ML19224A795
| ML19224A795 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 04/18/1979 |
| From: | Crocker L Office of Nuclear Reactor Regulation |
| To: | Boyd R Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19224A796 | List: |
| References | |
| NUDOCS 7905300381 | |
| Download: ML19224A795 (11) | |
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NUCLEAR REGULATORY COMMISSION
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%,f' b, h APR 181979 MEMORAND'JM FOR: Roger S. Boyd, Director, 0 vision of Project Management, NRR FRCM:
1.awrence P. Crocker, Technical Assistant to Director, DPM
SUBJECT:
SUMMARY
OF SPECIAL ACRS MEETING Enclosed is a brief sumary of the highlights of the special ACRS meeting held on April 16-17, 1979, to discuss the accident at Three Mile Island, Unit 2.
These are my views of the meeting and should not be taken as the official record. A verbatim transcript of the meeting is available and the ACRS will publish official minutes of the meeting.
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A Ff' b L. P. Crocker Technical Assistant to the Director Division of Project Management
Enclosure:
As stated cc: See next page 6
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Soecial ACRS Meetina Aoril 16-17,1979 A special ACRS meeting was held on April 16-17, 1979, to hear presentations about and discuss the accident at Three Mile Island Unit 2.
The agenda for April 16th included presentations by the staff, reports by Connittee members and consultants who had visited the site, and a presentation by Babcock & Wilcox. April 17th was spent largely in an open executive session and included a late afternoon meeting with the Commissioners. There was extensive media coverage of both days' sessions.
Acril 16 Staff Recorts Roger Mattson orchestrated the staff presentations and responded to many of the Committee questions during the day.
Steve Varga presented a preliminary view of the staff evaluation of the utility responses to IE Bulletins 79-05 and 79-05A. The evaluation was still in progress at the time of the meeting, but the staff expects to complete its review by April 20.
Preliminary examination indicates that the licensees understand the staff concerns.
Evaluation effort is being concentrated on those B&W plants that are operating (Rancho Seco; Oconee 1, 2 and 3; and Crystal R1ver). Three plants (AND-1, Davis Besse 1, and TMI-1) are currently shut down for other matters, and evaluation of responses for these plants is being deferred to the end of the evaluation process.
Bob Tedesco discussed with the Committee the activities of the Task Force he is heading which is evaluating the short term and long term actions to be taken in regards to feedwater transients in both B&W and othe pressurized water reactors.
Late in the day, Vic Benaroya presented a run down on the then current plant status and Carl Berlinger discussed the plans for long term cooldown.
Ccamittee Reoorts Mr. Etherington reported that he had spent about 21/2 days at the site. He was very impressed with the competence of both the staff and industry te&ms on site, but expre: sed concern at the ability to I SJ
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. place the plant in a natural circulation mode and keep it in that mode. He urged that all PWRs have precise instructions as to how to establish natural circulation and he stressed the importance of having some means to verify that natural circulation had been established. Dr. Caton noted that the plant might have difficulty going to natural circulation if the primary coolant is saturated.
Mr. Michelson (consultant) reconstructed the transient for the Committee based upon available strip charts and data points he had obtained.
Dr. Caton discussed the plans for cooldown, noting that several alternatives are available should natural circulation not work.
In his view, scmewhere between 30% and 45% of the zirconium in the core has been oxidized, with the damage occurring between 126 minutes and 176 minutes into the transient.
Mr. Ray noted that in his view, the on-site organization is very capable and that the support efforts by all parties have been out-standing. He reported that in his discussions with people at the site, he detected no indication of a casic lack of competence of the plant operators.
Mr. Etherington expressed concern that the operators had made no attempt early in the transient to fill the secondary side of the steam generators. However, Roger Mattson noted that the operators apparently felt that the situation was not out of hand until several hours into the transient.
Babcock & Wilcox Presentation Jchn MacMillan, Vice President of Babcock & Wilcox, discussed with the Committee the vendor's views on the accident, the actions the company has taken, and the implications for other B&W plants. A copy of his prepared remarks is attached. In summary, the company feels that there is nothing basically wrong with the system design, although there is additional information that should be furnished to the operators. He also noted the desirabi'ity of positive in-dication of power operated relief valve position, and an interlock to isolate certain containment penetrations on ECCS actuation rather than waiting for a high containment pressure signal.
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a 3-Acril 17 The Committee spent the day in open executive session discussing the factors involved in the TMI-2 accident and the icolications for both B&W plants and other PWRs. Mr. Etherington started the days session with an additional discussion of the problems involved with achieving natural circulation, noting that the heat sink has to be established at a sufficiently high level relative to the core to establish a driving head and that the system pressure has to be maintained higher than the saturation pressure to prevent void formation.
