ML19294C282
| ML19294C282 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 02/05/1980 |
| From: | Cavanaugh W ARKANSAS POWER & LIGHT CO. |
| To: | Seyfrit K NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV) |
| References | |
| 2-020-01, 2-20-1, NUDOCS 8003100051 | |
| Download: ML19294C282 (4) | |
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ARKANSAS POWER & LIGHT COMPANY POST OFFICE BOX 551 UTTLE ROCK ARKANSAS 72203 (501) 371-4422 February 5, 1980 WILLIAM CAVANAUGH 111 Vice President Generation & Construction -
2-020-01 Mr. K. V. Seyfrit, Director Office of Inspection & Enforcement U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 76011
Subject:
Arkansas Nuclear One - Unit 2 Docket No. 50-368 License No. NPF-6 Reactor Trip Test - 100%
(File:
2-1510)
Gentlemen:
As you are aware, on January 29, 1980, Arkansas Nuclear One Unit-2 conductea a Turbine Trip Test from 100% power.
As a result of the turbine trip, steam dump valves 2CV-0301, 2CV-0302, 2CV-0303, 2CV-0306 and the pressurizer spray valve 2CV-4651 opened, as designed, to lower primary and secondary side pressure.
Following the peak-ing of pressure in the primary and secondary systems, the steam dump valves and the pressurizer spray valve received close signals.
Apparently, at this time steam dump valve 2CV-0301 failed to close and pressurizer spray valve 2CV-4651 did not close completely (ap-proximately 1/4 of an inch open).
As a result of these valves re-maining open, the primary and secondary systems depressurized be-yond the point which would normally be expected as a result of a normal turbine / reactor trip.
Due to this depressurization the SIAS and MSIS activated as designed.
All safety systems performed as de-signed during the transient.
The operators diagnosed and corrected the malfunctions in a skillful manner using the new small break LOCA procedures which required securing the RCP's and going to natural circulation.
The result was a safe shutdown of the unit from a 100%
turbine / reactor trip within approximately 20 minutes with no safety limits exceeded.
In our conversation of January 30, 1980, you requested specific infor-
, mation on the steam dump valve failure, the pressurizer spray valve failure and the need to rerun the 100% turbine trip test.
The follow-ing is provided to address these points.
800310005\\
MEMBER MIDDLE SOUTH UTIUTIES RYSTEM
Mr. K. V. Seyfrit February 5, 1980 9
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The failure of steam dump valve 2CV-0301 has been diagnosed as a failure in the air system supplying the valve operator. This valve has since been successfully tested in varying manual and automatic modes. The testing sequences did not reproduce the failure therefore providing sufficient confidence to declare the valve operable.
The failure of 2CV-0301 to close during the 100% turbine trip test was attributable to the failure of the permissive solenoid in the air system.
The solenoid energized on the quick-open signal but f2iled to deenergize when the signal was removed.
When the mode of operation on the handswitch in the control room was turned from manual to off, the solenoid in series with the permissive solenoid de-energized, cutting off the air supply to the valve actuator, allowing the valve to close.
Engineering analysis and extensive testing has been in progress on the SDBCS valves since post core Hot Functional Testing.
Several modifications nave been made to improve the operability of these valves.
Drains have'been in-stalled on all the 10" SDBCS valve bodies to prevent condensation buildup in the valve which has caused improper operation on previous occasions.
A recent problem with vibration-caused stress failure of the stem brought about further modifications which have been made to the condenser dump valve 2CV-0306.
Stem guides and packing were installed and tests were performed which showed improved operation.
Evaluation on the resolution of the nume-rous problems encountered in operating thesa valves is still in progress.
Combustion Engineering has indicated that there are still further tests that they and Copes Vulcan would like to perform, and that based on results of these tests, the valves will be modified to reach the desired reliability.
In the interim period, the condenser dump valves, 2CV-0302, 2CV-0306 and 2CV-0303, will be operated in the automatic mode and the atmospheric dump valves, 2CV-1001, 2CV-1051, 2CV-0301 and 2CV-0305, will be in the "0FF" mode and will be operated remote manually if needed during a transient.
The failure of 2CV-4651, pressurizer spray valve, is similar to previous failures which relate to the valve actuator.
The actuator was manufactured by Borg Warner.
Failures have occurred which have been found to be caused by the loss of pressure of the hydraulic fluid due to inadequate seals and o-rings.
