ML20079L344
| ML20079L344 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 12/31/1983 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| References | |
| NUREG-1060, NUDOCS 8401260068 | |
| Download: ML20079L344 (21) | |
Text
_
e' o*
O' NUREG-1060 Ariswers to Questions About Updated Estimates of Occupational Radiation Doses at Three Mile Island, Unit 2 o
U.S. Nuclear Regulatory Commission Offico of Nuclear Reactor Regulation TMI Program Office
,f* "%,
5
~~
ODR NO O 00 O
P PDR
s NOTICE Availability of Reference Materials Cited in NRC Publications Most documents cited in NRC publications will be available from one of the following sources:
- 1. The NRC Public Document Room,1717 H Street, N.W.
Washington, DC 20555
- 2. The NRC/GPO Sales Program, U.S. Nuclear Regulatory Commission, Washington, DC 20f,35
- 3. The National Technical Information Service, Springfield, VA 22161 Although the listing that follows represents the majority of documents cited in NRC publications, it is not intended to be exhaustive.
Referenced documents available for inspection and copying for a fee from the NRC Public Docu-ment Room include NRC correspondence and internal NF.C memoranda; NRC Office of Inspection and Enforcement bulletins, circulars, information notices, inspection and investigation notices; Licensee Event Reports; vendor reports and correspondence; Commission paperr; and applicant and licensee documents and correspondence.
The following documents in the NUREG series are available for purchase from the NRC/GPO Sales Program: formal NRC staff and contractor reports, NRC-sponsored conference proceedings, and N RC booklets and brochures. Also available are Regulatory Guides, NRC regulations in the Code of Federal Regulations, and Nuclear Regulatory Commission issuances.
Documents available from the National Technical Information Service include NUREG series reports and technical reports prepared by other federal agencies and reports prepared by the Atomic Ermgy Commission, forerunner agency to the Nuclear Regulatory Commission.
Documents available from public and special technical libraries include all open literature items, such as books, journal and periodical articles, and transactions. Federal Register notices, federal and state legislation, and congressional reports can usually be obtained from these libraries.
Documents such as theses, dissertations, foreign reports and translations, and non NRC conference proceedings are available for purchase from the organization sponsoring the publication cited.
Single copies of NRC draft reports are available free upon written request to the Division of Tech-nical Information and Document Control, U.S. Nuclear Regulatory Commission, Washington, DC 20555.
Copies of industry codes and standards used in a substantive manner in the NRC regulatory process are maintained at the NRC L ibrary, 7920 Norfolk Avenue, Bethesda, Maryland, and are available there for reference use by the r'ublic. Codes and standards are usually copyrighted and may be purchased from the originating organization or, if they are American National Standards, from the American National Standards Institute,1430 Broadway, New York, NY 10018.
GPO Printed copy price: $3.25 A
a
NUREG-1060 Answers to Questions About Updated Estimates of Occupational Radiation Doses at Three Mile Island, Unit 2 ate Pu shed ee 1
=
s TMi Program Office Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Wcshington, D.C. 20555 a
l l
p.o. y
- \\.....*
+
3 4
+
l 9
II p -
r y
o
=
l a
d INTRODUCTION a.;;.5.; 3 The purpose of this question and answer report is to provide a clear, easy-to-M-N understand explanation of revised radiation dose estimates which workers are W.? s ;
likely to receive over the course of the cleanup at Three Mile Island, 3,;;Yest Unit 2, and of the possible health consequences to workers of these new
"'?.T:- %
estimates. We will focus primarily on occupational dose, although pertinent 4%.? "
questions about public health and safety will also be answered, spf.y
_e The answers to these questions, prepared by the staff of the NRC Three Mile M )-
j
[TlA '
Island Program Office, are based principally on the detailed examination D (f of occupational dose in Draft Supplement 1 to the " Programmatic Environmental
. f Impact Statement Related to the Decontamination and Disposal of Radioactive Wastes Resulting from the March 28, 1979, Accident at Three Mile Island, Unit 2"
/% 1 (PEIS), NUREG-0683 issued December 1983. The views expressed in this question J.H. W -
and answer report are those of the NRC staff.
N M--
g g.% -
Draft Supplement 1 to the PEIS on Occupational Exposure (NUREG-0683, Supp.1)
I'b. C f g[JJr is available for public comment.
Copies are available for inspection at the jg3 NRC TMI Program Office,100 Brown Street, Middletown, Pennsylvania,* the NRC Public Document Room,1717 H Street, N.W., Washington, D.C., and at the ld e.
, 7 rh V1 THI-2 Local Public Document Roaus at the Government Publications Section, State R[~ /
Library of Pennsylvania, Education Building, Commonwealth and Walnut Streets,
'v @Mt Harrisburg, Pennsylvania, and at the York College of Pennsylvania, Country Club Road, York, Pennsylvania.
s.EdQ:
Recuests for single copies of the PEIS Supplement should be addressed in Y.Wgi writi to the Director, Division of Technical Infomation and Document
' gga Contr, U.S. Nuclear Regulatory Commission, Washington, D.C.
20555.
.g.g n,,,,.,
~y gf' %
- f Send your comments to Dr. Bernard J. Snyder, Program Director, Three Mile Island Program Office, U.S. Nuclear Regulatory Commission, Washington,
- 0. C.
20555. They are due to NRC by February 29, 1984.
h4C?
gK rR kj,j ;
n-li Dr. Bernard J. Snyder, Program Director Three Mile Island Program Office A sR.
U.S. Nuclear Regulatory Cor. mission NA9 Washington, D.C.
20555 y N,g:'
v Q
- Heurs:
Tuesdays, Noon to 2 p.m.
~J Q(
Wednesdays, 5 p.m. to 8 p.m.
M. '
Thursdays, 3 p.m. to 5 p.m.
M ggd 3 9
'6
,: ;- 't,
..; 4 k$f h
Q.1.
Why has NRC issued Draf t Supplement 1 to the Programmatic Environmental Impact Statement at this time for cleanup operations at Three Mile Island, Unit 2?
A.
For two reasons. First, to revise the estimates of radiation doses I
workers are likely to receive during the entire cleanup.
Second, te reconsider what these revised estimates could mean to worker health.
's other infomation in the original Programmatic Environmental Impact Q.2.
i Statement out of date because Supplement 1 has been issued?
A.
No.
Draft Supplement 1 was issued for the sole purpose of updating estimates of radiation exposures and their possible eifects on worker health. This infomation supplements one part of the cleanup discussed in the original Programmatic Environmental Impact Statement. The original Statement remains the valid source of infomation for all other facets of the cleanup.
Q.3.
What are the revised estimates of doses workers could receive?
A.
When the original Programmatic Environmental Impact Statement was issued in March 1981, the radiation dose to the work force was estimated to be between 2,000 and 8,000 person-rem. According to revised estimates, cleanup workers are likely to receive a total col-lective radiation dose of between 13,000 and 46,000 person-rem for the entire cleanup project.
(For an explanation of person-rem, see the answer to Question 15.)
Q.4.
How could this increased dose range affect worker health?
A.
Statistically, these increased doso estimates slightly raise the chances of cancer for the group as a whole.
