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HEHORANDUM FOR:
Carlyle Michelson, Director.
b Office for Analysis and Evaluatio3' of Operational Data Harold L. Ornstein l
111RU:
Office for Analysis and Evaluation of Operational Data i
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FROM:
- John' Pellet '
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J Office for Analysis and Evaluation of Operational Data' 4
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StBJECT:
THI-1 RES.T RT -- REACTOR WATER LEVEL MON.ITORING I attended a meetin'g on the ab'ove subject on August 10.19,81 betwee'n GPUN Attached is a'. stlehdance l'ist from 'that mee' ting. The purpose of and NRC.
n the ~ meeting was to dYscuss a G. PUN draft letter. proposing a program'toward u
res616 tion of the v'esiel don'it' ring wquirements for THI-1 'res' tart.' Also o
attached to this memo are the above draft letter and the broad highlights of the meeting.
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John Pellet Office for Analysis and Evaluation of Operational Data Attachments :
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ATTENDANCd LIST NRC GPUN Harley Silver, NRR
- 4.Ed Wallace, Licensing Rick Jacobs, NRR' Bob Keaton, Systems Engineer Leo Rubenstein, NRR Dave Slear, Project Engin5ering John Stolz, NRR.
i Ernie.Rossi, NRR Larry Phillips, NRR Lenny.01shan, NRR James Shea, NRR
- i John Pellet, AE0D ~
Dom Dilanni, NRR-9
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C MEETING HIGHL'IGHTS--
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GPUN initiated a general discussio of the, letter by stating that they desired to get away from an "adysrsary' relationship yith NRC.o,n this issue and move toward a meeting of minds.
GPUN is 'not refusing'to add a level monitor but' rather wishes to have a firm understanding of how to use one prior to attempting to install one.
GPUN reiterated that the present ICC qvent guidelines are adequate for identified eve'nt's and 't'h'ey felt NRC concubed with this posi' tion.
- However,
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GPUN now understands that level monitoring may be of some use for unidentified events-where specific gu'idelines are not written.
GPUN is in the process of 7,-
discussing with the various users (CE, W, B&W, and EG&G)'.of level monitoring the
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uses of the various. water level instrumentation systems to detect water level, inventory, etc.
GPUN noted 'that the proposed program might conclude that no level monitoring was required buk they recognized potential uses and the staff desiresi
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and. intends for the program t'o select a vendor (noting the upper leve). GPUN management uncertainty on this. issue). f.The earliest probable installa' tion o(such a'iystem is the first refue' ling outage'after-restart (November,1982.given current schedule).
NRC's response was generall'y in the area of scheduling and timing.. NRC is-very h'esitant about slipping the dates (Rubenstein). Also,a"howto'u.se" effort'[
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was regarded as being very late and it was felt that GPUN should be beyond the currG point by'now.
The following comments or suggested modifications were offered on t.he GPUN draft letter:
(1) the NRC staff witness referred at the top of page 2 was Ross I
(2) The last four lines of the ' Activities" section stating that none of the current systems meet all criteria in NUREG-0737 was challenged by staff as
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incorrect and its deletion suggested (Phillips).
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The staff rejected the position.(second parag'raph of' page 2) that if level
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information ~was~not r'equ] red: o pEeclude ICC there was no need to install level instrumentation'(Phillips).
(4)
The possible uses described (third paragrapli of page'3) are the types of
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applications intended by the staff, and (5)
'GPUN should reexamine NUREG 0737 section II F 2 requirements of documentation espscially with respect to restart.
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100 Interpace Parkway.
Parsippany. New Jersey 07054 201 263-6500
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TELEX 13&482
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Writer's Direct Dial Nurnber:
_ August 1981 LTL 208 office of Nuclear Reactor Regulation
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Attn:
John F. Stolz, Cliief Operating Reactors Branch'No. 4 U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Sir:
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Three Mile Island Nuclear Station, Unit 1 (TMI-1)
Operating License No. DPR-50 Docket No. 50-2S9 Inadequate Core Cooling (II.F.2)-
NUREG'0737, Sectioh II.F.2 requires an evaluation ~of additional instru-mentation which might be used to detVc't the esistence of or approach to inadequate core cooling.
