05000302/LER-1990-001, :on 900122,RCS Leakage Value Exceeded Tech Spec Limits,Resulting in Plant Shutdown.Caused by Failed Packing on Block Valve Associated W/Porv.Valve Repacked & Washers Replaced
| ML20059C346 | |
| Person / Time | |
|---|---|
| Site: | Crystal River  |
| Issue date: | 08/28/1990 |
| From: | Boldt G, Stephenson W FLORIDA POWER CORP. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| 3F0890-18, 3F890-18, LER-90-001, LER-90-1, NUDOCS 9008310206 | |
| Download: ML20059C346 (6) | |
| Event date: | |
|---|---|
| Report date: | |
| 3021990001R00 - NRC Website | |
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U. S. Nuclear Regulatory Commission Atte.<it ion : Document Control Desk Washington, D. C. 20555 l
l Subject: Crystal < liver Unit 3 Docket tso 50 302 Operating License No. DPR-72 Licenses Event Report No. 90-01-01
Dear Sir:
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Enclosed is Licensee Event Report (LER) 90-01-01 which is submitted in accordance with 10 CFR 50.73.
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This s"pplement includes additional information relative to both cause and i
corrective action as a result of the root cause investigation.
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l Crystal River Unit 3 was operating in MODE I (POWER OPERATION) at 98% full power on January 22, 1990.
Reactor Coolant System (RCS) leakage calculations completed earlier that day showed that UNIDENTIFIED LEAKAGE was 0.3 gpm. At 1105, Reactor Coolant System leakage calculations indicated that UNIDENTIFIED LEAKAGE had increased to 1.3 gpm. This value exceeded Technical Specification limits. At 1205 operators began plant shutdown due to excess leakage. The plant entered an Unusual Event due to excess RCS UNIDENTIFIED LEAKAGE, in accordance with the plant Emergency Plan.
l Plant shutdown was completed at 1550. At 1700, operators isolated the leak.
The source of RCS leakage was identified as failed packing on the block valve associated with the Pilot Operated Relief Valve. The root cause for the packing failure was determined to be excessive torque applied to the packing flange gland bolts.
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EVENT DESCRIPTION
Crystal River Unit 3 (CR-3) was operating in MODE 1 (POWER OPERATION) at 98%
full power on January 22, 1990. At approximately 0815, while taking logs, the Assistant Nuclear Shift Su>ervisor (ANSS) noticed that airborne radioactivity levels were increasing in tie Reactor Building (RB) (NH). The ANSS then noticed that the RB sump (NH] was filling at a rate higher than normal.
The RB sump typically fills at a rate equivalent to less than 1 gpm. The sump fill rate at this time was 1.4 gpm. Fluid enters the sump as a result of leakage from systems within the RB, as well as condensation of moisture within the building.
The increased sump fill rate, together with increased RB radiation levels, were indicative of increased leakage in the building.
At 0835, Control Room Operators began Reactor Coolant System (RCS) (AB) water inventory balance calculations to determine if the (RCS) was the leakage source.
Inventory balance calculations completed earlier on January 22, 1990 showed that UNIDENTIFIED LEAKAGE was 0.3 gpm.
At 1105, inventory balance calculations indicated that RCS UNIDENTIFIED LEAKAGE had increased to 1.3 gpm. In accordance with the CR-3 Emergency Plan, the plant entered an Unusual Event. The Emergency Plan requires the declaration of an Unusual Event whenever RCS UNIDENTIFIED LEAKAGE exceeds 1 gpm.
l Plant Technical Specifications require that RCS UNIDENTIFIED LEAKAGE be no more than I gpm.
Whenever the plant exceeds this limit, Technical Specifications require that operators reduce UNIDENTIFIED LEAKAGE to less than 1 gpm within four hours, or place the plant in MODE 3 (HOT STANDBY) within the following six hours.
I At 1205 operators began plant shutdown in accordance with Technical Specification I
requirements.
Operators could not perform additional RCS inventory balance calculations during plant shutdown. Plant personnel monitored the RB sump fill rate during shutdown in order to obtain an indication of the RCS leak rate. The fill rate increased from the initial value of 1.3 gpm to as high as 13 gpm.
The plant entered H0T l
STANDBY at 1550.
Operators continued with plant cooldown following reactor shutdown. Operators terminated cooldown and stabilized the plant at 349'F and 445 psig at 1215 on January 23.