It is possible that this radiation dose could result ih two to six fatal cancers in the worker population.
Q.5.
The original Programmatic Environmental Impact Statement estimated that approximately one additional cancer deatt could occur because of radiation doses to the cleanup work force. Should this one possible death be added to the two to six fatal cancers predicted in the Supplement?
A.
No.
Q.6.
How does the potential for fatal cancer to cleanup workers compare with risks of fatal cancer to the entire U.S. population?
A.
The average member of the U.S. population has about a 1-in-5 c. hance of develcping fatal cancer. That is, for every 10,000 people living in the U.S., approximately 2,000 will die of cancer. For a member of the cleanup work force active in decontamination work over the course of the cleanup, the chances are about 1 in 4.9, based on statistical estimates.
).$.%,.
y
}5 Q.7.
Would nonfatal cancers also result from the level of radiation dose Qt workers could receive?
l A.
Yes. Statistically, the number of nonfatal cancers could be approxi-
% T" mately one and one-half to two times the number of fatal cancers, s.g 4 #,-
according to the best scientific estimates. That is, in addition to OV^
i the possibility of fatal cancers, there could be 3 to 12 nonfatal V..l e
cance rs.
(The basis for these estimates comes from a 1980 report of MS
?
the National Academy of Sciences' Advisory Committee on the Bio-Jy": 2;4 logical Effects of Ionizing Radiation.)
m ;;
%u ; g(
{
Q.8.
Would there be other adverse health effects?
c A.
Yes. There could be from 3 to 12 genetic effects in the offspring M5M of the workers. Should genetic effects occur, it is possible that
.F d..
they could occur in more than one generation of offspring.
f,g...
p.
W,,
Q.9.
Do these new estimates mean that individual workers will be exposed 3ytj to larger amounts of radiation than was previously thought?
"s. N Q.:.U.j E
E A.
No. NRC regulations strictly limit the amount of radiation that an
- 9 individual worker can receive. These regulations have been and will Gy.:%
g:q 5
continue to be strictly enforced.
g g
The additional radiation estimated may be distributed among a larger Sy..s number of workers, to. hat an individual worker will still receive no
.y { A t
g t-E more than the regulations pemit.
I'
[T (For additional infomation about these limits, see the answers to
?.
W 6, 9.T Questions 27 and 35.)
6 I
/ffD k
[T%
F Q.10. Will these new estimates result in increased health or safety risks to the public?
lgYha E
P A.
Other than the possibility for genetic effects discussed in the answer to
[~ f l
>t L
Question 8, the dose to workers will not affect the general public.
Generally, public health and safety will be enhanced because of fuel i
N E
g removal and cleanup.
4 s
- n..
L (cor additional infonnation about public protection, see Questions c.A;u 7
60, 83, and 91.)
- yi.f.
Q.11.
How can NRC, the Environmental Protection Agency, and other involved organizations be confident in the accuracy of their estimates of these 47s 4
-5 health risks to workers?
M* E.=
t
=
I A.
These estimates are based on principles developed by internationally k.(
IE recognized authorities on the health effects of harmful radiation.
p
=;lh.
h The data used to predict health effects for cleanup workers are those g
2 recommended by the U.S. National Academy of Sciences' Committee on the d, -V Biological Effects of Ioni7.ing Radiation; the United Nation's Scientific E-Committee of the Effects of Atomic Radiation; the National Council on T
Radiatior: Protection in the U.S.; and the International Commission on Radiological Protection.
B E!
=
g
__ Q.12. To what type of radiation will workers be exposed and why does the radiation have the potential to be hannful?
A.
Cleanup workers will be exposed to ionizing radiation. This type of radiation has enough energy to pass through living tissue. As it does, it can displace electrons from the atoms and molecules of the living tissue. Atoms or molecules with displaced (or missing) electrons are called ions.
(That's why it's called ionizing radiation.) Living tissue exposed to ionizing radiation may be damaged.
(See the answer to Question 51 for information about types of ionizing radiation.)
Q.13. What are some sources of ioniang radiation?
A.
Ionizing radiation can come from both natural and manmade sources.
Ionizing radiation found in nature includes - -
- cosmic radiation from outer space
- certain elements which occur naturally in the human body
- certain elements from the soil and rocks that may be contained in the things we eat and smoke Mantade sources include - -
- medical and dental X-rays
- radioactive materials used to detect and treat diseases
- nuclear power plant fuel and its b :coducts
- combustion of for,sil fuel (coal-fired power plants)
- fallout from nuclear weapon testing in the atmosphere
- consumer products (for example, color television tubes and some types of smoke detectors)
Q.14. What units are used to measure ionizing radiation?
)
A.
For its biological effects in people, it is measured in units called rems.
l To account for small exposures, rems are frequently broken down into thousandths of a rem, or millirems. That is, one rem equals 1,000 milli-rem.
Q.15.
If radiation doses are measured in rems and millirems, why does Draf t Supplement 1 to the Programmatic Environmental Impact Statement refer to worker dose in a unit called person-rem?
A.
Person-rem refers to the sum of individual radiation doses that may be received by members of a certain group, in this case workers
_ _ _ _ _ _ - - doing the actual cleanup work.
Person-rem is calculated by rulti-plyino the average dose per person by the number of persons in a group.
For example,1000 people each exposed to 1 millirem of radiation would have a collective dose of 1000 millirem, which is 1 person-rem.
Q,16. Why were estimates of worker dose in March 1981 lower than the most recent estimates?
A.
There are several reasons. The most important reason is that GPU Nuclear now has actual experience in perfonning decontamination in the reactor building at TMI-2. When the Programmatic Environmental Impact Statement wu written, the reactor building had been entered only five times, and that was so that workers could collect data about conditions in the buil ding. The actual cleanup of the reactor building had not begun at that point. Another important reason is that delays have made cleanup tasks more difficult to perfonn, as noted in the answers to the next three questions.
Q.17. What has experience since March 1981 shown?
A.
GPU Nuclear has learned that draining the highly contaminated water from the lower level of the reactor building did not lower radiation levels
, because the building surfaces covered by the water were also highly contaminated. They have also learned that decontaminating the surfaces at the upper levels of the reactor building is much more difficult than previously thought. This is probably because of the long time lapse between the accident and the start of the cleanup.
During that time contamination penetrated both unpainted concrete surfaces and the rust that formed on metal ' surfaces.
Q.18.
If all the money needed for the cleanup were available, would the increased risk from worker exposure be necessary?
A.
Although there is a relationship between the availability of funds and radiation doses to workers, that relationship is not a simple one and cannot easily be quantified.
Nevertheless, several issues seem clear.
A lack of funds causes delays.
Delays, in turn, can increase worker doses for two reasons.
First, workers must enter the reactor building periodically for routine inspection and maintenance activities and to take samples required to ensure safety. These entries, however, do not contribute to the progress of the cleanup.
Second, as time passes, the radioactive contamination becomes more difficult to remove because it seeps further into concrete and becomes part of the layer of corrosion that fonns on metal surfaces.
Q.19. Were delays, whatever their cause, considered in the updated dose estimates?