It also requires that the evaluation include reactor water level indication.. In response'to this requir'enen't', GPUN
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has been conducting an evaluation of such instrumentation to determine its usefulness-and practicality.
Our evaluation has included both in-house activities and participation in Owners Group activities.
The purpose of this letteris to summarize briefly these activities to out-line our planned program'and to identify to you certain.significant
- concerns which have arisen.
Activities We believe we have bee'n' focusing our ef. forts on a long tierm problem that requires very ca*refully considered judgments.
As discussed before the,
Atomic Safety and Licensing Board (ASLB) hearing on January 21. and 22, 1981 an'd documentation of prefiled testimony.of September 15,1980, GPUN '
, has been actively < engaged in the issue of inadequate. core cooling.instru __.._..,
mentation ir.cluding the p6rsuit of uses and the evaluation of'instrumenta-t-ion for measurement of water level. On March 19 and 20,.1981 inadequate cooling instrumentation was,further discussed by representatives of.NRC through cross-examination before the ASLB.
In Amendment 21 to the TMI-l Restart Report dated October 3, 1980, GPUN provided an additional evalua.
tion (by BW) concerning inadequate core cooling.
Finally, in meetings before the Advisory Committee on Reactor Safeguards (ACRS) on November 29 and December.4, 1980 and June 25 and July 10, 1981, GPUN provided addi-tional updating of, status of inadequate core cooling including water level.
We have attempted to understand the potential benefits of im-proved information against the additional complexity and risk associated e
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-2 with'new instrumentation systems in process piping and in the control We have already achieved a signific'aht"short term improvement room.
in this THI-2 Lesson Learned item through the use of additional and modified instrumentation and.. procedures that have been verified by detailed analysis by both our staff, B&W, and the NRC staff. This is also,supporteid by the ACRS Chairman's letters of December 12, 1980, June 9,1981 and July *l,1981 on this subject. Thus, our efforts support a deliberate process necessary Int this stage to assure s C
proper decision.
This delibertate process follows the normal engineer-
- ing method of development of functional criteria, identification of al~ternatiives, and selection of the preferred system prior to deta'iled,
engineering, procurement and installation.
This approach is the same as that supported by an NRC staff witness appearin.on this subj ect,
(see TMI-l ASLB Tr. 15956:15959).
One major.. thrust of.our evaluations has been an attedpt to understand
- the basic criteria for the additional information. We used as a starting point the criteria given in NUREG 0737. We found, however, as 3
discus. sed below, that these must be supplemented in order to arrive at a definitive set of criteria which could be used as,a. basis for existing or additional instrument selection. To this end, we' participated in.the evaluations.
The intent has been to determine which events the addi-tional instruments *151ght be used to detect, confirm or diagnose the existence or approach to.an ICC condition, toTdetermine which portion
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of the operating crew (e.g'.,
control panel operators, shif t supervisors, STA, etc.) would use the information, and to define what actions would be gaken or avoided based on the information.
In parallel with the development of criteria ve have also undertaken an evaluation of,available or proposed instrument's Mich might be ' utilized.
l We have partiicipated in the B&W Owner's Group evaluation as well as per-l
' forming our own in-house evaluation.
In add,ition, bec,ause of the con-I tinuing snanswered questions,- fe have recently: initiated an independent review by an outside consultant, Dr. Vijay Dhir of UCLA,.to define the advantages and disadvantages of existing and proposed systems and to consider whethdr additional, alternative, new approaches. exist which warrant examination. We have furthermore agreed to consult in a proposed program expansion by Penn. State University to continue' development of neutron detectors as a method of measuring reactor vessel water level.
