ML22230A207
| ML22230A207 | |
| Person / Time | |
|---|---|
| Issue date: | 05/25/1978 |
| From: | NRC/OCM |
| To: | |
| References | |
| Tran-M780525 | |
| Download: ML22230A207 (1) | |
Text
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ORIGINAL TO SECRETARIAT RECORDS NUClEAR REGULATORY COMMISSION IN f HE MATTER OF:
BRIEFING ON NEUTRON RADIATION EXPOSURES Place -
WASHINGTON, D. C.
Date -
MAY 25, 1978 ACE
- FEDERAL REPORTERS, I?-iC.
Official Reporters 444 North Capitol Street Washington, D.C. 20001 NATIONWIDE COVERAGl:
- DAILY Pages 1 -
30 Telephone:
(202) 3.J.7-3700
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25 BEFORE:
PRESENT:
UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION PUBLIC MEETING BRIEFING ON NUETRON RADIATION EXPOSURES Room 1130 1717 H Street, N.W.
Washington, D. c.
Thursday, 25 May 1978 1
The Commission met, pursuant to notice, at 3:05 p.m.
DR. JOSEPH M. HENDRIE, Chairman PETER A. BRADFORD, Commissioner RICHARDT. KENNEDY, Commissioner VICTOR GILINSKY, Commissioner Samuel Chilk, Secretary L. Barrett S. Block H. Denton.*,_
L. Gossick*
M. Grossman A. Kenneke R. Vollmer G. Zimmer
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P R O C E E D I N G S (3:05 p.m.)
CHAIRMAN HENDRIE:
I would like to talk about the
~riefing on neutron radiation exposures.
Lee, go ahead.
MR. GOSSICK:
Mr. Vollmer, as the agenda shows, we have another briefing here.
CHAIRMAN HENDRIE:
A distinguished panel.
.MR. BLOCK:
My objective is to brief the Commission on the status of neutron dose symmetry with *respect.to exposure at nuclear power reactors during reactor operations.
Neutrons are present in reactor containment.
We have regulations that require that radiation surveys be made prior to entry into radiation areas to prevent excessive radiation exposure.
Our regulations also require that occupational exposures be recorded for each individual exposure.
Now, these regulations are supported by regulatory guides that show how monitoring is to be performed.
With respect to neutron monitoring, reg guides 8.4 and 8.14 provide the technical guidance on neutron personnel monitoring.
Additionally, in our ~AR review by the NRR staff for I I
CP and OL applications and in spec.ti on by the Off ice of Inspectioh I
and Enforcement for operating reactor licensees, audits of applicants and licensees are respectively made to assure
3 sp2 compliance with these regulations and consistency with the 2 recommendations of the regulatory guides.
3 I would first like to give a brief discussion on 4 personnel dose symmetry so that the Commission will be aware of 5 the technical problems associated with this type of monitoring.
6 Could I have the first viewgraph, please.
7 (Slide.)
8 The first one shows four systems that are recommended 9 from regulatory guide 8.14, and I would like to go through each l O one of those individually.
11 The first is the calculated neutron dose equiy,alent 12 based on measurement of neutron dose equivalent and stay-time.
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I 13 For this technique a rem meter instrument-is used to measure the i 14 This instrument has been designed!
I neutron dose equivalent rate.
I 15 to measure the neutron rem dose rates independent of the spectraJJ 16 distribution of the neutrons.
.As will be shown later, this is a 17 very important feature of this kind of survey meter.
18 This dose rate, when multiplied by the time of 19 exposure, will give the rem dase to the individual.
20 The second recommended technique is the calculated 21 neutron dose equivalent based on the neutron to gamma dose 22 ratios.
23 By this technique, neutron and gamma dose rates are 24 determined in the occupied areas of containment using*a rem Ace-Federal Reporters, Inc.
25 meter as previously described and, again, a survey meter.
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neutron-to-gamma ratio is then established.
Since all occupational workers were gamma dosimeters, the dose readout from this dosimeter is multiplied by the end 4
gamma ratio to provide the neutron dose.
5 CHAIRMAN HENDRIE:
That is sort of a tricky space and 6
time averaging proposition, isn't it?
7 8
MR. BLOCK:
Exactly.
CHAIRMAN.HENDRIE:
That ratio will vary all over the 9
place as you come out f rorn the C"*ore.
10 11 MR. BLOCK:
That is true, sir.
CHAIRMAN HENDRIE:
Is there a fashion which reflects 12 how long people are in regions of various ratios?