A.
Yes, to a limited extent. The lower dose estimates in Draft Supplement 1 to the Programmatic Environmental Impact Statement (about 13,000 person-rem) assume little additional delay. The higher dose estimates (about 46,000 person-rem) allow for some delay, but are based on more or less continuous progress. None of the estimates take into account the worst case of delay, where workers receive relatively small doses year af ter year to keep the reactor safely shut down, but where no real progress
.in the cleanup is made.
FT
- i \\.Q Q.20. How do scientists arrive at the upper and lower numbers when they give 9 a[
the range of person-rem likely for the entire cleanup?
A.
Each cleanup task was analyzed in two ways to arrive at high and low es timates. For the low estimate, the radiation specialists considered d.
.E dose rate (the rems per hour) in the work area would be if previous
^
1 how long each task wETd take if the work went very well, and what the decontamination and shielding had reduced dose rates as much as can
'4 reasonably be expected, based on current cleanup experience. The number Q.'^..f of worker hours times the dose rate in units of rem per hour gave them
. Y f:
the low (or optimistic) estimate of dose (in person-rem) for each task.
.., _,7 The low estimates for all future tasks were then summed and added to the dose to date. This total gave them the low estimate of 13,000 person-rem ef for the alternative in which the fuel is removed prior to building decon-9;.;
tamination.
?TJ v...-,
For the high estimate, they considered how long the task would take if 5, ;. ~
+
things went slowly and if some tasks had to be redone.
They estimated gh the dose rate as if previous decontamination and shielding had been M.
W@J less effectiva than they would hope. These time and dose rate values were multiplied together and then summed in the same way)as for the low yn estimate.
This total gave them the high (or pessimistic estimate of 46,000 person-rem for the alternative involving fuel removal followed by M.f,.
reactor building decontamination.
Q.21. Given this increased range of worker exposure, why should the cleanup Nw go forward?
gfQ-1
' s.s e s A.
The TMI site is not suitable as a pennanent repository for radioactive Rd wastes generated by the accident.
(The reactor was designed for a nonnal D
operating life of about 40 years with an adequate margin of safety; it y Ja was not designed or built to contain radioactive wastes for an indefir.ite
'7 numt r of years, particularly when those wastes include damaged fuel and other hazardous byproducts fran an accident.)
Given that limitation, the eh-waste will have to be removed at some time in the future.
M.9.:
g < :.r
[3.
5 '..
Most of the short-lived radioactive material has already decayed to insignificant levels (that is, has essentially stopped emitting ionizing 3
radiation), and the dose rate currently affecting workers is due almost entirely to cesium-137, a radioactive material which has a 30-year half-(:Q life. A 30-year half-life means that if GPU Nuclear waited 30 years
%?
$W before cleanup, the dose rate would decrease to one half its present value.
However, cleanup workers have already learned that waiting makes cleanup jfp..
" $^ "
more difficult because contamination can penetrate building and equipment i
surfaces, as was noted in the answer to Question 17.
Since more effort would be required to remove contamination that had penetrated certain surfaces, waiting is not expected to reduce worker doses very much.
Another reason for going ahead with the cleanup is that there is a possibility, however slight, that some radioactive material could escape to the environment outside the reactor building. The risk of this happening, even though small, increases over time.
Q.22. What is the risk to the public of leaving the damaged fuel in the core?
A.
The damaged fuel in its present condition, under a boron-water solution, cannot ham anyone outside the reactor building. The borated water, the reactor vessel, and the reactor building all play a part in assuring safety.
But a small probability exists that in any given period of time something could happen to the borated water,to the reactor vessel, or to the building to impair safety. NRC cannot regulate for a limited perioci. They must look at long-tcnn conditions at TMI. The probability 1
of something eventually happening to the borated water, the reactor vessel or the building over a long period of time is too high to leave them in their present condition. Because of these possibilities, NRC has concluded that the building must be cleaned up.
(See the answer to Question 77 for an explanation of why the chemical boron is added to the water.)
_$m" 7.JTS a Q.23. What organizations are monitoring the radiation doses workers receive?
f a,.'J..
-. s.:
T';di 7 A.
Worker doses are monitoied by GPU Nuclear.
In addition, NRC has a full-time professional staff of radiation specialists at Three Mile Island.
MS They conduct ongoing reviews of the GPU Nuclear radiation protection program and the methods that GPU uses to monitor worker dosas.
Q.24. What kinds of radiation monitors are being used to measure worker doses?
A.
GPU Nuclear has a number of options as to the kind of radiation-monitoring instruments they can use.
A device called a dosimeter is used to register M:@i' the radiation dose a worker receives.
GPU Nuclear assigns each radiation (gd: 6.
worker a thermoluminescent dosimeter (TLD).
This device registers a worker's accumulated dose from ionizing radiation. The TLDs are analyzed
{'
or " read" every month, and the dose indicated for each worker is added to W.;..
previous readings for that individual.
- T.<.
yr #
GPU Nuclear also provides a direct-reading, or self-reading, dosimeter hb '
for each worker who enters a radiation area. Workers can read this ffp dosimeter during work to know how much dose they have received from gj ;
the time they enter a radiation area. Workers are required to read these devices before, during, and after work and report the results of their readings. These devices allow workers to tell immediately if a dose is larger than expected.
If it is, workers can leave the area at once. These devices also allow GPU Nuclear to keep track of each worker's dose between TLD readings and to detemine how much dose is being received for each job. These doses are then added to the worker's cumulative exposure record.
Both NRC and GPU officials review these records for their compliance with NRC regulations governing dose limits.
Other instruments, some in fixed locations and some carried by workers, are used to locate sources of radiation, to estimate the dose workers could receive, to detennine the concentration of radioactive substances in air, and to do other specific jobs.
fif C.
. g. A ;>
Filtered ventilation systems, instruments for monitoring airborne radio-
.$..N.-
activity and respirators are in use to minimize the possibility that
'.Fj. k) plQ workers could inhale, swallow, or otherwise get radioactive materials into their bodies. To monitor for such a possibility, GPU Nuclear requires
.l i. J.
all workers to be measured for internal radiation before they are t. "V; employed and at least once a year thereaf ter. A worker suspected of R" Ji?
internal contamination is examined in a special radiat. ion-detection Ff.!U ?
device for this purpose (a "whole-body counter") and, depending on the Q't.p;..
results, may also have urine and/or fecal samples analyzed.
g,;cy..;
n._
Q.25. What range of dose will the dosimeters measure?
c- ( N.--
K..: y A.
At TMI, TLDs used by workers are good from about 10 millirem to 200 rem
'yi..;;
(200,000 millirem). For self-reading dosimeters, the range is not as 0.;gp~.$
large, but it is more than sufficient to cover the dose that a worker could receive during a single entry to the reactor building or in Y h.i.
perfomin; work in any other radiation area.
- Q...
- ;g -
These dosimeters also warn workers of overexposures because they are f~ g # '
~~
equipped with alams that sound when radiation readings reach a certain T.
point. Should the alarm sound, workers would leave the area immediately.
