Part 21 Report - 1998-390

 
 

ACCESSION #:  9803190378

                       LICENSEE EVENT REPORT (LER)



FACILITY NAME:  R. E. Ginna Nuclear Power Plant           PAGE: 1 OF 7



DOCKET NUMBER:  05000244



TITLE:



EVENT DATE:  02/09/98   LER #:  1998-001-00 REPORT DATE:  03/11/98



OTHER FACILITIES INVOLVED:                          DOCKET NO:  05000



OPERATING MODE:  1   POWER LEVEL:  100



THIS REPORT IS SUBMITTED PURSUANT TO THE REQUIREMENTS OF 10 CFR

SECTION:

50.73(a)(2)(ii)

OTHER-Part 21



LICENSEE CONTACT FOR THIS LER:

NAME:  John T. St. Martin - Technical

            Assistant                       TELEPHONE:  (716) 771-3641



COMPONENT FAILURE DESCRIPTION:

CAUSE:  B   SYSTEM:  DA   COMPONENT:  RK   MANUFACTURER:  B386

REPORTABLE NPRDS:  N



SUPPLEMENTAL REPORT EXPECTED:  NO



ABSTRACT:



On February 9, 1998, the plant was in Mode 1 at approximately 100% steady

state reactor power.  It was discovered that Boraflex degradation in the

Spent Fuel Pool, greater than was assumed in the criticality analysis,

had occurred.  This is reportable under 10 CFR 50.73 and 10 CFR 21.



Interim corrective action included removing spent fuel assemblies from

selected degraded storage rack cells and maintaining a high concentration

of soluble boron in the Spent Fuel Pool.



The cause of the Boraflex degradation was high cumulative gamma radiation

exposure and the subsequent dissolution of the boron from the Boraflex

matrix.



Corrective action to prevent recurrence is outlined in Section V.B.



END OF ABSTRACT



TEXT                                                          PAGE 2 OF 7



I.   PRE-EVENT PLANT CONDITIONS:



     On February 4, 1998, the plant was in Mode 1 at approximately 100%

     steady state reactor power.  In activities unrelated to plant

     conditions, RG&E and contractor personnel began performing "Boron-10

     Areal Density Gauge for Evaluating Racks" ("BADGER") testing for

     spent fuel storage racks containing Boraflex panels.



     Each cell of the Ginna Station Region 2 spent fuel storage racks

     contains two Boraflex sheets (panels).  Each cell can store one fuel

     assembly.  These Boraflex panels are 144 inches in length and are

     positioned adjacent to the stored fuel assemblies, sandwiched

     between stainless steel sheets.  The design is such that water

     exchange may occur both at the panel edges and up through the

     Boraflex region of the rack assembly.



     NRC Generic Letter (GL) 96-04 (Boraflex Degradation in Spent Fuel

     Pool Storage Racks) was issued June 26, 1996.  GL 96-04 requested

     that licensees assess the capability of the Boraflex to maintain a

     5-percent subcriticality margin and submit to the NRC a plan

     describing its proposed actions if this subcriticality margin cannot

     be maintained by Boraflex material because of current or projected

     future Boraflex degradation.  As stated in the Generic Letter,

     Boraflex dissolution appears to be a gradual and localized effect

     forewarned by relatively high silica levels in the pool water.



     Rochester Gas and Electric (RG&E) responded to this GL in a letter

     dated October 24, 1996.  (Refer to Ginna Docket No. 50-244, letter

     dated October 24, 1996, from R.C. Mecredy (RG&E) to USNRC, "Response

     to NRC Generic Letter 96-04".) In this response, RG&E committed to

     perform blackness testing on selected Boraflex panels to obtain data

     on the physical condition of the Boraflex panels in 1997.  RG&E

     subsequently revised the commitment date to the first quarter of

     1998, in a letter dated December 22, 1997.  This was done primarily

     due to the availability of personnel and equipment from Northeast

     Technology Corporation (NETCO), who were contracted to perform the

     more rigorous "BADGER" testing, which RG&E felt was more appropriate

     than blackness testing.  (Refer to Ginna Docket No. 50-244, letter

     dated December 22, 1997 from R.C. Mecredy to USNRC, "Revision to

     Blackness Testing Schedule Per GL 96-04".)



     RG&E contracted with NETCO to perform "BADGER" testing, and

     determined which 24 Boraflex panels to perform this "BADGER" testing

     on.  These panels were selected based on a representative cumulative

     gamma radiation exposure, ranging from a low of 9.9 E+8 rads to a

     high of 4.19 E+9 rads.  Testing started on February 4, 1998.

     Initial results were reported to RG&E on February 9, 1998.



