ML20053B523
| ML20053B523 | |
| Person / Time | |
|---|---|
| Issue date: | 01/25/1982 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-1937, NUDOCS 8205280508 | |
| Download: ML20053B523 (13) | |
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1 MEETING MINUTES CLASS-9 ACCIDENT SURCOMMIT WAh 6 g DENVER, COLORADO l
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DECE*iBER 16-17, 1981 su
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The ACRS Subcommittee on Class-9 Accidents met on December 15-17, 1981 at the
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Rodway Inn, 4590 Quebec Street, Denver, Colorado.
The Subcomittee met with representatives of the NRC Staff to discuss the status of the NRC's development of a policy statementcon the Severe Accident Rulemaking and the licensing of new CP applications and the proposed FY83 budget for the Accident Evaluation and Mitiga-tion Decision Unit.
The intent of these discussions was to discuss the NRC Staff's current thinking on the Severe Accident Rul emaking and the licensing of new CP's and the research work in the Accident Evaluation ar.d Migation Decision Unit.
These discussions were held in closed sessions which addressed this issue.
The Subcommittee also met with representatives of Commonwealth Edison and the NRC Staff to discus the Zion PRA Study and the NRC investication of the effectiveness of accident migations features which might be added to the Zion and Indian Point Plants (NUREG 0850).
These discussion were held in open session.
A copy of the notice for this meeting is included as Attachment A.
A list of attendees is included as Attachment B.
A schedule for this meeting is included as Attachment C.
The handouts for this meeting are included in the ACRS files. The meeting was begun at 1:00 p.m. with a short executive session in which Dr. Kerr, the Subcom-mittee Chairman, summarized the objectives for the day's meeting. The meeting was adjourned at 7:00 p.m. on December 16, 1981 and was convened again at 8:00 a.m. on December 17, 1981.
The meeting was concluded at 12:25 p.m. on December 17, 1981.
l The discussions held between 1:00 p.m. and 4:00 p.m. on December 16, 1981 were held in closed discussion. The remainder of the meeting was held in open 8205280508 820125 PDR ACRS 1937 PDR I
CLASS-9 MEETING MINUTES January 25, 1982 session.
The Subcommittee heard presentations from NRC-RES, NRC-NRR, Common-weal th Edison, and their consultants.
The meeting was attended by ' '. Kerr, Subcommittee Chairman; J. Ebersole, D. Okrent, P.
Shewmon, D. Ward, W. Mathis, and C. Siess, Subcommittee Members; H. E. Etherington, P. Davis, and S. Siegel, Subcommittee Consultants.
R. Savio of the ACRS Staff was the Designated Federal Empl oyee.
The following discussions were held in Closed Session.
NRC Staff Proposed Approach to the Severe Accident Rulemaking - R. Benero, NRC-RES Robert Benero, NRC-RES, discussed the status of the NRC staff development of a policy statement on Severe Accident Rulemaking and the licensing of new CP appli-cations.
The policy statement currently under consideration by the NRC staff, I
would permit plants to be sited at locations similar to those required by current siting practices.
The policy statement concludes that the current generation of reactors, with the implementation of the post TMI CP requirements and the insights gained from application of PRA will be able to meet Commission safety goals.
In this policy statement PRA is recognized as an acceptable methodology for assessing a plant design against a safety goal, and as a device for identifying cost effec-tive safety improvement.
A PRA will be required for every new CP application.
The policy statement places emphasis on the use of standard plant designs and proposes that the FDA's be granted by rulemaking, effective for some period of time (probably about 10 years).
The specific requirements proposed for new CP applicants would be:
i CLASS-9 MEETING MINUTES January 25, 1982 (a) The demonstration of compliance with the current Commission regulations, including the POST TMI requirements.
(b) The completion of a PRA, the demonstration of adherance to the Commission safety goal, and a commitment to install cost-effective safety features within the guidelines of Commission safety goal policy (i.e., on a specified cost / risk reduction basis).
(c) Adherance to the current version of the SRP.
(d) Proper resolution of all applicable USI.
Several options are proposed for the initiation t,f a Severe Accident Rulemaking, with the earlist calling for the issuance of a proposed rule in mid-1983, and the latest calling for the issuance of a proposed rule in mid-1985.
The IDCOR work would be consistent with the issuance of a proposed rule in mid-1983.
A proposed siting rule is to be issued in early 1983.