13 COMMISSIONER KENNEDY:
Is this a uniform distribution?
14 That is, the ratio will be roughlyc.the-,.,same at eight feet out 15 from the core no matter where on the periphery?
16 MR. BLOCK:
What you'..a:re saying is almost true.
We 17 find that, foriinstance, in containment during the surveys that 18 have been made for neutron straining, the ratio seems to be 19 fairly consistent.
That is for St. Lucie, as an example, it was 20 about a factor of seven, and for Farley.it was a little bit less 21 than that.
The neutrons were hiiJher than the gamma doses.
The 22 factor of seven was a neutron-to-gamma.
In Farley, the gamma 23 was higher than the neutrons, but the ratio seemed to be pretty 24 consistent.
One can g~t a good handle on the neutron dose if Ace-Federal Reporters, Inc.
25 one knows the gamma dose by using this ratio.
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It has been used at Lawrence Livermore laboratories, 2 as well.
It is pretty well known.
3 OMMISSIONER GOLINSKY:
Wouldn't it vary from reactor 4 to reactor?
5 MR. BLOCK:
It might vary from reactor to reactor.
6 There is some consistency in the ratio within the area of the 7 measurernent:tblock.
The various types of shielding ~-- in1.1.1some 8 cases, water bags, sand, or concrete blocks -- makes it vary.
9 That will depend on the particular --
10 CHAIRMAN HENDRIE:
Why does the ratio -- I'm surprised.
11 You say the ratio seems to be relatively constant over --
12 13 MR. BLOCK:
This is within containment, of.;course.
CHAIRMAN HENDRIE:
Once you get away from the primary 14 reactor, the shielding arc;mnd the reactor vessel, so that you 15 are.seeing a gamma field which was primarily activation product, 16 primary piping, plated out and so on,
- I,wouJ.d-c:t.hink that the 17 neutron over a general gamma dose would drop down toward zero.
18 MR. BLOCK:
We are talking about the ratios that have 19 been established based(1on neutron
- streaming from the gap between 20 the reactor pressure vessel and the primary shield.
I will 21 describe that in a little while.
22 MR.
GRIMES:
It is on the operating floor, so it is 23 a scatter from this stream-out through the annulus around the 24 vessel.
Ace-Federal Reporters, Inc.
25 MR. BLOCK:
In research reactors it would be a little
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bit different, but the situation we find t-0day in containment, it seems to be fairly consistent.
The third technique used for monitoring is the albedo neutron dosimeter.
.I.boring.
Two f.eatures need to be noted for this type of moni-The first is that this dosimeter is sensitive to neu-trons over the entire energy spectrum.
to a dose of one millirem.
It has sensitivity down Secondly, theddosimeter overestimates the neutron dose unless corrections are made in accordance to the-neutron spectrum that the individual is exposed to, and the neutron source used in the calib~ati&n~
These dosimeters are rarely used in the nuclear power industry methods.
used?
since licensees probably prefer the other three At present albedo --
COMMISSIONER BRADFORD:
The dosimeters are rarely prefer either the badges or the first two?
MR. BLOCK:
The first or the fourth.
Generally, they aren't being used at DOE facilities, and each contractor has his own dosimeter.
I have one here that I would like to pass to you so you can get a look at what they look like.
It is scotch-taped because it was a little difficult to get apart.
I will pass it, and you can see it.
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Inside there are two TLD chips.
This particular 2
dosimeter has been designed for gamma monitoring.
It can be 3
converted into an albedo by adding two more lithium flouride 4
chips.
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9 10 11 12 Now, the final personnel dosimeter recommended by reg guide 8.14 is NTA f iim or the neutron f ilm._badge.
Tfuis dosimeter can only be used under the following conditions: that fading of the signal due to humidity must be controlled; that the dose contribution foL,neutrons with -.
energies below.7 MEV be small -- that is, this dosimeter is not sensitive to neutrons of energies less than.7 MEV; and that a large area of the film must be scanned by a *microscope so that 13 good statistica,l 1.data can be achieved.
14 15 16 I also have some film similar to NTA film, although NTA film looks more like dental X-ray film than it does what I am going to present you, but I thought you might want to look at 17 these.
I 18 19 As mentioned earlier, during reactor operations, neutrons are present in containment.
The next viewgraph shows the 20 source of these neutrons.
21 (Slide.)
