ML20056B720
| ML20056B720 | |
| Person / Time | |
|---|---|
| Site: | Monticello  |
| Issue date: | 12/20/1971 |
| From: | Mcelroy D NORTHERN STATES POWER CO. |
| To: | Morris P US ATOMIC ENERGY COMMISSION (AEC) |
| References | |
| NUDOCS 9102080427 | |
| Download: ML20056B720 (14) | |
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Dr. Peter A.
Morris, Director Division of Reactor Licensing United States Atomic Energy Commission i
Washington, D.C.
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Dear Dr. Morris:
Attached is a copy of a letter which was hand delivered on Friday, December 17, 1971, to Mr. Merritt having to do with our release of low-level radioactive water from our Monticello l
Plant.
I thought you would be interested in this and I have no objection to your giving the attached letter distribution within your organization, if you feel it beneficial.
I would like to take this opportunity to wish you and your i
staff a Merry Christmas and a Happy New Year.
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McElroy W
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Executive Vice President U
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December 17. 1971 Regulatory g
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& Ft? w aI9'3 0-71 Dear Mr Merritt
--c Following is a description of the general sequence of events that led to the discharge of waste water from the radioactive portions of the Monticello reactor.
It is necessarily somewhat simplified in an effort to be communi-cative about' the essential facts. Obviously, I must rely on highly techni-cal information furnished me by others, but to the best of my information and belief, it is accurate.
The specific questions raised by the PCA staff are listed as an attachment.
These questions were received orally over the phone and I hope they have 4
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been accurately stated.
In essence, they ask the primary questions of:
- 1) What causes this particular discharge?
- 2) What has been done an'd what can be done to prevent or minimize the activity levels of this particular discharge?
- 3) What are the details (activity level, time of discharge.
etc) of this particular discharge?
Not asked, but of equal importance, is the question whether future discharges will occur.
An attempt will be made to answer both the stated and unstated i
questions.
The plant was shut down on November 12 to perform maintenance on several pieces of equipment.
It was shut down at this time in anticipation of the coming'therefore important to have the capacity of the Monticello Pla winter season when electric demands upon the NSP system are high and it is This plant supplies approximately 155 of the total generating capacity of the NSP system.
It is theref ore important to have this plant fully operational in time for the winter season.
As previously discussed with the PCA staff, one of those maintenance functions required removal of baffles from the " torus." This is the large doughnut-shaped container at the base of the reactor.
Please see the attached schematic diagram.
The function of the torus is to hold a very large quanti ty 'of water--
5581
N C' THERN ST.'As ES POWER C TMPANY 4
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lir Grant 'J Merritt rage 2 December 17, 1971
- i approximately 500,000 gallons--as a heat sink to condense steam into water.
The torus water, because of its contact with reactor steam, picks up over a period of time small amounts of radioactivity.
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4, To work on the baffles in this large container first required that the l
water contained thcrein be removed.
it is very clean water--water that has been extensively treated to remove impurities such as minerals, chemicals, etc. As such, this water has economical value to the operation of the total reactor system and is carefully husbanded.
If this high quality water is-wasted by discharge into the river or any other means, it eventually must i
be replaced with additional water which must be subjected to the same exten-sive and expensive cleanup process.
The point is that from the narrow para-l matcr of economics alone, quite apart from regulatory requirement or questions I
of public health, it is in the best interest of economical plant operation to preserve, c.onserve, use and reuse such water to the greatest extent possible.
As a general operating principle, such high quality water is discharged from i
the plant only as a matter of last resort when there are no feasible alternatives.
With this general statement in mind, examine the current situation.
The torus l
must be emptied. Approximately 500,000 gallons of water must be dealt with, l
1 water with an activity level so low it approximates public health standards i
for drinking water as it comes directly f rom the torus. When the plant was shut down on November 12, virtually every available bit of storage capacity was used to hold this water as it was pumped from the torus.
The large portion i
(approximately 250,000 gallons) was and is yet stored in the steam condenser J
itself.
