IR 05000282/1979026
| ML19260C243 | |
| Person / Time | |
|---|---|
| Site: | Prairie Island  |
| Issue date: | 11/05/1979 |
| From: | Choules N, Oestmann M, Warnick R NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION III) |
| To: | |
| Shared Package | |
| ML19260C239 | List: |
| References | |
| 50-282-79-26, NUDOCS 7912260105 | |
| Download: ML19260C243 (8) | |
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U.S. NUCLEAR REGULATORY COMMISSION
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OFFICE OF INSPECTION AND ENFORCEMENT
REGION III
Report No. 50-282/79-26 Docket No. 50-282 License No. DPR-42 Licensee: Northern States Power Company 414 Nicollet Mall Minneapolis, MN 55401 Facility Name:
Prairie Island Nuclear Generating Plant, Unit 1 Inspection At:
Prairie Island -Site, Red Wing, MN Inspection Conducted: October 2 and 3, 1979
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//!d.!7h Inspectors:
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(P M. J. Oestmann ll
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ar ick r$i @ $ ef jy/f/yp Approved By: R Reactor Projects Section 2
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Inspection Sumary Inspection on October 2 and 3, 1979 (Report No. 50-282/79-26)
Areas Inspected:
Special, announced inspection of steam generator tube rupture. The inspection involved 69 inspector-hours onsite by five NRC inspectors.
Results: No items of noncompliance or deviations were identified.
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DETAILS
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1.
Persons Contacted G. Neils, General Superintendent, Nuclear Power Plant Operation
- F. Tierney, Plant Manager J. Brokaw, Plant Superintendent, Operations and Maintenance E. Watzl, Plant Superintendent, Plant Engineering and Radiation Protection R. Lindsay, Superintendent Operation A. Hunstad, Staff Engineer D. Schuelke, Superintendent, Radiation Protection J. Linville, Plant Chenist E. Ward, Manager, Nuclear Environmental Services (NSS)
L. McDonnell, Chief, Section of Radiation Protection, Wisconsin Department of Health and Social Sciences B. Breitenstein, Radiation Section, Minnesota Department of Public Health The inspectors also interviewed several other licensee employees, including members of the radiation protection, operations and engineering sections.
- Denotes those attending exit interview.
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2.
Steam Generator Tube Rupture On October 2, 1979, at 2:33 p.m. the licensee informed the Region and the NRC incident response centers using the control room dedicated phone line that Unit I had an apparent steam generator tube rupture.
Shortly after receipt of this information a team of five inspectors was dispatched to the site by chartered aircraft. The team consisted of two operations inspectors, two radiological control inspectors and one environmental inspector. The team departed DuPage County Airport at 4:40 p.m. and arrived at Red Wing, Minnesota Airport at 6:15 p.m.
The team was met at the airport by the Goodhue County Sheriff Deputy and a city of Red Wing policeman and transported to the site, arriving at 6:50 p.m. on October 2, 1979.
Based on the review of plant recorders and plant trip data, discussion with licensee personnel, and from inspectors observations of actions, the following is a summary of events and actions associated with the steam generator tube rupture in the No. 11 steam generator.
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TIME EVENT / ACTION 10/2/77 2:14 p.m.
Control room received high radiation alarm on IR-15, steam jet air ejector radiation monitor. Health Physics requested to obtain air ejector grab samples.
2:21 p.m.
Received low pressurizer pressure alarm. Reactor pressure 2119 psig.
2:22 p.m.
Received low pressurizer level alarm. Pressurizer level 15.9%.
2:23 p.m.
No. 11 charging pump started.
2:24 p.m.
No. 13 charging pump started.
+9 seconds Reactor trip from low pressurizer pressure.
(Less than 1900 psig).
+14 seconds Safety injection from low pressurizer pressure.
SI sequence initiated.
(Less than 1815 psig).
+14 seconds No. 11 and 12 steam generator low low level trips.
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+33 seconds Pressurizer pressure started to increase due to initiation of safety injection. Minimum pressure reached was approximately 1790 psig.
2:25 p.m.
Operators verified all automatic safety injection action had occurred.
2:26 & 2:27 p.m.
Reactor coolant pumps manually tripped.
2:30 p.m.
Emergency alert declared.
2:38 p.m.
Reset safety injection.