- 1. n -
Q.26. Will a long-tem survey of the medical histories of cleanup workers be
,Q,b.j conducted by GPU Nuclear?
.f A.
No such survey is planned at this time. GPU Nuclear keeps medical records on workers while they are employed by the company, but other than that
'Q j there is no long-tem survey program.
Such a survey would not be M p-;
1/ A 6
statistically meaningful because of the relatively small number of health effects expected when compared to the normal incidence of cancer d j. >
+
- p and genetic diseases.
(See the answer to Question 6 for figures about
.h,; ;49 the normal incidence of cancer.)
.. h.t #%
Doses that individual workers have been and will continue to receive d#0 throughout the cleanup are well within the requirets in NRC regula-ONj tions and are typical of doses for other radiation workers.
Mvs p.;
Q.27.
Do NRC regulations spell out how much radiation a worker can receive?
{,Q A.
Yes. A radiation worker may receive no more than 3 rem of radiation Gg %
dose in any three-month period.
No worker may average more than 6 rem
-2 per year for each year past age 18.
There is also another more limiting MF.
guideline in NRC regulations (Code of Federal Regulations, Title 10, U i }.
Part 20, " Standards for Radiation Protection") requiring that all fgf:
. &,:$m N
NRC-licensed facilities make every reasonable effort to maintain radiation ex-W '.
posures as low as is reasonably achievable.
The term H V.
"as low as is reasonably achievable" means as low as is
$G:
reasonably achievable taking into account the state of 34' c O.{X technology, and the economics of improvement in relation to benefits to the public health and safety, and other societal and socioeconomic considerations....
1.le:.'
h k.
-.-i......,
E
____ _ _ _ _ _ _ _ _ _ _ Q.28.
Does GPU Nuclear have a program to comply with these guidelines?
A.
Yer. GPU Nuclear has a dose-reduction program to comply with the ALARA
( As Low As is Reasonably Achievable) principles.
This program is the responsibility of upper-level management with the authority to carry out the program. As part of tne program, all workers receive training in how to limit radiation doses. GPU Nuclear officials review equipment modifications and work procedures and control who may enter radiation zones.
Shielding and protective equipment ano clothing are also used, as appropriate.
(The types of training workers receive are explained in the answer to Question 44.)
Q.29. What steps does the dose reduction program involve?
A.
First, GPU Nuclear identifies significant sources of worker radiation doses. Then they evaluate the various alternatives for removing, decontaminating and/or shielding workers from these sources. They then select a method for reducing the radiation and carry out an evaluation to detennine whether the cleanup work can be performed under existing procedures. Then GPU Nuclear gives the nethod an extensive review to consider the benefit in worker dose reduction that can be expected.
NRC also reviews all such procedures for how well they comply with ALARA guidelines, Q.30. What controls does NRC use to ensure that worker doses are limited?
g A.
Special procedures are in place at TMI for reviewing GPU Nuclear's work.
Before GPU Nuclear begins any part of the cleanup involving radioactivity, they must submit plans, procedures, and safety analyses to NRC radiation specialists for approval.
Q.31. Has NRC rejected any of GPU Nuclear's cleanup proposals?
A.
Yes. NRC has rejected approximately 10% of the proposals reviewed and required GPU Nuclear officials to modify or further justify them.
Q.32. What dose reductions have been achieved so far as a result of the dose reduction program?
A.
The so-called " transit dose" (that is, the dose to a worker who enters the reactor building, goes upstairs to the main work area, and then leaves the reactor building) has been reduced from an average of 40 millirem per entry to an average of 16 millirem. The program has also reduced radiation in particular work areas.
For example, the average dose rate on the first floor was 430 millirem per hour when entries were first made in the fall of 1980.
By late 1982, but before the dose reduction program began, the rate was 350 millirem per hour.
In the summer of 1983, it was down to about 140 millirem per hour.
Q.33. What are the goals of the dose reduction program?
l A.
The goals of the dose reduction program are specific radiation reductions in various areas of the building at specified stages of the cleanup. The dose reduction goals become lower for the later stages of cleanup.
Ultimately, the goal is to reduce the dose rate in most of the building work areas to 10 millirem per hour and reduce airborne concentrations so that workers no longer have to wear respira-to rs.
( A detailed description of the licensee's dose rate reduction goals is given in Table 2.1 of Draf t Supplement 1 to the Programmatic Environmental Impact Statement.)
Q.34.
How does 10 millirem per hour compare with the dose rote inside the reactor building of a normally operating plant?
A.
This dose rate is comparable to that in a very clean operating plant, or to one that has operated for only a short period of time.
Q.35.
Does GPU Nuclear also have radiation dose limits for workers? If so, what are they?
A.
Yes. GPU Nuclear has established limits to ensure tnat NRC regulations will not be violated. Almost all workers are limited to i rem every three months, a dose rate below the NRC limit. Those workers whose jobs require doses of 1 to 2 rem in any three-month period must receive special prior authorization from GPU Nuclear's Radiological Engineering Manager after the need for these dose levels have been reviewed.
If a worker's job were to require 2 to 3 rem in a three-month period, the approval of both the Radiological Engineering Manager and the Radiological Controls Director would be required. These approvals are very difficult to obtain.
Q.36.
How many person-rem have workers received since the accident in March 1979?
A.
As of August 22, 1983, workers had received approximately 1,700 person-rem since March 28, 1979.
Q.37.
What level of doses have cleanup workers eceived during the cleanup at TMI on an annual basis, and how do these compare with the dose levels pemitted in NRC regulatinns?
A.
We show a breakdown of this information on page 1.9 of Draf t Supplement 1 to the Programmatic Environmental Impact Statemnt. The infonnation, combined for TMI Units 1 and 2, shows that 9,915 workers have received less than 1 rem per year since 1979. Another 509 workers have received 1 to 2 rem per year; 111 workers have received 2 to 3 rem per year; 20 workers have received 3 to 4 rem per year; and only 7 workers have received 4 to 5 rem in any one year. No workers have received more than 5 rem per year. More of the total dose received was incurred at Unit 1 than at Unit 2.
Furthermore, the doses at TMI-2 are lower than the doses received by workers at the majority of NRC-licensed reactors.
Q.38.
How many rem could the average worker expect to receive during the cleanup?
.- A.
There is probably no average worker because the majority of those involved in cleanup are involved in design, engineering, planning, and support functions; these workers do not enter radiation areas very of ten and generally average less than rem per year. The workers who do cleanup work in the reactor building will receive a larger dose, but cleanup experience to date indicates that they receive much less than the maximum allowable dose permitted by NRC regulations.
Q.39.
What adverse health effects are possible from this icvel of dose?
A.
The health effects will depend, of course on a number of factors, s
including the age and health of the worker, the actual amount of dose received (at THI and elsewhere), and the time period over which the dose is received.
For example, consider a 30-year old person who works nine years and receives 1 rem per quarter for each year worked (that is, 9 x 4 = 36 rem). Statistically, that person has a 1 in 210 chance of premature death from cancer. This is in addition to the 1-in-5 probability of death from cancer from other causes, which is the average for the entire U.S. population.
Q.40.
How many workers will be involved in the cleanup?
A.