22 This is a simplified geometrical model of neutrons 23 streaming in PWRs.
24 Ace-Federal Reporters, Inc.
Now, as I just mentioned, the RPV or the reactor pressure vessel, and the primary shield are the confinement or 25
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confine the cavity where the neutrons are streaming.
Yoµ can 2
see the pathway in which they stream into containment.
3 At present we are not sure of the fraction of the 4
spectrum where energy is less than.7 MEV., but since this is in 5
the coptairunent area, entry is.. controlled by personnel whe-n the 6 reactor is at power.
7 During initial startup comprehensive neutron measure-8 ments are made to evaluate the effectiveness of existing shield-9 ing.
Some licensees are not installing shielding over the*
10 annula gap to reduce the neutron exposures in reactor contain-11 ment.
You can see the one-foot water bag piacement that several 12 reactors are using to cut the radiation levels down.
13 The staff has been reviewing submittals proposed for 14 the s'hielding and evaluating its effectiveness for several 15 reactors.
16 COMMISSIONER BRADFORD:
They began putting 17 recently putting in these water bags?
18 19 20 MR. BLOCK:
Yes.
Within the last year or two.
COMMISSIONER BRADFORD:
Why wasn't it done before?
MR. BLOCK:
I guess the problem was such that they 21 probably used administrative controls and found that that was 22 not an effective way of reducing the neutron explosions that --
23 COMMISSIONER BRADFORD:
Limiting the --
24 MR. BLOCK:
Yes.
I am going to go through that in Ace-Federal Reporters, Inc.
25 one minute.
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9 A recent telephone survey of aful regional offices with respect to entry into containment brought forth the follow-ing information.
month.
Entry is usually made about two to three times a Generally, teams of two to four people make the entry, with one of these people being a house physics technician with a rem meter so he can determine wheretthe dose rates are and keep people out of trouble at the higher areas.
The time in containment runs from five to 60 minutes.
Neutron surveys are normally made prior to anybody entering the area or for dosimetric techniques are used with the NTA film, used in about 30 to 40 percent of the react.ors.
And doses *generally have been running about 10 millirem per person per entry.
Individual annual doses for~those that make the entries normally run from 100 to 500 millirem per year.
From the above we estimate that neutron occupation exposures contributes less than 1 percent of the total annual occupational exposure burden at a plant.
They don't provide at present a very large occupational burden.
That is a man rem.
COMMISSIONER BRADFORD:
Out of the people who worked for the plant?
MR. BLOCK:
Yes.
COMMISSIONER BRADFORD:
It is higher for those going into containment?
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25 10 MR. BLOCK:
Compared to all that work at the plant, that's right.
I think the average plant now brings in the order of 500 man rem per year, and we estimate less than five man rem per neutrons per year.
COMMISSIONER BRADFORD:
What percentage of the total plant personn~l go into containment?
MR. BLOCK.:
I would say -- I have tried to find out that data, and I think of the 30 some odd thousand people, maybe 400, go into containment to make these kinds of measurements.
Is.Barbara Brooks here?
I believe she gave me that information last week.
CHAIRMAN,HENDRIE:
They make the measurements --
MR. BLOCK:
To make the routine adjustments and inspections.
COMMISSIONER KENNEDY:
There are how many thousand?
MR. BLOCK:
22,000.
MR. BARRETT:
We had 22.
That would have been 4-to 500 with neutron exposure.
30,000?
MR. BLOCK:
There aren't that many people --
COMMISSIONER BRADFORD:
That is spread across the MR. BLOCK:
The one percent is spread across the 500 man rem per plants.
COMMISSIONER BRADFORD:
That is spread across the 30,000.
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MR. BLOCK:
If you want to do the ari thmatic that way,j 2 it would be.
3 COMMISSIONER BRADFORD:
So that the relevant figure 4 which is -- it would be the percentage of those people actually 5 exposed to it would be much higher.
6 MR. BLOCK:
I think you can say that the 500 man rem 7 per plant would have to be multiplied by, say, 68 operating 8 reactors, in that order of magnitude.
And then the five man rem i 9
10 11 12 would also be multiplied by -- I don't think all of the reactors have this problem, but I am just basing that one percent on an individual r-eactor where, if we assume that the average reactor is providing 500 man rem gamma dose, the neutron dose would be 13 on the order of less than five man rem.
14 MR. GRIMES:
I think it is much less than one per-.
15 cent, but assuming that it_ was one percent for the 30,000 people 16 then it would be less than 10 percent for the 500, if you 17 figured it that way -- it would be a little more than that.