II.  DESCRIPTION OF EVENT:



     A.   DATES AND APPROXIMATE TIMES OF MAJOR OCCURRENCES:



          o    February 9, 1998: Event date.



          o    February 9, 1998, 1445 EST: Discovery date and time.



          o    February 9, 1998, 1528 EST: NRC is notified of this

               condition per 10CFR50.72 (b) (1) (ii) (B).



TEXT                                                          PAGE 3 OF 7



     B.   EVENT:



          On February 9, 1998, the plant was in Mode 1 at approximately

          100% steady state reactor power.  In activities unrelated to

          plant conditions, the preliminary results of "BADGER" testing

          were reported to RG&E personnel.



          During Spent Fuel Pool "BADGER" testing, degradation beyond the

          four (4) inch gap assumption of the criticality analysis was

          noted on selected boraflex panels.  This data indicates that

          some panels have undergone dissolution beyond expected levels.

          One panel had experienced up to 100 inches of dissolution.

          This is considerably more than was previously identified by

          other plants.



          The Ginna Station Updated Final Safety Analysis Report (UFSAR),

          Section 9.1.2.1.12, states: "Fuel storage racks using nuclear

          poisons additional to those inherent in the structural

          materials shall be designed and fabricated in a manner to

          prevent inadvertent removal of the additional poison by

          mechanical or chemical action."



          Specific results of the "BADGER" testing were as follows:



          o    16 panels with cumulative gamma exposures greater than or

               equal to 2.47 E + 9 rads had different degrees of

               degradation.  11 of these panels showed small degrees of

               dissolution around gaps and panel edges.  Two other panels

               showed edge dissolution in the lower 60 inches of the

               panel.  The remaining three panels had gaps and

               dissolution ranging from 20 inches to 100 inches, which

               exceeded the assumptions of the criticality analysis of

               record.



          o    Eight panels had cumulative gamma exposures lower than

               2.47 E + 9 rads.  These panels showed either uniform boron

               content or had only slight dissolution along the edges.



          o    Preliminary assessment indicates that up to 184 storage

               rack cells may have one or more adjacent panels with

               cumulative gamma exposures above 2.4 E+9 rads.



          The Plant Operations Review Committee (PORC) met on February

          10, 1998, to review these results.  PORC directed that

          administrative controls be established to maintain a high

          concentration of soluble boron in the Spent Fuel Pool (SFP).



     C.   INOPERABLE STRUCTURES, COMPONENTS, OR SYSTEMS THAT

CONTRIBUTED

          TO THE EVENT:



          None



     D.   OTHER SYSTEMS OR SECONDARY FUNCTIONS AFFECTED:



          None



TEXT                                                          PAGE 4 OF 7



     E.   METHOD OF DISCOVERY:



          This event was self-identified by RG&E personnel after review

          of the initial data from the "BADGER" testing, as provided by

          NETCO.



     F.   OPERATOR ACTION:



          Primary Systems Engineering personnel notified Operations

          supervision, who notified the Control Room operators.  The NRC

          Senior Resident was notified at this time.  At approximately

          1445 EST on February 9, 1998, plant staff determined that a

          non-emergency one hour notification, per 10CFR50.72

          (b)(1)(ii)(B), should be made to the NRC Operations Center.

          The Shift Supervisor made this notification at approximately

          1528 EST on February 9, 1998.



     G.   SAFETY SYSTEM RESPONSES:



          None



III. CAUSE OF EVENT:



     A.   IMMEDIATE CAUSE:



          The immediate cause of the plant being in an unanalyzed

          condition was the Boraflex degradation identified by the

          "BADGER" testing.



     B.   INTERMEDIATE CAUSE:



          The intermediate cause of the Boraflex degradation was

          dissolution of the boron from the Boraflex matrix.



     C.   ROOT CAUSE:



          The underlying cause of the dissolution of boron from the

          Boraflex matrix is attributed to a high cumulative gamma

          radiation exposure, aggravated by washout-accelerated

          dissolution of the Boraflex, caused by pool water flow through

          the panel enclosures.



TEXT                                                          PAGE 5 OF 7



          When Boraflex is subjected to gamma radiation in the pool

          aqueous environment, the silicon polymer matrix becomes

          degraded and silica filler and boron carbide are released.

          Since irradiated Boraflex typically contains 46 percent of

          crystalline silica and 50 percent of boron carbide, in a 4

          percent silicone rubber matrix (polydimethyl siloxane polymer),

          the presence of silica in the pool indicates the likely

          depletion of boron carbide from Boraflex.  The loss of boron

          carbide is characterized by slow dissolution of the Boraflex

          matrix from the surface of the Boraflex and a gradual thinning

          of the material.



