during the last
refuel outage.  The degradation of the seating material causes it to
stick to the seating surface after long periods of solenoid energization,
resulting in a delay in the valve opening after solenoid de-energization.
The delay, in turn, causes the subject control rod to exceed its TS
Control Rod Scram Maximum Insertion Time requirement to notch position
43.

The SSPVs containing batch 314 Viton seating material were replaced.
Perry Nuclear Power Plant, General Electric, and the Automatic Switch
Company are working to resolve the SSPV problem.  Augmented Control Rod
Scram Maximum Insertion Time testing will be performed to provide further
confidence in the effectiveness of the corrective actions taken.

END OF ABSTRACT

TEXT                                                          PAGE 2 OF 9

I.   Introduction

     On December 11, 1994, at 2045, during Technical Specification (TS)
     Surveillance testing of control rod scram insertion times, TS
     Limiting Condition for Operation (LCO) 3.1.3.2 ACTION c.1 was
     entered due to the number of "slow" control rods exceeding twenty
     percent of a ten percent sample of the control rods.  This ACTION
     required the plant to be in at least HOT SHUTDOWN within twelve
     hours.  Enforcement discretion was requested, and granted on
     December 11, 1994, at 2230, to allow continued testing to identify
     control rods that may have been subject to degraded insertion times
     and to provide for timely corrective action for identified rods.
     The initial duration of the enforcement discretion extended until
     December 16, 1994, at 2230.

     On December 12, 1994, at 0845, TS LCO 3.1.3.2 ACTION c.1 was
     exceeded when the plant was not placed into HOT SHUTDOWN condition.
     This event is being reported pursuant to 10CFR50.73(a)(2)(i)(B) as
     operation prohibited by the plant's Technical Specifications.

     At the time of the event, the plant was in Operational Condition 1
     at 80 percent of rated thermal power.  The reactor vessel pressure
     was approximately 1000 psig with reactor coolant at saturated
     conditions.

II.  Background Information

     Grand Gulf Nuclear Power Station Experience

     Perry Nuclear Power Plant became aware of potential problems with
     Scram Solenoid Pilot Valves [PSV] (SSPVs) due to difficulties at the
     Grand Gulf Nuclear Power Station (GGNS).  Control rod scram time
     tests performed at the GGNS in May, 1994 identified that 25 of 191
     control rod insertion times to notch position 43 were "slow" (0.320
     to 0.390 seconds) and that an additional 8 insertion times failed to
     meet the TS limits for operable rods (greater than 0.390 seconds).

     GGNS root cause analysis endorsed a material problem with SSPV
     seating material located in the disk holder sub-assembly supplied in
     pre-assembled top head assemblies.  The root cause analysis
     indicated that a problem may exist with seating materials (Viton
     manufactured post-1991).  The failure mechanism is believed to be
     associated with degradation of the seating material which causes it
     to "stick" to the seating surface.  This results in a delay in
     venting the air actuators on the inlet and outlet scram valves, and
     concurrent "slow" control rod scram time to notch position 43.
     Testing performed by General Electric (GE) indicates a relationship
     between degradation in SSPV response time and the cumulative
     solenoid energization time.

TEXT                                                          PAGE 3 OF 9

     Perry Nuclear Power Plant Experience

     The Perry Nuclear Power Plant (PNPP) SSPVs, Automatic Switch Company
     (ASCO) Model Number HVA1768161, were replaced during the most recent
     refuel outage in 1994 (RFO-4).  Of the 177 SSPVs installed during
     the outage, 132 were confirmed to contain Viton batch 314 material
     which is known to have been manufactured post-1991.  Scram time data
     was obtained during startup from RFO-4 on July 27 and August 2 - 4,
     1994.

     The RFO-4 scram time data indicated that the PNPP control rods met
     the TS LCO 3/4.1.3.2 for maximum insertion times.  However,
     statistical analysis of the RFO-4 scram time data supported a
     potential that a failure mechanism could exist which would result in
     "slow" actuation of SSPVs.  An offset (approximately 0.01 second
     increase) was observed in scram time distribution from historical
     PNPP scram time data for control rods with certain lots of SSPVs
     using batch 314 Viton material.  Control rods with non-batch 314
     SSPVs exhibited a normal distribution.  In addition, a relationship
     was observed between the cumulative energization time of the SSPVs
     and the scram time in that a statistically significant upward shift
     in the data mean values was noted at 195 hours energization time.

