ML20149M582
| ML20149M582 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 02/22/1988 |
| From: | NRC OFFICE OF SPECIAL PROJECTS |
| To: | |
| Shared Package | |
| ML20149M581 | List: |
| References | |
| NUDOCS 8802260135 | |
| Download: ML20149M582 (2) | |
Text
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SAFETY EVALVATION BY THE OFFICE OF SPECIAL PROJECTS INVOLVING TAYC0 ICHITER PERFORMANCE TENNESSEE VALLEY AUTHORITY SEOUOYAH NUCLEAR POWER PLANT, UNITS 1 AND 2 DOCKET NOS. 50-327 AND 50-328
1.0 INTRODUCTION
As presently designed, there are 64 Tayco Igniter Assemblies in the Sequoyah Containment, 22 in the lower compartment and 42 in the upper compartment.
The igniter assemblies are arranged in two redundant trains, each train consisting of 32 assemblies. These assemblies were all originally equipped with flat overhead shields to deflect any spray from above.
In the later part of 1982, the NRC staff expressed a concern to the Tennessee Valley Authority (the licensee) that spray-induced turbulence in the upper compartment could entrain a sufficient amount of water to bypass the overhead shield and cool the igniter below its ignition threshold. The licensee took steps to alleviate this concern by enlarging the overhead shields to protect the igniter from direct impingerent throughout a 100 cegree spray angle and by conducting a number of tests to study igniter performance. After enlarging the shields and completing the test the licensee concluded that the modified igniter assemblies were satisfactory for operation in the upper compartment spray environment; however, the staff felt that additional testing was necessary and imposed license conditions that required further igniter testing.
2.0 EVALUATION The licensee assigned Factory Mutual Research Corporation (FFRC), to conduct the additional testing.
FMRC found that the igniter quenched at a lower spr3y flux (flow rate / containment X-Area) than anticipated from earlier tests conducted by the of0.9 gal / min /ft}icensee. This failure to reach the desired spray flux goal led the licensee to redirect the testing toward extending igniter performance by enclosing it in a perforated cylinder that wculd shield it from spray in all directions.
Several evolutionary shield designs with various hole sizes and percentages of open area were tested before settling on the optimum combination. The test results indicate that the hydrogen concen-tration and the spray flux impinging an the igniter are the only significant parameters to igniter combustion performance in the spray environment. More importantly, the tests demonstrated that the proposed cylindrical shield by itself is very effective in maintaining an adequate igniter temperature even under the maximum spra within the crane rall)y flux of 1.8 qal/ min /#t" (assuming all spray falls while still allowing ignition at a lean hydrogen concentration of 6.6 volume percent which is below the 8 volume percent conservatively used as input for the licensing analyses with the CLASIX code.
The licensee believes that there is tufficient justification for accepting the upper conpartnent igniter assenblies as currently installed.
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3.0 CONCLUSION
The NRC staff concludes that the current upper compartrent i "iter assemblies
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are acceptable for the following reasons:
1.
There are only 10 out of 6a essemblies thet are e ffected by the containment sprays.
2.
The licensee has analytically dem nstrated with the CLASIX computer code thet it is highly unlikely that flamabi. mixtures would ever be present t
in the upper compartrent due to probable burning in the lowr e.ompartment or ice ccedenser plenum by 22 ignitar assemblies.
3.
If the 10 igniter assemblies were quenched by the sprays, hydrogen would be controlled by the remaining 32 functioM r.g assemblies in the upper containment, 4 of which are located above the sprays.
4 If the 10 igniter assemblies are quenched by the sprays, in the worst case condition, there would be a zone of na combustion ir the vicinity around the sprays until the sprays are turned off. Once the sprays are turned off the 10 af'ected igniter assemblies would resure burning any hydrogen that built up in the sprays vicinity.
The overt'l effect of quenching the 10 inniter assemblies would be a delay in the burning of the hydrogen.
For the re0 sons stated above the staff concludes that the present Secuoyah design of the Tayco Igniter Assemblies is accepteble for assuring the combustion of hydrogen inside containment.
Principal Contrsbutors:
P. Fearn, T. Potella b.
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