NRC cannot say for certain at this time because of things like nonnal turnover acang workers and the need for specialists in various disci-plines.
In Draf t Supplement 1 to the Programmatic Environmental Impact Statement, NP.C estimated that about 10,000 workers would eventually be involved.
Q.41.
Is the work force made up only of GPU Nuclear people?
A.
GPU Nuclear, its contractors, and other GPU utility personnel make up the cleanup work force.
Some NRC and Department of Energy personnel and some of their contractors will also receive some dose.
Q.42. What's the age range of cleanup workers?
A.
They range between 18 and 70 and are primarily male. The average ag'e at present is 42.
Q.43.
You indicate that there are some women in the work force. Could a woman of childbearing age work in areas contaminated by radioactivity?
A.
Yes. All women radiation workers receive training for work in radiation zones when they are first hired and annually thereafter. At these train-ing courses they are provided with NRC's guidance on exposure of the fetus.
In addition, the doses received by women employees are maintained separately on a special computer code and are reviewed weekly by the Radiological Engineering Department.
When any woman's dose approaches h rem, which is the NRC-recommended limit for a fetus, the woman is contacted and again reminded of the guideline and the reason for it.
When a woman radiation worker becomes pregnant she is given the opportunity to limit her dose, whenever possible, without her job being put in jeopardy.
i si
- Q.44.
Are all radiation workers informed about the possible risks they face?
A.
Yes.
In accordance with NRC regulations, all radiation workers receive training in the subject. Workers receive three types of training. New employees are given both classroom and on-the-job training. All employees are also given annual refresher courses, both in class and on the job.
Finally, all workers about to enter a radiation area are given a pre-job briefing that infonns the about the nature of the task, the radiation levels anticipated, and the types of protective clothing and respirators they will have to wear.
In addition, women who work in radiation zones are given special instructions and a copy of NRC's recommended guidelines on the protection of the fetus.
Q.45.
Have discussions been held with unions representing cleanup workers about the nature of the work and about the potential risks?
A.
Yes. Some meetings have been held and NRC plans to hold additional meetings in the future.
Q.46.
Have outside workers been brought in because regular workers might use up their quarterly or annual dose limits?
A.
No, they have not.
Q.47. What kind of protective clothing do workers wear in contaminated areas?
A.
Protective clothing.is selected for the conditions in the work area and also for the job the worker will be doing. At a minimum, workers are required to wear one pair of coveralls, a hood, and a respirator (an air filter for breathing) for all work in the reactor building. For work in wet areas, plastic outer clothing is also used.
A.48.
Isn't it hard for the workers to get their work done in all that pro-tective clothing?
A.
Yes.
It is a problem because the clothing is both bulky and hot to wear. Workers in areas with high temperatures may wear ice vests to cool themselves.
Q.49.
Do protective clothing and respirators protect workers from receiving a
. radiation dose?
A.
Yes and no.
Protective clothing and respirators help to protect workers from becoming contaminated by radioactive material, but they do not keep them from receiving a radiation dose from sources of penetrating gamma will not shield against some radiation.) plains why protective clothing radiation.
(The answer to Question 51 ex Even though respirators are not effective against some types of airborne radioactive materials, these types of contamination are not present in the reactor building atmosphere at TMI-2 in concentrations high enough to be hazardous to worke rs.
Q.50.
Why is it important to cover workers with protective clothing?
~.
_ _ _ _ _ _ _ _ A.
A worker's skin must be protected for two reasons.
First, if radio-active material gets on the skin, the material continues to give off radiation until it is removed.
Second, radioactive material on the skin has a chance of being taken inside the body if the skin is broken.
Finally, workers must avoid swallowing or inhaling radioactive material because the material will continue to give off radiation until it is eliminated from the body, a process which could take from several hours to several years.
Q.51. What kind of radiation will protective clothing stop?
A.
There are three types of ionizing radiation:
alpha, beta, and gamma.
The one that gives workers at TMI a whole-body radiation dose is pre-dominantly gamma radiation.
("Whole-body" refers to radiation exposure in which the entire body rather than an isolated part -- an arm or leg --
is exposed.) Gamma radiation is like the X-rays used in medicine and dentistry in that it will penetrate clothing and other lightweight material s.
It takes something heavy, like lead or a lot of water, to s te-i t.
Alpha and beta radiation are responsible for much less of the rad.
ion dose.
Alpha radiation is stopped by almost anything (a piece of paper, human skin, clothing, etc.) and is therefore only a health problem if it gets inside the body. Beta radiation is more penetrating than alpha radia-tion. Although some beta radiation can penetrate protective clothing, its effects are greatly weakened as a result.
It can affect the lens of the eye and other soft tissues, but it is easily shielded by the plastic eye cover of the respirator or by ordinary safety glasses.
Q.52. Were alternative cleanup plans considered in Draft Supplement I to the Programmatic Environmental Impact Statement that might result in lower occupational doses?
A.
Yes. Three alternatives were considered, but cnly one of these was found to result in significantly lower worker doses.
Q.53. What was the first alternative for cleanup discussed in Draft Supplement I?
A.
The first alternative considered was to clean the reactor building thoroughly before removing the damaged fuel from the reactor.
Q.54.
Does the present cleanup plan differ from this plan?
A.
Yes. The current plan calls for removal of the fuel as soon as possible (while implementing a plan to reduce worker exposure) and completion of the building cleanup later.
Q.55. Why isn't the original plan going to be folluwed?
... A.
The cleanup of the reactor building and equipment will require more time and involve more radiation dose to workers than was originally J
anticipated.
Removing the fuel is considered too important to leave
]
~"
until af ter the building cleanup is completed.
Also, removing the fuel is likely to cause some additional contamination, necessitating that s)me areas in the reactor building be cleaned again.
Q.56.
Why is removing the fuel so important?
+
A.
For three reasons.
First, the fuel is the source of the majority of radioactivity in the reactor building at TMI-2.
Second, the presence of the fuel in the reactor represents a potential hazard to workers and the 7
public because there is a small chance that the fuel could begin a self-sustaining chain reaction and give of f unwanted heat and radiation.
Third, scientists and engineers expect to learn a lot about preventing and controlling nuclear accidents from examining the damaged fuel from TMI-2.
Q.57.
Af ter the fuel is removed, why don' t workers seal the building shut for 30 years rather than t 9e +he risks associated with decontami-nating the rest of the building?
A.
The main reason for not accepting thh approach is concern for the safety of the public. As long as there are potentially hannful levels of radiation in the reactor building, workers will r.eed to make periodic inspections, take samples, change filters, and do other work to protect y
the public.
All these activities will expnse workers to radiation without contributing toward pennanent removal of the radioactivity.
In addition, as was discussed in the answer to Question 21, the radio-active chemical cesium-137 has a 30-year half-life, so the amount of radioactivity it emits would decrease only by one-half in 30 years.
More time and therefore more exposure would be required to clean the building, even after a 30-year wait. Waiting also increases the difficulty of decontamination.
However, if there were reason to expect A%
breakthroughs in useful robotic technology to save workers from C) significant radiation doses, there could be merit to this approach.
g.p j.
a}. :
(For infonnation about the potential use of robots, see Questions 59
....f through 68.)
h}U r
Q.58.
