ML20070R825

Proposed Test Program to Demonstrate Operability in Spray Environ

ML20070R825
Person / Time
Site:	Sequoyah
Issue date:	01/31/1983
From:	TENNESSEE VALLEY AUTHORITY
To:
Shared Package
ML20070R819	List: ML20070R816 ML20070R825
References
PROC-830131, NUDOCS 8302040044
Download: ML20070R825 (3)

Text

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ENCLOSURE

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PROPOSED TBST PROGRAM TO DEOMONSTRATE IGNITER OPERABILITY IN A SPRAY ENVIRONMENT TRINESSEE VALLEY AUTHORITY JANUARY 1983 9 .

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. I. INTRODUCTION I Throughout the fall of 1982, TVA conducted a series of tests at ite Singleton Materials Engineering Laboratory (SME) to demonstrate the operability of the Permanent Hydrogen Mitigation System (PHMS) igniter assembly in the spray environment expected in the upper compartment of the Sequoyah Nuclear Plant. Detailed descriptions of these tests and their results were prot .ded to the NRC in a TVA letter dated November 1, 1982, and in informal transmittals in early December 1982. However, the NRC staff concluded in the Sequoyah Safety Evaluation Report Supplement No. 6 (SER) that " Additional spray tests are needed to confirm satisfactory operation of the Tayco igniter in a spray environment." The NRC subsequently imposed the following condition in the unit 1 operating license: 2.C.(22).D.2 " Additional tests shall be performed on the Tayco igniter to demonstrate that the igniters will initiate combustion in a spray environment such as that expected in the upper compartment of the ice condenser containment." The proposed test program outlined herein is intended to satisfy this license condition.

II. BACKGROUND The PHMS igniter assembly was originally designed with a shield to prevent impingement of the containment spray from overhead in order that an adequate surface temperature for ignition could be maintained.

However, the NRC staff believes that "some impingement of spray droplets on the igniter is expected in containment due to the presence of convective currents with velocities on the order of the droplet terminal velocity." In response to this concern, TVA enlarged the spray shield to ensure overhead protection within a solid angle _of at least 50 degrees frua the vertical. In addition, the SME spray testing program was extended to establish the relationship.betseen igniter surface temperature and a directly impinging spray mass flux. This combination of improved protection and'a more extensive data base was not accepted by the NRC, evidently because the residual amount of spray impingement on the igniter under the shield due to turbulence in the upper compartment could not be precisely quantified. It could then be inferred from the SER that the required additional spray tests are intended to realistically model the turbulence levels,in the upper compartment environment while verifying that lean hydrogen " mixtures can be ignited by the igniter assembly complete with shield. With an emphasis on detailed physical modeling of upper compartment turbulence levels, such tests would require a specialized facility backed by an extensive amount of analytical support. Upon receiving the license condition and supplementary information in the issued SER, TVA contacted seven different testing organizations about conducting such a test. Based on ,

discussions with these experimenters, we have concluded that it would be difficult to conduct 3 reasonable scaled test that would verify ignition of hydrogen while simultaneously simulating the upper compartment turbulence. Therefore, TVA is proposing an alternate approach to verifying igniter performance as described in the remainder of this document.

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• III. TEST OBJECTIVE ,

. TVA proposes to satisfy the license condition by conducting a series of small-scale tests to verify the capability of the PHMS igniter to ignite lean hydrogen mixtures without the protection of a spray shield in the spray envirorcent that might be expected to occur in the Sequoyah upper compartment. Direct exposure of the igniter to the spray in the test would be a more severe condition than any turbulence-induced spray Lapingement that might realistically be expected under the spray shield in the plant. While this direct ap; roach may be overly conserv:=.tive, it is preferable to the inherent uncertainties associated with a program that would attemps both to accurately model upper compartment turbulence and to verify ignition of hydrogen.

IV. TEST APPROACH Following our decision to pursue a conservative approach to verify igniter performance in the spray environment, we contacted experimenters at Factory Mutual Research Corporation (FMRC), Wyle Laboratories, and SME to discuss informally the practicality of the concept, requirements for test apparatus, and importance of various physical parameters. As a result of these discussions, TVA is proposing to conduct a series of fairly small-scale tests in a facility similar to the combustion tube used by FMRC in their microfog studies sponsored by ERRI and the ice condenser utilities and described in TVA's fifth quarterly report to the NRC on hydrogen research. We envision a ver,tical combustion tube up to a few feet in diameter and height with the capability to contain a lean hydrogen-air mixture around an igniter that is directly exposed to a spray equivalent to the upper compartment environment. The tube would be equipped with instrumentation to detect ignition of the mixture. The

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physical relationship between the spray nozzle (s) and the igniter would be arranged so that wall or floor effects on the spray pattern would be minimized. An attempt will to made and verified by measurement to ensure that the spray flux at the plane of the igniter will be spatially uniform. Parameters of interest that would be addressed include spray mass flux, spray temperature,' spray droplet size, spray ve10 city, hydrogen concentration, and igniter temperature. The test series would be arranged so that appropriately conservative conditions (such as a spray mass flux at the igniter equivalent to 100 percent of the average upper compartment flux) would be investigated first. We intenc to terminate the testing program once ignition is achieved, thus quantifying the capability of the igniter. This stepwise approach should establish igniter operability in a spray environment in the most expeditious, economical, and straightforward manner.

V. CURRENT STATUS TVA has not selected a subcontractor or facility for this proposed testing program. We do not plan to pursue formal negotiations until we receive NRC acceptance of our approach. However, assuming a reasonable progression of events, the proposed program should be able to be completed during 1983

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