ML20128H571
| ML20128H571 | |
| Person / Time | |
|---|---|
| Issue date: | 05/17/1996 |
| From: | NRC ADVISORY COMMITTEE ON NUCLEAR WASTE (ACNW), Advisory Committee on Reactor Safeguards |
| To: | Shirley Ann Jackson, The Chairman NRC COMMISSION (OCM) |
| Shared Package | |
| ML20128H560 | List: |
| References | |
| ACRS-GENERAL, NACNUCLE, NUDOCS 9610090395 | |
| Download: ML20128H571 (7) | |
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FINAL DRAFT 1B MJS/BJG May 17, 1996 The Honorable Shirley Ann Jackson Chairman U.S. Nuclear Regulatory Commission Washington DC 20555-0001
Dear chairman Jackson:
SUBJECT:
HEALTH EFFECTS OF LOW-LEVELS OF IONIZING RADIATION The health effects of ionizing radiation are central to many of the regulations that are promulgated by the Nuclear Regulatory Commission (NRC).
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.tly, phe validity of the Mpg $i!
M dose-response relationships in the area of low doses and low dose rates has been questioned.
It is the purpose of this letter to recommend a course of action for the Commission in the review and analysis of this important issue.
Our discussion and recommendations concerning this subject derive from the first' meeting of the Joint Subcommittee of the Advisory Committee em Reactor Safeguards (ACRS) and the Advisory Committee on Nuclear Wasts (ACNW), held on March 26, 1996, as well as j};;=&f;Gdeliberations by each Committee.
Presentations were made by members of the NRC staff, including the visiting medical fellow, and representatives from institutions and agencies, including the National Council on Radiation Protection and Measurements (NCRP), the Health Physics Society, and the
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Massachusetts Emergency Management Agency.
Written comments were also received from the public.
Most national and international scientific committees dealing
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with the subject take the view that the safest approach to regulation is one that relies on the lin:::, n; thr :h:ld LNT model of response to doses of ionizing radiation.
This model holds that the ill health effects observed at high doses and high dose rates (mainly among atomic bomb survivors) can be extrapolated linearly to low doses and low dose rates, down to the smallest doses.
The NRC staff prepares regulations based on this model, one of the basic questions in this field is whether the LNT model is valid at the low doses enccantered in many of the regulatory domains.
The increasing emphasis placed by the Commission on risk-informed regulation makes it imperative that the actual health risk of low levels of ionizirq radiation be assessed accurately.
The NRC is currently funding a contract with the NCRP to make a critical evaluation of the LNT assumption.
While the ACRS and ACNW have not reached any conclusions on the validity of the LNT model, and will continue to study the matter, we consider the issue of sufficient importance to recommend that the commission initiate independent and special technical investigations to provide an impartial review of the data and their quality.
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3 The presenos of unavoidable background radiation and the need for very large samples have made it difficult in the past to provide definitive data on the validity of the LNT model.
As with all small-effect phenomena, the quality of the data and the statistical interpretation of the results govern the ability of any study to contribute to the testing of the model.
- However, investigators in the field have recently been able to provide methods to account for the impact of confounding factors such as variation in background radiation.
Some studies in the United States as well as in China, Sweden, Poland, and'. Canada have
'l arrived at conclusions tha*. do not support the LNT model.
Othed i
research concludes that it is likely that at least a threshold or i
i perhaps a corresponding zero equivalent point with beneficial l
risk decrements (horsesis) exists at lower doses.
i A notable example of the latter was a 10-year study by Johns Hopkins University of U.S. shipyard workers which, we were told, i
showed lower mortality, no increase in malignancies among workers exposed to radiation when compared to those who were not exposed, i
and no
. worker effect."
This study may be particularly i
signifi the invacigators sought to find evidence to l
support the"IJPF model.
Another study, of Canadian women patients 1
in tuberculosis sanitariums who underwent repeated fluoroscopy to monitor response to therapy, is used frequently to show the validity of the LNT model, but examination of data at lower doses shows significant beneficial effects.