18 COMMISSIONER BRADFORD:
I don't know how to do the 19 mathematics, but that doesn't leap out at me from the ratio of 20 500 for 30,000.
21 22 people.
23 24 MR. BLOCK:
The 500 is man rem and the 30,000 are I haven't done that arithmatic.
CHAIRMAN HENDRIE:
I don't think that you can calcu-I Ace-Federal Reporters, Inc.
25 late it from those ratios.
It is certainly true that those
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12 plant personnel who get the neutron exposures will also be high-exposure individuals among the population of the 30,000.
MR.*GRIMES:
- That's right.
I think, typically, a few hundred millirem compared to several rem for the people that go.inoo containment.
MR. DENTON:
What was the highest individual neutron 7 exposure that you have?
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25 MR. VOLLMER:
I think of those that get exposed to neutrons, about 90 percent of their exposure is gamma and about 10 percent is neutron.
Of those who do get exposed.
COMMISSIONER BRADFORD:
At one particular plant?
MR. VOLLMER:
I think that is a general average.
MR. BLOC1<:*
On the average.-
Now, there are some individuals who get higher than 10 percent, but there aren't too many of those
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5 13 In reference to the points just mentined, the I&E staff, in addition to their normal licensing audits, are reviewing -- will review the neutron dbsimeter procedures at individual reactors during their normaily-scheduled inspections to determine.whether licens.ees are performing 6
neutron measurements in accord to the reg guides.
7 More detailed information will be available on the 8
status of neutron occupational exposure, including 9
occupational.man-rem, when I&E concludes their studies.
10 Hopefully, Commissioner Bradford Mill have better data in the
.I 1 future on that.
12 NRR has also asked research to fund the program to 13 collect information on the neutron energy spectral 14 distribution and the capability of existing systems to monitor 15 these distributions accurately.
This will be a confirmatory 16 study to determine whether or not our present guidance gives 17 adequatB safety margins.
If the program shows that a major 18 fraction of dose contribution is from energies less than.7 19 Mev, MEA film may not be a monitoring device we.will continue 20 to recommend to nuclear reactor licensees.
21 The research would also allow evaluation of the 22 degree of overestimation of neutron exposures whenever albedo 23 dosimeters are worn by the licensees who are using or who plan 24 to use these devices.
25 The next view graph indicates the proposed research
627.05.2 mte 14 program.
2 (Slide.)
3 This is a synopsis of the program which is much more 4
detailed in scope.
But what we plan on doing is having the 5
contractor measure the neutral spectral distribution inside 6
and outside the reactor containment.
From the spectral 7
distribution he will calculate the dose equivalent rate, which 8
I put "theoretical" in quotes.
ActuaJ.ly,.we call that in 9
quotes J*true.*11 10 He will then measure the neutron dose equivalent
,1 I 12 13 rates with the survey meters or the rem meters, and compare the theoretical or true dose rate with the measured dose equivalent to show the effectiveness of the survey meters.
14 After these operations are performed 1 he wilJ. compare the four 15 neutron personnel dosimetric techniques which I have just 16 outlined with the theoretical and the survey meter values, to 17 determine the degree of accuracy of each system.
And Leslie 18 will provide conclusions with respect to each Qf the 19 measurement techniquese 20 COMMISSIONER KENNEDY:
Assuming calculations were 21 actual values.
22 23 MR. BLOCK:
Yes, we will assume that the theoretical numbers are the true, quote, "true", values.
24 At present, a contractor has not been selected to 25 perform this research.
But we have -- we will have our
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3 15 research people --- they are very active in trying to get this resolved.
One final technical point that should be brought to 4
the CommissionJs attention.
Dr. Harry RQsse of Columbia 5
University has proposed, based on his review of Hiroshima and 6
Nagasaki data, among other data, that the biological 7
effectiveness of neutrons should be increased.
He suggested 8
an increase of a factor of ten.
. 11 12 13 14 spectrum?
15 COMMISSIONER GILINSKY:
A factor of ten?
MR. BLOCK:
Yes
- CHAIRMAN HENDRIE:
Across the board?
MR. BLOCK:
Yes.
CHAIRMAN HENDRIE:
A.11 the,way up and down the
- t MR. BLOCK:
That*'s what I under:.stand.
16 If this increase is accepted by the scientific 17 community, including the NRC, it will mean that assigned doses 18 to personnel exposed to neutrons would be greater than those 19 presently calculated or measured using our present values for 20 biological effectivenass of what we now call quality factor.
