ML20215K694

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Forwards Comments on Use of Hydrogen Burners in Graphite Moderated Nuclear Reactors Per 870501 Request.Nrc Concludes No Addl Efforts Re Hydrogen Control in Commercial Power Reactors in Us Warranted
ML20215K694
Person / Time
Issue date: 06/10/1987
From: Stello V
NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO)
To: Cranston A
SENATE
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ML20215K697 List:
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NUDOCS 8706250419
Download: ML20215K694 (6)
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' The Honorable Alan Cranston.

United States' Senate Washington.D.C.

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Dear Senator Cranston:

'Your-letter of May 1, 1987 requested our comments on the use of hydrogen burners in graphite moderated nuclear reactors., Attached to your request

-was.an article regarding:a " hydrogen match" cited by a constituent.

Our response, provided in the enclosure, addresses these matters.

Sincerely.

Or16 L31 signed bE 1

Victor Stella a

Victor Stello, Jr.

Executive Director for Operations

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Enclosure:

Hydrogen Control in'U.S.

Commercial Power Reactors DISTRIBUTION:

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I Hydrogen Control 'in U.S.. Connercial Power Reactors j

The;importance of.. addressing: combustible gas g'eneration, principally hydrogen,-

.'as'a consequence of reactor accidents has been recognized in the U.S. since n.

the. early ' days of commercial, power reactors.. Hydrogen is of_ concern in reactor -

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" safety sincerthe combustion:of hydrogen can threaten the integrity.of the-

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containment structure which encloses the nuclear reactor or cause the failure.

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'i iof important, safety equipment' inside the containment. Hydrogen is generated;

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Lduring suchiaccidents' principally as a result of the reaction of: steam with

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. overheated fuelzrods.- Basically, the metal fuel' rod reacts with water in the.

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- vapor phase l(steam).to produce a. metal oxide.and hydrogen gas.-

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' Eerly requirements for dealing with! hydrogen production', fdevelopediduring. the v

1960s, required the operators of nuclear plants-to provide safety systems. to i '

ideal..with thelvarious: sources of hydrogen produced during an accident. The-q

TMI-2' accident' focused' attention 1on the potential consequences of; generating

. hydrogen-during severe ~' accidents". As.a consequence of the TMI-2 accidentiand.

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Lin-consideration of more severe accidents,.the NRC issued new regulations requiringL additional hydrogen safety systems.-

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ALvariety-~of' strategies;are used 'at U.S. nuclear plants 'to deal with potential-j L

hydrogen generation.. Small:volumecontainments(MarkIandII)usedfor. boiling L

water reactors;are made. inert with nitrogen; i.e., nitrogen is substituted for? et cir inside the containme'nt building, so that: combustion is prevented. Medium-P, l

volume containments-used to enclose reactors in boiling water. reactor Mark..III
plants and pressurized water reactor' ice condenser plants have installed electrical igniters to burn the hydrogen before it reaches threatening levels.

Large. volume containments : by virtue of their. size, and strength, are. judged to have sufficient inherent capacity to withstand the effects of hydrogen combustion._

.The " hydrogen match" referred to in the magazine article'(published in

" Breakthrough by Boardroom Reports") was developed at-Sandia National 1 Laboratories as' par.t of an' extensive.research program on' hydrogen related issues ' conducted for the NRC..As 'noted. the owners of. boiling water reactor Mark III: plants and pressurized water reactor ice' condenser plants have already installed electrical igniters to control large releases of hydrogen.- ' These igniters utilize the same basic approach'to hydrogen control as that intended by the p

" hydrogen' match"; i.e., burn hydrogen before it accumulates to unsafe: levels.

-The difference between.these alternative ignition devices lies in the-p~s

difference. in' the detailed engineering. principles of operation, not -in the w

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! ultimate. design objective. The electrical igniters _ installed in nuclear power

'i plants have been tested and shown to be reliable for igniting hydrogen at safe levels.

The igniters developed at Sandia National Laboratory would require additional extensive testing in order to demonstrate a similar level of reliability.

Following the reactor accident at Chernobyl, the NRC initiated an investigation to determine if there were any implications from the Chernobyl accident on the safety of U.S. commercial reactors.

With regard to hydrogen combustion, the-generation of large quantities of hydrogen was apparently not considered as part of the Soviet design.

In the Chernobyl plant, large amounts of zirconium l

in the reactor core coupled with high temperatures during the accident resulted

'1 in hydrogen generation.

A significant difference between the Chernobyl plant and nuclear plants in the U.S. is the presence of. graphite in the reactor core. Only one U.S. commercial reactor (FortSt.-VrainNuclearGeneratingStation)usesagraphitemoderator.

The design of this reactor is significantly different than the Chernobyl. plant.

The Fort St. Vrain _ Nuclear Generating Station uses helium as a primary coolant and does not use metal fuel rod cladding, thus reducing the potential for the reaction producing hydrogen during accidents associated with water cooled or moderated reactors. The Chernobyl reactor was a water cooled reactor with metal' fuel rod cladding. There is no analogy, therefore, between what happened at Chernobyl and the consequences of postulated accidents at the Fort St. Vrain plant with respect to potential hydrogen generation.

The NRC has concluded, following the preliminary evaluation of the Chernobyl accident, that no additional efforts relative to hydrogen control in commercial I

. power reactors in the U.S. are warranted. As a corollary, the NRC has determined that our current regulatory position and research program in conjunction with the study of severe accidents at U.S. reactors is adequate to ensure the public health and safety.

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1 The Honorable Alan Cranston

. United States Senate Washington, D.C.

.20510

Dear Senator Cranston:

Your" letter of May 1, 1987 requested our comments on the use of hydrogen burners in graphite moderated. nuclear reactors. Attached to your request

'was an article regarding a " hydrogen match" cited by a constituent.

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Our response, p, ovide { in' the enclosure, addressgs these matters.-

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ictor Steilo, Executive Director e'ations (6r Op/ r

Enclosure:

Hydrogen Control in U.S.

Commercial Power Reactors I

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ENCLOSES. LETTER FROM MICHAEL FEITLER CONCERMING (USE.0F.(HYDROGEN BURNERS:IN' GRAPHITE MODERATED NUCLEAR' REACTORS-g

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SUBJECT:

Us'e'of hydrogen burners'n graphite moderated nuclear reactors!

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