05000254/LER-2002-001
| Event date: | |
|---|---|
| Report date: | |
| Reporting criterion: | 10 CFR 50.73(a)(2)(i)(A), Completion of TS Shutdown 10 CFR 50.73(a)(2)(v)(D), Loss of Safety Function - Mitigate the Consequences of an Accident |
| 2542002001R00 - NRC Website | |
PLANT AND SYSTEM IDENTIFICATION
General Electric - Boiling Water Reactor, 2511 Megawatts Thermal Rated Core Power Energy Industry Identification System (EIIS) codes are identified in the text as [XX].
EVENT IDENTIFICATION
Reactor Shutdown due to Failure of Reactor Recirculation Jet Pump A. � CONDITION PRIOR TO EVENT Unit: 1 � Event Date: January 9, 2002 � Event Time: 1416 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.38788e-4 months <br /> Reactor Mode: 1 � Mode Name: Power Operation � Power Level: 100% Power Operation (1) - Mode switch in the RUN position with average reactor coolant temperature at any temperature.
B. DESCRIPTION OF EVENT
On January 9, 2002, at 1416 hours0.0164 days <br />0.393 hours <br />0.00234 weeks <br />5.38788e-4 months <br />, Quad Cities Nuclear Power Station Unit 1 control room received indications of a jet pump [P] [AD] failure. These indications consisted of a reactor [RCT] level spike up by 6 inches and then back down, a drop in reactor power from 100% to 91%, a decrease in reactor pressure and core plate differential pressure and an increase in total core flow. � A non-licensed operator was dispatched to take jet pump readings.
At 1439 hours0.0167 days <br />0.4 hours <br />0.00238 weeks <br />5.475395e-4 months <br />, a main steam line (MSL) [SB] high radiation alarm was received. At 1442 hours0.0167 days <br />0.401 hours <br />0.00238 weeks <br />5.48681e-4 months <br />, oscillations in the Unit 1 "B" recirculation pump flow were noted, followed by a trip of the Unit 1 "B" recirculation pump motor.
At 1445 hours0.0167 days <br />0.401 hours <br />0.00239 weeks <br />5.498225e-4 months <br />, the Unit 1 Operator reduced "A" Recirculation pump speed and started to insert control rods to shut the unit down. At 1521 hours0.0176 days <br />0.423 hours <br />0.00251 weeks <br />5.787405e-4 months <br />, Unit 1 jet pump 19/20 was declared inoperable due to greater than a 10% difference from established patterns.
Technical Specification 3.4.2.A was entered, requiring Unit 1 to be in Mode 3 within 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. At 1708 hours0.0198 days <br />0.474 hours <br />0.00282 weeks <br />6.49894e-4 months <br />, an Emergency Notification System notification was made for the failure of the jet pump.
At 1748 hours0.0202 days <br />0.486 hours <br />0.00289 weeks <br />6.65114e-4 months <br /> the Unit 1 reactor entered Mode 2, and at 1830 hours0.0212 days <br />0.508 hours <br />0.00303 weeks <br />6.96315e-4 months <br /> the Unit 1 reactor was subcritical. At 2158 hours0.025 days <br />0.599 hours <br />0.00357 weeks <br />8.21119e-4 months <br /> the mode switch was put in the shutdown position and the reactor entered Mode 3. At that time, the Technical Specification action statement was exited.
C. CAUSE OF EVENT
The preliminary root cause of the failure of jet pump #20 was failure of the hold-down beam due to intergranular stress corrosion cracking in the transition portion of the beam. If necessary, a revised report will be submitted upon completion of the root cause evaluation. The crack was located in an area of the jet pump hold-down beam that is not covered by the inspection requirements of BWRVIP-41, "BWR Jet Pump Assembly Inspection and Flow Evaluation Guidelines." Therefore, although Quad Cities Nuclear Power Station implemented the requirements of BWRVIP-41, including periodic inspections of the required areas of the jet pump hold-down beams, the transition area of the beam was not required to be inspected and the crack was not identified prior to failure.
The "B" recirculation pump motor trip and the MSL high radiation alarm were also a result of the failure of the jet pump hold-down beam. The "B" recirculation pump motor tripped due to the introduction into the recirculation pump impeller of a piece of the jet pump hold-down beam.
The MSL high radiation alarm was due to the changes in flow dynamics and mixing in the annulus region of the vessel due to the jet pump failure, and the resultant increase in ammonia levels. The redirected flow of the ammonia, which includes Nitrogen-16 as a component, and the resulting decrease in efficiency of the steam dryer, caused elevated levels of the ammonia to be carried over into the main steam lines, causing the increased radiation levels.
D. SAFETY ANALYSIS
The safety significance of this event was minimal. Although the reactor shutdown and cooldown were accomplished with normal means, all emergency core cooling systems were operable during this event. The failure of the jet pump was readily detected from diverse plant parameters displayed in the control room, and the reactor was shut down within eight hours of the initial indications.
The structural integrity of the jet pump supports the capability of reflooding the core to two-thirds core height during a design basis loss-of-coolant accident (LOCA) (i.e., a double-ended guillotine break of a 28" reactor recirculation pipe). Had the jet pump failed during a LOCA with no other single failure, the total ECCS inventory delivered to the core would be well in excess of the licensing basis case with the worst single ECCS failure.
Additionally, the containment response during a LOCA with a failed jet pump was determined to be within the UFSAR-assumed response, because the UFSAR assumes that the equalizer valves are in the abnormal open position.
This report is being submitted in accordance with 10 CFR 50.73(a)(2)(i)(A) as "the completion of any nuclear plant shutdown required by the plant's Technical Specifications," and in accordance with 10 CFR 50.73(a)(2)(v)(D) as an "event or condition that could have prevented the fulfillment of the safety function of structures or systems that are needed to mitigate the consequences of an accident.
E. CORRECTIVE ACTIONS
Immediate Corrective Actions:
The unit was shut down, the failed jet pump was repaired, and all of the original-style BWR/3 jet pump hold-down beams were replaced with BWR/4 jet pump hold-down beams.
The Unit 1 "B" recirculation pump impeller was replaced.
An operability evaluation was performed to support operation of Unit 2 from the time of the jet pump failure until the start of the next Unit 2 refueling outage (about 34 days).
Completed Corrective Actions:
All of the original-style BWR/3 jet pump hold-down beams on Unit 2 were replaced with BWR/4 jet pump hold-down beams.
F. PREVIOUS OCCURRENCES
No previous occurrences of jet pump hold-down beam failures at Quad Cities Nuclear Power Station were identified.
G. COMPONENT FAILURE DATA
The jet pump hold-down beam was an original design (BWR/3) beam made of Inconel X-750, by Willamette Iron and Steel Co. and forged by Berkeley Forge and Tool, Inc.