At risk of seeming to be overly simplistic, the steam condenser is a large shell which ordinarily contains steam from the reactor while the steam.
i is being cooled f rom vapor to water form.
Because the plant was not operating, i
the condenser could be used f or this purpose.
The 250,000' gallons weigh i
s 1,750,000 pounds. The water stored in the condenser in no way comes in contact t
with river water. That still left approximately 250,000 gallons to be stored.
i Using other tants, in-plant storage was found for all except 42,000 gallons.
Of this amount,10,000 gallons eventually were discharged to the river on f riday, November 19.
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There is on the f ourth floor of the reactor building a large pool of water--
somewhat like a swimming pool in configuration,- though deeper. This pool will be used -in the future -(probably next April) to store spent fuel elements under water af ter they have been removed f rom the reactor for examination or while ~
awaiting shipment to a reprocessing f acility.
Since the plant is yet operating on its initial fuel loading, no spent elements had ever been in the fuel pool.
The water and pool therefore were not contaminated by fuel storage._ In an ef fort to respond to staff concern about the November 19 discharge and, in fact, to reduce discharge activity levels to the louest possible level, approx-imately 32,000 gallons of the fuel pool water was pumped from this_ pool into the sample tank and thence to the river over a four-day period, Ncvember 21-24.
Data on the activity levels of these releases were widely publicized at that time. Fuel pool levels were restored with the balance of torus water.
The a
pool was and is now essentially full.
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NORTHERN STATES POWER '
'OM PANY Mr Grant J Merritt page 3 December 17, 1971 which involved an extraordinarily large volume of wate storage space currently available witoin the plant was used.
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It then became necessary to remove the baffles, i e, to put men inside the toru s.
This necessarily resulted in waste water with a low icvel o men performing this flushing operation, as well as those later removing the The baffles and doing other maintenance work in hot areas, wear clothing which must be laundered in the plant facilities.
gathered for analysis in the plant laboratory. Constant samplesof water are ment elsewhere in the plant was opened, even as mir.or as a single pipe o ing, waste water resulted.
The installation of certain sensing devices July 14, resulted in waste water. recommended by the AEC to prevent recurre tional waste' water carefully collected.All of these activities resulted in addi-cleanup systems to remove minerals (and with it, radioact up to reactor grade water su that it may Le stored for reuse.y) to bring it while more extensive during the shut-down period, is an ongoing function at Maintenance, all times.
large amounts of waste water.flohever, the present maintenance activities all prod to the maximun. cxtent tossible, lloweverAll of this water is being extensively treated to move the water through the c'.canup sy, stems.the sheer voluae makes it difficult plant storage space was utilized to store this additional water.Every possible bit of in was pumped into the fuel pool.
Some of it The condensate storage tanks were filled.
Storage space was used which cannot continue to be used once the plant is in operation.
of approximately 30,000 gallons.For example, there is a tank called a surge tan provide a place to store for limited times surges or pulses in the flow o water in the condensate system.
This is not uncommen.
has piping which serves essentially this same function. Every home water system is now full.
Even this surge tank
'used without regard to its design intent to store water duri the plant is shut doan.
The maintenance work currently underway must continue.
This work must be continued if the plant is to be retur Waste water is contin-To provide adequate "frectoard" (room for additional storage) in the plant and to provide storage capacity for the continuing transfer of water through purification systems, it is necessary to release two batches totaling approx-imately 15,000 gallons at the present time.
To make this release f rom ti.e stored water of the lowest activity levels, water was pumped days ago from
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NORTHERN STATES POWER C9MPANY Mr Grant J Merritt page 4 December 17, 1971 the fuel storage pool into a tank which is part of the floor drain system.
This tank connects via a pipini system with the discharge canal. San.ples l
were taken from this tank on December 13 for analysis. One set of samples was picked up by a staff member of the MilC on Decen.ber 13.
Another set was analyzed by the plant laboratory.
The results of both analyses have been in possession of the MilC/pCA since December 14.
