Text

Forwards Addl Info Re Interim Distributive Ignition Sys. Includes Revision to FSAR Section 6.2.5.7,scoping Document for Testing Sys & Changes to Emergency Operating Procedures
	ML19338C638
Person / Time
Site:	Sequoyah
Issue date:	08/14/1980
From:	Mills L; TENNESSEE VALLEY AUTHORITY
To:	Schwencer A; Office of Nuclear Reactor Regulation
References
	NUDOCS 8008180330
	Download: ML19338C638 (18)
	v • d • e

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' s TENN ESSEE VALLIY A T -C.4.~'

.w2 -;.:cca m e.t e;- :: - -1 400 Chestnut Street Tower II

.IHIS DOCUMENT COUTAINS August 14, 1980

% POOR QUAllTY PAGES Director of Nuclear Reactor Regulation Attention: Mr. A. Schwencer, Chief Light Water Reactors Branch No. 2 Division of Licensing U.S. Nuclear Regulatory Commission Washington, DC 20555

Dear Mr. Schwencer:

In the Matter of the Application of ) Docket Nos. 50-327 Tennessee Valley Authority ) 50-328 The additional information on the Sequoyah Nuclear Plant unit 1 interim distributive ignition system (IDIS) listed below is enclosed for your review.

Enclosure 1 is the revision which will be made to the Sequoyah Nuclear Pltat FSAR section 6.2.5.7 and includes additional FSAR figures 6.2-140 through 6.2-147 These FSAR revisions and figures describe the IDIS r.M the location of the igniters inside containment. This rvrision to the FSAR will be included in Amendment 63.

Enclosure 2 is a copy of the TVA Division of Engineering Design scoping document for testing the IDIS.

Enclosure 3 lists the changes which will be made to the Sequoyah Nuclear Plant Emergency Operating Instructions (E0I's) to identify plant conditions where operation of the IDIS is required. The plant E0I's will be revised by August 21, 1980.

The analytical work performed by TVA and W^.tr 3 h ooe in support of the IDIS design was transmitted to MC J r ;*< letter to you dated August 8, 1980. The informatici t 'yky i .! by that letter together with the system description p:covide. W Enclosure 1 constitute TVA's safety evaluation of these proposed measures for hydrogen control.

Very truly yours, TENNESSEE VALLEY AUTHORITY

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L. M. Mills, Manager '

f Nuclear Regulation and Safety f//

Enclosures

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ENCLOSU:2.1 SEQUOYAH NUCLEAR PLANT FSAR REVISIONS - INTERIM DISTRIBUTED CONTROLLED HYDROGEN IGNITION SYSTEM 6.2.5.7 Interim Distributive Ignit.4.on System Due to the ice condenser design and relatively small containment volume, the postaccident hydrogen concentration is higher for ice condenser contain=ents than it is for a dry containment. ,

At TMI-2, the core was uncovered to the extent that severe core damage with resulting hydrogen generation from zirconium-water reaction occurred. This ultimately led to hydrogen release to the containment atmosphere and a subsequent assumed hydrogen burn which produced a 28 lb/in g pressure spike. This pressure spike occurred in a containment of a volume of approximately 2.3 million cubic feet. The Sequoyah containment volume is approxi=ately one-half that of TMI-2 (i.e. ,1.2 million cubic feet), has a design pressu.c of 12 lb/in g and an ultimate pressure 2

capability of approximately 43 lb/in 8 The ultimate pressure of 43 lb/in g would be reached at Sequoyah if there is a zirconium-water reaction of approximately 25 percent, if the approximately 520 pounds of hydrogen produced is released into the containment, and if all the hydrogen is burned adiabatically.

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. e Different aspects of hydrogen generation, control, and mitigation were investigated. This includes a limited study of risk similar to WASH-1400, the identification of representative transients which would lead to some core degradation, and the evaluation of the more important concepts for the prevention er mitigation of the consequences from hydrogen combustien. The migitation concepts evaluated t

include inerting containment, filtered / vented containment, "Halon" suppression, igniters, an additional containment, and coupled centainments. From this evaluation it was decided that an additional reduction of overall risk may be achieved in the interim by the installation of a distributivo ignition system at Sequoyah unit 1. TVA is concurrently studying in greator detail degraded core 4

conditions and several of the citigation concepts mentioned i

carlier for their applicaton as a long term, permanent solution.

l 6.2.5.7.1 System cascription The interim distributive ignition system is designed to

> burn hydrogen inside the containment in the event of an accident in which excessive hydrogen is generated inside the reactor vessel and released into containment. It is 1

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I de .gned to ignite the hydrogen prior to it reaching a dangerously high level. This system is intended to back up the safety-grade hydrogen recc=biner system, but it is not a safety-grade system itself.

