ML19308A676
| ML19308A676 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 11/07/1979 |
| From: | Harold Denton Office of Nuclear Reactor Regulation |
| To: | Mello S AFFILIATION NOT ASSIGNED |
| Shared Package | |
| ML19308A677 | List: |
| References | |
| NUDOCS 7911280169 | |
| Download: ML19308A676 (3) | |
Text
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F Mr. Steven Mello 12 Liberty Street E. Taunton, MA 02718
Dear Mr. Mello:
This letter is in response to your inquiry regarding the sequence of events in the Three Mile Island accident and regarding nuclear reacters in general.
I apologize for not providing an answer to you sooner but, a3 you are aware, the Commission and staff have been occupied with continued support of the efforts at Three Mile Island, Orders to other facilities, appearances before the President's Commission and various enmnittees of Congress that are investigating the Three Mile Island accident, and the realignment of our own resources and prioriticis to give immediate attention to the problems resulting from the accident.
In response to your inquiry regardi.19 the Three ".ile Islar.d accident, it was not until several days after the accident that the Nuc1 car Regulatory Commission (NRC) staff was able to enmpile a preliminary picture of the sequence of events. We are continuing to investigate this sequence of events.
Specific questions you raised are answered beloiv:
i Question: What caused the reactor core to leak?
Answer:
Under nomal operating conditions, the radioactive fission products are contained within the fuel pellets and the cladding surrounding a stack of i
fuel pellets.
In the accident the cladding on many of the fuel rods ruptured allowing the radio-active fission products to leak into the cooling water and subsequently into the containment building.
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question: llow do you know what is going on with the core?
Answer:
The conditions in the core are inferred from instruments that measure parameters like (1) the water pressure in the reactor vessel, (2) the tenperature of the water as it exists the core, (3) water level in the pressurizer, (4) the neutron flux outside of the reactor vessel, and (5) the amount of radioactivity in the water circulating M;7 ?: ::n wnes >
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Question:
Is there a valve that could relieve the gas i
bubble in the top of the reactor vessel?
l Answer:
Valves are provided on the top of the-reactor vessel to bleed air from the vessel when the vessel.1s being filled with water. The valves are located at the top of the control rod drive l
housings and their position is manually controlled from inside the containment.
If these valves were remotely controlled from outside of the con-taf ruent the bubble of non-condensable gas inside the vessel could have been relieved into the corde t.
tainment. However, this was not the case.
Question:
Is it true that by 1990, 30% of our total electric usage will be supplied by nuclear power?
Answer:
At the present time about 13". of the total amount of electricity generated in the United States comes from nuclear power plants. This percentage is pro-jected to grow to about 20% in the mid 1980's.
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Question: What'is a core meltdown?
Answer:
After a reactor core is made subcritical (the chain
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reaction stops), the core continues to generate heat t
from the decay of radioactive fission products. The 1
l heat generation rate is a function of the time after i
i the reactor shutdown. If the fuel is not cooled, this
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l heat will lead to melting of the fuel pellets and the
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cladding.
It has been calculated that the melted fuel (which continues to gerierate heat) could melt through the steel reactor vessel and the concrete containment
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vessel.
l The emergency cooling system in a nuclear plant is designed to prevent the loss of cooling to the core; especially the loss of cooling that would result from the rupture of a large pipe.
In the case of Three Mile Island, instead of a large pipe break there was a loss of coolant through a stuck-open valve on the pressurizer.
The emergency core cooling system did come on automatically, but its operation was taken over by the operator. One of I
our preliminary conclusions is that this operator action contributed to the severity of the accident.
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., l NOV 0 71979 Mr. Steven Mello.
.A The detailed description of a particular reactor can be found in the Safety Analysis Report (SAR) for that reactor. The SAR is a document prepared by the applicant \\for a license to build ami operate a nuclear l
plant. The NRC places a complete copy of a SAR in a library close to each proposed and operating reactor site. Libraries in Messachusetts containing an SAR of one or nere nuclear plants are listed below:
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Greenfield Community college 1 College Drive
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Greenfield, Massachusetts 01301
' ~. ~,. W (413) 774-3131.
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frit Plymouth P'ublic Library
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North Street
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Plymouth, Massachusetts 02360
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(617)746-1927 s
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The Carnegie Library
,,y Avenue A m ci Turner Falls, Massachusetts 03176
~3l' E (413) 863-4484
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l Sincerely,
.g Orit ssisiped by
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i H. R. Desten i
Harold R. Denton, Director AJ Office of Nuclear Reactor. Regulation l
j DISTRIBUTION Docket 50-320 NRC PDR LPDR HRDe.iton i
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