21 Other scientists, however, feel that Dr. Rosse-'s 22 factor of ten should be reduced to a factor of about two to 23 four, based on risk factors.
Still others feel that no 24 changes 25 COMMISSIONER KENNEDY.:
What was that?
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16 MR. BLOCK:
Leukemia.
Still others feel that no change should be made from 3
the present value.
The National Council on Radiation 4
Protection, the NCRP and the ICRP, both are reviewing Rosse~s 5
position.
Nhile the NRC is developing a staff paper on the 6
subject, it will be some time before a final decision is made.
7 However, even if a change is made in the biological 8
effectiveness of neutrons, it would still not be a very 9
important 'factor, as compared to the total occupational 10 exposure to all workers from gamma radiation.
JI CHAIRMAN HENDRIE:
It would, however, bring up the 12 exposed, that smaller exposed population who routinely enter, 13 14 15 16 17 18 19 20 21 22 23 24 25 do maintenance work and spotchecks at containment operations.
It would take the equivalent up to the gamma and the beta exposure.
MR. BLOCK:
Yes.
CHAIRMAN HENDRIE:
Yes.
That would mean that it would be large enough so that it would, in effect, cut in half their burnout timeso MR. BLOCK:
Would reduce their occupancy time, that is exactly true.
There would have to be some strong regulatory measures taken if this is consummated.
CHAIRMAN HENDRIE:
There are some incentives to improve the shielding a little bit.
You have got enough neutrons bouncing around up there so you are getting
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YouJre getting a mild activation of all of the structural materials.
The whole place begins to --
MR. GRIMES:
If the stay-time method is used, it is applied in a conservative manner.
the highest dose rate in the area.
In other words, you take It makes it more worthwhile to get accurate measurements of the actual CHAIRMAN HENDRIE:
And to knock down the high spots.
MR. GRIMES:
Yes.
MR. BLOCK:
Absolutely.
The bottom line of. this presentation with respect to the Washington Post column can be summed up as follows:
that those licensees using NTA film are receiving a fraction 14 of their dose from neutrons of energies less than.7 Mev, and 15 that this fraction is not being recorded on their film.
So 16 that there is some underestimation of dose to workers using 17 NTA film.
18 We expect that our research effort wiil resolve the 19 magnitude of this fraction based on the spectrum measurement.
20 Nevertheless, since the neutron exposures recorded from other 21 dosimetric methods have shown the neutrons to be small in 22 23 24 comparison to the gamma exposures, we do feel this is not a significant problem
- Since the effectiveness of the albedo dosimeters, 25 which is the alternative to NTA film, is also strongly
627.05.6 mte 2
3 18 dependent on the energy spectrum, but provides overestimation of the neutron dose, the research program will indicate the correction factor that need be applied tn provide a correct 4
occupational neutron dose.
5 This issue was discussed with the ACRS on April 7th 6
of.this year, and we have received no recommendations beyond 7
those taken by the staff.
8 That concludes my formal presentation.
9 10 JI 12 13 CHAIRMAN HENDRIE:
Vic?
COMMISSIONER GILINSKY:
No.
COMMISSIONER BRADFORD:
r'm trying to get some idea of the history of this problem.
You said licensEes have been installing additional protections against radJation over the 14 last year or two?
15 MR. BLOCK:
Yes, we have been pu_tting in these water 16 bags that I showed you in the second view graph.
17 COMMISSIONER BRADFORD:
What trigger.ed that?
18 MR. BLOCK.:
The thing that triggered that, for 19 instance, in St. Lucy they.were getting dose rates as high as 20 65 rem per hour, and that was intolerable.
They had to reduce 21 the dose rates to --
22 23 24 25 MR.BARREIT:
What happened in the last fe.w years has been the changes in design in the cavity out in here.
- Really, our designed plants, let~s say, of ten years ago, they had smaller gaps between the reactor vessel and the wall.
As
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5 19 sub-compartment pressure analyses,were being done on LOCAs, the concern came up that there might be high pressures that would blow these walls out.
So this gap was opened up in newer designed plants.
Calvert Cliffs is one of the first ones where they opened this up to several feet instead of 6
several inches.
7 This ailowed streaming to start coming out.
That's 8
when people started backfitting the shields.
9 COMMISSIONER BRADFORD:
The particular matter that 10 triggered the article was in part a memorandum that suggested
..I I 12 13 that this information should be passed on to the licensing boards.