They are in agrecarent and we presume there is no question about the numbers.
A ccpy of the itSP analysis is attached for refere'nce. Analysis was performed both for a gross beta-gamma count and for individual isotopic identification.
It is this water now in the sample tank consisting of approximately 10,000 gallons of the isotopic content and activity level stated in the analysis which we intended
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to release as the first of two discharges.
At this point in the narrative, and at risk of redundancy, several questions might be answered:
- 1) Does the water now in the sample tank have the lowest activity levels of any stored in the plant? Answer:
fio. Water in the fuel pool is constantly circulated through the cleanup system for that facility.
Thus, its activity level is lower than the hater in the sample tank by several orders of magnitude.
The obvious question is why not release this water rather than that which is now in the sample tank.
To release the fuel pool water obviously requires that it be transported via pipes from the pool to the sample tank for release to the river.
It is certain this very low-level water will pick up activity while being transported from the pool to the sample tank.
Unknown and undeterminable in advance is the question.of just how much activity will be picked up.
I am infenned that there is at least a charce the activity of fuel pool water will be hig.he_r than r
that now in the sample tank by the time it reaches the tank. Even if it is not higher, the best that can be expected is that it will 1
be virtually the same activity level as the t.ater now in the sample 1
i tank.
In the effort to te most responsive to your concern, we are going to transport the fuol pool water to the sample tank using pathways which will give ;ra greatest opportunity to preserve the present high quality of the fuel pool water.
It must be borne in mind that once this is done, and if higher activity levels result, it will not be possible to again exchange the water.
Every time the water is transported, activity.is added.
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NOP"YERN STATES POWER CC" 'PANY i
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page 5 4
t December 17, 1971
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- 2) Is there additional storage capacity in the plant to defer l ['t release?, Answer:
There is capacity to store additional water i
j but this capacity should not be used for two reasons: First, there must always be some room available in the event of unfere.-. [
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seen contingencies which require fast accessibility to storage.
l, How much room must t'e reserved is a matter of operating judgn.cnt t
which cannot be nego.tiated or delcgeted.
h'e attempt to operate the plant in all ways in a conservative fashion.
Even in the present condition, our cperating personnel feel that sound oper-ating prudence has been compromised.
This cannot continue.
Second, to continue to store the 15,000 gallons to be dis-charged is no solution as the discharge must eventually occur when 100% of storage capacity is reached.
That will be in a few days at the present rate of maintenance activities.
- 3) is there anything more that can be dcne to this water to reduce activity levels? Answer:
Probably not.
The only pos-sibility is to again recirculate the water through the deminer-alization f acilities.
lhe water has already been circulated through those facilities.
The demineralization facilities work on a principle much akin to a bater sof tener.
Resins take out the minerals and certain other chenical contamirants and thus reduce the activity.
The resins (like zeolite in a sof tener) becoae less and less efficient each time water passes through them.
The reduction in efficiency is exponential.
While the resins are periodically changed, in our judgment even changing the resins and recirculating the water again will have little further effect as virtually all impurities have l'een removed 1
already.
The laboratory analysis did or can previde supporting
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data.
Additionally, there is the probability previously dis-cussed (which can only be raised and not quantified) that by recirculating this water through the piping system te run it through the den.ircralizers may even, increase its activity level from activity picked up in the piping.
- 4) 'What is the effect of unavailability of the circulating water pumps? Answer:
If neither circulating water pump were available, controlled releases would be limited to that dilution which could be achieved with other available pumps such as the service water and makeup pumps.
The radwaste water that would accrue during pump maintenance period toeld, in all probability, have to be stored in tanlage provided for such contingencies.
There must be a prudent level of freebeard for such circumstances.
and operating practices hhich permit undue accun.ulation of rad-l l
waste water nust be avoided thrcugh proper controlled releases.
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NORTHERN STATES POWER COMPANY l
Fir Grant,J Merritt Page 6 Deccn.ber 17, 1971 l
We intend to use one of the two circulating punts to dilute the discharge.