The system censists of 30 thermal resistance-type igniters distributed throughout containment (locations shewn in Figures 6.2-141 through 6.2-146). The ignitor mounting details are sh0xn in "igurc 6.2-147. The transformer shown in Figure 6.2-147 is capable of operating in a temperature environment greater than 350 F. The standby lighting circuit supplies the transformer with 120V ac which is dropped down to 14V ac for the igniter. At 14V ac and f

8 amps, the exposed portion of the igniter fod will reach approximately 1720 F. These igniters have been adapted for direct installation into the existing standby lighting circuits. This lighting circuit, described in FSAR Section 9.5 3 2, is powered from shutdown boards which have nor=al and alternate ac power supply and, in the event of their failure, is fed from the diesel generators. The only modification to the existing standby lighting system is that this system will be normally dcenergized at the standby lighting cabinets once the igniters are installed and will only be turned en by the operator af ter a LOCA.

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The standby lighting cabinets are located in the auxiliary building, about 150 feet from the main control room and at essentially the same elevation, and are easily accessible following an accident.

It is noted that the interim distributive ignition system will not generate any more negative effects on containment integrity than uncontrolled hydrogen ignition. Rather, by burning hydrogen at a concentration as low as possible, the resulting transients in pressure and temperature are expected to be lcwer than what cay result in the case of uncontrolled ignition.

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O ENCLOSURE 2 SEQUOYAH NUCLEAR PLANT CIIT 1 TESTING REQUIREMENTS - INTERIM DISTRIBUTED CONTROLLED HYDROGEN IGNITION SYSTEM 4

TVA SEQUOYAH UNIT (S) 1 SCOPING DOCUMENT FOR PREOPEMTIONAL TEST NO. TVA- 65

Title:

Operational Test of the Interim Controlled Hydrogen Ignition System

Prepared by:

J. J. Wilder Date Submitted by:

L. W. Lau Date Approved by:

G. F. Dilworth Date A I

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i 1.0 References 1.1 Interim Controlled Distributed Hydrogen Ignition System

- Phase 1 - Design Criteria.

2.0 Discussion of Test The operational test of the interim controlled hydrogen ignition system will verify the voltage and temperature at the igniter plugs. Also, this test will establish the baseline

urrent readings for performing the periodic surveillance test of the hydrogen ignition system.

3.0 Test Objectives The purpose of this test is to verify that this system, once in;talled, will provide ignition sources of a specified temperature. In addition, by measuring the current at the standby lighting cabinet af ter testing all igniters for proper temperature, a baseline can be established for future periodic surveillance tests.

4.0 Acceptance Criteria This test will verify that:

a. The ac voltage at the output of the igniter transformers is no greater than 14 volts and no less than 11.5 volts.

b. That the temperature of each igniter is at least 1500 F.

5.0 Additional Testing Af ter verifying that all igniters meet the acceptance criteria in section 4.0 above, measure the current in each circuit at the standby lighting system cabinet and record the results on Table 1, attached.

6.0 Prerequisites The standby lighting system must be operational. In particular penetration protection fuses must have been installed and the remaining lighting locations where igniters are not installed should have their bulbs removed.

7.0 Environmental Conditions No special environmental conditiens are required for this test.

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i 8.0 Special Test Equipment S Special instrumentation to be used includes an optical pyremeter and a volt and amp meter.

90 Scope of Testing '

This test will cover only operational verification of the igniter system. The igniters will not be tested in place for their ability to burn hydrogen, nor will an endurance test be performed in situ.

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TABLE 1 Igniter Current Circuit Current 10A 10B 10C 11A 11C 12A 123 12C Data in this table to be used to verify current readings taken during surveillance testing.

Note: There are no igniters on circuit 11B; therefore, no current reading is required.

ENCLOSURE 3 SEQUOYAH NUCL'E.AR PLANT UNIT 1 EMERGENCY OPERATING INSTRUCT!ON MODIFICATION -

INTERIM DISTRIBUTED CONTROLLED In. '.JGEN IGNITION SYSTEM The emergency operating instructions (E0I's) will be modified to include the operation of this new system by an operator after an accident. The E0I's will be revised to include the following modifications by August 21, 1980.

1. E01-0, "Immediate Actions and Diagnostics Unit 1 or 2," R2:

Add to II.B:

"For unit 1 only

11. Dispatch an operator to the standby emergency lighting cabinet to initiate the controlled distributed hydrogen ignition system."

2. E0I-1A, " Loss of Reactor Coolant Unit 1 or 2," R12:

"Fer t: nit 1 only Note: Verify the controlled distributed hydrogen ignition system was actuated in E0I-0, section I1.3.11. Also verify that they have been loaded on the diesel generators if offsite power has been lost."

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ML19338C638

Text

Dear Mr. Schwencer:

Title:

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