United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 80-07: BWR Jet Pump Assembly Failure

                                                       SSINS No.: 6820 
                                                       Accession No.: 
                                                       8002280648 

                                UNITED STATES
                       NUCLEAR REGULATORY COMMISSION 
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                                April 4, 1980

                                                      IE Bulletin No. 80-07 

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 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 
10-6 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 10-3 
gpm while A recirculation loop flow remained at 49 x 10-3 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 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. 

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

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

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 probable 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-3 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 inspections 
     including any deficiencies thus identified and corrective actions 
     taken. 

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

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 
.

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

     bulletin, written justification 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 not 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 in b. below on a daily 
          basis, and following recirculation pump restart, and following 
          unexpected changes observed in core flow indications, 
          recirculation system flow indications, or established powercore 
          flow relationships. 

     b.   If any of the following deviations occur during surveillance, 
          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 powercore 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. 

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. 
.

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

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 these items, written 
     statements of this information, signed under oath or affirmation. 

Approved by GAO, B180225 (ROO72); 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 Tuesday, July 23, 2013