We cannot use both pun'ps because l.
icing occurs at the intake structure which would ordinarily l
be prevented, when the plant is operating, by returning warmed water from the condenser through the intake. Use of one punp will provide a dilution flow of 139,000 gallons per minute.
The rate of release from the floor drain sample tank will be controlle'd to keep gross beta-gan,ma levels in the discharge caral well within one one-bundredth of present federal limits. The maximum possible release rate from the floor drain sample tant is 50 gallons per minute.
With a dilution flow of 139,00G gallons per minute, the gross beta-gamma levels in the discharce canal would be about two-tenths of one percent (0.21) of present federal limits.
We actually would plan. to release f rom the floor drain sample tant at a rate of about 30 gallons per mirute, which means that gross radicactivity levels in the discharge canal would be less than two-tenths of one percent of present federal limits.
- 5) What else can be done with this water to eliminate or l
reduce the volume at the present time? Will the problem continue? Answer:
Since there are no additional storage facilities at the plant-at the present time not rescrved
^
for freeboard, there are only two other possibilities. One is to bring on the site temporary storage such as tank trucks.
As you know, use of such tank trucks would violate existing PCA regulations, assumir.g you consider such low level wastes as " pollutants." The other possibility is off-site shirn'ent and disposal by a licensed waste contractor.
Solidification facilities were not designed to accommodate this additional burden.
However, all of these methods raise the more basic question of how such low level wastes should be handled in the futurc.
'It is in'portant to understand that the plant was designed and licensed to dispose of high activity wastes by solidification and low activity wastes by dilution release under controlled and regulated specification.
When the reclainied volume of
- ^
water exceeds the requirements for reuse, there is no means within the system to handle the water other than by release.
4-The problem will be an ongoing one for the life of the L
plant. Clothing will continue to be washed, the laboratories will continue to make analyses, piped gland seal leakage from l
many pumps and joints will continue.
While the plant is l
exceptionally tight in this respect, and all this water is l
carefully collected and treated in systems designed for this.
purpose, contamination from oils, grease, chemicals, etc, is L
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i NORTJiERN STATES POWER COMPANY s
,e Mr Grant J Merritt Page 7 -
December 17, 1971 inevitable. This lpw activity water (this must be emphasized)
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is extensively treated to reclaim as much as possibic.
How-ever, not all this water can be reclaimed for reuse and the basic problem will continue.
Even censtructing additional storage will not solve the problem of waste water which can-not be reused.
Even for the reusable water, measures now being utilized are temporary, stop-gap efforts which do not solve the more fundamental policy question of what disposal method is appro-priate.
Even using fuel pool water is a temporary solution which happens to solve the problem at this point in plant life.
Once spent fuel has been stored in the pool (next spring some time) that reservoir can no longer be used as a source of super low activity water. Thus both the present situation and in-evitable future conditions require that some fundamental, policy guidelines be developed.
We will continue for the time being to supply information of the nature de-scribed in Mr Larkin's letter of Dicember 14.
The fundamental problem we f ace is that there are no practicable workable guidelines with the MPCA l
on which anyone can rely.
l In a letter dated April 2 to Dr Howard Andersen, Robert H Engels, president of NSP, stated that:
" Based on the best advice and analysis that could be secured
..., we are willing to assert that the plant will meet the gross beta-gamma limits for all liquid releases now set out in the Minnesota permit."
i Mr Engels also reaffirmed hSp's commitment to mect the goals and objectives
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of the MPCA when the Monticello pern.it was formulated.
In a letter dated April 3, you asked for airplification of our understanding of the plant's ability to meet specific isotopic lir.its contained in the MPCA permit.
I responded in a letter dated April 5,1971. My statement that the specific limits would be met on each of the isotepes in liquid l
j discharges, except for tritium, was based en our sincere hope and best I
knowledge at that time.
It was an attempt to predict in precise detail the future operating conditions of a very complex system.
It must be remembered that the plant was still in the start-up and testing stages and had not yet gone into commercial operation.