During shutdown, operators observed indications that the RCS leak was coming from the area around the Pressurizer (AB, PZR).
In order to test for possible leakage sources, Operators closed the Block Valve [AB,SHV) associated with the Pilot Operated Relief Valve (PORV) (AB,RV]. They observed that leakage appeared to stop or decrease when they closed the Block Valve (Tag number RCV-ll).
Operators desired to have the PORV available during shutdown. Therefore, they 1
reopened RCV-II, and kept the valve open until the reactor [AC, RCT) was shut j
down.
At 1700, operators closed RCV-ll and lef t it closed.
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.m.eeco.-3.u,mn With RCV-Il closed, the Sump fill rate decreased to 0.5 gpm.
Operators began an RCS inventory balance calculation at 2115. At 2330, inventory results showed that RCS UNIDENTIFIED LEAKAGE had decreased to 0.4 gpm.
At 2330 the plant exited the Unusual Event.
During cooldown, and following completion of cooldown, plant personnel entered the Reactor Buildina in efforts to locate the exact source of RCS leakage.
By 1830 plant personnel identified failed packing on RCV-ll as the leakage source.
The design of RCV ll is su:h that valve packing is not exposed to RCS pressure if the valve remains closed.
Therefore, utility management personnel decided to deenergize RCV ll in the closed position, and intended to keep the valve deenergized for the duration of the current fuel cycle.
On February 13, 1990, the plant shut down and cooled down for maintenance. The plant began heatup on February 19, 1990 following completion of maintenance activities.
During this outage, plant personnel replaced packing in RCV-II.
The valve was-returned to service during plant heatup.
At the time of this report, RCV-11 leakaCe appears to have stopped. If leakage does not resume, RCV-11 will remain in service.
CAUSE
Technical Specifications required plant shutdown due to Reactor Coolant System UNIDENTIFIED LEAKAGE in excess of I gpm.
Plant personnel identified failed packing on RCV-Il as the source of leakage.
At the time of original issue of this report, plant personnel had not determined the root cause of the packing failure. Subsequent investigation determined that failure was caused by excessive torque applied to the packing gland flange bolts l
when the valve was repacked in April of 1986. Excess torque was applied due to I
personnel error when changing packing materials, i
The design of RCV-Il includes belleville washers which act as a spring to maintain compressive load on the valve packing.
(Please refer to Figure 1.)
Valve RCV-ll was originally packed with a material that required a relatively high torque.
In April of 1986, plant personnel replaced the original packing with a new material, using the old torque values.
The new packing uses anti-extrusion rings to hold the packing in place.
The anti-extrusion rings failed due to the force resulting from the applied torque. Failed anti-extrusion l
rings allowed packing to be forced from the valve by F.CS pressure.
Plant personnel failed to characterize the change of packing material as a plant modification. if this change had been recognized, existing procedures would have I
invoked review and approval of torque values and other design parameters. Other packing changes have been classified as plant modifications in the past; therefore, this is considered an isolated incident.
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,4 we % =.mn [Y1NT ANALYSIS The RCS leakage rate never exceeded the normal flow capability of the Makeup System (CB].
Plant shutdown and subsequent cooldown were controlled at all times. All radioactive material released from the RCS was contained within the Reactor Building.
No radioactive material was released to the general public.
CORRECTIVE ACTIONS
Operators closed and deenergized RCV-Il following identification of the leakage source. The valve remained closed and deenergized during plant operation. Plant perennel repacked RCV-Il during the February 1990 maintenance outage.
Based on the ic ults of a failure analysis, plant personnel calculated torque values to be used when repacking RCV-II.
The valve was repacked and the belleville washers were replaced. The new belleville washers were not as stiff as those originally irstalled.
The softer washers, along with the new torque values, reduced the compressive load on the new packing. This work was performed during the 1990 refueling outage.
The failure to recalculate torque values appears to be an isolated event.
Current administrative controls require review of all modifications before implementation.
These controls should prevent recurrence of this event.
The results of the failure investigation have been presented to maintenance personnel.
PREVIOUS SIMILAR EVENTS
1 This is the second sent in which Technical Specifications required plant shutdown due to RCS leakage. On January 28, 1982, CR-3 was forced to shut down due to RCS UNIDENTIFIED LEAKAGE.
In that event, a through wall crack developed in Makeup and Purification System piping, resulting in excessive leakage.
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