United States Nuclear Regulatory Commission - Protecting People and the Environment

IEB 80-07 BWR Jet Pump Assembly Failure (Generic Letter 80-27)



GL80027                                                  SSINS No. 6820 
                                                         Accession No.: 
                                                         8002280648 
                                 UNITED STATES 
                         NUCLEAR REGULATORY COMMISSION 
                     OFFICE OF INSPECTION AND ENFORCEMENT 
                            WASHINGTON, D.C.  20555 

                                                 IE Bulletin No. 80-07 
                                                 Date:  April 4, 1980 
                                                 Page 1 of 4 

BWR JET PUMP ASSEMBLY FAILURE 

Description of Circumstances: 

On February 2, 1980, Commonwealth Edison Company (CECo) reported that a jet 
pump failed in Dresden Unit 3 while operating at about 67 percent of full 
power in a coastdown mode to a refueling shutdown.  Observed changes in 
plant parameters during the event indicated an individual jet pump failure 
had occurred.  In accordance with T.S., an orderly plant shutdown was begun 
to bring the unit to cold shutdown was within 24 hours. 

The plant parameter changes reported by the licensee were (1) generator 
electrical output decreased from 539 to 511 MW electrical, (2) core thermal 
power decreased as indicated by decreased APRM readings and steam flow to 
the turbine, (3) indicated total core flow increased from 97.6 to 104.7 x 
106 lb./hr., (4) core plate differential pressure decreased from 16.1 to 
13.8 psid., and (5) B recirculation loop flow increased from 49 to 54 x 103 
gpm while A recirculation loop flow remained at 49 x 103 gpm.  These changes 
were readily observed by the operator in the control room and it was 
postulated that a jet pump had failed.  Individual jet pump readings were 
taken, the jet pump operability surveillance was performed, and an apparent 
failure of jet pump No. 13 was determined. 

Following vessel head removal and defueling, TV camera and visual 
inspections of the jet pumps and vessel annulus revealed the hold-down beam 
assembly of the suspect jet pump had broken across its ligament sections at 
the mean diameter of the bolt thread area.  Failure of the beam assembly 
resulted in pump decoupling at the diffuser connection.  Subsequent insitu 
ultrasonic examination of all other jet pump hold-down beams, using a 
special UT technique developed by General Electric (GE), revealed ultrasonic 
indications of cracking at the same location in 6 of the remaining 19 beams 
examined. Initial estimates of crack depth ranged from 6 to 20 mils.  A 
sketch of the typical jet pump assembly is shown in Figures 1 and 2. 

On March 15-16, 1980, insitu ultrasonic examination was performed on all 20 
jet pump hold-down beam assemblies at Quad Cities 2 (currently shutdown for 
refueling).  One beam was found to contain a crack indication estimated to 
be in excess of 100 mils depth in the same location on the beam as found at 
Dresden. 
.

                                                 IE Bulletin No. 80-07 
                                                 Date:  April 4, 1980 
                                                 Page 2 of 4 

On March 28, 1980, Boston Edison reported that ultrasonic examination 
revealed crack indications in three (3) hold-down beam assemblies at Pilgrim 
Unit 1. 

The beam assemblies having crack indications are scheduled for replacement 
during the current refueling outage of the above units.  A metallurgical 
analysis has been initiated by GE to determine the probably cause(s) of the 
cracking. 

General Electric notified utilities having operating BWR units with jet 
pumps of this potential problem on March 17 and 18, 1980.  The NRC staff was 
advised on March 19, 1980 as to the actions being taken by GE in this 
regard.  The staff was also notified of a hold-down beam failure experienced 
at a foreign BWR facility. 

On the basis of information provided by General Electric and the recent 
experience at Dresden Unit 3, Quad Cities Unit 2 and Pilgrim Unit 1, concern
arises that the hold-down beam assemblies and subsequent jet pump function 
may degrade significantly during operation.  This potential for degradation 
could lead to jet pump disassembly and possibly reduce the margin of safety 
during postulated accidents. 