The 1994 report of the i
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4 United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR)'has an extensive appendix detailing cellular repair mechanisms (called " adaptive response mechanisms") that could contribute to an explanation of a threshold, or, if such cellular responses were stimulated by low doses of radiation, to an explanation of beneficial effects.
In contrast, some of the public comments received by the Joint ACRS/ACNW Subcommittee suggested that the LNT model underestimates the harmful effects of low doses of radiation.
Also an NCRP Report, " Principles and Application of Collective Dose in Radiation Protection," issued as late as November 1995, and discussed with the Joint Subcommittee at its March 26, 1996 meeting, finds that "...from the point of view of the scientific bases of collective doses for radiation protection purposes, it is prudent to assume the effect per unit dose in the low-dose region following single acute exposures or low-dose fractions is a linear response."
In the face of conflicting views, the general belief of the national and international committees dealing with the matter has been that using the LNT model for regulatory purposes is a safe and conservative approach, and if there is error, it should be on the side of enhanced protection.
HoWover, if there is a health benefit at low doses, euehthis logic is cle:rly sistchen and centinuing th: current policies v uld ple : th: 00;;i0:10n in the
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- iti:n 20 F v ting this i:.cfit f::
- rring M Even if there is no health benefit, there are significant societal costs associated with this conservatism that could be avoided or reduced if a threshold level could be established below which no harm occurs.
The basic principle of risk-informed regulation is to prevent a situation where scarce resources are misspent to avoid negligible risks, while significant risks remain unattenuated for want of resources to deal with them.
Owing to the potentially significant costs of the present conservatism, we conclude that a reexamination of the regulatory model is appropriate.
It is obvious that agreement on
- ::icntific:11j 5:::f g y a,c ;r t.. -. dose-response model is made more difficult by the differing voices on this subject within the scientific community and those outside of this community, including regulators, policy makers, and members of the public. The'M ask M now is t: p::vid: an, impartial review of Mii the data and their quality in the face of the extensive applicat the LNT model in regulations and scientific opinion.
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w psy g r @ e NRC ch uld create an independent body to examine and critically evaluate all the current scientific evidence on the relationship between low dose and health effects with special emphasis on the experimental conditions and
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6 practices and the quality control exercised.
To ensure independence, the expertise of the participants in this review should include it;;rtial information scientists who are experienced a
'xpert in assessing the quality and treatment of data and expera..antal results.
Suen emphasis is designed to overcome any bias of dose-response experts, many of whom are strongly committed to their traditional positions.
This approach has the advantage of being able to reach out to experts and institutions with little or no prior position on this issue.
If, instead, the Commission prefers to support only the limited NCRP evaluation of the LNT assumptions, we recommend that the need for special attention be conveyed to the NCRP.
Such attention should include (a) ;;;ig :::t Of 12; rti:1 GEBEEliWesE t @ ttEF M Eff @, M ]scjantists t: th:
tudy n:t :nly Ott$$M ttiahphose who are " recognized experts" with a reputation built on the LNT model, (b) n dditi:n:1 :::p n:nt b cdd:d te th:
- tudy
- th:t :n 1 ; rti:1 sii? sis. ihi._tf6. H...il_iirf?..tlEBT.d_E_t_F_S_E-.T.GV entity with expertise in statistics or information science, litt!
n67[?f g,g n such as the National Institute of Standards and Technology (NIST), vill ::::=in: th: :::: d t:
as we1 {sijthe NCRP study committee, and (c) : r:g:::t t: th: "C""
t: :::t :::uredly includ: in its re"iew consideration of essentially all studies related to the LNT.
The Committees are unanimous in their opinion that the goal of
7 these studies should be to ground regulatory actions on good science, supported by evidence and as independent as possible of extraneous factors.
The Committees believe this topic to be of very great importance and plan to continue their analysis and review of information.
i Advisory Committee on Reactor Safeguards Advisory Committee on Nuclear Waste O
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05/18/98 A4: 27 FAI 5058210345
@ 002 To:
u.:=m From: Dana A. Powers
Subject:
HEALTH EFFECTS OF LOW-LEVELS OF IONIZING RADIATION Many thanks for the conference phone call on Friday and the revisions proposed by Shack and Kress to the draA letter on low-levels ofionizing radiation. Both have clarified much about the intention of the draft letter for me. I regret that I have to be such a ' pain' on t' his matter which is apparently far more transparent to other members of the Joint Subcommitteejthad it is to me.