Is that being done?
MR. BLOCK:
Except for the briefing of the ACRS, I 14 am not too sure what measures have been taken.
15 MR. VClLLMER:
A memorandum was sent to the project I 6 management.
I don-'t know if they have forward eg it yet --
17 MR. DANTON:
It has been recommended that it be 18 forwarded to the boards.
I don-'t know the exact status of 19 whether it has arriveD there or not.
20 MR. GROSSMAN:
I don-'t remember if I have seen the 21 recommendation or not.
I wiil check.
22 C0MMMISSI0NER GILINSKY:
Who recommended it?
23 24 25 MR. GRIMES:
NRR recommended to ELD that appropriate board be notified.
COMMISSIONER GILINSKY:
They were notified?
627.05.8 mte 2
3 20 MR. DANTON:
Yes.
COMMISSIONER GILINSKY:
It is held up in ELD?
MR. GRIMES:
The paper is someplace between the 4
originator and the board.
5 CHAIRMAN HENDRIE:
You want to defend yourself?
6 MR. GROSSMAN:
I just don-'t know whether it is with 7
us or, if so, how long.
8 CHAIRMAN HENDRIE.:
When in doubt, always say it is 9
in transit.
IO COMMISSIONER KENNEDY:
The paper we are talking JI about, the memo of January 25th, 1978?
12 MR. GRIMES.:
I believe so.
Do you have the 13 14 15 16 17 chronology.?
MR. BLOCK:
Yes..
Would you show Slide 7, View Graph 7?
We have a chronology of events coming up.
I think it started on January the 25th with the Zimmer memo and --
COMMISSIONER KENNEDY.:
There were two memoes on the 18 25th.
One went to Bob Minogue, the other to Roger Boyd.
19 MR. BLOCK:
The Roger Boyd is the one that is 20 mentioned there.
I think then on March the 6th the memo was 21 written from Vollmer to Higgenbotham from I&E, requesting 22 23 I&E.reviewing the licensing. monitoring program to confirm the statements made in the Zimmer memo.
24 June Allen then sent a letter to Roger Boyd 25 regarding the Zimmer memo, too, and asked several questions to
627.05.9 mte 21 2
the staff.
The Levine research was signed on April the 3rd.
However, that particular letter started through the staff in 3
mid-February, and it took until April 3rd to get it to 4
research.
5 On April 7th, I briefed the ACRS on this data.
On 6
April the 14th, Ho.ward Rosenberg called me on th.e Zimmer memo 7
and we spent considerable time on the telephone during the 8
rest of that month and into May, going through questions he 9
raised and some comments he made in his column that were 10 shocking to me.
But as I pointed out to him, he had the 11 freedom of the press and there wasnJt too much that I could do 12 with respect to what he was going to say, except suggest that 13 they were incorrect.
14 (Slide.)
15 On May the 9th, he called me after the column had 16 been released on May the 8th and asked me NRCJs reactions, 17 which I suggested to him were not -
at least my personal 18 reaction was not very good.
19 On May the 12th, we sent June Allen the response to 20 her question.
21 COMMISSIONER KENNEDY:
What did that response say?
22 MR. BLOCK:
I have a copy of it.
23 MR. GRIMES!
It essentially transmitted the internal 24 memoranda which had requested that inspection and enforcement 25 do the review, and memo to research requesting and giving the
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.I 1 12 13 14 15 16 17 18 19 20 21 22 23 24 25 22 scope of the research required; and answered several specific questi~ns, most of the material that we have given to you in this briefing.
MR. DANTON:
I recall that this item was a category two, in our original response to Congressman Dingell.
And category two is in the process of -
the boards are being notified.
Let me get back and see when the boards were notified.
That was some time back.
We just donJt have people here today who can remember the exact date.
CHAIRMAN HENDRIE:
I am not sure what the boards are going to do with it.
I assume they would be following it with a staff comment rather rapidly as to its place and meaning in the scheme of.things, ;which I donJt find to be very significant, but -
COMMISSIONER BRADFORD:
What is the relevant occupational exposure standard?
I gather that the reg guide will tell you how to meet the regulation, but -
MR. DANTON:
Part 20.
MR. GRIMESJ Three rem per quarter combined neutron gamma exposure.
There is also a limitation, an integrated limitation on age, which averages out about five rem per year.
COMMISSIONER BRADFORD:
Where does "as low as reasonably achievable" fit into that?