Pressurizer pressure greater than 2000 psig. SI pumps remain operating.
2:41 p.m.
No. 11 steam generator identified as generator with ruptured tube. Steam generator was isolated by closing the "A" Main Steam Isolation Valve.
2:42 to 3:10 p.m.
Reactor coolant system cooled down to about 450 F Tave and pressure decreased to approxi-mately 950 psig by steaming the No. 12 steam generator and opening the pressurizer power operated relief valve (PORV). During the oper-ation of the PORV the presucrizer relief tank 1616 165
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rupture disc ruptured due to pressure buildup from the PORV. The pressure and temperature reduction was necessary to equalize pressure between the reactor coolant system and the secondary side of the No. 11 steam generator.
(Note: PORV was not opened until pressurize level was on scale at 2:56 p.m.).
2:47 p.m.
Stopped No. 11 and 12 RHR pumps.
2:48 p.m.
Blocked low pressure SI.
2:56 p.m.
Stopped No. 12 SI pump.
Pressurizer level on saale.
3:00 p.m.
Site emergency declared.
3:06 p.m.
Stopped No. 11 SI pump. Re-established letdown flow and reactor coolant pump seal leak off flow.
3:15 p.m.
Reactor coolant system at 910 psig and 455 F.
Pressurizer level was approximately 60%.
3:30 p.m.
Reactor coolant system boron was 1927 ppm.
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3:50 p.m.
Started a slow cooldown of the reactor coolant System.
7:10 p.m.
Stopped No. 11 charging pump.
9:24 p.m.
Bumped No. 12 reactor coolant pump for 20 seconds.
This was not performed until a safety evaluation of starting the pump was completed by the licensee.
The evaluation indicated the pump could be started without any unusual transients of temper-ature, pressure, or level.
9:28 p.m.
No. 12 reactor *aolant pump started and left running to increase the cooldown rate.
No unusual transients were noted during the pump starts.
10:00 p.m.
Site emergency was lifted.
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10/3/79
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00:35 a.m.
Reactor coolant system pressure 547 psig, temper-ature 345F and boron 1955 ppm.
Pressurizer level 50%.
06:40 a.m.
RHR pump started.
Reactor coolant pressure 390 psig, tenperature 318F, and boron 2068 ppm.
Pressurizer level 42%.
Cooldown using RHR started.
13:00 a.m.
RCS cold shutdown.
Members of the NRC team were at the site from October 2, 1979, at 6:50 p.m. to 12:00 p.m. on October 3, 1979.
The team departed the site when the reactor was near the cold shutdown condition. The resident inspector was at -the site after the team departed.
Described below are the activities and findings of the team.
a.
Operations Inspectors The operations inspectors spent most of their time in the con +.rol room.
Plant parameters such as radiation levels, temperature, pressure, boron concentration, pressurizer level, and steam generator levels were monitored throughout the entire
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time period the inspectors were en site.
The starting of reactor coolant pumps and RHR pumps were observed. Discussions were conducted with both operators and management as to the sequence of events during and after the event.
Logs, computer printouts and strip charts were reviewed for the event. From these discussion and reviews it appears anat the plant was operated in accordance with established emergency and normal operating procedures during the event.
A review of the event data showed that the pressurizer level was off scale low for approximately 30 minutes, starting shortly after the tube rupture occurred.
When safety injection was initiated, pressurizer pressure increased from 1790 to 2000 psig within abc.
4 minutes, but level did not return on scale at this time. npparently as pressure was increased the leak through the tube increased and the flow from the safety injection pumps decreased as the pressure approached shut off head. The situation apparently existed such that the acutal addition of
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water to the reactor coolant was small. The licensee's preliminary estimate of steam generator tube leak was about 380 gpm at around 2000 psig.
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At about 2000 psig the charging flow and safety injection flow
based on operations observations are estimated to be about 400 gpm From this rough estimate, actual gain in level at around 2000 psig could be on the order of 20 gpm. When pressure was reduced by opening the PORV, the operator noticed the safety injection flow increased to 600 gpm with only one SI pump operating, and pres-surizer level quickly increased.
No items of noncompliance or deviations were identified during this inspection.
b.
