ML20032B776
| ML20032B776 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek, Cooper, Arkansas Nuclear, River Bend, Waterford, South Texas, Comanche Peak, Fort Calhoun, Fort Saint Vrain  |
| Issue date: | 07/02/1981 |
| From: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| To: | ARKANSAS POWER & LIGHT CO., GULF STATES UTILITIES CO., HOUSTON LIGHTING & POWER CO., KANSAS GAS & ELECTRIC CO., LOUISIANA POWER & LIGHT CO., NEBRASKA PUBLIC POWER DISTRICT, OMAHA PUBLIC POWER DISTRICT, PUBLIC SERVICE CO. OF COLORADO, TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| References | |
| NUDOCS 8111060295 | |
| Download: ML20032B776 (2) | |
Text
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UNITED STATEC
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NUCLEAR REGULATORY COMMISSION e.
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,I REGION IV 1
811 RYAN PLAZA ORIVE, SUITE 1000 Q-DT[g ARLINGTON, TEXAS 76011 o....
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July 2, 1981 l
Gentlemen:
The enclosed IE Circular is forwarded for your information and appropriate action. No specific response is required.
If you have questions regarding this matter, please contact this office.
Sincerely, l
b jj G W frarl V. Seyfrit Director
Enclosures:
1.
IE Circular No. 81-10 2.
List of itecently Issued IE Circulars I
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IE CIRCULAR 81-10 Licensee Facility / Docket Number _
Arkansas Power and Light Conpany Arkansas Nuclear One,' Unit 1 & 2 Little Rock, Arkansas 50-313; 50-368 Nebraska Public Power District Cooper Nuclear Station Columbus, Nebraska 50-298 0maha Public Power District Fort Calhoun Station Omaha, Nebraska 50-2P5 Puolic Service Company of Colorado Fort St. Vrain Generating Station Denver, Colorado 50-267 Gulf States Utilities River Bend Beaumont, Texas 50-458; 50-459 Houston Lighting & Power Company South Texas Project Houston, Texas 50-498; 50-499 Kansas Gas & Electric Company Wolf Creek Wichita, Kansas STN 50-482 Louisiana Power & Light Company Waterford-3 New Orleans, Louisiana 50-382 Texas Utilities Generating Company Comanche Peak Steam Electric Station Dallas, Texas 50-445; 50-446 l
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1 SSINS No.: 6835 Accession No.
8103300400 IEC 81-10 UNITED STATES MUCLEAR REGULATORY COMMISSION OFFICE OF INSPECTION AND ENFORCEMENT WASHINGTON, D.C.
20555 IE Circular No. 81-10 July 2, 1981 Page 1 of 3 STEAM VOIDING IN THE REACTOR COOLANT SYSTEM DURING DECAY HEAT REMOVAL C00LDOWN Description of Circumstances:
On April 11, 1981, Florida Power Corporation's Crystal River Unit 3 facility (a 2451,4T Babcock & Wilcox reactor) was in Mode 5 (Cold Shutdown).
The Decay Heat Removal (DHR) system was in operation taking a suction on the "B" hot leg and injecting cooled liquid back into the vessel downcomer.
The Reactor Coolant System (RCS) water temperature was approximately 106 F as indicated by the DHR pump suction temperature.
RCS pressure was about 50 psig and being maintained by use of pressurizer heaters and auxiliary spray from the DHR system.
The plant had been cooled down from 520 F to approximately 270 F (measured by the cold leg RTDs) over a 13 hour1.50463e-4 days <br />0.00361 hours <br />2.149471e-5 weeks <br />4.9465e-6 months <br /> period, at which point DHR cooling was initiated and reactor coolant pumps (RCPs) were shut off.
The plant was on DHR for 15 hours1.736111e-4 days <br />0.00417 hours <br />2.480159e-5 weeks <br />5.7075e-6 months <br /> before the 106 F, 50 psig conditions were reached.
At this point, when the operators commenced spray of the pressurizer via the auxiliary spray line to decrease RC3 pressure, the pressurizer level began to increase from about 82 inches to 180 inches indicating that a void of approximately 300 cu.ft. existed in the reactor coolant system.
Upon seeing the level increase, the operator concluded there was a steam void in the system.
He also noticed the "A" loop wide range hot leg RTDs were reading approximately 30c F, which is slightly above the 50 psig saturation temperature.
Spray was s'rminated and emergency feedwater flow was initiated to the "A" Once Through Steam Generator (OTSG) cooling the "A" loor hot leg.
About seven hours later sufficient cooling wac achieved to drop pressurizer level.
The plant depressurized without void formation.
On June 2, 1981, a similar event occurred at McGuire Unit 1.