Individual members and consultants presented their recommendationt as to things needing attention by either the staff or the industry.
Much of the day was spent discussing these matters, as sunnarized below.
1.
Core Exit Thermoccuoles (0krent)
Much better use of the thermocouple information could be made if the system were geared to provide information directly to the operator, rather than, for example, as input to the plant computer. The core exit thermocouples should be used to provide operator information for all plcnts. Correct temperatures sFould be displayed or recordcd within the capability of the thennoccuples - not question marks above arbitrary cut off point.
There may oe an incentive to have excessive tenperature readings al a nned. Use of thermocouples could provide a means of partially satisfying previous Conmittee concerns regarding early indication of gross fuel failure. The instruments need not be safety grade and there is no need for the staff to embark on an immediate big program of getting thermocouples installed. The important thing is to use fully the instrumentation that is now available.
2.
Additional Instrumentation to Follow the Course of An Accident (Okrent)
Additional information for tne operators is necessary - not necessarily geared to Reg Guide 1.97.
Should be implenented on operating reactors immediately - staged implementation if necessa ry.
Unable to specify precisely what instrumentation is desired, but should concentrate on that instrumentation that will help an operator determine what is going on.
Not necessary to get all of Reg Guide 1.97 instrumentation at this time, but should have much of the 1.97 instruments plus additional.
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Reduction of Frecuency of Challenge to Protection Systems (0krent)
Staff and industry should examine actions that can be taken, particularly regarding support e' Jiplent (SUch as feedwater), to reduce the frequency of challenges to the protection systems.
Seiss pointed out that this should encompass a reduction of anticipated transients in general. Lipinski (consultant) pointed out that in connection with the feedwater failure challenge ra te, special attention should be given to the differences between the once-through steam generators and the U-tube steam generators since the former require an early reactor trip to avoid difficulty.
4.
Iodine Releases (Lavroski)
Staff should reexamine uses of iodine removal equipment and procedures.
Detecnine why we have been unable to prevent iodine ieleases at TMI-2 and what changes need to be made for im-provements in the future.
5.
RHR System (Lawroski)
Reluctance to use the RHR system has been noted.
Feels we should relook at RHR to detennine what changes need to be made so that system is usable under all plant conditions.
Specifically, there may be a need to qualify the system and perhaps to upgrade for higher pressures.
6.
Chenical Analysis Cacability (Lawreski)
Concern that lack of staff expertise (at least that immediately available) led to erroneous conclusion regarding quantitj of oxygen available in reactor vessel, which in turn was responsible for the exaggerated worries about possible :1ydrogen detonation.
7.
Consultant Lipinski furnished a list of equipment and matters that he recocmends as needed or highly desirable:
a.
Adequate instrumentation to follow the course of an accident.
b.
Reactor water level instrurentation.
c.
Containment water level instrumentation.
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Instrumentation to indicate the presence of natural cirtulation.
e.
Primary coolant status relative to saturation temperature.
f.
Use of core outlet thermocouples.
g.
Early scram on loss of heat sink.
h.
A secuence of events recorder (would record all pertinent information about plant status upon actuation by an out-of-spec variable).
- i. Reexamine reliability of heat sink. Are two stnam generators adequate?
- j. Remote operated vents on reactor vessel and at system high
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Direct position indication for power operated relief valve.
1.
Status indication in control room of operability of all emergency equipment, including. status of block valves, breakers, switches, etc., that could defeat safety system.
Could have interlocks on operation.
Reexamine control system failures that lead to safety system m.
challenges.
Should invoke sincie failure criteria on transient analyses.
n.
In addition to considering failure of equipment to actuate on dema 71, consider also the failure to stop on demand once ic has been actuated.
Should astablish performance reguirraents on contrei r.ystems o.
to assure that system failures (ar;d pro'.0ction sytt?n challenge.;) do not exceed an acceptable numLor.
(Canadians reportedly have such requirements. )
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. 8.
Remote San.olino Cacability (Lawroski)
We should relock at our requirements for sampling to assure that there is a capability of collecting samples under accident conditions as well as during normal plant operation.
9.
Emergency Ecuiceent (Lawroski)
We should look at the TMI-2 accident and determine what emergency equipment should be immediately available for use in future emergencies.
10.
Emergency Plannino (Lawroski)
A relook at emergency planning is in order in light of the lessons learned at TMI-2.
11.
Ooerator Training (Lawroski)
What emphasis is placed on operator training to assure that operators are aware of the importance of keeping the core covered? What parameters in particular are operators instructed to watch? Which of these are considcred to be the most important?
Mr. MacMillan was asked to respond to this for B&W.
