ML20043C160
| ML20043C160 | |
| Person / Time | |
|---|---|
| Issue date: | 05/29/1990 |
| From: | Taylor J NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Walker R HOUSE OF REP. |
| Shared Package | |
| ML20043C161 | List: |
| References | |
| NUDOCS 9006040143 | |
| Download: ML20043C160 (10) | |
Text
1.[j-[ g May 29,1990
' The Honorable Robert S. Walker
.U.S. House of Representatives j
Washington, D.C. 20515
Dear Congressman Walker:
.In response.to.your May 8, 1990, letter and the. April 22,1990,-' letter from your-
' constituent, Mr. Douglas Hess, I am enclosing information pertaining to the design philosophy of nuclear power. plants.
This includes information on the i
effects of design basis accidents.and severe accidents on the pressure within
- the reactor containment building;.
I trust this information is responsive to your request.
Sincerely.
Original Signed Bys James M. Taylor':
James M. Taylor Executive Director for Operations q
Enclosure:
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Enclosure Response to Congressman Robert S. Walker Nuclear power plants are designed to incorporate multiple barriers to prevent the release of radiation to the public and environment. This multi-barrier.
concept consists of three separate barriers each designed to very high standards.
The first barrier consists of an enclosed cylindrical cladding that. surrounds-the fuel pellets and is designed to contain the radioactive materials. The second barrier is the reactor coolant system, which is designed to withstand high pressures and temperatures. Because this barrier surrounds the first barrier, it will contain any fission products that escape through the cladding.
The final barrier is the reactor containment building, which is a leak-tight boundary designed to accommodate the maximum calculated temperatures and pressures following a credible accident.
After construction, a nuclear power plant is maintained to prevent the release of radiation throughout its life through constant analytical reevaluation and the use of periodic testing of all safety systems including the containment.
This includes interval leakage testing of the reactor containment building and the penetrations through the containment. All nuclear power plants test the reactor containment building for leakage under the maximum calculated accident pressures 3 times every 10 years. This is supplemented by testing all penetrations through the reactor containment building for leakage every 2 years. 'Because the containment penetrations are the most obvious sources of leakage in the very unlikely event the first two barriers are compromised, the ccmbined testing programs ensure that the containment remains as a leak-tight boundary throughout the plant's life.
Federal regulations regarding the licensing of a nuclear power plant require that the reactor containment building be designed to withstand a design basis accident. The limiting design basis accident for the reactor containment building typically is the instantaneous guillotine rupture of the largest pipe in the reactor coolant system. Typical containment pressures resulting from this postulated accident range from about 15 to 60 psi depending on the specific containment design.
Generally, structures will respond differently to pressure increrses, depending on the rate of rise in pressure. The letter of April 22, 1990, from Mr. Douglas Hess states that "all the pressure would come at the same time." However, the containment response to pressure increases is more independent due to its large size and mass.
In order for pressure increases to have an amplifying effect on the containment design, it would require a significant pressure increase in a matter of just a few milliseconds. This rate of pressure increase is impossible to achieve through the characteristic release of a water-steam mixture that occurs when a pipe ruptures. Therefore, in its study of pressure loads on the containment, the Nuclear Regulatory Commission is mainly interested in the maximum pressure attainable. As an example, following the rupture of the largest pipe within the containment, the steam released within the containment will cause the resulting pressures to rise to their maximum value within 20 to 200 seconds. However, such pressures are well within the design limitations of the containment. This time period of 20 to 200 seconds is substantially greater than the few milliseconds necessary for any amplifying factors caused by the resulting pressure increases.
9 Before the accident at Three Mile Island, Unit 2, the containment was designed solely to resist the design basis accident. However, since this accident and since the accident at Chernobyl, the Nuclear Regulatory Comission has developed pro 5 rams to evaluate the capability of the containment to withstand accidents far beyond the original design basis. These accidents beyond the
-original design. basis are referred to as " severe accidents" and encompass the complete spectrum of accident scenarios, including the complete meltdown of the reactor core. Although these programs are not yet complete, the Nuclear-Regulatory Comission has reached several significant conclusions. These conclusions indicate that the containment can-withstand peak pressures of 2-1/2 to 3 times that of the design pressure without losing its integrity, and that pressures resulting from the majority of postulated core-melt events will not exceed this value. Initial results of the Nuclear Regulatory Commission's evaluation do not identify a need for any modifications to containment designs for overpressure protection, except for the plants that utilize Mark I containments. The plants with Mark I containments are to install a hardened vent from the containment. -In addition, the licensees are performing detailed analyses at all U.S. nuclear power plants to determine the capability of each plant to withstand a severe accident. These analyses are scheduled for completion in the next several years and, where appropriate, any weaknesses will be corrected.