Dr. Okrent noted that PRA as currently used, neglects some accident sequences (such as sabotage, and in some cases earthquakes), contains a high degree of uncertainity in many areas (such as common mode failures and the effects of system inter 3ction), and that some important accident sequences may not have been discovered.
Dr. Okrent questioned the use of a methodology which evaluats the effectiver: ass of severe accident migation features on the basis specified by the NRC Staff proposed policy statement.
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CLASS-9 tiEETING MINUTES January 25, 1982 o
J.
- Larkins, Accident Evaluation and Mitiaation - Planned Research for FY82 NRC-RES John Larkins, NRC-RES, discussed the current proposal for the FY83 budget of the Accident Evaluation and Mitigation Decision Unit.
An outline of the budget proposal is as follows:
Millions of Dollars
_FY FY FY FY 82 83 84 85 Severe Accident Sequence Analysis (SASA) 2.3 2.8 3.2 3.4 Behavior of Damaged Fuel 18.0 27.0 29.0 28.0 Fuel fielt Behavior 3.4 3.4 2.6 1.9 Fission Product Release Transport 4.3 6.7 8.5 5.5 Hydrogen Behavior and Control 2.9 3.6 3.2 2.7 Containment Safety Margins 1.2 2.1 2.5 2.9 32.1 45.6 49.0 44.4 Individual program milestones are summarized in pages 1 to 9 of the attach-ment.
The following discussions were held in open session.
G.
K.
Klopp, Commonwealth Edison Summary of Zion Probabilistic Safety Study fir. G. Klopp, Commonwealth Edison, discussed the results of the Zion Probabilistic Safety Study.
The report concluded that risk was dominat1d by a few scenarios.
They were:
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CLASS-9 MEETING MINtJTES January 25, 1982 o
(a)
Seismic events resulting in an accelerttion at the site in excess of 0.49 to 0.6g are estimated to contribute 90% of the total risks.
These events have an estimated mean annual frequency of 5.6 X 10-6/yr.
Accelerations of this size would cause a loss of AC power with an eventual failures of the RCP seals and loss of heat sink, makeup water, and containment cooling.
(b)
The interfacing system large LOCA (RHRS - Primary system interface) is estimated to contribute 5% of the total risk.
The annual mean frequency is estimated at 2.0 X 10-7/yr.
(c)
Loss of all AC power and auxiliary feedwater, following a loss of load and of offsite power is estimated ?o contribute 3% of the total risk.
The impact af the addition of a core ladle, of a filter vent system, and of an improved diesel driven containment soray system were evaluated.
The filter vent system and the improved containment spray system are estimated to reduce risk by a factor of 1.5 to 2.0.
The risk reduction associated with the core ladle is not significant. The improved containment spray was the only one of the three systems judged to be cost effective.
The risk associated with the Zion plant was calculated to be less than the WASH-1400 PWR plant / site.
It was concluded that it does not represent an undue portion of the total risk to the public from commercial nuclear power plants.
CLASS-9 MEETING MINUTES January 25, 1982 It was noted that the Zion study does not treat sabotage, and deals with systems interactions in a limited way.
It was also noted that the question of unorganized low probability high consequence accident sequences was not formally addressed.
The meeting was adjourned at 7:00 p.m.
December 17 1981 - Status of NRC Evaluation of the Effectiveness of Mitigation Features for Zion / Indian Point - J. Meyer, NRC-NRR James Meyer, NRC-NRR, discussed the NRC preliminary assessment of the effec-tiveness of accident mitigation strategies at the Zion and Indian Point plants (NUREG-0850, Volume 1). The NRC Staff originally intended to base a decision on the requirement of additional accident migitation features at these plants on the risk reductions that could be achieved by the use of these features. This was based on the assumption that these plants,because of their location in high oopulation areas, produced a large fraction of the total risk to the public from nuclear power plants. The NRC Staff now believes that population density may not be controlling and that the assessment.of risk to the population should consider the specific design features of the plant.
The NRC Staff is proposing that a requirement for a migation stragegy not be adopted unless a risk reduction factor of 10 or more can be identified. Dr.
Okrent stated that this was not consistent with NRR Staff policy in other areas and noted that the analysis being used neglects some possible accident sequence.
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CLASS-9 MEETING MINUTES January 25, 1982 The NRC Staff is proposing the following functional requirements for any accident migitation features which may be required:
(1)
For combustible gas control, either (a) provide for the controlled burnir.g of an amount sufficient to reader the containment building inert by oxygen depletion in such a way that thermal or pressure loadings from controlled burning do not cause vital equipment or the containment building to fail; or (b) render the containment atmosphere inert either before or after accident initiation in such a way that there is no disabling pressure loading on the containment building.