The following actions are to be taken by licensees of GE designed BWR-e and 
BWR-4 facilities with operating licenses: 

A.    Plants Now in Scheduled Refueling Outage Prior to Restart 

      1.    Visual inspections assisted by TV camera shall be conducted to 
            assess the integrity of the jet pump structures, the hold-down 
            beam assembly, hold-downs, wedge and restrainer assembly. 
            Particular attention should be given to areas of unusual wear, 
            failed keeper welds or other evidence of distress that could be 
            indicative of loss of beam assembly preload. 

      2.    Ultrasonic examinations, utilizing GE procedure TP-508.0642 
            (Rev. A) or equivalent, shall be conducted to assess the 
            integrity of the jet pump hold-down beams at the mid-length 
            ligament areas bounding the beam bolt. 

      3.    Upon completion of the inspections required by paragraph 1 and 2
            above, the appropriate NRC regional office shall be promptly 
            notified, followed by a 14 day written report, on the results of
            the inspection including any deficiencies thus identified and 
            corrective actions taken. 

      4.    When startup for power operation begins, the surveillance 
            described in Item P.2 shall be initiated. 

.

                                                 IE Bulletin No. 80-07 
                                                 Date:  April 4, 1980 
                                                 Page 3 of 4 

B.    Plants Currently Operating or Resuming Operations 

      1.    The NRC staff has determined that the operating plants warrant 
            inspection as required by paragraph 1 and 2 above.  Therefore, 
            licensees are requested to provide within 30 days of receipt of 
            this bulletin, written justifications for any continued 
            operation until these inspections are made and any defects thus 
            identified are corrected. 

      2.    For plants intending to justify continued operations or resume 
            operation, the following surveillance, if no already performed, 
            shall be initiated within 10 days after receipt of this bulletin
            and shall be continued until the plant technical specifications 
            are revised or the cause of beam failure has been identified and
            corrected.  This surveillance should improve the ability of the 
            plant to identify an early indication of jet pump degradation or
            failure.  Individual jet pump differential pressure readings 
            should be recorded and used to establish a data base for 
            expected characteristics for each jet pump.  Periodic 
            surveillance readings and individual jet pump trends when 
            evaluated against this data base should assist in providing 
            indication of jet pump degradation and supplement other 
            conditions checked to determine jet pump operability. 

            a.    Prepare the necessary procedures and perform jet pump 
                  operability surveillance including the items specified on 
                  b. below on a daily basis, and following unexpected 
                  changes observed in core flow indications, recirculation 
                  system flow indications, or established power-core flow 
                  relationships. 

            b.    If any of the following deviations occur during sur-
                  veillance, evaluate and record the reason: 


                  (1)   The recirculation pump flow differs by more than 10%
                        from the established speed-flow characteristics for 
                        that pump. 

                  (2)   The indicated total core flow is more than 10% 
                        greater than the core flow value derived from 
                        established power-core flow relationships. 

                  (3)   The diffuser to lower plenum differential pressure 
                        reading on an individual jet pump exceeds the 
                        expected characteristics established for that pump 
                        (B.2 above). 

3.    If it is determined that a jet pump is inoperable or significantly 
      degraded, the reactor shall be shutdown in accordance with technical 
      specification requirements. 

.

                                                 IE Bulletin No. 80-07 
                                                 Date:  April 4, 1980 
                                                 Page 4 of 4 

4.    Review your procedures for instructing plant operators regarding 
      identification and response to sudden individual jet pump failure. 
      Revise procedures as required and instruct operating staff of any 
      changes. 

C.    Reporting Requirements 

      The information in Items A.3, and B.1, is requested under the 
      provisions of 10 CFR 50.54 (f).  Accordingly, you are requested to 
      provide within the time periods specified in this items, written 
      statements of information, signed under oath or affirmation. 

Approved by GAO, B180225 (R0072); clearance expires 7-31-80.  Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

Attachments:
Figures 1 and 2
  Jet Pump Sketches

Page Last Reviewed/Updated Monday, June 17, 2013