ML20205K127
| ML20205K127 | |
| Person / Time | |
|---|---|
| Issue date: | 10/29/1986 |
| From: | Soffer L Office of Nuclear Reactor Regulation |
| To: | Schwartz S NRC OFFICE OF INSPECTION & ENFORCEMENT (IE) |
| Shared Package | |
| ML20205J677 | List: |
| References | |
| FOIA-87-7 NUDOCS 8704010517 | |
| Download: ML20205K127 (11) | |
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. _ . '##.e'.%g'o g UNITED STATES NUCLEAR REGULATORY COMMISSION
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- E WASHING TON, D. C. 20555
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NOTE T0: Sheldon A. Schwartz, Deputy Director, DEPER, IE FROM: Leonard Soffer, Regulatory Improvements Branch, DSR0
SUBJECT:
CHERNOBYL IMPLICATIONS ASSESSMENT REPORT: SECTION IV.I. ADEQUACY OF EPZ DISTANCES Enclosed is a revision of the draft of section IV.I. " Adequacy of EPZ Distances", of the Chernobyl implications assessment report. This revision incorporates coments made at the meeting of October 20, 1986, as well as those of your transmittal to T. Speis, dated October 27, 1986. I believe this draft should, therefore, supersede these previously dated versions.
9 Leonard Soffer Regulatory Improvements Branch 4
Division of Safety Review & Oversight
Enclosure:
As stated ;
cc: T. Speis B. Sheron D. Matthews IE -
E. Podolak, IE G. Sege l
l 9 3);-29-7 6/53 8704010517 070330 PDR FOIA SH,OLLY87-7 PDR
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1 IV.1 ADEQUACY OF EMERGENCY PLANNING ZONE DISTANCES
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- 1. Statement of the Issue Following the Chernobyl accident, the population from a zone having a radius of 30 kilometers (18 miles) was evacuated in stages. This has been enntrasted with U.S. emergency planning, which involves planning fer a plume exposure pathway emergency planning zone (EPZ) having a radius of .
10 miles. In addition, concerns regarding contaminatiort of food products extended nyer a wide region, including areas outside of the Soviet Union.
The issue is, what are the implications of the Chernobyl accident with regard to the edequacy of the 10 mile plume exposure pathway EPZ and 50 miles ingesti.. exposure pathway EPZ, as used in the U.S.?
- 2. Current Regulatory practice Emergency planning is currently required (10 CFR 50.47) for all U.S.
nuclear power plants for two concentric zones having radii of 10 and 50 miles (except for plants with power levels below 250 Mwt). The inner zone, referred to as the plume exposure pathway EPZ, is one where the principal exposure sources would be from'the radioactive plume and from materials deposited on the ground. The outer znne, referred to as the ingestion exposure pathway EPZ, is one where the principal exposure would be from ingestion of contaminated watar or foods such as milk and fresh vegetables.
The sizes of these zones were determined from considerations given in NUREG-0396. These specifically included consideration of the accident risks from the complete spectrum of severe accident releases given in
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2 WASH-1400. In addition, a distance of 10 miles was also chosen for the inner zone based on the conclusion that " detailed planning within 10 miles would provide a substantial base for expansion of response efterts in the event that this proved necessary." (NUREG-0654)
Approval of both on-site and oft-site plans are required for full power licensing. The plans are also required to comply with a detailed list of standards, as given in.10 CFR 50.47.
In practice, the 10 mile plume exposure pathway EPZ has become a source of considerable misunderstanding. Many people appear to believe that, in
- the event of an accident, a relatively hasty evacuation by everyone within this area would be the only effective protective action. This misconception may also be fostered by periodic exercises having scenarios which call for substantial evacuation of this zone, plus the requirement I
that licensees submit evacuation time estimates for various sectors of the zone. Hence, it is not surprising that this zone has come to be mistakenly referred to as the evacuation planning zone.
- 3. Work In progress
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There has been significant interest in re-evaluating emergency planning, i this area began to be of interest shortly after the Three Mile Island accident when observers noted the relatively small amounts of iodine released compared to the amounts of noble gases. This led a number of observers to claim that severe accident releases or " source terms" were much lower than previously estimated. Since the severe accident releases estimated by WASH-1400 provided the bases for the sizes of U.S. EPZ's, this had significant implications for emergency planning.
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3 A major NRC research effort began about 1981 and has been underway since then to obtain a better understanding of fissinn product transport and release under severe accident conditions. This " source term" research has included a very large and extensive contractor effort, including the development and application of new computer codes regarding core-melt phenomena and containment performance. It aise included an extensive review effort by peer reviewers, industry groups, and an independent The assessment under the auspices of the American Physical Society.
report explaining and detailing this revised methodology to calculate ,
accident source terms was recently published in July 1986 as NUREG-0956.
