ML19323F561
| ML19323F561 | |
| Person / Time | |
|---|---|
| Site: | Vermont Yankee, Hatch File:NorthStar Vermont Yankee icon.png |
| Issue date: | 05/07/1980 |
| From: | Reid R Office of Nuclear Reactor Regulation |
| To: | Drey K AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML19323F562 | List: |
| References | |
| NUDOCS 8005290184 | |
| Download: ML19323F561 (3) | |
Text
a g.g;J{o
?^f).
jo acgjo UNITED STATES
[g yg NUCLEAR REGULATORY COMMISSION g
,.7, WASHINGTON, D. C. 20$55 F
% *e * /
May 7,1980 Dockets Nos. 50-321, 366 and 271 Mrs. Leo A. Drey 515 West Point Avenue University City, Missouri 63130
Dear Mrs. Drey:
Your letter to the Nuclear Regulatory Comission dated March 25, 1980 has been referred to me for reply. My review of your letter suggests a potential misunderstanding of two technical issues for General Electric Boiling Water Reactors:
(1) the methods of post accident combustible gas control and (2) the inerting with nitrogen of Mark I containments and its potential for increasing radioactive materials inventory in the reactor coolant.
Please note that I have not had the benefit of reviewing the UPI story in the St. Louis Post Dispatch on March 20, 1980.
The Conmission's current regulations for licensing power reactors require that the design of containment systems include provisions for combustible gas control; that is, following postulated accidents, the facility can control the concen-tration of hydrogen or oxygen to assure that flammable concentrations do not result.
Following a postulated loss-of-coolant accident, hydrogen may accumulate within the containment as a result of metal-water reaction between the fuel and its cladding, and as a result of radiolytic decomposition of the emergency cooling water.
If a sufficient amount of hydrogen is generated and oxygen is available in sufficient quantities, the subsequent ignition of the hydrogen might lead to failure of the containment.
There are two principal methods that are used to satisfy this requirement. The method used by most facilities is the inerting of the containment with nitrogen.
By maintaining an inerted atmosphere and by maintaining the oxygen concentration to less than 4%, the possibility of hydrogen combustion is minimized.
This noraal inerting system is supplemented by safety grade containment atmospheric dilution systems for maintaining oxygen concentrations below ignition concentration.
The second method of satisfying our requirements is to provide for a combustible gas control system.
Neither Vermont Yankee nor Hatch Unit No. 2 containments are inerted.
For these facilities, and as permitted by our regulations, they can accomodate the effects of hydrogen that may be released during a loss-of-coolant accident without a loss of safety function. These two reactors are licensed on this basis.
In the case of Hatch 2, the facility also has hydrogen recombiners which typically would not be required to operate until about a week (minimum) to several months (maximum) following an accident. Nevertheless, as a result of the THI-2 Lessons Learned Task Force, members of the staff reconnended that Vermont Yankee and Hatch 2 containments be inerted on the basis that the accident at TMI-2 may have resulted in an amount of metal-water reactor and hydrogen The j
generation in excess of the amounts considered in current regulations.
80 0529 0 /N
i Mrs. Leo A. Drey,
Comission's decision at that time was to defer rule making (i.e., formal change to our regulations) pending a more thorough evaluation of questions related to rate and amount of hydrogen generation, the need to control it, and the means of doing so.
Recently the staff presented to the Comission a proposed interim requirement recomending rule making.
I believe this to be the report you referred to in your letter.
A copy is enclosed for your information. The report is a technical basis for the staff's recomendations. As of this date, the Commission has not ruled on this issue. You will note that the report proposes interim hydrogen control requirements for not only Mark I, but also Mark II containments (none of which are presently licensed). A listing of licensed reactors with Mark I containments is included as Enclosure 2.
In regard to your second expressed question, the inerting of Mark I containments The has no effect of the nitrogen-14 concentration in the reactor coolant.
containment volume is physically separated from the reactor coolant system and is normally isolated. The principal contribution to carbon-14 releases from a boiling water reactor is the thennal neutron reaction with oxygen-17 in the Carbon-14 can also be produced by neutron activation of nitro-reactor coolant.
gen-14inthegrywell.
Flug levels in th#s volume are substantially lower (approx-imately 4 x 10 neutrons /cm - sec) than in the primary coolant. However, since the drywell atmosphere is isolated, the inerting of boiling water reactors has virtually no effect on the annual quantity of carbon-14 that is released from boiling water reactors.
I trust this letter is responsive to your request.
Sincerely, Y
Robert W. Reid, Chief Operating Reactors Branch #4 Division of Licensing
Enclosures:
1.
SECY 80-107 2.
History of Plants l
1 LISTING OF BOILING WATER REACTORS WITH MARK I CONTAINt1ENTS Oyster Creek Nine Mile Point 1 Dresden 2 and 3 Millstone Monticello Quad Cities 1 and 2 Pilgrim i
Brown's Ferry 1, 2 and 3 Vermont Yankee Duane Arnold Peach Bottom 2 and 3 Cooper Hatch 1 and 2 l
Brunswick 1 and 2 Fitzpatrick Enrico Fermi 2 Hope Creek 1 and 2 i
i l
_