Because of the impossibility of checking the fluid pressure reg-ularly, AP&L has been studying the possibility of replacing the pressurizer spray valves actuators.
At this time, plans are to install Limitorque SMB-000 motor actuators during the current outage which can be converted to modulating controlled actuators at a later date.
A bistable control circuit will emulate the modulating control in the interim period and provide more reliable service than the E/H actuator. The new contiguration will be tested for proper control logic, adequate flow capability, and acceptable stroke time during hot standby prior to resumption of power operation to ensure that all requirements of the system are met as set forth in the FSAR.
The objective of the 100% Turbine Trip Test, as outlined in Test Procedure 2,800.01, Appendix RR, is to demonstrate system performance following a turbine trip from normal 100% power.
The Acceptance Criteria for this test are as follows:
Mr. K. V. Seyfrit February 5, 1980 The plant control systems function satisfactority following t!
The following FSAR safety analysis limits should not be ex-ceeded:
Maximum steam generator pressure less than 1135 psia Maximum reactor coolant system pressure less than 2500 psia Maximum pressurizer level less than 100%
The plant operating procedures and operator actions were ad-equate to cope with a turbine trip.
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The following statements regarding the acceptance criteria of the turbine trip test can be made for the test which was performed January 29, 1980, on ANO-2.
1.
All safety systems performed as designed including those which normally would not have been utilized following a turbine trip.
2.
The maximum steam generator pressure reached was 1091 psia, which is below the 1135 pisa limit.
The maximum reactor coolant pres-sure reached was 2382 psia, which is below the 2500 psia limit.
The maximum pressurizer level reached was less than 60%, which is below the 100% limit.
3.
The plant operating procedures and operator actions were acequate to cope with the turbine trip and to diagnose and correct the mal-functions which occurred in the steam dump system and the pressur-izer spray system.
The results of the January 29 test compare to the expected results as analyzed in the ANO-2 FSAR section 15.1.10 (Excess Heat Removal Due to Secondary System Malfunction).
In this analysis for a Steam Dump and Bypass System malfunction, the pres-surizer is expected to empty and the SIAS is initiated due to the depressurization of the primary side.
4.
The control systems generated proper control signals as designed.
However, one non-safety related steam dump valve (2CV-0301) failed to close and the non-safety related pressurizer spray valve (2CV-4651) failed to completely close which prevented the SDBCS and the pressurizer pressure control system from accomplishing their design objectives.
Due to the failure of the pressurizer spray valve and the steam dump valve, there have been questions raised as to the validity of the 100% turbine trip test which was perf;cmed January 29, 1980.
Reviews by the ANO plant staff
' and the Manager of Nuclear Operations of the January 29 test results indicate that not only did the January 29 test meet the acceptance criteria and test objectives of the 100% Turbine Trip Test, but that it went beyond and demon-strated that even under adverse circumstances the plant control systems, ope-rator actions, and procedures were adequate to cope with a 100% turbine trip.
Mr. K. V. Seyfrit February 5, 1980 In addition to the January 29 Turbine Trip Test, two turbine trips from approximately 90% power had been previously experienced at ANO-2.
These two non-test transients have been documented in ANO transient Reports 2-80-02 and 2-80-03 and have been reviewed by the ANO plant staff and the Plant Safety Committee.
These transients were " clean" turbine trips, with no complications and no similar valve problems.
For the above mentioned reasons, we feel that the January 29, 1980, Turbine Trip Test and the two previous turbine trip transients demonstrated that the plant control systems, operator actions, and procedures are adequate to cope with a turbine trip from high power.
We do not intend to re perform a turbine trip test from 100% power.
Modifi-cation of the pressurizer spray valve operators will be accomplished during the current outage if electrical power supplies are available for both.
If not, at least one will be mccified prior to startup.
Tests will be conducted on the modified pressurizer spray valves at hot standby prior to powtr opera-tion.
Until further modifications to improve operability of the atmospheric steam dump valves are made, 2CV-0301, 2CV-0305, 2CV-1001, and 2CV-1051 will be operated manually during power operation and will be controlled adininis-tratively.
Following the current outage, a 20% turbine trip test will be performed.
As in the past, we will work with the NRC through the Resident Inspector. He will be briefed on our program concerning these valves and will be kept in-formed of our progress prior to startup, which should be mid-February.
Very truly yours, g
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WilliamCavanaugh,fi WC: DEJ: s km
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