MR. GRIMES:
In our review of the licenseeJs operating license applications, we review a program to assure
627.05. 11 mte 2
23 that they have a system within their facilities to review operations that they are going to perform within the 3
containment or anyplace else for maintenance, to try to 4
maintain exposures as low as reasonably achievable.
5 COMMISSIONER BRADFORD:
Then those that are ongoing 6
now are in fact looking for the kind of devices that were 7
shown on that other slide?
8 MR. GRIMES:
We are looking for -- I would say yes, 9
and in the cases where that is not provided, there would have JO to be perhaps a cost-benefit analysis done to justify that the exposures saved would not it would not be beneficial to 12 spend the money, which is not great, to install the shield.
13 14 COMMISSIONER BRADFORD:
What have you been saying in the last few months, to the extent that there have been 15 reviews going on in most plants?
16 17 18 19 20 21 22 23 24 25 MR. GRIMES:
New plants have the shields, yes.
62]. 06. 1 gsh 2
3 24 CHAIRMAN HENDRIE:
I can remember Stone and Webster long ago;about the balance off between the opening up compartment so they didn't pressurize much in case the 4
pipe ble.w against the -- inevitably you get some operational 5
exposure problems that derive from that opening.
6 It was probably recognized as a general way of --
- 7 COMMISSIONER BRADFORD:
In Zimmer-'s memo, he says 8
that it has come to his personal attention that personnel 9
at commercial power reactors are achieving some neutron 10 exposure which heretofore has been unknown.
J l 12 13 Doe~ he mean all reactors or some reactors?
It is sort of a cryptic phrase.
MR~ GRIMES:
We tnok it to mean *all reactors.
I 14 believe Mr. Zimmer is in the audience., if he.wishes to speak 15 up and contribute.
He ~as given our briefing materials 16 also.
I think he is in general agreement.
17 MR. ZIMMER*:
What I meant by that was that the 18 reactor that I was informed of, they.were using NTA film 19 and it was suspected that the neutron exposure spectrum 20 was below the 7.00 KV that is usually able to be read with 21 the NTA.
22 Therefore, the neutron exposure.was not known 23 because of the use of NTA film.
24 COMMISSIONER BRADFORD:
What*percentage of the 25 reactors, in fact, use the film?
62.7.06.2 gsh 2
25 MR. BLOCK:
30 to 40 percent.
CHAIRMAN BRADFORD:*
Very few use the dosimeters?
3 The rest are about equaily divided?
4 MR. BLOCK*:
The stay time and the end gamma ratio 5
are th.e preferred methods.
The albedos, we are going to 6
hope that the albedo systems will be used by ail because 7
passive dosimeters are much better than making measurements 8
and then timing them, in what Commissioner Kennedy thought 9
was an unknown time and a varying field.
JO However, the albedo dos.imeters at the present time
.I 1 are about three to four times more expensive than NTA film.
12 and there is perhaps a co.st benefit that we are going to 13 try to resolve.
It Miil be resolved if we find in our 14 research that 90 percent of the do~es received by energies are 15 less than 0.7 MEV-16 That being the case, we would have to disallow the 17 use of NTA film.
And, hopefwly, at that point, the albedo 18 dosimete.r system would be used upon.more licens.e.e*s.
19 MR. GRIMES.:
Probably with a different calibration 20 technique than presently used that tends to overestimate 21 by perhaps a factor of 50 what the neutron dose is.
22 23 24 COMMISSIONER KENNEDY.:
The pre sent est_imate MR~ BLOCK:
That is what we hope to find in our research.
But Millstone did a study using threshold 25 detectors and found that a very large fraction of their
627.06.3 gsh 2
26 sp.ectrum based on their methods.was of energies less than O. 7 MEY.
3 It is inevitable that a great deal of the neutrons 4
are going to be of energies less than O. 7 MEY because of the 5
scattering.
You have a. shield that is sca.ttering where the 6
neutrons are being scattered from -
they scatter as they 7
go from the annulus and in containment.
8 So there has to be a fraction of that energy.
9 CHAIRMAN HENDRIE.:
There is an awful lot of hydrogen JO bearing material around in that concrete.
J 1 MR. GRIMES.:
Of course this is balanced some.what 12 by the fact that the higher energy neutrons are much more 13 14 15 16 effective in delivering dose than the lower energy neutrons.
Even though ther.e may be *more neutrons belo.w O. 7, the effective dose, itJs not necessarily much larger.
MR. BLOCK:
NTA is not completely bad.