     Scram time data from RFO-4 was insufficient to project SSPV response
     time for longer term solenoid energization.  TS Surveillance
     Requirement 4.1.3-2.c requires control rod scram time testing at
     least once per 120 days of power operation.  This is significantly
     longer than the maximum energization time (23 days) for which PNPP
     test data was available.  Because scram time offset appeared to
     change with SSPV energization time, additional testing to monitor
     this phenomenon, prior to the 120 day surveillance interval, was
     determined to be prudent.

     The SSPVs had been energized for 49 days on September 24, 1994.
     Although not required by TS Surveillance frequency, scram time
     testing was performed to determine if degradation was occurring in
     the response time of the PNPP SSPVs.  An initial test sample of 20
     control rods was selected to provide a statistical confidence level
     of 95% in SSPV performance.  Data from the September 24 and 25, 1994
     interim testing as a whole did not indicate degradation in
     performance of the suspect (Viton batch 314) SSPVs at 49 days of
     continuous energization.

III. Event Description

     Control rod scram time testing commenced at 09:50 hours on December
     10, 1994, in accordance with TS Surveillance Requirement 4.1.3.2.c,
     which requires control rod scram time testing at least once per 120
     days of power operation.  This testing consisted of a designated
     initial test sample of 18 control rods.

TEXT                                                          PAGE 4 OF 9

     On December 11, 1994, at 2045, testing had been completed for 12 of
     the initial test sample control rods, with the following initial
     results.

     - 8 acceptable rods (scram times to notch position 43 met TS 3.1.3.2
       LCO), - 4 "slow" rods (scram times to notch position 43 greater
       than TS 3.1-3.2 LCO, but OPERABLE),
     - 0 inoperable rods.

     Results also showed that rods tested met TS 3.1.3.2 LCO times to
     notch positions 29 and 13.  Upon identification of each "slow" rod,
     testing of adjacent rods began in accordance with TS requirements
     concurrent with replacement of the affected SSPV prior to additional
     sample testing.  Testing of the adjacent rods identified additional
     control rods which were "slow" to notch position 43.  Subsequent
     scram time test results for control rods with replaced SSPVs were
     acceptable.  Specific test results were documented in Letter
     PY-CEI/NRR-1896L, "Request for Enforcement Discretion with Respect
     to Control Rod Insertion Times," dated December 12, 1994.

     On December 11, 1994, at 2045, the scram time for test sample rod 12
     was identified as exceeding the maximum scram insertion time limits
     of TS 3.1.3.2.  TS LCO 3.1.3.2 ACTION c.1 was entered due to the
     number of "slow" control rods exceeding 20% of a 10% sample of the
     control rods, thus requiring the plant to be in at least HOT
     SHUTDOWN within 12 hours.  The plant was therefore required to be
     placed in HOT SHUTDOWN by December 12, 1994, at 0845.

     Enforcement discretion with respect to TS 3.1.3.2 LCO ACTIONS c.1,
     c.3, and c.4 was requested from the NRC and granted on December 11,
     1994, at 2330, until December 16, 1994, at 2330, to allow continued
     scram time testing to identify control rods that may have been
     subject to degraded scram insertion times to notch position 43, and
     to provide for timely corrective action for identified rods.

     Compensatory measures utilized for the duration of the enforcement
     discretion included:

          1)   implementation of corrective action to replace SSPVs for
               all control rods identified as having scram insertion
               times to notch position 43 exceeding the scram insertion
               time limits of TS LCO 3.1.3.2, and immediate corrective
               action implementation for control rods with scram
               insertion times identified in excess of TS LCO 3.1.3.2
               ACTION a.1,

          2)   reactor power not to exceed 85% rated thermal power, and

          3)   administrative reduction of the Maximum Fraction of
               Limiting Critical Power Ratio (MFLCPR) acceptance criteria
               to 0.990 from 1.00 until repairs were completed on the
               rods which had been identified as "slow".

