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 Tuesday, March 09, 2021