Would decontaminating the entire reactor building before renoving the p@
fuel lower the radiation dose to workers?
j.c
.m
/$ W,
A.
Probably not. The current cleanup will likely r esult in from 13,000 to d {/
46,000 person-rem.
Decontaminating the reactor building first will n.t '.
likely result in from 12,000 to 42,000 person-rem.
This is really not W,c.,
a significant difference in view of the large degree of uncertainty in gp these estimates.
yy gr - ;:w..
- -l' ; l~ -
?g ~
.M-I FEM 9 sui
- r Q
}
h ;~.n9 fy Q.59. What were the other alternatives considered, and would they reduce
>>s, worker exposure?
g h@C M
A.
A second alternative would be to design and build equipment to
. ~.i vacuum the fine fuel particles out of the reactor vessel through one d
0 of the small openings in the reactor top (or head) where a small TV camera has already been inserted for a visual inspection of the core.
$ 2.,
Unfortunately, this alternative would result in just as much radiation J Q..
dose to the workers as the current plan.
- s 9 f..;
The third alternative considered was to remove the fuel, just as pro-ff, posed in the current plan, but then wait until robots were available
- + i.
to finish the reactor building cleanup. This alternative would
$.e.
fE lower worker radiation doses and it would get the fuel out as soon as E(p. -
possible, but no one can be sure that this alternative is technically 1
feasible.
we Q.60. Aside from risks to cleanup workers, is one cleanup alternative safer A
for the public than the others?
}FT W*
A.
Although the alternative cleanup methods were all selected to meet the objective of protecting the public, there are slight differences in how well they do so. The current cleanup plan provides for the Cfg.
earliest possible removal of the damaged fuel, and we believe that
- n.,
its removal is important to public safety and peace of mind. Because Q.ij the other alternatives put certain other tasks before fuel removal,
(?,
- they are slightly less desirable from the standpoint of public health
, p* /
and well-being.
In the third alternative, the fuel would be removed W :'
first, but there would be a significant delay in cleaning the rest of 9.N the facility while robot technology is being developed. The effects on lv f public safety of such a delay have not been evaluated, but they are not expected to be as beneficial as proceeding with the cleanup.
?.' h D4 Q.61. What do you aean by " technically feasible" in connection with robots?
WS
. g u,..
[h("
A.
Cleaning the building by robotics could not begin in earnest until robciic technology has advanced beyond its present stage of develop-W.
ment.
No one can at this time say how long such developments would take.
M E.2.G.
Q.62. What is the difference between " robots" and " robotics"?
'? "2
.. c '
A.
To most of us, robots conjure up the devices we see in science fiction J
~l movies. They are,nobile, self-contained, and able to perfonn a wide W
-Q variety of tasks -- and sometimes they have personalities.
The current state of robotic technology is a long way from producing such ver-satile devices, however. The tenn robotics, as used here and in Draf t Supplement 1, refers to the technology of remotely controlled devices which can do one or perhaps two jobs well. These are the types of devices that would have to be used at TMI.
bp '
l - k,.
- p-
' Q.63. How much could the radiation ~ dose to workers be reduced by using robotic techndlogy?
7 t
A.
This alternative 'would reduce worker dose by about 40% -- to between y'"
6,900 to_ 28,000 person-rem.
'Q.64. /If this alternatije' is not feasible now, could it dventually be used?'
i g
A.
- Yed,tIf developmen'ts in robotics are rapid.
w Q.65. Assuming that developments in:robotic -technology permitted their use-cin the cleahup, would-the robots become contaminated?
1
. \\.
W t
A.
Yes. Workers would probably have to take special precaution to pre-4
?
ventivital parts, such' as electronic circuitt, from becoming contami-nated, but any. part that came in contact with contaminated building surfaces or equipment would become contaminated.
t Q.66.- Would workers decontaminating theirebott be exposed to contamination and radiation?
!r "
.A.
- Workers"would be :protecte(from c t nination by the same type of pro-
'tective, clothing and regp,tratory-protectioh that they now wear in the reactor building. They_would, hewever, be exposed to some radiation, and they would receive some radiation dose.
c e
Q. 67. - Hosmuch?'! O i
~
2 A..
Current estimates are that they would receive between 5% and 15F of the dose they would_ receive if-the work being done by robots were done manually.
Q.68.
If robotic technology was advancing fast enough.so that its use was
' ' feasible would~ workers at' TMI-2 still-be e.xposed to radiation during n
j
.the period while the robotics technology was being developed?j y
r A.
Yes. fThere a're certain t sks that would be. required whether or not
[
cleanup work was go_ing ~ on.BEstimatesjare th'at these tasks could result in worker exposure of' between aboutf2 and 31' person-rem per year.
,7 l,
~
L Q.69.. What are th'e most up-to-date estimates of doses workers could receive from each cleanup task?
y, 4
p A.
, Disassembling the reactorfand. removing the fuel is expected to require
-between 2,600 ano 15.0003 person-rem; cleaning the reactor building and equipment, 5,900 to 21,000 person-rem; and all other activities,- includ-L ing-work to date, between 4,500 and 9,900 person-rem.
k r
' 's I?
i-
/(
r
.I
~
r
>,2
.<g,e>
e er..e --
,-,,-y
,e,+,..c-
.-,..r,,,,-,,e
,ew,e...
wry------.,.,u v~.,--1,y-,y.-,
- - +,,.v..
-=.re
-p.---y
.,1-
_ _ _ _ _ _ _ _ _ _ _ Q.70. That seems like quite a large dose for the "other activities." What are they?
A.
They include the dose reduction program. decontaminating the reactor's
~
primary cooling system, cleaning the auxiliary and fuel-handling building, managing and transporting radioactive wastes, routine inspection and maintenance activities, and those cleanup activities completed so far.
(Details about the dose reduction program are discussed in Questions 28 and29.)
Q.71. Why do estimates of doses workers could receive vary so widely for each task? For example, the range for cleaning the reactor building and equipment varies from 5,900 to 21,000 person-rem.
A.
Even though the engineers and radiation specialists have a good idea of the cleanup required for most of the reactor building and equipment, there are still unknowns.
One big unknown is the condition of the basement of the reactor building, because it was under contaminated water for so long.
Some decontamination is being done froa above this level, but radiation specialists can only estimate what the dose rates will be when hands-on decontamination has begun. They also must estimate the amount of time workers will spend on each task. Given these unknowns, it really is not surprising that there is such a difference between the high and low estimates.
For the low estiaate, the assumption was made that the work would be done in the shortest time at the lowest dese rates.
For'the high estimate, the assumption was made that everything would take the maximum amount of time at the highest dose rate that might be estimated.
Q.72.
How are workers being protected from contamination at ti;c present time?
s A.
Clesnup workers wear the protective clothing and respiratory protec-tion discussed in Question 47. After each entry to the reactor building, each worker is examined for contamination after the protective clothing is removed.
Only a few workers have been contaminated.
In each case, simple decontamination methods, such as washing the affected area, eliminated the contamination.