          The rate of silica release from Boraflex is influenced by the

          water exchange to and around the Boraflex panels.  The rate of

          dissolution also increases with higher pool temperature and

          gamma exposure.  Experimental data indicates that once silica

          reaches an equilibrium value, the rate of dissolution is

          dramatically reduced.  An increase in pool water flow past the

          Boraflex panels can disturb any localized silica equilibria.



          This event is NUREG-1022 Cause Code (B), "Design,

          Manufacturing, Construction / Installation".



IV.  ANALYSIS OF EVENT:



     This event is reportable in accordance with 10 CFR 21 and in

     accordance with 10 CFR 50.73, Licensee Event Report System, item (a)

     (2) (ii) (A), which requires a report of, "Any event or condition

     ...  that resulted in the nuclear power plant being ...  In an

     unanalyzed condition that significantly compromised plant safety".

     The amount of Boraflex degradation is greater than that assumed in

     the criticality analysis, which placed the SFP in an unanalyzed

     condition.



     An assessment was performed considering both the safety consequences

     and implications of this event with the following results and

     conclusions:



          There were no operational or safety consequences or

          implications attributed to the Boraflex degradation because:



          o    RG&E had been maintaining a high concentration, greater

               than 2300 parts per million (PPM), of soluble boron in the

               Spent Fuel Pool (SFP).  This value is being monitored

               weekly.



          o    Calculations show that 1450 PPM of soluble boron is

               required to compensate for a complete absence of Boraflex

               in all the panels in Region 2, while maintaining the

               reactivity condition K sub eff < 0.95 under all postulated

               off-normal conditions (i.e., fuel misload accident).



          o    There are no credible sources of boron dilution that would

               be expected to decrease SFP boron concentration below the

               required 1450 PPM.



TEXT                                                          PAGE 6 OF 7



          o    RG&E is developing strategies to minimize or eliminate the

               need to credit Boraflex in Region 2 of the SFP.  There are

               several possible options being considered or implemented:



               a.   Region 1 of the SFP will be re-racked with new

                    storage racks that incorporate borated stainless

                    steel.  This work is scheduled for completion prior

                    to the 1 999 refueling outage.  The Region 1 storage

                    racks do not contain Boraflex, and the re-rack will

                    provide additional storage space in non-Boraflex rack

                    cells.



               b.   Licensing actions to obtain credit for soluble boron

                    in the SFP may be pursued in accordance with

                    NRC-accepted methodology.  This credit could justify

                    analyses to assure that the fuel would remain

                    subcritical, even if this boron were replaced with

                    pure water.  If pursued, this will require a separate

                    license amendment.



               c.   Licensing actions to obtain credit for neutron

                    absorber material (control rods, absorber rodlets,

                    and/or absorber panels) may be pursued.  Such

                    absorber material could be strategically placed in

                    Region 2 locations to support the criteria outlined

                    above.  If pursued, this would also require a license

                    amendment request.



               d.   More restrictive storage patterns can be utilized in

                    Region 2.  If pursued, this would also require a

                    license amendment request.



     Based on the above, it can be concluded that the public's health and

     safety was assured at all times.



V.   CORRECTIVE ACTION:



     A.   ACTION TAKEN TO RETURN AFFECTED SYSTEMS TO PRE-EVENT NORMAL

          STATUS:



          o    Procedures have been changed to ensure administrative

               controls are in place to verify at least 2300 PPM of

               soluble boron is maintained in the SFP.



          o    Spent fuel assemblies were removed from selected degraded

               storage rack cells, so that for Boraflex panels with

               cumulative gamma radiation exposure greater than 2.47 E +

               9 rads, the configuration is bounded by the current

               criticality analysis of record.



TEXT                                                          PAGE 7 OF 7



     B.   ACTION TAKEN OR PLANNED TO PREVENT RECURRENCE:



          o    Administrative controls will be established to prevent

               storage of spent fuel assemblies in designated cells, as

               determined by the Reactor Engineer or designee, to ensure

               the configuration is bounded by the criticality analysis.



          o    Long term strategies will be pursued that do not credit

               Boraflex in Region 2 of the SFP.



VI.  ADDITIONAL INFORMATION:



     A.   FAILED COMPONENTS:



          The Boraflex panels in the Ginna Station SFP were manufactured

          by Brand Industrial Services Corporation (BISCO), and have been

          in the SFP since 1984.



     B.   PREVIOUS LERs ON SIMILAR EVENTS:



          A similar LER historical search was conducted with the

          following results: No documentation of similar LER events with

          the same root cause at Ginna Station could be identified.



     C.   SPECIAL COMMENTS:



          Due to the amount of Boraflex degradation, the industry will be

          notified of this event via Nuclear NETWORK.



*** END OF DOCUMENT ***