(2)
For control of gradual overpressurization of the containment building, provide a means to passively remove the energy causing overpressurization (e.g., using a reliable system not dependent on ac power) so that the containment building pressure is brought below the design pressure within about 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> of initiation of control measures.
The basis for the 12-hour period recommended is the need to limit the total leakage that would occur at pressures in excess of those the building was designed to withstand.
(3)
For control of basemat penetration, assure that interactions between the core and concrete are limited by establishing a coolable debris bed in the reactor cavity.
Devices which met the functional requirements would in NRC's opinion prevent the failure of the containment building from the most likely core melt accidents.
The transulation of these requirements into conceptual design criteria will be addressed in Volume 2 of NUREG-0850.
l CLASS-9 MEETING MINUTES January 25, 1982
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The NRC believes that the design requirements for core melt accident mitiga-tion features should be evaluated on a best estimate basis. They believe that the design and quality assurance requirements should include the following:
Group C quality standards (ASME Boiler and Pressure Vessel Code, Section (1)
III, " Nuclear Power Plant Components," Class 3) shall be applied to the mechanical and fluid mitigation systems or their component parts.+
The mitigation system shall be designed to remain functional for all (2) of the operating basis environmental conditions, including the loads imposed by an operating basis earthquake (OBE), unless the dominant risk for which the mitigation system is being designed is initiated by a seismic incident greater than the OBE, in which case more stringent seismic requirements shall be imposed.
(3) For more severe external environmental conditions than desemined in (2),
the plant shall be shut down for inspection of the mitigation system The mitigation system shall be evaluated for design-basis loads, (4) including the safe shutdown earthquake (SSE), in order to ensure that there will be no gross failure which might affect or impair the r
I functioning of safety-related components and systems relied upon for t
design-basis events.
(5) The mitigation system shall be capable of performing their functions in the most limiting environment realistically estimated to occur as a result of the accidents they are designed to mitigate.
The interfaces between the mitigation system and nuclear safety-related (6) components and systems shall be designed to the same safety grade (or quality group) and seismic loading requirements as the safety-related l
component or systems.
With the exception of additional containment building isolation valves or (7) valving between interfacing safety-related systems, the mitigation system shall be of reliable design and construction but need not meet the single failure criterion.
The mitigation system shall be capable of functioning independently of (8) all offsite and onsite ac power systems for a period of time expected to be required for restoring ac power.
9 CLASS-9 MEETING MINUTES January 25, 1982 (9) The mitigation system shall be capable of manual operation and control from the control room.
(10) The mitigation system shall be capable of being backfitted into the Zion and Indian Point plants.
(11) The incorporation of the mitigation system shall not compromise design basis safety requirements.
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Federal Register / Ve!. 46. N2. 230 / Tuesday. December 1,1981 / Notices 3s387 M"
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DeM Normber 25.1 set.
extent practicable, these closed sessions Deted November 34.sest.
gy,
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)sha C Hoyle, will be held so as to mintml=
pahn C Hoyle, N
j Advisory Coetmitter Manonement Officer.
Inconvenience to members of the public Advisory Gunnaistee Ma.mement Offreer in atisDdance.
Fa Du m.eme Fund n-ow,ses.ml ya Du es-asse med It-a-et. Des enj He agenda foe subfect meeting shall numa cons vess. ewe enuma,isee res ew be as follows:
Advisory Committee on Reector p.m t
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'o of Ine s impat tefeguanis SubcommNtee on Close-9 Dursday. December 27. Nef-&JO Notice of Receipt of an Application.,
Pununnt to10 CRllan(bW c
Meeting o.m. untilthe conclusion ofbusiness.
De ACRS Subcommittee on Class-g During the initial portion of the please take notice that the Nuclear Accidents wiU hold a meeting on meeting. the Subcommittee, along with Regulatory Commission has received the December ts and 17.1981. at the
. any ofits consultants who may be following application for an export /
Redewey Inn. 4590 Quebec at I-70.
present, wiU exchange preliminerY import lloonse. A copy of each Denver.CO ne Subcommittee will views regardmg matters to be application is on file in the Nuclear continue its review of wre melt considered during the h=1=nise of the Regulatory Commission's Public t2 Y.
mitigation systems and degraded core meeting.