TEXT                                                          PAGE 5 OF 9

     On December 15, 1994, scram time testing was completed for the
     complete core population of 177 control rods with a total of four
     rods identified as "INOPERABLE" and 26 rods identified as "slow" per
     Technical Specifications.  By that time, the four "INOPERABLE"
     control rods already had their SSPVs replaced and were restored to
     OPERABLE status.  Corrective actions had been completed for eight of
     the "slow" control rods; however, additional enforcement discretion
     time was needed to complete corrective actions on remaining "slow"
     control rods to exit the HOT SHUTDOWN requirement of TS 3.1.3.2 LCO
     ACTIONs c.1, c.3, and c.4.  On December 16, 1994, an extension of
     enforcement discretion was requested from the NRC for an additional
     seven days ending on December 23, 1994, at 2230 or until compliance
     with the Technical Specifications had been achieved, whichever
     occurred first.  The requested extension and its justification was
     documented on Letter PY-CEI/NRR-1897L, "Request for Extension of
     Enforcement Discretion with Respect to Control Rod Insertion Times,"
     dated December 16, 1994.  This extension of enforcement discretion
     was granted on December 16, 1994, at 1515.

     On December 17, 1994, at 2206, NRC enforcement discretion with
     respect to TS 3.1.3.2 Control Rod Scram Maximum Insertion Times
     expired when compliance with Technical Specifications was achieved.

IV.  Cause of Event

     The cause of this event is attributed to the degradation, over time
     of solenoid energization, of the Viton batch 314 seating material
     located in the disk holder sub-assembly used in some of the Scram
     Solenoid Pilot Valves replaced during RFO-4.  The degradation of the
     seating material causes it to stick to the seating surface resulting
     in a delay in the valve opening after solenoid de-energization.  The
     delay, in turn, causes the subject control rod to exceed its TS
     Control Rod Scram Maximum Insertion Time requirement to notch
     position 43.  GE and ASCO testing as well as PNPP diagnostic testing
     support this determination.

V.   Safety Analysis

     The control rod system is designed to bring the reactor subcritical
     at a rate fast enough to prevent the Minimum Critical Power Ratio
     (MCPR) from becoming less than 1.07 during the limiting power
     transient analyzed in Chapter 15 of the USAR.  This USAR analysis
     shows that the negative reactivity rates resulting from the scram,
     with the average response of control rod drives as given in the
     specifications, provide the required protection and MCPR remains
     greater than 1.07.  The occurrence of scram times longer than those
     specified should be viewed as an indication of a systematic problem
     with the rod drives.

TEXT                                                          PAGE 6 OF 9

     The Control Rod Drive Hydraulic [AA] (CRDH) system provides the
     hydraulic driving head for insertion, withdrawal, and scramming of
     control rods.  Each control rod (drive) has a Hydraulic Control Unit
     (HCU) which provides the scram function.  The CRDH system provides
     water at 1720 psig to the HCU.  Each HCU contains a scram
     accumulator as well as several air operated valves to direct the
     water pressure to the control rod drive for insertion, withdrawal,
     and scramming of the control rod under various conditions.  The
     Scram Solenoid Pilot Valve (SSPV) is a dual solenoid operated valve
     which, when de-energized, vents air from the actuators of both the
     scram inlet and outlet valves, allowing them to open and provide a
     flow path for CRDH system and accumulator pressure to scram the
     control rod.  Each of the SSPV dual solenoids is energized from a
     separate Reactor Protection System bus (A or B) and both of the
     solenoids must be de-energized for the SSPV to perform its function.

     The control rod scram is designed to bring the reactor subcritical
     at a rate fast enough to prevent fuel damage.  The
     accidents/transients that are "scram time sensitive" are those where
     the scram time can impact on the Minimum Critical Power Ratio (MCPR)
     or the vessel overpressurization limit.

     In the current fuel cycle, the limiting event for MCPR is the Load
     Reject with No By-Pass valve actuation (LRNBP), and for
     pressurization it is the Main Steamline Isolation Valve (MSIV) fast
     closure with a neutron flux scram (with no credit for the scram
     signal from MSIV position).  Loss-of-Coolant Accidents do not set
     MCPR limits nor lead to overpressurization concerns, and other
     events such as Rod Withdrawal Errors or Rotated Fuel Bundles are not
     impacted by scram times.  Therefore, the examination of the impact
     of a delayed scram initiation concentrated on two areas: a
     re-analysis of the limiting scram time sensitive events, and reviews
     of the assumptions of the original analyses which serve as the basis
     for the Control Rod Maximum Scram Insertion Time Specification.