Revised ' risk profiles for 5 representative U.S. LWR's are in preparation
-- which will apply this methodology. This effort is expected to be published as NUREG-1150, for comment, by January 1987.
While this research effort was in progress, the staff had identified emergency planning as an area to be re-evaluated, depending upon the outcome o'f the effort. Industry groups too, have indicated a strong interest in this area. Baltimore Gas & Electric Co. (BG&E) has requested a reduction in the size of the plume exposure EPZ for the Calvert Cliffs site from 10 miles to 2 miles, based upon source term research results.
In addition, both IDCOR and the AIF have claimed that a two-mile EPZ would, in view of revised source term estimates, provide an equivalent or greater degree of protection than the ten-mile EPZ, given WASH-1400 i
source terms. .
l During this period, the staff also explored alternatives to the 1
conventional emergency planning strategies, making use solely of WASH-1400 source terms. This led to the assessment of a concept known
4 as " graded response" which called for a prompt response, such as evacuation, within about two miles of the plant, to be followed by a continued assessment of accident conditions, identification of any contaminated areas, and a relocation of affected populations from these areas. A staff conclusion that such an approach had merit has been held in abeyance pending the outcome of the source term effort.
- 4. Assessment .
4.1 Accident Response Assessment ,
- 1. The-Chernobyl release occurred with essentially no warning time, a
-- high initial energy of release (producing an initial plume height of about 1200 meters), and a release duration of about ten days.
While the release fractions are considered comparable to the more severe release categories of WASH-1400, and release durations of similar magnitude are also considered more realistic based upon recent research, the zero warning time is considered to be unique to the RBMK design.
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- 2. Residents in the town of Pripyat (about 5 kilometers NW of the plant) were initially advised to minimize t'he time spent outside and to keep windows closed. (Testimony by M.E. Sanders, FEMA) At about 8 AM on April 26, all outdoor activities were banned and potassium i iodide (KI) was administered to school children. Most of the initial releases were carried above and around Pripyat. The decision to shelter on the day of the accident, rather than evacuate, appeared to have been based upon several factors. These included relatively low
5 radiation levels (the Soviet protective action levels are 25 and 75 rem to the whole body) measured in Pripyat, while at the same time l In addition, l
bigh levels were measured along evacuation routes.
Pripyat contained many multi-story buildings which affordbd good rhelter, and finally, mass transport for the approximately 45,000 residents was not inanediately available. The Soviet report on the accident stated that the decision to shelter resulted in the people of Pripyat receiving gamma radiation doses 2 to 5 times less than the levels measured in the streets. ,
By 'early April 27, radiati6n conditions in Pripyat worsened. By then,
- arrangements had been completed for over 1000 buses to arrive from Kiev for transport. Evacuation of Pripyat was ordered to commence at about 2 PM (approximately 36 hours4.166667e-4 days <br />0.01 hours <br />5.952381e-5 weeks <br />1.3698e-5 months <br /> after the initial release) and was completed about three hours later. Residents of Pripyat were estimated generally to have received relatively low doses of 1.5 to 5 rad of gamma radiation exposure and 10 to 20 rad beta radiation exposure to the skin.
It is n'ot clear whether this initial evacuation extended beyond Pripyat, out to a distance of 10 km (6.2 miles), or was confined only to Pripyat itself.
- 3. Some time later (perhaps a few days to a week after the initial release) an additional evacuation of all the residents within a 30-kilometer zone, except for those already evacuated, was ordered.
A delayed evacuation such as was carried out in this second stage is better deserving of the name relocation, rather than evacuation. It .
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6 is not known over what time period it occurred, but it appears to have required extensive resources, since a considerable number of farm livestock as ve:1 as about 90,000 persons were also relocated.
Indications are that most residents within this area received doses less than 10 rem, although individuals in several communities could have received doses of 30 to 40 rem.
- 4. It is not clear over what distances the Soviets had pre-planning.
The Soviets indicated at the IAEA meeting in Vienna that their .
response plans had only limited value and that they had to resort to "ad~ hoc" response. This appears to have involved a very large effort
-- utilizing the military as well as other centralized elements on a national level. The basis for selecting 30-kilometers as the area for these actions is not known. This distance appears to have been
! selected based upon observed contamination levels and may have combined aspects of both the plume exposure and ingestion exposure zones contemplated by U.S. criteria. It is important to recognize that protective actions were carried out in a staged or phased fashion, both with respect to distance as well as time. Whether this was planned or merely occurred as part of the ad hoc response to the accident is not known.