(See the answer to Question 24 about radiation-detection devices.)
Q.73 What type of radioactiva naterial accounts for the major source of con-tamination?
o
.A.
Cesium-137 is the major contributor to worker dose because it emits gamma radiation.
Strcatium-90 is also a problem, but because it emits beta radiation, protective clothing reduces worker exposure.
~(See the answers to Questions 49, 50, and 51.)
Q.74. Where did these radioactive materials come from? Aren't they present in normally operating reactors as well?
l
-~
. ~.
17-
]
. A. -
Yes. They are present-in.all reactors, but they are usually trapped in the fuel. The accident'at TMI-2 damaged much.of the fuel, resulting -
- in' the release of'these radioactive materials.
r Q.75. When tarkers remove the top (or head)-of the reactor. vessel, will the
. fuel expose, workers'to large doses tof radioactivity?
?
-A.
No '. : When the head is removed', the fuel will be under at least 10 feet of water, which will' shield' the, workers (as noted in the answer to
. Question 51). i Head removal, however, will entailL some radiaticn dose i
from contamination on structures on the underside of the-head. Radiation-protection measures will be implemented ~to reduce this dose.
Q.76. When the dam 6ged fuel in the core is removed, will it be exposed to the air 'or will -it be moved under water?
n J
- A.
Thelfuel will be kept under water at all-- times to shield the workers f-om; radiation. The canisters 'into which the fuel will be placed will also:be kept under.-water, not only while they are filled, but continuously until they are placed in' shielded, crash-resistent casks for shipment.
Q.77. Would worker' exposure je reduced if the fuel was not removed and the entire reactor. vessel was flooded with water?
A. -
Workers 'are exposed to radiation only when they are inta radiation area, so in that. sense you could reduce worker doses substantially.
'(2,600 to115,000 person-rem) by leaving the fuel in place forever-_-if that were acceptsble from a safety standpoint. NRC, however, believes that the riskiof leaving -the_ fuel in place.is unacceptable in the long tem. Accordingly, the fuel willl have to be removed.
~
?The fuel is currently flooded ~'with a. boron-water solution and will-continue to be' throughout defueling.~ Boron is added to the water because it-absorbs'the neutrons (atomic _ particles) necessary for the
. uranium fuel' to sustain a chain reaction. Without a chain reaction,
.the fuel.will-not achieve criticality and hence will not-produce-
' additional radiation or heat.
In a normally operating reactor, this chain. reaction:is carefully controlled _ to. produce the steam that rotates' 1
. turbines to generate electricity.
Q. 78. - Has any sampling been done to measure radiation levels under the
- reactor vessel ; head?J-E 5Yes. - Radiation detection devices provide,this infonnation.
In A.-
- addition, samples ~of reactor coolant water are-taken regularly,.and L
- therelis an ongoing program to sainple 'both the particulate' material
'inside-the reactor and the damaged fuel itself.
~
- Q;79.U What are current radiation levels? '
CA.
Radiation' levels below tile reactor, vessel head are about 200 to 1,000 I,
rem per hour. Remember that these are radiation levels instde the reactor vessel.m They=do not represent. readings in areas where workers lwill be positioned;to remove the head and fuel. These' tasks-will be perfonned _in areas with lower radiation levels.
i.
e m+,
,,e-
,>,.,,w--
,.,,--,y
-,---.,yr-,.-,yy,,,,,re.,
ym,,-,c
,w,.,-,-,,,,-~%-,-
e-q-4,-m
- ,,,-+
ei, -,
- 'Q.80.
What would happen if radiation levels are higher than expected when the reactor head i= lifted?
A.
The sampling procedures detailed in Question 78 will ensure that this type of surprise doesn't occur.
Even so, there will he -procedures in effect should something like this happen. For instance, if radiation levels at a particular point reach a certain-level as the head is lifted, then the head could be. replaced immediately.
Further, workers will be instructed to leave the building if radiation reaches levels that could result in worker doses exceeding pennissible levels.
Even though all the data have not been accumulated at this writing, GPU Nuclear and NRC
'will have-sufficient data 'to know what to expect before the head is lifted.
Q.81. -What would the risk be for a-worker who received an overexposure?
A.
The risk to a worker from an overexposure would depend on the level of dose received. An overexposure-usually means receiving more radiation dose than was planned.
For ex' ample, an overexposure may mean
. exceeding GPU Nuclear's 1-rem-per-three-month-period limit without having the special authorization reautred or it may mean exceeding NRC's 3-rem-per-three-month-period limit. The response to Duestion 39 notes that a worker who receives 36 rem during the entire cleanup has a 1 in 210 chance of premature death from cancer induced by the dose.
If the dose due to overexposure were 36 ren, the risk would be about the same.
0.82.
Would flooding the area'around the reactor vessel cut down on the radiation-level that workers could be exposed to when the head is j
lifted?
l A.
Flooding the area c*ound the reactor vessel could potentially reduce worker doses.
Prior to flooding, several time-consuming modifications would be required. As one example, a high-volume water decontamination system.would have to:be installed to prevent-the flood water from itself becoming a ma,ior source of radiation. The potential' reduction in doses to workers would be too small to.fustify flooding the area for a " wet" l
head lift.
0.83.
Can radiation trapped inside the reactor building penetrate the walls to the outside environment?
A._
Yes, to a very limited extent.
Radiation is reduced in intensity as it
. passes through heavy materials.
(This is why you get a good image of dense tissues like bene on an X-ray film, but less dense tissues, like the
' heart, do not show up well.)
The strongest sources of radiation at TMI-2
- are in areas of the building below ground level. They are shielded not only by the building itself, which is made of reinforced concrete several l'
feet thick, but also by the ground.
In addition, the inside of the entire l-building is lined with a 3/8-inch thick steel liner. ' Radioactive materials in the upper part of the building do emit some radiation that passes through i
the approximately 3-1/2 feet of concrete and steel that fonn the reactor dome.
r
' If. cesium-137, for example, gives a dose ~ rate of 100 millirem per hour L
-inside-the -dome, this. rate is reduced 10,000 times to 1/100 of a millirem per hour on the outside surface of the dome.- This level of radiation would
' be virtually impossible to measure at the plant property boundary.
'Q.84. ;Can radioactive materials contaminate the reactor building's steel liner?
.A.
Yes. :There -is some radioactive contamination on the steel liner,-
- especially at the lower elevations of the building.
.Q.85.. Will this contamination be; difficult to-remove from the steel liner?
i A.
The. liner is ane of the easier surfaces to. decontaminate.
It has a
. painted surface, and workers do not expect to find much contamination beneath'the paint.
Q.86. ;Can radioactive contamination penetrate concrete surfaces inside the reactor building?
'A.-
Unpainted concrete surfaces within the building'are expected to be highly contaminated since concrete is~ a porous material.
.Q.87.
How can you tell how far the contamination has penetrated the. unpainted.
concrete: surfaces?
-- A..
Samples of ' concrete from structures in the upper areas inside the reactor building are~ still being taken and analyzed, but workers expect contami-nation. may have penetrated only the first few tenths of an-inch. For samples of concrete that were underwater, they expect that contamination may have. penetrated up to a few inches.