     Re-analyses of the Load Reject with No By-Pass and MSIV Closure
     events was performed, which assumed the single failure of the
     highest worth rod to insert, and the remainder of the rods received
     the Reactor Protection System scram signal with an additional delay
     of 70 milliseconds from that assumed in the standard analysis.  This
     70 millisecond time delay corresponds to the time difference (for
     notch position 43) between the standard analysis assumption and the
     point at which the rod would be declared "inoperable" by the
     Technical Specifications.  As an example, the standard analysis
     assumption for the time to notch position 43 at 1050 psig is 320
     milliseconds (0.32 seconds), and the rod would be declared
     inoperable if its scram time exceeded 390 milliseconds (0.39
     seconds).  If any rod scram times to notch position 43 are measured
     during scram time testing at up to 70 milliseconds slower than the
     times assumed in the standard analysis, they are treated by
     Technical Specifications as "slow" rods, but not inoperable.  The

TEXT                                                          PAGE 7 OF 9

     re-analysis assumption of a 70 millisecond delay simulates that
     every trippable rod in the core is held up by its scram solenoid to
     the point that they would all be as "slow" as allowed without being
     declared "inoperable".

     The results of the analyses of these two limiting events identified
     that the effects of the scram initiation delay were minimal.  For
     MCPR, the change in Critical Power Ratio during the LRNBP event (the
     "delta CPR") was examined.  In the original reload analysis for
     Cycle 5 (the current fuel cycle), the delta CPR was 0.15.  In the
     re-analysis, the delta CPR was 0.16, a change of only 0.01 from the
     base case.  The MCPR limit for each fuel bundle type in the PNPP
     core is determined based on performance of various limiting
     transients, and for six of the seven fuel bundle types, the current
     MCPR limits are set by the Rotated Bundle Analysis, which is not
     scram time sensitive.  For the remaining fuel type (the 10 gad rod
     GE10 fuel), adding the additional 0.01 delta CPR makes the LRNBP the
     most limiting transient for that fuel type.  This has been accounted
     for by implementing an administrative penalty on the parameter used
     during power operation to ensure the MCPR limits are met, i.e., the
     Maximum Fraction of Limiting Critical Power Ratio (MFLCPR).  The
     MFLCPR acceptance criteria was administratively reduced to 0.990
     from 1.00 until repairs were completed on the rods which were
     identified as "slow".  Implementing the penalty in this manner
     applied the 0.01 delta CPR universally across the fuel types,
     although only the one fuel type was limited by the re-analysis.  In
     practice this had limited impact, since the core was not currently
     being operated near the limits.

     The change in peak vessel pressure during the MSIV Closure event was
     also examined.  In the original reload analysis for Cycle 5, the
     peak pressure was calculated to be 1294 psig, well below the TS
     2.1.3 Safety Limit of 1325 psig.  In the re-analysis, the peak
     pressure was calculated to be 1296 psig, also maintaining adequate
     margin to the 1325 psig limit.

     Reviews were performed of the assumptions in the original analyses
     that support TS LCO 3.1.3.2 "Control Rod Maximum Scram Insertion
     Times".  The purpose of these reviews was to determine the
     significance of any rods which might experience scram times slower
     than those examined in the re-analysis of the LRNBP event discussed
     above; i.e., with times more than 70 milliseconds slower than the
     original analysis values.  The Technical Specifications direct that
     these rods are to be declared inoperable.  The analyses that serve
     as the basis for the ACTIONs of LCO 3.1.3.2 assume that there are as
     many as nine control rods that are inoperable (one (1) "stuck" and
     eight (8) inoperable but trippable) in addition to seven (7) more
     "slow" rods.  The eight inoperable rods were assumed to scram slowly
     enough that they do not contribute to meeting the scram reactivity
     curve.  Although this analysis provides the basis for allowing up to
     16 rods to be "slow" (in the above described combination of one
     stuck, eight "slow" to the point of being inoperable,

TEXT                                                          PAGE 8 OF 9

     and seven more "slow"), the current Technical Specification limits
     the total number of "slow" (including slow to the point of
     inoperability) rods in the core at any one time to seven.  These
     seven can, therefore, be any combination of "slow" or inoperable
     rods, as long as no more than one is a "stuck" rod.  This is
     reflected by ACTIONs a.1, a.3, b, c.2, and c.4.