9
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' The Honorable Robert S. Walker U.S. House of Representatives T
Washington, D.C. 20515
Dear Congressman Walker:
In response to your May 8,1990, letter and the April 22,1990, ' letter from your constituent, Mr. Douglas Hess, I am sending you information on the design philosophy of nuclear ~ power plants and the effects of design basis accidents and severe accidents on the pressure within the reactor containment building.
This information is enclosed.
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I believe this information is responsive to your request.
If I could be of further assistance, please co tact me.
Sincerely, James M. Taylor Exebytive Director fo Operations
Enclosure:
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The Honorable' Robert S. Walker
.U.S. House of Representatives-F Washington, D.C. 20515-r
Dear Congressman Walker:
In, response'to your May 8,1990, letter-and the April 22, 1990', letter'from your-
- constituent, Mr. Douglas Hess, I am sending you information on the design
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i This information is enclosed as Enclosure 1..
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If I could be of further assistance, please contact me.
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i Sincerely, L
James M. Taylor Executive Director
'N for Operations
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' The Honorable Robert'S.-Walker LU.S~ HouseLof Representatives..
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- Washington, D.C. 20515
Dear,
Congressman Walker:
Lin: response'to'your May 8, 1990, letter and the April 22, 1990, letter from your constituent, Mr. Douglas Hess, I am sending you information on the design.
philosophy of nuclear power plants and the effects of design-basis accidents and severe accidents on the pressure within the-reactor containment building.
- This informat'ipn is enclosed as Enclosure 1.
I believe this nformation is responsive to your request.
If I could be of further assistance lease contact me.
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Sincerely, James M. Taylor
\\ExecutiveDirector for Operations
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Enclosure:
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The Honorahle Robert S. Walker U.S.Houseb{ Representatives.
j Washington, 20515
' Dear Congressina lker:
In response to your constituent, Mr. Do\\May 8,1990, letter and the April 22, 1990, letter from your uglas Hess, I am sending you information on the design philosophyofnuclear4owerplantsandtheeffectsofdesign-basisaccidents and severe accidents on\\the pressure within the reactor containment building.
This information is enclosed as Enclosure 1.
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S<incerely, James M. Taylor Execut10e Director for Operations N
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iThe Honorable Robert S. Walker-U.S. House of Representatives E
Washington,.D.C. 20515 0
Dear Congressman-Walker:
t In response to your May 8,1990 letter, and the April 22, 1990 letter from your constituent, Mr. Douglas Hess, I am sending you information on-the design i
. philosophy of nuclear power plants and the of fects of design-basis accidents and severe accidents on the pressure withir the reactor containment building.
.This information is enclosed as Enclosure 1.
l I believe this -information is responsive to your-request.
If I could be of further assistance please contact me.
j Sincerely, James M. Taylor Executive Director for Operations
Enclosure:
As stated a
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NUCLEAR REGULATORY COMMISSION
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. WASHINGTON, D. C. 20555
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'EDO Principal Correspondence Control A
FROM:.
DUE:'05/
/90
-EDO CONTROL:- 0005448 DOC DT:': 05/08/90 FINAL' REPLY:
-Rep. Robert S. Wallier
- TO : :
-o
-Chairman Carr
-FOR SIGNATURE OF:
- GRN CRC NO: 9010508-
. Executive Director lDESC:'
ROUTING:
ENCLOSES ~ LETTER FROM DOUGLAS E. HESS CONCERNING
-; SAFETY-OF REACTOR CONTAINMENT BUILDINGS DATE:.05/10/90-ASSIGNED TO:
CONTACT:-
'NRR Murley SPECIAL INSTRUCTIONS OR REMARKS:
NRR RECEIVED: MAY 11, 1990 ACTION:
DST THADANI.
NRR ROUTING:. MURLEY/MIRAGLIA PARTLOW CRUTCHFIELD GILLESPIE RUSSELL-T SMYRE ACTIO" DUE TO J'!RR D)RECW gy y.) V fh JW F/
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OFFICE OF THE SECRETARY
' CORRESPONDENCE CONTROL TICKET ^
' PAPER NUMBER::
CRC-90-0508-LOGGING DATE: May'10.90l
- ,o
-ACTION OFFICE:
'EDO:
V AUTHOR:'
Robert Walker--Const Ref
- AFFILIATION:
U.S.
HOUSE OF REPRESENTATIVES t
'. LETTER-DATE:
'May 8 90-FILE CODE:
SUBJECT:
Concerned about the safety of-reactor containment:
buildings ACTION : -
- Direct Reply f
DISTRIBUTION:-
OCA to-Ack, Chairman l
4 SPECIAL HANDLING: None
. NOTES:
. Douglas Hess t
DATE DUE:
May 23 90 SIGNATURE:'
DATE SIGNED:
AFFILIATION:
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Wd Off. EDO o u.S h-90_
Time 800
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