ML20209F639
| ML20209F639 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 05/31/1985 |
| From: | Tucker H DUKE POWER CO. |
| To: | Grace J NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION II) |
| References | |
| 414-85-08, 414-85-8, NUDOCS 8507120509 | |
| Download: ML20209F639 (6) | |
Text
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e DUKE POWER GOMPANY P.O.190x 33189 3
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May 31, 1985
^?j 09 Dr. J. Nelson Grace, Regional Administrator U. S. Nuclear Regulatory Commission.
Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 Re: Catawba Nuclear Station, Unit 2 Docket No. 50-414 Significant Deficiency No. 414/85-08
Dear Dr. Grace:
Pursuant to 10 CFR 50.55(e)(1)(iii), please find attached Significant Deficiency Report No. 414/85-08.
Very truly yours, f
Hal B. Tuck r LTP/mjf Attachment cc: Director INP0 Records Center Office of Inspection and Enforcement Suite 1500 U. S. Nuclear Regulatory Commission 1100 Circle 75 Parkway Washington, D. C. 20555 Atlanta, Georgia 30339 Mr. Jesse L. Riley Dr. K. Jabbour Carolina Environmental Study Group Office of Nuclear Reactor Regulatiou 854 Henley Place U. S. Nuclear Regulatory Commission Charlotte, North Carolina 28207 Washington, D. C. 20555 Robert Guild, Esq.
P. O. Box 12097 Charleston, South Carolina 29412 Palmetto Alliance 2135 Devine Street Columbia, South Carolina 29205 NRC Resident Inspector Catawba Nuclear Station
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501
CATAWBA NUCLEAR STATION Significant Deficiency No. 414/85-08 Overpressurization of the Residual Heat Removal (ND) System During Cold Hydro Identification: On April 19, 1985, a portion of the Unit.2 Residual Heat Removal,(ND) System was pressurized above the design pressure of 600 psig.
The ND system experienced a maximum pressure of 2000 psig for about three hours. This incident is similar in nature to that which occurred on April 20, 1985, in which overpressurization and rupture of the Volume Control Tank occurred. Refer to Significant Deficiency Report No. 414/85-06, dated May 22, 1985.
Initial Report: On May 3, 1985, Chuck Burger of NRC Region II, Atlanta, Georgia was notified of the incident by R. C. Gamberg, T. L. Utterback, and S. D. Alexander of Duke Power Company, 422 S. Church Street, Charlotte, N. C.
28242.
Summary: During preparation for Cold Hydrostatic Testing, a mini hydro of the Reactor Cooling (NC) System was in progress in which the NC system was taken up to 2000 psig.
While maintaining this pressure, a walk down was conducted to inspect for leaks. When several relief valves were discovered leaking, it was determined that overpressurization of oth r systems had occurred. The NC System was subsequently depressurized.
The ND System was to have been isolated from the NC System for this test, but two isolation valves at the hydro boundary were left open which allowed NC pressure to enter the ND System via a temporary test line. Refer to Enclosure 1 for a diagram of the ND System.
Also, a valve which would have provided a relief path from the ND relief valves to the Recycle Holdup Tanks had been previously closed to support Unit 1 operations.
Portions of the ND System, the Boron Recycle (NB) System and the Nuclear Sampling (NM) System were overpressurized to 2000 psig for about three hours.
Background:
The NC System Cold Hydrostatic Test is performed in accordance with the following two controlling procedures:
Temporary Operating Instruction - TOI/2/A/6150/01 - Initial Filling and Venting the Reactor Coolant System and Control of NC System for NC Hydro Construction Procedure CP-1072 - Hydrostatic Test of the Unit 2 Reactor Coolant System and Portions of Associated Piping (Cold Hydro)
TOI/2/A/6150/01 provides instructions to pressurize the NC System to 2200 psig.
Procedure CP-1072 provides instruction to increase NC System from 2200 psig to between 3107 and 3292 psig.
A Mini-Hydro is performed before the actual Cold Hydro I ressure is reached.
The purpose of this is to check for leaks.
Step 5.2.15 of TOI/2/A/6150/01 states, "The NC System may now be pressurized as desired ip to 2200 psig."
Several pressure plateaus are selected up to this pressure to check for leakage. Pressure plateaus of 1000 psig and 2000 psig were selected to perform leakage checks.
ND System Suction Isolation Valves 2ND1B, 2ND2A, 2ND36B, and 2ND37A (see ) automatically close to isolate the ND from the NC System as the NC System pressure exceeds 600 psig.
The ND discharge piping is protected from NC System pressure by two check valves in series, two sets per train (2NI175, 2NI82; 2NI176, 2NI94; 2NI180, 2NI71; 2NI181, 2NI60). Each ND discharge line contains a normally open motor-operated valve (2NI173A and 2NI178B). These valves can be closed to further isolate the ND from the NC System. The ND System discharge piping has a maximum design pressure of 615 psia (600 psig).
Each train of ND contains a relief valve (2ND31 and 2ND64) to protect this piping. These valves are set to relieve pressure at 600 psig to a common header which discharges into either Recycle Holdup Tank. However, the Recycle Holdup Tanks are on the Unit I side of the Security Interim Barrier and have both been utilized for Unit 1 Operation. A Unit 1/ Unit 2 boundary valve in the common relief header separates the relief valves from the Recycle Holdup Tanks. Valve INB395 was closed at the time of the incident. Therefore, the relief path was blocked for relief valves 2ND31 and 2ND64. Valve INB395 had been closed for two reasons:
1)
To prevent Unit I contamination from reaching Unit 2 areas; and 2)
To prevent non-contaminated water on Unit 2 from entering the Unit I radwaste processing systems.