Our experience since the Monticello plant went into concercial operation June 30,1971, has shown that it will be impossible for us to meet the specific limits on every isotope in our future liquid releases.
For example, 4
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NORTMERN OTATES POWER COMPANY Mr Gran't J Merritt Page 8 December 17, 1971 comparison of the limit for cesium-137 in federal regulations and the proposed MPCA pennit, shows that the PCA limit is 100 nillion times more restrictive than the limit under present federal regulations.
The pending discharge will i
not meet that more restrictive limit.
I presume additional deviations will occur in the future for other isotapes.
I have attached a table comparing the proposed MPCA isotopic concentrations with those in present federal regulations.
The proposed MPCA permit for Monticello says in Special Condition 15:
"It is emphasized ti'at public and environmental radiation protection practice is based upon a concept of very long term protection, rather than only inmediate or mon.cntary protection.
The generally accepted I.C.R.P. limits are designed to restrict radiation exposure, on a continuous basis and over a lifetime, to levels that will not pro-duce detectable or significant somatic or genetic herm? The annual average release rate limits contained in this Permit also refer to continuous lifetime radiation exposure, rather than to momentary levels, and are considerably niBre stringent than could be permitted j
according to the I.R.C.P. recommendations.
Hence, the slight transitory (E.G., daily) variations around these limits that are to be normally expected should not result in overexposure to radiation of any member of the public, and should therefore not be viewed as cause for great alarm or for hasty and unreasoned action."
It is our intent to keep releases from the Monticello Plant at the lowest possible icvels, and we will not exceed ore ene-hundredth of levels allowed under present federal reculations.
I reiterate that we will attempt to abide by the spirit of the MPCA guidelines for the plant but that there will be deviations f rom those guidelines.
We have taken e number of positive steps to rcach accord with your Agency, and he hope to continue in a spirit of cooperaticn.
The fuel pool water will be transferred to the sample tank.
I understand that a MHD staff member picked up a sample of the fuel pool water at 3:00 on Friday af teraoon.
Once the transfer is completed, your staff and 11HD staff will be notified of the availability of a sample.
I am informed you can expect a call sometime Saturday, probably Saturday morning. The release is scheduled to begin 11:00 Monday morning.
However, in no event will the release be sooner than 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> from the time you are notified a sample from the sample tank is available to you.
This is in accord with our previous 4
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Mr Grant J Merritt Page 9 Decerrber 17, 1971 discussions on procedure.
Should the time of discharge for any reason occur later than 11:00 Monday, you and the Mt.D t.ill be given at least two hours' notice of any such delay.
4 Very truly yours Roland W Ccnistock Director - Environmental Affairs
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- 1) A complete deceription of alternative ways of dealitU with the pro-;
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posed discharge other than in the river.
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2)
A discussion of efforts made to minimize activitics to the lovent' 9
possible level. For example, the extent to which this diccharge has been treated in the vaste vater decontamination cystem of the fuc1 pool.
j 3)
What is the present status of other in-plant water storage facili-ties and if any room is availabic, an explanation of why that capacity cannot now he utilized.
4)
If both of the circulating water pumps are not available, a discus-sion of the impact or cuch unavailability, on dilution rates and concen-tration factors of the diccharge.
5)
An explanation of why this additional build up of water occurred, i.e., what are its cources?
6)
Itecice specification of the time at which the discharge vould be made, the flow rate and the period of time over which the diccharge l
vould be conducted and the total tumiber of gallons to be di.scharged.
l 7)
A statement of policy on the impact of the company'c proposed activi-ties in relationchip to the commitments contained in R W Comstock's Ictter of April 5,1971.