Oak Ridge 17 uses it.
They use alb.edos in para11.el with it, because, you 18 see, the NTA film at least can teil you the fraction qf 19 neutrons that are greater than say a half MEY.
20 If you are very careful in your analysis of an 21 NTA film, you can.read energies down to o.ne-half an MEY.
22 So, they can look at the fraction of their doses that are 23 being contributed by neutrons of a half MEY closer, because 24 the albedo gives you everything and you don 1 t know which 25 fraction is of low or high energies.
627.06.4 gsh 2
27 That is a nice trick that they use to isolate the fraction due to higher energies.
3 Now some of the licensees are using the stay-time 4
in parallel with the NTA film. Even those these 30 to 40 5
percent may be using NTA.film, they perhaps aren-'t all basing 6
the dose on that particular device.
They ari just using that 7
as perhaps a back-up to look at the higher energies.
8 COMMISSIONER BRADFORD:
Dr. Zimmer, let me ask you 9
10 11 12 13 what would you take away from your sentence in your memo to Mr. Board?
I understand from another source that neutron fields of 25 KV Reutrons, superimposed on the one over E neutron-'s spectrum existed at PWR,which is known about.
14 What is the significance of that in terms of what 15 we have been talking about?
16 OR. ZIMMER:
Genera.lly, it is accepted or expected --
17 COMMISSIONER BRADFORD:
Is that the Millstone study 18 you were just referring to, or is that another?
19 MR. BLOCK:
That is Farley.
20 DR. ZIMMER:
Normally, they expect there one over 21 E spectrum for distribution of neutrons from a reactor.
22 What had been found in that case from Lawrence 23 Livermore was that there was a 25 KV neutron spectrum 24 superimposed on the one over E spectrum.
25 So that what I understood from Dale Hankins was it
627.06.5 gsh 28 was a substantial 25 KV spectrum which is not monitored 2
.with NTA film.;
Whereas, with the one over E spectrum, a major 3
portion of your 4
CHAIRMAN HENDRIE:
That is also sornething you 5
expect around this kind of shielding because there is a 6
25 kilovolt window in the iron neutron cross-section.
7 So you expect to see a little blip.
8 MR. BLOCK:
Yes.
I had a copy of their data and 9
you can see that little blip.
10 J 1 12 at Farley CHAIRMAN HENDRIE:
Yes.
COMMISSIONER BRADFORD:
Would that be a unique 13 CHAIRMAN HENDRIE:
No.
It depends on whether the
';;j,-
14 shield designer has paid any attention to it. It is no 15 great shakes to avoid having pathways out of thi reactor 16 cavity which are pretty much iron.
You can take things around 17 corners and make sure that you have got good chunks of 18 concrete, hydrogen-bearing material that intercept all such 19 path.ways.
20 It complicates shield design a little bit. Sometimes.
21 you get to the point where you are balancing between mechanical 22 simplicity and strength and the seismic resistance into 23 24 fancier shapes for shielding.
Furthermore, those calculations get pretty tricky.
25 Until you get it build and run it, you~d never know whether
627.06.6 gsh -
,~
2 3
4 5
6 7
8 9
JO J l 12 13 14 15 1 6 17 18 19 20
.2 I 22 23 24 25 29 you have covered everything.
That~s why a foot of water put in later on, or if you leave a place where you can get a tank with a foot of water in it, that is a nice thing to have.
Anything further?
COMMISSIONER BRADFORD:
I.would like to know the answer to that question about the licBnsing boards.
MR. GRIMES:
I will supply that.
CHAIRMAN HENDRIE:
Thank you very much.
(Whereupon, at 4:45 p.m., the hearing was adjourned.)
- e.
30 DISCLAIMER This is-an unofficial transcript of a meeting of the United St~tes Nuclear Regulatory Commission held on MAY 25, 1978 in the Commission's offices at 1717 H Street, N. l*i., \\*lashington, D. c.
The meeting \\'-las open to public attendance and observation.
This transcript has not been revie\\*Jed, corrected, or edited, and it may contain inaccuracies.
The transcript is intended solely for general informational purposes.
As provided by 10 CFR 9.103, it is not part of the formal or infom.al
- record of decision of the matters discussed.
Expressions of opinion in this transcript do not necessarily reflect final de.terminations or beliefs.
No pleading or other paper may be filed with tr1e Commission in any proceeding as the result of or _addressed td any statement or arg:zment contained herein, except as the Commission may authorize.