Radiological and Environmental Inspectors Upon arrival at the site at 6:50 p.m. on October 2, 1979, the inspectors met with the licensee to discuss the status of the plant and the environmental impact of the releases of radio-activity from the air ejector resulting from a Unit I steam generator tube rupture. The inspectors were also briefed on the plant status by the NRC Resident Inspector.
The licensee reported that the relesse of off gases was 7.4% of the licensee's technical specification limits. Ninety-five percent of the release consisted of xenon-133, xenen-135, and krypton-87. No radioiodine activity was detected in the release.
The licensee also reported that 3000 gallonsofleakagecollectedintheturbinebuildjngsumpwas released to the discharge canal and contained 10 microcuries per milliliter of xenon gas dissolved in the water. The inspector
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verified the calculations of the release.
By midnight, October 2-3, 1979, a total of about 27.5 curies of radioactive material was released to the environment.
The licensee stated that no detectable activity above background was found in air particulate filter samples taken from the onsite air sampling stations.
In addition, health physics surveys taken by the licensee onsite and offsite showed no detectable activity above background.
Using portable survey meters and samplers, the inspectors measured ambient radiation levels and quantified airborne radioactivity concentrations.
A 10 minute particulate air sample (300 cubic feet) was obtained outside of the resident inspector's trailer by the inspectors at approximately 7:30 p.m: The inspectors also obtained a soil a~i vegetation sample in the same area near the resident inspector's trailer and made direct radiation measure-ments. The direct radiation measurement was 0.01 - 0.03 mR/hr, essentially background. The trailer was located downwind (at that time approximately 8:00 p.m.) of Unit I and 2 turbine building. The inspectors then made a direct radiation measure-ment using the Eberline E500B GM portable on the west side of the turbine building and as far north and south as they could go, i.e.,
to the security fence.
No readings above background were detected.
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The inspectors met with the State of Minnesota Department of Public Health Emergency Team members who also reported that no radiation levels above background were detected offsite. The State of Minnesota DPH and the State of Wisconsin Department of Health and Social Services had collected air particulate filters, charcoal adsorbers, soil, vegetation, water, milk, and thermolumi-nescent dosimeters at different 106 tions in both states around the plant site.
Results of analysis showed no detectable activity levels above background.
Both State agencies responded to the incident in a timely manner and performed their duties in a pro-fessional manner.
In addition to the health physics surveys, the inspectors. collected air particulate, soil, and vegetation samples. Results indicated the levels were at background.
The inspectors observed the licensee implement his emergency plan and implementing procedures. No problems were identified in the licensee's conduct of his plaa and procedures.
The licensee utilized a weather vane on top of the containment building to measure wind speed and direction. This information is recorded in the control room.
The licensee has available a meteorology tower onsite which meets the criteria of Regulatory Guide 1.23 but the data on wind speed and direction, delta temperature, are not read out in the control room. Data from
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this tower would be more representative of real time meteorology rather than that from the weather vane for offsite dose deter-minations.
In addition, no overlays of isopleths for dose deter-minations were available.
The licensee's emergency plan lacked demographic data for the sixteen sectors surrounding the site. The Goodhue County Emergency Plan does have demographic information for individual townships.
Such information can be used for a demographic chart, however, additional data would be required from the other areas surrounding the plant.
The licensee has two onsite indicator stations with air particu-late filter and charcoal adsorber and TLDs and two offsite control stations. The inspectors found that the' licensee had just replaced the eight quarterly TLDs at four environmental monitoring stations on the morning of the incident. No TLD replacements were avail-able for a second changeout (i.e., post-incident) until provided by Hazelton Inc. on the day after the incident. A licensee repre-sentative stated that spare TLDs will be kept at the site.
No items of noncompliance or deviations were identified in the environmental monitoring area during the course of this inspec-tion; however, as discussed via telephone with the licensee on October 31, 1979, the NRC will be requesting that the existing bl6 169-7-
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program be upgraded in the near future. As a direction, the licensee has made a commitment 3first r,tep in this to i:nprove offsite monitoring capability by mid-1980.
3.
Exit Interview Two inspectors met with Mr. Tierney at the conclusion of the inspec-tion on Octcher 3,1979. The inspectors summarized the purpose and the scope o! the inspection and the findings.
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1/ Letter to H. Denton, NRR from L. Mayer, NSP, dat-ed October 17, 1979.
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