     Therefore, during the discretionary enforcement period, from a
     safety analysis standpoint, there is no significance to rods found
     to be "slow", since every rod in the core could have been "slow" and
     the safety parameters of concern would have continued to be met.  In
     addition, the situation where several rods are found to be slow to
     the point of inoperability is also bounded, from a safety analysis
     standpoint, in that the existing Technical Specification permits up
     to seven such rods to exist in the core at any one time.  This event
     is not considered to be safety significant.

VI.  Similar Events

     A previous similar event was documented by LER 89-030.  On November
     25, 1989, the malfunction of two SSPVs due to improper seating
     material resulted in a violation of Technical Specifications.  The
     causes for the November 1989 event were inadequate implementation of
     the Nonconformance Control Program and personnel error in the
     assessment of test results.

     An event that occurred on October 1, 1990, resulted in the discovery
     of malfunctioning SSPVs from a single lot installed in the plant
     during a refueling outage, and resulted in a 10CFR21 notification on
     December 11, 1990.

     Another previous similar event was documented by LER 91-018-01.  On
     October 6, 1991, the plant was shut down in accordance with
     Technical Specifications as a result of two adjacent control rods
     exceeding maximum insertion scram time limits.  The cause of the
     slow control rods was SSPV failure.  A combination of contaminants
     found on the valve disk and seats was believed to have formed an
     adhesive which could have bound the valve seat.  The suspect SSPVs
     were from the same lot remanufactured by ASCO in November 1990.  The
     49 valves from that suspect lot were removed and steps were taken to
     reduce the potential for introduction of contaminants into the
     valves.

     Because none of the previous similar events involved the use of
     post-1991 batch 314 Viton components within the SSPVs, it is not
     reasonable to expect that the corrective actions associated with
     these events could have precluded the December 1994 event.

TEXT                                                          PAGE 9 OF 9

VII. Corrective Actions

     The SSPVs containing batch 314 Viton seating material were replaced
     by December 30, 1994.  The replacement valves used were both new
     valves with post-1991 non-batch-314 Viton seating material and
     refurbished valves with pre-1991 Viton seating material.

     PNPP, GE, and ASCO are working to resolve the SSPV problem.
     Augmented Control Rod Scram Maximum Insertion Time testing will be
     performed to provide further confidence in the effectiveness of the
     corrective actions taken.

Energy Industry Identification System (EIIS) codes are identified in the
text as [XX]

ATTACHMENT TO 9501230060                                      PAGE 1 OF 1

     CENTERIOR
          ENERGY

PERRY NUCLEAR POWER PLANT     Mail Address:       Robert A. Stratman
                              P.O. BOX 97         VICE PRESIDENT -
10 CENTER ROAD                PERRY, OHIO 44081   NUCLEAR
PERRY, OHIO 44081
(216) 259-3737

          January 11, 1995
          PY-CEI/NRR-1901L

          United States Nuclear Regulatory Commission
          Document Control Desk
          Washington, D.C. 20555

          Perry Nuclear Power Plant
          Docket No. 50-440
          LER 94-023

          Gentlemen:

          Enclosed is Licensee Event Report 94-023 concerning Slow
          Control Rod Insertion Times Result in Technical Specification
          Violation.

          If you have questions or require additional information, please
          contact Mr.  James D.  Kloosterman, Manager - Regulatory
          Affairs at (216) 280-5833.

          Very truly yours,

          CRE: sc

          Enclosure:     LER 94-023

          cc:  NRC Project Manager
               NRC Resident Inspector Office
               NRC Region III

          Operating Companies
          Cleveland Electric Illuminating
          Toledo Edison

*** END OF DOCUMENT ***



Page Last Reviewed/Updated Thursday, March 29, 2012