). Q. 88. What methods can be used to remove contamination from unpainted con-crete surfaces?
~
A.-
The most effective methods are those that chip away the surface of the
- concrete. Machines that do this have been used.successfully to clean concrete surfaces in the auxiliary building.
Q.89.. :Does the sandblasting method of scrubbing surfaces ' release contaminated particles into the atmosphere?
- A.
Dry sandblasting ~1s seldom used for decontamination without a vacuum
" attachment to collect particles-that would =otherwise spread contamination.
The so called vacuum blasting and various wet-blasting techniques have
~
. been 'used successfully where contamination-is not too deep. -(Wet blast-ing involves the use of jets of high pressure water.)
_... ~... -.. -..,... - _. -.... ~ _, - _..... - -, _.,..
/' '
- Q.90. Have contaminated materials in the reactor building since the accident lessened the' building's capacity to prevent these materials from leaking to the outside er,vironment?
A?
No. ~ The building materials at THI and other reactors were selected.
designed, and fabricated to be resistant to radiation.
Normal physical
- processes,'such as
- rust caused by high: humidity and degradation caused by caustic-cleaning materials, may over an extended period of time weaken the capability of the reactor building to contain the accident-generated material.: This'is one incentive to decontaminate the-building so that it-3 s not ~1ef t.in its present condition. GPU Nuclear conducts a continuous 1
environmental-monitoring program to evaluate building conditions.
Q.91 Does any radioactive material escape to the.outside environinent when
. workers enter and leave the reactor building? If so, how much?
'A.
Now that the krypton gas has been vented and the reactor building is con-tinually being ventilated to the outside through high-efficiency air:
filters,-there is little radioactive contamination, except for particulate meterial. These particles are trapped by filters in the_ ventilation system and.cannot reach the'outside environment.- Some contaminated particles. cling to the protective clothing that workers wear, and this leaves the reactor building on the clothing. Even so, virtually ~ none of this material reaches theJenvironment outside the building.because of stringent controls on how this clothing is _ handled in the changing area where workers remove their protective garments.
Q.92. Are explosions possible during any part of the cleanup?
f here is virtually no possibility of an-explosion; associated with T
A.-
- the cleanup.1: 0f course, the potential always exists that a hose under high : pressure could burst, something that would be hazardous to workers
-in -the immediate _ vicinity. - Also,:there has been concern about the pos-
.sibility of a pyrophoric explosion.
- Q.93L What are pyrophoric. explosions?-
A.;
Pyrophoric explosions result from the extremely rapid burning of very reactive metals. For example, metallic sodium undergoes pyrophoric burning (orLexplosion) in air or if wet. Less-reactive metals, such as alumin.um, magnesium, and zirconium, will undergo.pyrophoric reactions if they are finely powdered. -
The-zirconium tubes that surround the uranium fuel could undergo-pyrophoric reactions if exposed to air. al.though the tubes are now under water and will remain there throughout the cleanup.
(Wet particles may undergo-pyrophoric reactions when exposed to air, but such reactions do not take place under
- water. ) However, this possibility was investigated. Tests were also made on ' samples ~ of' reactive metals ^taken from the structures near the top of the reactor vessel. Based on the results of these investigations and tests,
.such explosions are considered highly unlikely.
Nevertheless, workers will perform fuel removal tasks:very carefully to avoid even the small chance of such an explosion.
Q.94. What radiation dose is received by truckers who haul radicactive waste from THI to waste disposal locations?
A.
Truck drivers who haul radioactive waste are radiation workers and '
are subject to the same NRC dose limitations as other radiation workers (see Question 27).
In addition, the U.S. Department of Transportation (DOT) limits the dose rate in the driver's seat of any vehicle hauling radioactive material to 2 millirem per hour.
For a trip of 2300 miles from TMI to Richland, Washington, the driver might spend up to 60 hours6.944444e-4 days <br />0.0167 hours <br />9.920635e-5 weeks <br />2.283e-5 months <br /> in the truck cab, thereby receiving 120 millirem on the trip.
The return trip most likely would not involve the transportation of radioactive material.
For an extreme case, consider a truck driver who spends 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br /> per year driving, half of that hauling radioactive material, with the maximum allowable dose rate of 2 millirem per hour in the cab. The driver would receive at most 2,000 millirem (2 rem) per year, a dose well below the NRC guideline of 5 rem.
. Q.95. What are the potential adverse health effects these doses could result in?
A.
'The risk to a truck driver receiving 2 rem per year for 9 years would be approximately h the risk to the worker we discussed in Question 39, or about a 1 in 420 chance of premature death from cancer.
- U. S. vvy n.-a i PRINTING OFFICE: 1983-421-299:202 l
i
/
v Nucu m iov m o-.cowvss,oN
...<>., wo n,*,
r v., N.. s,,
g,.
BIBLIOGRAPHIC DATA SHEET NUREG-1060y mt.
. u.... N, i.cc N --n a
,,,1<
.w.u.,,, a wars to Questions About Updated Estimates of
, 0
- 1...,0.,fo,a,, o Oc pational Radiation Doses at Three Mile Island,
- ooN, Uni 2.
Dec er 1983
....,0..
oo.
g,.a ecember 1983 9
OJE cTe1.$a,WWoRa UNs, NuwetR 0 PERFORWiNG ORG.Nt2
, as N.wt.NO M.iLe%.DDRE55 tWW te Co.ed Three Mile sland Program Office Office of N lear Reactor Regulation io"aww*a U.S. tiuclear gulatory Commission Washington, D 20555 J
n i,okso.w o.a.
.,.,,oNN.
o...t.o o..
,~ m e,c,
, 2..... o,..,0 Three Mile Island rogram Office Office of Nuclear actor Regulation Public Outreach U.S. Nuclear Regula, ry Commission
'a remoo coveaso,, a e
Washington, DC 2055 e
13 Su*,LtutN,.R Y No,ES
\\
This document provides answe to que#tions concerning new radiation dose estimates for cleanup workers at Three le fand, Unit 2.
Answers to these questions are b d on information in Draf t Supplement 1 to the
" Programmatic Environmental Imp Statement Related to Decontamination and Disposal of Radioactive Wastes Resultin.'fr the March 28, 1979, Accident, Three Mile Island Nuclear Station, Unit 2," NUR -068 Its al v WyomD$.ND DOCuut N,
.L v 515 I SO Di scR e,, o* 5 k
,, g,c,u,g,.,c<.ss.. c.ooN g
,. w.o.o,
.c.,
......t..<,..
....N.
Unclassified X
Unl~ ited
,5l.O' c55'"c'"o*
}
" "'c5 s
L
/
EAMI sounta class em f.:: NUCLEAR REIULATORY COMMISSION rostscsasetsruo
-. WASHINGTON, D.C.- 20M6
--,$5$ g.
etnuit n 131
, OFrCAL SUSWdESS.
PENAt TY POR PANATE USE. 6300 T'
>H
- ~,
4 Z,
3 m
m
~
W s
F
):;
2l
_,0 '
C E
H P4 a
..O
+
l ii,,,,
'