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NSIs NORTHERN STATES POWER COMPANY M I N N E A f*C LI S. M I N N E S OTA-Eg d og v
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o December 28, 1971
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g JAN3 ;g7y g
DD uu Dr. Peter A Morris, Director g
Division of Reactor Licensing
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United States Atomic Energy Commission Washington, D C 20545 to g
Dear Dr. Morris:
MONTICELLO NUCLEAR GENERATING PLANT Docket No. 50-263 License No. DPR-22 Modifications to Main Steam Flow Element Throat Pressure Taps Summary Comments From the time of the initial rise to power of the Monticello Nuclear Gener-ating Plant, the pressure differentials measured across the Main Steam Line Flow Elements were lower than the design characteristics of the nozzle. The design of the nozzle was reviewed and the reason for the observed behavior identified. A design modification to the throat tap was proposed and tested.
The structural integrity of the modified flow element assembly has been ana-lyzed. This modification work has been completed on the Monticello nozzles during the present outage. A special test procedure during the forthcoming startup will verify the expected characteristics of the nozzle.
Discussion During the Monticello Startup Test Program, it was found that the pressure differentials across the Main Steam Line Flow Elements were approximately 40% of that expected from calculations. The response was repeatable, fol-lowing a basic flow-squared relationship. The problem appeared to be generic for that flow element design since all four Monticello verturi nozzles, as well as those in the Fukushima I, Tsuruga, and Nuclenor Plants gave a similar response. An investigation was immediately initiated among Northern States Power, General Electric, and Pennutit. It was theorized that a leakage path existed such that the full pressure differential from the upstream tap to the throat tap was not sensed by the flow switches. Tests performed by General Electric later confirmed this theory.
General Electric proposed a design modification of the nozzle to eliminate the leakage path problem. The original flow element was constructed with a l
piezometer ring around the circumference of the throat with eight f" holes used as pressure taps. The modification proposed to bore a one-inch hole from the point at which the instrument pressure tap entered the steam line 9102080424 711220 i
^2 CF ADOCK 05000263:
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- N HERN OTATEO POWER MPANY Dr. P A Morris December 28, 1971 into the nozzle throat; a tight-fitting sleeve would then be inserted so as to eliminate the effect of the leakage path. Tests were conducted using a nozzle similar to the Monticello design having the proposed modification.
The test results showed that the measured pressure differential agreed with the calculated value. Testing further revealed that the distance from the flow element to the nearest bend in the main steam line was sufficient to give accurate data from a single throat tap device. A stress analysis per-formed by General Electric has verified the structural integrity of the mod-ified nozzle assembly.
I On November 16, 1971, representatives from Northern States Power and General Electric met with Mr. Benaroya and Mr. Knuth of your organization. In accor-dance with the discussion at that meeting, work was initiated immediately to make the proposed modification. The installation procc-dure was reviewed and approved by the Operations Comittee on November 19, 1971. The work was done under Pemutit supervision with a qualified factory welder making the seal weld on the sleeve inserts. In addition, Quality Assurance Person.el from Northern States Power followed and documented the work very closely.
i On the ascent to i._.i power following the present outage, we will verify the i
flow nozzle responses in an orderly procedure to be reviewed and approved by j
the Operations Comittee. The outline of the procedure, as discussed below,
{
was also reviewed at the recent Safety Audit Comittee meeting. The set points of the "high steam flow differential pressure" switches which isolate
)
the reactor on high steam flow will initially be left at their present values.
(This differential pressure set point corresponded to 113% of rated steam flow prior to the modification and is expected to correspond to about 71% of rated steam flow with the modified nozzle.)
If data up to 60% of rated steam flow falls within the test acceptance criteria, the isolation set points will be set to the extrapolated value corresponding to 100% of rated steam flow.
If the data up to 80% of rated steam flow falls within the test acceptance criteria, the set points will be set at the extrapolated value corresponding to 140% of rated steam flow. If the data up to 100%
of rated steam flow falls within test acceptance criteria, the set points will be left at 140% of rated steam flow.
A detailed report from General Electric on the Main Steam Line Flow Element modifications udll be forwarded as soon as it becomes available. In addi-tion, we will notify your office of the results of special testing follow-ing our power ascent.
Yours very truly, h
L 0 Mayer, P.E.
Director of Nuclear Support Services LOYMlN/br l
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