McGuire had not achieved criticality but had heated up using RCPs.
While reducing RCS temperature and pressure to achieve a cold shutdown condition, a steam void was apparantly formed in the reactor vessel head area when the system was vented.
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IE Circular No. 81-10 Page 2 of 3 The plant had initiated Residual Heat Removal (RHR) cooling and turned off RCPs at about 318 F.
At a RCS loop temperature of 160 F and a pressure of 6C psig, the vessel head was vented.
The operators observed a pressurizer level increase of three to four percent, indicating the presence of a steam there was no decay heat to drive natural circulation as there would have been for an operating plant.
The system was repressurized, the reactor coo? ant pumps were restarted tu uniformly cool the system and the plant was taken to cold shutdown.
Discussion:
These events were apparently caused by insufficient cooling of the large masses of hot metal in regions such as the reactor vessel head, upper "J" leg (B&W), steam generator walls, and reactor pressure vessel nozzles prior to initiating DHR cooling.
Local stagnation and stratification of the fluid in the upper head region while on DHR cooling may also have contributed to the problem.
While the coolant passing through the care was being maintained relatively cool by the DHR system, coolant in the RCS hot legs and in the upper head region was essentially stagnant.
This allowed the coolant to be heated to saturation temperature, or to remain at relatively high temperatures because of the stagnant conditions.
This resulted in steam void formation when the system was depressurized.
The operators correctly diagnosed the system voiding at both Crystal River 3 and McGuire 1 and took appropriate corrective actions to bring the plants to cold shutdown.
While these events were not a concern due to the availability of the DHR system at both Crystal River and McGuire and the lack of core heat production at McGuire, the NRC believes transmittal of this information is appropriate, since voiding in the RCS is a concern if operators fail to recognize these conditions.
Also, normal natural-circulation flow is reduced by voids in hot legs and sufficiently large reactor vessel voids.
j IE Circular No. 80-15, June 1980, and NRR Generic Letter No. 81-21, May 1981, were directed at the possibility of voids being formed in the reactor vessel head region during natural circulation cooldown.
It is important that reactor operators recognize that voiding can occur in other portions of the RCS (e.g.,
in the "J-leg" of B&W reactors) and under conditions other than natural circulation cooldown so that timely and correct action is taken.
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- i Circular 81-10 Page 3 of 3 Recommended Actions for Holders of an Operating License and Near-Term Operating Licensees (NTOL)":
1.
Review your operating procedures dealing with plant cooldown and emergency and/or abnormal pro edures that address natural circulation to assure that sufficient information is available for operators to recognize the symptoms of RCS voiding and take appropriate actions to recover from a voided condition.
Special attention should be directed to the information provided regarding the Jrystal River and McGuire even.; in order to ascertain if they bring to light any conditions you did not consider during your review and revision of natural circulation and shutdown cooling procedures that were required in IE Circular 80-15, and NRR Generic Letter No. 81-21.
2.
Each licensed operator should be informed of the matters discussed in this circular.
3.
Consider including this information in your operator training and retraining classes.
No writtern response to this circular is required.
If you need additional information with regard to this matter, contact the Director of the appropriate i
NRC Regional Office.
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- NTOL is cefinea, for the purpose of this circular, as a plant currently scheduled to recieve an OL prior to January 1, 1983.
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IE Circular No. 81-10 July 2, 1981 RECENTLY ISSUED IE CIRCULARS Circular Subject Date Issued To No.
Issued 81-02 Performance of NRC-2/9/81 All power reactor facilities Licensed Individuals (research and test) with an While on Duty Operating License (OL) or Construction Permit (CP) 81-03 Inoperable Seismic 3/2/81 All power reactor facilities Monitoring Instru-(reasearch and test) with an mentation Operating License (OL) or Construction Permit (CP) 81-05 Self-Aligning Rod End 3/31/81 All power reactor facilities Bushings for Pipe with an Operating Licenses Supports (0L) or Construction Permit (CP) 81-06 Potential Defi-iency 4/14/81 All power reactor facilities Affecting Certain with an Operating License Foxboro 10 to 50 (OL) or Construction Permit Milliampere Transmitters (CP) 81-04 The Role of Shift Tech-4/30/81 All power reactor facilities nical Advisors and Impor-with an Operating Licenses (0L) tance if Licensee Event or near-term Cperating.icenses (0L)
Reports 81-07 Control of Radioactively 5/14/81 All power reactor Contaminated Material facilities with an Operating License (0L) or Construction Permit (CP) 81-08 Foundation Materials 5/29/81 All power reactor facilities with an Operating License (OL) or Construction Permit (CP)
Enclosure
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