ML20035H648
| ML20035H648 | |
| Person / Time | |
|---|---|
| Issue date: | 04/26/1993 |
| From: | Shewmon P Advisory Committee on Reactor Safeguards |
| To: | Selin I, The Chairman NRC COMMISSION (OCM) |
| References | |
| ACRS-R-1518, NUDOCS 9305060153 | |
| Download: ML20035H648 (4) | |
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,E ADVISORY COMMITTEE ON REACTOR SAFEGUARDS WASHINGTON, D. C. 20555 o.
April 26, 1993 The Honorable Ivan Selin Chairman U.S.
Nuclear Regulatory Commission Washington, D.C.
20555
Dear Chairman Selin:
SUBJECT:
SECY-93-087, " POLICY, TECHNICAL, AND LICENSING ISSUES PERTAINING TO EVOLUTIONARY AND ADVANCED LIGHT-WATER REACTOR (ALWR) DESIGNS" During the 396th meeting of the Advisory Committee on Reactor' Safeguards, April 15-17, 1993, we discussed the NRC staff posi-
- tions, delineated in SECY-93-087, on policy, technical, and licensing issues pertaining to evolutionary and advanced-light-water reactor designs.
During this meeting, we had the benefit of discussions with representatives of the NRC staff and of the-documents referenced.
We have discussed these issues during-several of our previous meetings and provided comments and recommendations in the reports referenced.
We are in general agreement with the staff's positions in SECY 087; however,_we have concerns regarding some issues'and offer'our comments and recommendations as follows.
(The section titles and letter designations correspond to those in SECY-93-087.)
I.
SECY-90-016 ISSUES E.
Fire Protection In our April 26, 1990 report, we pointed out that redundant' train separation is likely to be the most significant feature leading to reduced fire risk.
We recommended that the proposed fire protection enhancements' include'separa-tion of environmental control' systems. (i.e.,- separate heating, ventilating, and air conditioning (HVAC) systems for each train).
The staff responded-by conceding.that-separate HVAC arrangements may be needed, although-other options'may be available to.the_ designer.
The Commission endorsed the staff's response.
We remain concerned that a common normal ventilation system (such as that proposed for the ABWR)'will-be difficult to design'to prevent the effluent from a' postulated accident in one train of engineered safety features from' reaching essential mitigating equipment in the other trains and
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The Honorable Ivan Selin 2
April 26,'1993 creating conditions that exceed their environmental qualifications. Of particular concern is the capability of ventilation dampers to isolate the effects of high energy pipe ruptures in confined compartments served by the common HVAC system.
G.
Hydrocen Control The staff claims that it has sufficient basis for under-standing hydrogen behavior to go forward with licensing criteria.
It has not been demonstrated to us that this basis is' as extensive, or applicable, as the staff be-lieves.
Further, the AP600 and ABB-CE System 80+ designs have containments that are more susceptible to significant damage from hydrogen detonation than most existing and evolutionary plants.
This requires that the licensing criteria for this issue be reconsidered.
H.
Core Debris Coolability The staff has weakened the position taken in SECY-90-016 by not requiring that the core debris be adequately quenched.
We believe that the present criterion for coolability, 2
namely a cavity floor area greater than 0.02m /MWt, is not soundly based.
We recommend that the staff validate containment response to core-on-the-floor accident sequenc-es by independent analyses using, for example, MELCOR, or CORCON and CONTAIN.
J.
Containment Performance We agree with the requirement that containment stresses not exceed ASME Code Service Level C for metal containments, but it is not clear how electrical penetrations through the containment should. be considered.
Such penetrations utilize nonmetallic electrical insulation as a portion of the containment boundary and need further consideration.
L.
Ecuiement Survivability We agree that passive plant design features provided only for severe accident mitigation need not be subject to the environmental qualification requirements of 10 CFR 50.45.
We believe,'however, that such mitigation features must be designed to provide reasonable assurance that they will operate in the severe accident environment for which they are intended and over the timespan for which they are needed.
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The Honorable Ivan Selin 3
April 23, 1993 II. OTHER EVOLUTIONARY AND PASSIVE DESIGN ISSUES Q.
Defense Against Common-Mode Failure in Diaital Instrumenta-
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tion and control Systems i
The staff's second recommendation is that the vendor or applicant analyze each postulated common-mode failure for each event that is evaluated in the accident analysis i
section of the safety analysis report (SAR).
We recommend that the scope of this assessment include consideration of i
common-mode failures during all events postulated in the SAR (e.g., fire, flood, pipe rupture, and extensive' loss. of i
essential power sources) -and not be restricted'to those events discussed in Chapter 15, " Accident Analysis."
T.
Control Room Annunciator (Alarm) Reliability The staff's basic recommendation is that the Commission
=
approve the position that the alarm system for ALWRs meet the applicable EPRI requirements for redundancy, indepen-dence, and separation.
These requirements do not include the use of Class 1E equipment and circuits.
The staff also.
seeks approval of an_ additional position that goes beyond; the EPRI requirements.
This position is that " alarms that are provided for_ manually controlled actions for which no.
automatic control is provided and that are required for the safety systems to accomplish their safety functions,.shall meet the applicable ~ requirements for Class 1E equipment and circuits."
We-believe that-the staff needs _ to provide clarification and additional' justification for this position.
t Collectively, our identified issues represent a significant array of incompletely addressed concerns. We urge that.they be addressed on a timely basis to ensure their early consideration by the design
-teams.
Sincerely,.
Paul Shewmon Chairman
References:
+
1.
SE.CY-93-087, dated April 2, 1993, for the Commissioners, from James M.
- Taylor, Executive Director for Operations,
- NRC,
Subject:
_ Policy, Technical, and Licensing. Issues Pertaining to -
l Evolutionary and Adva'nced Light-Water Reactors (ALWR) Designs
s
.l The Honorable Ivan Selin 4
April 23, 1993 2.
' Report from Paul Shewmon, ACRS Chairman, to Ivan Selin, NRC Chairman,
Subject:
Computers in Nuclear Power Plant Opera-tions, March 18, 1993 3.
Report from David A. Ward, ACRS Chairman, to James M. Taylor, Executive Director for Operations,
- NRC,
Subject:
Draft Commission Paper, " Design Certification and Licensing Policy Issues Pertaining to Passive and Evolutionary Advanced Light Water Reactor Designs," September 16, 1992 4.
Report from David A.
Ward, ACRS Chairman, to Ivan Selin, NRC Chairman,
Subject:
Digital Instrumentation and Control System Reliability, September 16, 1992 5.
Report from David A. Ward, ACRS Chairman, to James M. Taylor, Executive Director for Operations,
- NRC,
Subject:
Issues Pertaining to Evolutionary and Passive Light Water Reactors and Their Relationship to Current Regulatory Requirements, August 17, 1992 6.
Report from David A. Ward, ACRS Chairman, to James M. Taylor, Executive Director for Operations,
- NRC,
Subject:
Issues Pertaining to Evolutionary and Passive Light Water Reactors and Their Relationship to Current Regulatory Requirements, May 13, 1992 7.
Report from Carlyle'Michelson, ACRS Chairman, to Kenneth M.
Carr, NRC Chairman,
Subject:
Evolutionary Light Water Reactors Certification Issues and Their Relationship to Current Regula-tory Requirements, April 26, 1990 4
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