The flow diagram containing this valve includes a note which states, " Valve is to separate Unit 2 relief valve header from Unit I for construction purposes.
This valve should be locked open when Unit 2 is brought into operation."
There was no clear identification of the functional requirements for this valve.
==
Description:==
The NC System pressurization began on April 18 at 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br />.
Letdown to the Chemical and Volume Control (NV) System was established per TOI/2/A/6150/01 by the day shift, and by shift turnover the procedure had been completed to the point prior to isolating and securing the ND System. A Procedure Change was written to TOI/2/A/6150/01 to have isolation valves 2NI173A and 2NI178B closed prior to exceeding 385 psig in the NC System. The operator was instructed to follow the procedure, but was told not to sign-off the steps.
As the NC System pressure approached 385 psig, ND Pump 2B was secured (ND Pump 2A was not running). Also, the ND pump suction valves were closed. The next step in the procedure was not performed at this time.
It states, "Close valves 2NI173A and 2NI178B." The operator felt that the series check valves would prevent the ND discharge piping from being overpressurized. The operator was unaware that a temporary test line was piped up to bypass the
. discharge check valves in order to pressurize the piping up to hydro-boundary valves 2NI173A and 2NI173B. This was done to avoid the removal of the check valve internals.
The operator was also monitoring the ND Pump discharge pressure gauges in the Control Room throughout the time that NC pressure was increasing. These gauges monitor the pressure between the pump discharge and the pump discharge check valves 2ND10 and 2ND44. However, these pressure indications are isolated from the pressurized piping by check valves 2ND10 and 2ND14. The gauges did not indicate higher than 200 psig on Train A and 400 psig on Train B throughout the incident.
The operator also thought that he would be given instructions on when to close 2NI173A and 2NI178B. No instructions on closing these valves were given. NC System pressure was in the process of being increased to 1000 psig.
Throughout this time, the NC System pressure was present in the ND discharge piping via the temporary test line.
At 0200 hours0.00231 days <br />0.0556 hours <br />3.306878e-4 weeks <br />7.61e-5 months <br />, the NC System pressure reached 1000 psig. The pressure was held at 1000 psig and personnel performed a walkdown to check for leaks. No leaks were found. The NC System pressure was then increased. At 0315 hours0.00365 days <br />0.0875 hours <br />5.208333e-4 weeks <br />1.198575e-4 months <br />, the NC System pressure reached 2000 psig. The pressure was held there to perform another walkdown. Several leaks were found, including leaks from relief valve 2ND31 and 2NM296. At 0630 hours0.00729 days <br />0.175 hours <br />0.00104 weeks <br />2.39715e-4 months <br />, the NC System was depressurized.
A subsequent review revealed that portions of the ND System, the Boron Recycle System, and the Nuclear Sampling System, were overpressurized to 2000 psig.
Analysis:
Several causes contributed to this event. One of the causes was that the ND discharge piping did not have any relief protection during the Mini-Hydro. When the Unit 1/ Unit 2 relief path isolation valves were originally closed prior to Unit 1 operation, the~possible consequences on Unit 2 were not fully considered. Also, the isolated relief paths were not identified by the procedure preparers or reviewers, or associated test personnel.
An additional factor was the lack of clear instructions to the operator who had been receiving instructions from various individuals prior to the overpressurization of ND.
These persons had been directing the operator to perform certain steps of the procedure. The operator expected to receive instructions as to when to close 2 nil 73A and 2NI178B, but was unsure from whom these instructions would come. All instructions for the Operator should have come through his immediate supervisor.
The instructions made to the operator concerning not signing steps were not in accordance with Operations Management Procedure 1-4, Use of Procedures, which requires steps performed to be signed-off when required. The operator did not perform the step which would have isolated ND because he was not signing the steps.
Safety Implications: There were no radioactive material releases, radiation exposures, or personnel injuries as a result of this incident.
The temporary test lines were used to bypass the check valves because the Cold Hydro boundary includes the piping up to isolation valves 2NI173A and
- 2NI178B. The temporary test line method was selected to prevent removing the check valve internals. The temporary test linen were needed only for Cold Hydro. These lines will not be in place when Hot Functional Testing is performed.
During future testing and operation, the check valves will block the higher NC System pressure. Should these valves begin to leak, the relief valves will be available to relieve pressure to the Recycle Holdup Tanks, because the Unit 1/ Unit 2 boundary valve will be open, or a temporary relief header will be used which has been installed to preclude a future similar problem.
Corrective Action: The following corrective actions have been taken:
1)
A review of NC Hydro boundary valves and Unit 1/ Unit 2 boundary vaives was performed.
2)
A temporary relief header was installed which will be used for the ND relief valves which go to the Recycle Holdup Tank.
This temporary relief header relieves into the Unit 2 Turbine Building Sump.
3)
Prior to restarting Cold Hydro after the Volume Control Tank rupture (SD 414/85-06), the interface organization between Milestone Startup and Operations was formalized with specific channels for communication.
It should be noted that future tests will not require this type of interface between these groups. The designation of specific coordinators for the remainder of Cold Hydro Testing established an organization for testing which will prevent the operators from receiving instructions from anyone other than their immediate supervisors.
4)
The appropriate personnel were instructed on the use of Operations Management Procedure 1-4.
5)
A Non-conforming Item Report (NCI) was originated to identify and evaluate areas of possible overpressurization on the ND, NB, and NM Systems.
The final resolution of the NCI will assure that any areas of over-pressurization are identified, evaluated and repiired as necessary. A follow-up report will be submitted by July 15, 1985 describing the status of all further corrective action and a schedule for its completion.
9 O
9 ENCLOSURE 1 CATAWBA NUCLEAR STATION UNIT 2 ND SYSTEM SIMPLIFIED DRAWING 2NDP LOOP C O
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