..To date, our evaluation has con.luded -none of the systems currently
'.. "under development mee't' al'1 t[he NRC criteria for detection systems as listed in NUREG 0737.
Additionally, combi 6ations of instrumentation also do not appear to meet established NRC criteria as written.
Concerns The status of our evaluations to date was presented to the IMI-l Sub-Committee of the Advisory Committee on Reactor Safeguards (ACRS) at
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their meeting 'on June 25 and 26,1981.
At that time, we pointe'd out that certain key i'ssu'es rd' hrding th,e use of I'he su.ggested additional g
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instruments remain unsettled..
Our major concern is how filieet the specific requirement of NUREG 0737 that instrumentation should " provide.an unambiguous, easy to interpret, indication of inadequate core cooling (ICC)".
We use the term ICC to refer to those core conditions at which she limits' of 10 CFR 50.46
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would' be exceeded.
It thus represents a'non-mechanistic condition beyond the design basis. Its significance in the present operating pro-i cedures is that if such conditions are being approached (as indicated by the core. thermocouple readings), the operator is directed to take extraordinary measures in order to improve core cooling.
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We do not yet understand how water level could be used for. an analo'gous purpose.
The water level and its rate of change with time vary enor-mously fof'different size leaks and leak locations.
The attached figure 1, for example, sh' ws the calculated water level for different size o
small breaks.
For large breaks the level drops even more quickly and risults in. temporary uncovery of the core.
For all of these leak sizes and locations, however, the emergency core cooling systems will function
~ to ensure that ICC does not occur. We hive found no method by which water level information -during a real accident could be interpreted to
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indicate that the emergency core cooling systems were not.. functioning'.
as intended and/or that inadequate core cooling was being approached.
~ We have scheduled meetings with each of the PWR vendors and plan to
-discuss this mat,t,er with them.
As we discussed during our recent presentation to the Advisory' Committee on Reactor Safeguards, we have identified other possib,le.uses for va,ter level or related information. One possible dse would be to determine whether venting the hot legs was necessary'or desirable, and to guide any such venting operations.__Another possible. use for. example, would be in conjunction with the existing saturation meters to determine whether HPI flow could be reduced or t'erminated. We vould appreciate your guidance as to whether these types of applications are consistent with the criteria.as defined.in NURIG 0737 requirement for detection of ICC.
Program
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As exhibited in figure'2 of the GPU Nuclear Program for' resolution of the Inadequate Core Cooling Instrumentation / Water Level,(Item II.F.2) consists of a further evaluation of the three major areas:
The uses of the leading contenders (CE,( ),'B&W and EG&G)' vater 1.
level instrumentation systems to detect water level, inventory, etc.
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The adequacy of presently or soon to be available instrumenta-tion (Reactor Vessel Differential Pressures, Heated Thermocouples, and R C Hot Leg J.~evel)' proposed by the NSSS Vend, ors (Westinghouse, Combustion Engineering and Babcock and Wilcox).
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The new ideas being developed throughout the industry (Penn State University - Neutron Monitoring and a study by Dr. Vijay Dhir on ICC - Water Level Instruments).
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The" evaluation period will include meetings and discus ~sions with vendors and consultants during the month of August to' develop an integrated summary leading to a technical recommendation on inadequate core cooling instrumentation including evaluation uf wi'ter level during. the month of October.
By November a submittal to NRC concerning our technical recem-mendation will be made.
Conclusion
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GPUN is continuing'its evaluation of possible ins'trumentation 'in accord.
ance with the requirements of; NUREG 0737'.*~ Furthermore, GPUN believes
...that the progran. delineated above represents reasonable progress, is respo'nsive to the ACRS, and is capable,of leadi_ng towards resolution of, this issue with,the, staff.
Sincerely, e
j H. D'. Hukill Director,TM.I-i i
Enclosures l
cc:
H. Denton
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B. H. Grier
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L. Barrett D.--DiIanni H. Silver ',
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