The staff was asked to respond both _. TMI-2 in particular, but also for plants in general.
- 12. On-Line comeuter (Ray)
The need for an on-line computer to assist operators should be emphasized.
13.
Radiaticn Chronology (Shewron/0krent)
The staff was asked to provide to the Committee a chronology of the radiation readings during the TMI-2 event. The chrcnology should provide information as to what readings were taken, when the observations were made, where they were made. What is desired is a time history of radiation readings throughout the plant similar to the existing event sequence.
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- 14.
5, hared Facilities (Okrent)
Does the TMI-2 experience raise any questions regarding sites with shartd facilities? Would like to meet with the staff to discuss.
- 15. Contincency Plans (Okrent)
Questioned whether the Committee. should recommend initiation of studies of contingency plans.
(It is not clear just what Dr. Okrent has in mind).
16.
Isolation of Breaks (0krent)
Questionec problems in connection with isolation of breaks.
It is not : lear that under all conditions breaks should be isolated. This is a matter that should be discussed further with the 1:aff.
- 17. Simulation Cacability (Okrent)
Questioned whether the Committee should recommend that the NRC acquire its cwn capability for the simulation of anomalous transients.
- 18. Consultant Michelson brought up a nu.mber of items that he felt warranted Committee consideration:
a.
The need to know tenperatures around the primary loop to assure natural circulation.
b.
What should be done to account for single failures or un-wanted operator action while in the natural circulation mode?
c.
What should be done about very small breaks? Instrumentation may not be suitable to enable operator to follow small break transients. Analyses need to be done to cover full range of small break sizes and locations. Such analyses need not be highly sophisticated since progress of resulting transients is very slow moving. Without such analyses, it is not clear 168 086 em
Enclosure I
, whether isolation of a break is in the directicn of safety.
Procedures should be developed to tell the operator wnether or not to intervene in small break transients.
d.
Consideration should be given to the possibility of core dryout, followed by flooding with cold water. Potential for severe thermal shock to fuel as 'well as possible water hammer problems in primary system.
e.
In fluid systems, it is most difficult to monitor all variables necessary to assure proper system operability.
Such monitoring becenes increasingly difficult if carried to ancillary support systems.
For example, valve position indicators rapidly become larger than the valves they are monitoring in support systems. Such monitoring is very complex and, in Michelson's view, we will have to rely to a large extent on adninistrative procedures.
- 19. Containment Isolation (Fraley)
Recommended that the Ccamittee develop a position on containment isolation, to assure that non-essential penetrations are isolated at the proper times.
20.
Sumo Pumo Monitor (Fraley)
Recormended that the Cannittee develop a position regarding containment sump pump operation that would require monitoring and isolation when appropriate.
21.
Ecuipment Oualifications (Fraley)
Suggested that the Committee cause a relock at equipment that is not now qualified for accident environment.
It may be desirable to harden this equipment so that it will be operable following an accident.
This might include upgrading of the RHR system to higher pressure and capability to operate after accident.
Summa ry Following the discussion of the various topics brought up by the members and consultants, the Committee scribe, J. Jacobs, was requested to read a list of those matters that had been mentioned that required staff action. The listing provided by Jacobs is as follows:
168 087 "W=*
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1.
Analysis of PORV to deternine its capability to function under all corditions it is likely to encounter.
2.
Assure that small breaks are analyzed and procedures developed so that operators do not make the wrong con-clusions.
3.
Analysis of fission products from primary coolant of TMI-2.
4.
Doctrnentation regarding ratural circulation tests and ine stances where B&W plants have had to rely on natural circulation.
5.
Assure that operators are provided with adequate in-strunentation to recognize danger signals concerned with natural circulation, and procedures as to Scw to get plants into the natural circulation mode.
6.
?rovide additional informatien on radiation levels in TMI-2 containment.
7.
Evaluate the differences between once-through and U-tube steam generators with respect to loss of heat sink under transient conditions.
Does the steam generator design affect the plant capability for load-following?
8.
Assess the potential benefit of early scram upon loss of feedwater and turbine trip.
9.
Assess the level of operator training with regard to the necessity for keeping the core covered.
Emphasize training of TMI-2 operators in particular.
10.
Provide a chronology of radiation readings taken fran the plant during the transient.
There was considerable discussion as to whether the Committee should write an additional letter to the Commission as a result of this meeting.
It finally was decided that a letter should not be sent until the menbers have had a chance to reflect on the proposed i68 088 9
.- recommendations and until the absent members have had a chance to review. However, a draft of a letter was prepared, and this draft was read to the Commissioners during their meeting with the Committee on the afternoon of April 17. An approximate version of the contents of that draft letter is attached as Enclosure 2.
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