The revised letter does not really address my original points that:
- radiation damage is more complicated than a simple dose-response relationship,
- if we ate to recommend in this area, our recomm*aMon should addness the broad range ofissues at stake rather than focusing on one nanow controversial topic, and
- it is unhkely that findings of unilateral exammations could be translated into revisions of the existing regulations.
l But, I accept the idea at least in principle that a piecemeal approach to the subject may be i appropriate. I feel, however, that the current draft letter does not accurately state the ' oints and p
recommendations that the Joint Subcommittee wants ACRS and ACNW to endorse. I.'et me make some specific comments about the letter including editorial comments and perhaps my concems will become apparent:
- paw 1: With regard to the last sentence in this paragraph, I do not knoiw that the Commission.weats to review and analyze the issue at all. In fact, I think it emerges toward the end of the leemr thatsuch a review and analysis is the actual recommendation that is being,made.
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- paragraph 3: In the last sentence of this paragraph the issues at hand are related to the emphasis on risk informed regulation. We should remember that in adopting a stance involving risk information the Commission did not abandon the concept of defense-in-depth. Their suppor:
of risk-based regulation is not especially strong as reflected by the " informed" term. In areas of great uncertamty such as the effects oflow -level dose response relationships defense in-depth may be a more useful guiding principle than risk. It is, in any case, not obvious to me that the Commission must use its resources to address the issue. Cannot an applicant propose rulemakmg and defend a position seeking relief from burdens of the linear hypothesis?
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05/18/96 14:37 F.d 5058310345 2003
- paragraph 4; line 6: ".... independent and special technical investigation...."
The letter does not indicate what the study is to be independent of. It would appear from te
'etter as now wrttten that the NCRP study is to do exactly what is requested. I now know that it is this study and those who will conduct it that the letter objects to. The reasons for such objections are not ever stated. Similarly, later in the paragraph a call is made for impartial review. The letter does not say that it is believed that the proposed study by NCRP will not provide such an impartial review. I now know that this is in fact what is believed. The letter does not sate or defend this view, so a reader may well think that the planned NCRP study is adequate.
- paragraph 5; line 3: I thmk this phrase should be reworded. Such an obviously biased phrase really detracts from a letter demanding an impartial exammation of a subject.
....any study to contribute to the testing of the model." I thmk what is meant here is
..results of any study being used to test the :nodel."
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- paragraph 6: Do you really mean that no healthy worker effect was detected in the study? If so, I would thmk it a very dubious study indeed. Perhaps what is meant is that the investigators were able to correct for the healthy worker effect.
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- paragraph 6 -last sentence: This sounds remarkably like Lamarckian biologyJ l
-paragraph 7: Why isn't the quote the last word on the subject? I prestigious group of experts has examined the data and hypotheses and published a conclusion it can deferui. I know the authors of the letter don't thmk a full exammation of the available data was condbeted-in an unbiased manner. But, the letter does not say this nor does it say why the experts areibelieved to be such bad guys. This leads me to thmk the authors just don't like the conclusion and they want to stack the supreme court with inexperienced people until they can get a vote that g9es their way.
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i The logic may not be correct but the conclusion may not be w
- paragraph 8: last sentence on page 4 l
arguent here and you don't present a basis for conclusion. Is it going to be cost-effhetive to go the route you plan? I think the proposed study is a waste of money because it can't res11t in the change of re@ona. I know the regulations are a pain in the neck to follow, but I dotnot know tnat they are especially expensive to follow, nor do I Know that implementing changes with the heavy costs of=*daing will be cheap. Ought we have something akin to a regulatory analysis to support our position?
- paragraph 8 on page 5:
Again, I call your attention to the fact that risk is not the only or even the most important basis for regulation. The current approach can be defended on the basis of defense in-depth just as many other regulatory positions are defended.
- paragraph 8 last line on page 5 I believe this is the real recommendation - re examme the regulatory model.
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