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4.2 Assessment of Implications
- 1. The specifics of the Chernobyl release are unique to the RBMK design, ]
and represent a near " worst case" in terms of the risks of nuclear energy. Because of differences in reactor design, the probability 1
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7 cf a severe accident is considered to be lower at U.S. commercial nuclear power plants. In addition, severe accidents at U.S. plants would typically progress over a longer time period, resultirg in longer warning times, and the amounts of activity released would be j
generally considerably less 'because of the substantial containments around each U.S. plant. Therefore, accidental releases for U.S.
reactors are expected to be no greater (and probably considerably l 1ess) with regard.to the amounts of radioactivity released, and to have considerably greater warning ,
times. For these reasons, assessment of the adequacy of U.S. EPZ distances in terms only of-the Chernobyl release is unwarranted.
- 2. There are some useful implications that can be drawn from the Chernobyl accident and the response to it, however. It appears that relatively prompt protective actions (those taken within the first few hours),
such as evacuation and sheltering, may generally be adequate to avoid early health effects and achieve a good degree of dose savings within relatively short distances. Furthermore, sheltering may be preferable to evacuation under certain conditions, especially if an initially elevated plume occurs and good sheltering is available.
However, where an initial decision is made to shelter close to the reactor, a good monitoring capability plus the ability quickly to notify the populace of any changed conditions appears to be essential.
In one respect it is difficult to compare the effectiveness of sheltering at Chernobyl and U.S. practices for protective actions because of the large difference in protective action levels between the two l
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8 countries. However, it is recommended that the U.S. further explore the relative advantages and disadvantages of sheltering vs. evacuation at close distances for a variety of accident release, meteorological and shelter conditions given our own protective action guides.
- 3. For large releases, protective actions may be warranted over significant distances and may possibly extend beyond areas originally designated for pre-planning. Such actions appear to have a reduced degree of urgency than these taken at shorter distances ,in that they .
can be carried out over a longer time period (of the order of one or more days) and still result in relatively low risk levels to the public. Such actions are likely to consist of sheltering and/orrelocation(delayedevacuation). The possibility that 1
protective actions may extend beyond the range of a pre-desigrated planning area should be recognized, but need not be a cause for undue f concern if this is accepted as a possiblity, if the reduced urgency and longer time scale for response are acknowledged, and if a capability exists on an "ad hoc" basis to extend the range of accident response, as needed. One of the bases for selection of thi 10 mile plume exposure EPZ was, as stated earlier, that " detailed planning l within 10 miles would provide a subs'tantial base for expansion of l response efforts in the event that this proved necessary."
Based on Conclusions 2 and 3, there is nothing in the Chernobyl' accident and response that implies that the 10 mile plume exposure pathway EPZ in the U.S. is inadequate with regard to the ability to plan and carry out a full range of protective actions for the population within this zone, as well as beyond it, if the need should arise.
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- 4. For large releases, concerns over contaminated water and foods such as milk and fresh vegetables may extend over very large distances, well beyond the 50 mile ingestion exposure pathway EPZ. This would involve monitoring and control efforts by a nuirber of states as well as the federal government, and could have trans-national implications, as occurred for the Chernobyl accident.
Because of the existing infrastructure and close coordination among state i
and federal organizations involved in radiation protection and control, a ,
high level of capability already exists to handle such a situation.
Nev'ertheless, the Chernobyl accident does carry an implication that the role intended by the 50 mile ingestion EPZ should be re-assessed in light of these considerations.
- 5. Conclusions and Recommendations
- 1. Assessment of the adequacy of U.S. EPZ distances in tenns only of the Chernobyl release is unwarranted.
- 2. Additional research should further explore the relative advantages and disadvantages of sheltering vs. evacuation at !
close distances for a variety of accident release, j meteorological and shelter conditions.
- 3. Protective actions taken in response to an accident can be expected tn be carried out in a staged or phased fashion both with regard to distance and time. High priority actions may be adequate over relatively short distances, while lower priority actions could extend over significant distances, possibly beyond those designated for pre-planning.
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- 4. There is nothing in the Chernobyl accident and response that implies that the 10-mile plume exposure pathway EPZ in the U.S.
is inadequate with regard to the ability to plan and carry out a full range of protective actions for the population within this zone, as well as beyond it, if the need should arise.
- 5. The role intended by the 50 mile ingestion pathway EPZ should be re-assessed.
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