Document Room located at 1717 H qi rulemaking. Notice of this meeting was he Subcommittee will then hear Street. NW., Washington. D.C.
published October 29.
presentations by and hold discussions A request for a hearing or a petition in accordance with the procedures with npresentatives of the NRC StaH.
for leave to intervene may be filed as outlined in the Federal Register on their consultants. and other interested December 31.1961. Any request for g
be September 30,1981. (46 R 47903), oral persons regarding this review.
hearing or petition for leave to intervene shah be sened by ee mqueste w or written statements may be presented Further information regarding topics petitioner upon the applicant. the t2 by members of the public. recordings to be escussed, wheen se meeting Executive Legal Director. U.S. Nuclear wiU be permitted only during those has been cancelled or rescheduled, the Regulatory Commission. Washington, ggo portions of the meeting when a Chairman s ruling on mquets fw ee D.C.20555, the Secretary U.S. Nuclear transcript is being kept. and questions g.
may be asked only by me nbers of the opportunity to present oral statements Regulatory Commission, and the Subcommittee. Its consultants, and Staff. And the time allotted therefor can be Executive Secretary. Department of Persons desiring to make oral obtained by a prepaid telephone call to State. Washington.D.C. 20520.
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statements should notify the Designated the cognizant Designated Federal in its review of applications for Federal Employee as far in advance as Employee. Dr. Richard Savio (telephone license to export / import production oc practicable so that appropriate 302/634-3287) between 8:15 a.m and 5:00 utilization facilities, special nuclear arrangements can be made to allow the p.m est.
material or source material noticed hg*
necessary time during the meeting for I have determined. in accordance with berein, the Commission does not such statements.
Subsection 10(d) of the Federal evaluate the health, safety or f
ne entire meeting will be open to Advisory Committee Act, that it may be environmental effects in the recipient p blic attendance except for those necessary to close some portions of this nation of the facility or material to be expated.
sessions during wnich the Subcommittee meeting to protect proprietary and finds it necessary to discuss proprietary Industrial Security information. De Date..nis 24th day of November at and Industrial Security information. One authority for such closure is Exemption Bethesda, Maryland.
or more closed sessions may be (4) to the Sunshine Act. 5 U.S.C.
For the Nuclear Regulatory r a.u.iiaalon.
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12/15/81
.s PROPOSED AGENDA - DECEMBER 16-17, 1981 CLASS 9 - ACCIDENT'S SUBCM41TTEE MEETING RODWAY INN, DENVER, COLORADO TELEPHONE No. 303-320-0260 December 16, 1981 1.
Executive Session (0 pen) 1:00 - 1:15 pm 2.
Status Report - Severe Accident 1:15 - 3:30 pm Rul emaking (a) Status Report on NIC policy on 1 1/2 hr aoproach to severe accident e.
rulemaking and interim licensing -
R. Bernero BREAK 15 min (b) Subcommittee discussion 30 min 3.
RES Accident Evaluation and 3:30 - 5:00 pm Mitigation Research - J. Larkins (tentative)
(a)
Introduction (b) Sumary of FY82 and proposed FY83 and beyond programs and proaram funding (c) Relationship to the Severe Accident Rul emakings 4.
Discusions on the Zion Probabilistic Safety 2 Hrs 5:00 - 7:00 pm Study (a)
Introduction - NRC Staff l
(b) Presentations by Commonwealth Edison and Consultants l
l (1) Overview (2) Description of Methods (3) Results i
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12/15/81 Class-9 Accident's Proposed Agenda 1 i
December 17, 1981 5.
Executive Session (0 pen) 8:00 - 8:15 am 6.
Discussion on NUREG - 0850, Vol.1,
" Preliminary Assessment of Core Melt Accidents at the Zion and Indian Point Nuclear Power Plants and strategies for Mitigating their Efforts - Analysis of Containment Building Failure Modes" -
J. Meyer (a) Summary of NUREG-0850 Results 8:15 - 10:00 am and Conslusions
- 1) Dominant Sequences -
Basic / Assumptions
- 2) Failure Modes
- 3) Structural Analysis
- 4) Radiological Source
- 5) Risk Analysis BREAK 15 min (b) Technical Areas Being Pursued 10:15 - 12:00 Noon by the HRC
- 1) Hydrogen and C0
- 2) Further Structural Analysis
- 3) External Events
- 4) SequencesVand$
- 5) Role of Operators
- 6) Liquid Pathway
- 7) Radiological Source Term l
l (c) General Discussion 12:00 - 12:30 pm l
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