ML19257B424
| ML19257B424 | |
| Person / Time | |
|---|---|
| Site: | Crane  |
| Issue date: | 11/28/1979 |
| From: | Jay Collins NRC - TMI-2 OPERATIONS/SUPPORT TASK FORCE |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8001160182 | |
| Download: ML19257B424 (4) | |
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TMI r/f NRR r/f NOV 2 81979 CENTRAL FILE 4
- N NRC PDR JTCollins l
MEMORANDUM FOR: Harold R. Denton, Director, NRR t
FROM:
John T. Collins, Deputy Director, TMI Support I
SUBJECT:
TRIP REPORT - RESTRICTED HEETING OF OECD i
I On October 24-26, 1979, I attended a restricted specialist meeting "On the Behavior of Off-Gas and Ventilation Systens Under Accident Situations" at the Nucicar Research Center, Karlsruhe, Federal Republic of Germany.
The meeting was sponsored by the Cormittee on the Safety of Nuclear Instal-lations (CSNI) of the OECD Nuclear Energy Agency. The restricted meeting una attended by 40 participants from 11 countries and 2 international organizations. Enclosure 1 contains a list of the participants and is a copy of the formal agenda. Copies of the formal papers -
are available from the writer upon request. Although the meeting was fornally approved by CNSI in November 1978, it took on added significance as a result of the March 28 accidnat at Three Mile Island.
Specialist agree that off-gas and ventilation systems are an integral part of the radioactivity containment system of all nuclear facilities and that a good deal of experience exists with regard to their design, construction and ability fo fulfill their intended function under nomal operating conditions. However, specialist agree that there is a need to design these systems to operate as efficient containment barriers in case of accident situations where the conditions under which they have to perform may be widely different from routine operations and may also be affected by fire and explosions. In this regard, there is a recognition that infomation on the behavior of a11-gas and ventilation systems under accident' conditicas is relatively limited due to the small number of serious mishaps which have so far affected nuclear facilities and to the limited possibilities for measuring the relevant data.
The scope of the meeting was to exchange information and riews among spec-ialist on the behavior of off-gas and ventilation systems under accident conditions. Although such systems differ for nuclear power stations and fuel cycle facilities, all installations were covere'd, since the philosophy and means of protecting the off-gas and ventilation system against possible damage due to abnormal operating conditions are relatively similar. In view of the need to have extended free discussions on sensitive issues touching possibly proprietary information on industrial processes, partici-pation was limited to 40 specialist in order to derive the maximum benefit f766 274' 8 0 01160 /h
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i Harold 1. Denton, Director s.
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from the meeting. There was no detail record of the discussions, however, the conclusions and reco-andations were summarized by a small group com-posed of the Session Chairpersons and Scientific Secretarias. The summary I
i report was subsequently submitted to the Committee On The Safety of Nuclear Installations, OECD, at their meeting in Paris on November 8-9, 1979, for approval and implementation. The U.S. is represented on this committee by Saul Levine, Director, NRR.
The meeting centered around the following three topics:
1.
Identification of accident situations relevant to off-gas and venti-lation systmas. The participants agreed that the following parameters need to be considered in identification and description of accident situations: temperature, pressure transient, gas velocity, bumfrfity, concentration of inactive and radioactive aerosals, presence and generation of corrosive materials and radiation field.
Impact of accident situations on the behavior of off-gas and ventilation 2.
The effects of the parameters noted in 1 above need to be systems.
evaluated for off-gas and ventilation systems and components in use in various type of nuclear facilities. In view of thia, design and plant features are important to limit accident consequences and damage to such systems and components.
3.
Consideration of future R & D work, design and testing of off-gss and ventilation systems in order to minimize the impact of accident ditua-tions. is a copy of the su::ssary report prepared by the Steering Com-mittea for Nuclear Energy, which contain the major conclusions and recocanendations derived from the meeting. The salient points from this report are discussed below.
Most specialist agreed that greater emphasis should be placed on the design of an adequate containment system. This can be accomplished by location of equipment and components with a high potential for releases of radio-active material in structures designed to contain the accident. This would reduce the degree of reliance placed on the off-gas and ventilation systems to control such releases.
Most specialist agreed that plants can be designed to trap radioiddine adequately in accident situations. However, data are available which shows serious in-service deterioration of charcoal adsorbers. A prine example of this was observed at TMI where a significant fraction of the iodine which reached the charcoal bed passed through it.
As a result of this, the following items deserve additional considerations in research programs: a) ageing,imeathering, poisoning and desorption; b) alternative imprignants and adsorbants; and c) in-service test procedures.
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Harold 1. Denton, Director Most specialist agreed that increasing the residence time and bed depths can greatly improve the trapping capability of the charcoal adsotWar and could be implemented imediately. For example, over a year ago the German Reactor Safety Commission implemented regulations requiring that all charcoal adsortrers have a minimum bad depth of 20cm (8") as a result of studies conducted at the Karlsruha Nuclear Research Center. The Com-mission is currently considering a proposal to increase the bed depth to 50cm (20"). In light of our experience at THI, I believe that we shculd seriously consider similar requirements. However, at this time, I would not reconnend going to 20" bed depth, but I would support a position requiring no less than 8" bed depth or a residence time of no less than 1 minute.
Most of the specialist agreed that REPA filters will only parform ade-quately under a limited range of environmental parameter, which are unlikaly to be maintained under some accident conditions. For this. reason, it is necessary to either protect the HEPA filters from environmentaI conditions or devise alternative filters which could withstand the predicted conditions.
All specialist agreed that there is a real need to better define accident conditions. Without this information, it is nearly impossible to stipulate the required perforsance of charcoal adsorbers and HEPA filters under various accident conditions.
The Steering Committee gave recognition to the fast that several countries are presently doing work in the areas discussed above, b felt strongly that a small group be established by CNSI to coordinate cc.$oing research activities, establish new research programs and make available to member countries the use of testing facilities to minimize duplication of work.
I believe the NRC should support this positicn.
The underlying theme of the meeting was that at this time, we don't know as much as we should about the performance of the off-gas and ventilation systens under accident conditions. Until there is a better definition of the accident, it may be necessary to impose interim criteria to increase our reliability in these systems to mitigate the consequence of an accident.
In my op In my opinion, the meeting was extremely worthwhile, and I went to express my appreciation to all those who made it possible for me to attend.
John T. Collins Deputy Director TMI Support ec'st See Next Page r
1766~276~
Harold R. Denton, Director -
Enclosures:
1.
List of Participants 1.
to m i AgasUd 3.
Sunsaary Report prepared by the Steering Connaittee for Nuclear Energy ec:
E. Case R. Voll:aar D. Hullar W. Kreger R. Bangart R. Ballamy W. Houston S. Levine D. Eisenhut W. Russell R. Fraley f766 277 I
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