ML20140E198
| ML20140E198 | |
| Person / Time | |
|---|---|
| Issue date: | 03/24/1986 |
| From: | Stello V NRC OFFICE OF THE EXECUTIVE DIRECTOR FOR OPERATIONS (EDO) |
| To: | Fraley R Advisory Committee on Reactor Safeguards |
| Shared Package | |
| ML20140E202 | List: |
| References | |
| ACRS-GENERAL, NUDOCS 8603270329 | |
| Download: ML20140E198 (11) | |
Text
______ -
March 24, 1986 MEMORANDUM FOR:
R. F. Fraley, Executive Director for ACRS FROM:
Victor Stello, Jr.
Acting Executive Director for Operations
SUBJECT:
RESPONSE TO ACRS QUESTIONS ON CONTAINMENT VENTING Your February 21, 1986, memorandum requested the NRC staff to provide responses to seven questions proposed by Dr. Okrent as background for the March 12, 1986 meeting of the subcomittee on Safety Philosophy, Technology and Criteria.
Enclosed are the staff responses to these questions.
Needless to say, much technical ar' policy review work remains to be accomplished in this area.
i Origiral sic.,ed by Victor Stello,,
Victor Stello, Jr.
(
Acting Executive Director l
for Operations I
Enclosures:
As stated 1
cc w/ enclosures:
l E. Rossi T. Rehm J. Sniezek R. Minogue J. Heltemes G. Cunningham f
R. W. Houston
)
D. Vassallo l
, h(
G. Hulman hy
/
J. Collins
[
v Retyped in DEDROGR office 3/20/86 (Memo only) 8603270329 860324
/.
PDR ORG NEXD I'
,h 0FC : DBL:RSB
- DBL:AD D: DBL
- D:DFHT DD:NRR
- D:NRR EDO ji/
NAME :MWH0DGES:jh :GLAINAS
- RBERNERO
- WRUSSELL
- DEISEf: HUT
- HDENT0tl
- VSTELLO DATE :
3/ /86
- 3/ /86
- 3/ /86 3/ /86 3/ /86 3/ /86 3/i//86 pFFTf701 PFFORD [ppy
RESPONSE TO ACRS QUESTIONS ON CONTAINMENT VENTING 1.
What is tne overall plan of action and schedule of the staff with regard.to containment venting EPGs?
Responses:
Following the accident at TMI-2, the BWR Owners' Group started developing symptomatic emergency procedure guidelines. Consistent with the requirements of Item I.C.1 of NUREG-0737, these guidelines address conditions beyond design basis accidents and with multiple failures. The early BWR Owners' Group guidelines addressed containment venting to prevent catastrophic failure of the containment. Containment venting has been considered as an appropriate action for conditions which threaten containment integrity since the approval of Rev 2 to the BWR emergency procedure guidelines (EPGs) on February 8, 1983. Since the approval of Rev 2 to the EPGs, much has been learned about the limits of operability of isolation valves and depressurization systems under high containment pressure conditions.
Also, the study of severe accidents has highlighted the need to vent in extreme cases.
All of this new information will be considered in Rev 4 to the BWR c
EPGs. The NRC staff has seen a draft of Rev 4 to the EPGs and has met with the BWR owners to discuss the draft. We will review Rev 4 to the EPGs when it is submitted.
Westinghouse guidelines do not explicitly address containment venting.
2.
Please provide the ACRS with a copy of the current containment venting EPGs for Mark III and indicate the status of the NRC Staff's review of the reactors EPGs and any plants specific implementation of these EPGs.
Responses:
(a) Current approved containment venting EPGs for Mark III are the Rev 3 procedures attached. HCOG has submitted additional procedures for hydrogen control; these are in the November 12, 1985 letter attached.
(b) Status of the NRC staff's review of BWR Owners Group EPGs.
The staff completed its review of the BWR Owners Group EPGs, Revision 3 and by a letter dated November 28, 1983, transmitted a Safety Evaluation Report (SER) to the BWR Owners Group.
In the SER, the staff listed the following items as significant open issues and requested that these open issues be resolved in the proposed Revision 4 to the EPGs:
(1) Criteria for defining containment venting pressure, r
l (2) Further justification of the conservatisms in determination of j
drywell spray flow rate, and I
2-(3) The Secondary Containment and Radioactive Release Control Guideline.
The submittal of Revision 4 to the EPGs by the BWR Owners Group was scheduled for February 1986, but has not been formally submitted to date. Completion of the review by the staff was projected for September 1986, assuming a February submittal.
(c) Plant specific implementation of the EPGs.
The BWR EPGs call for emergency containment venting as the last step in a sequence of procedural steps involving operator actions designed to reduce containment pressure.
In_the SER for the BWR EPGs, the staff established an interim limit of twice the containment design pressure for venting with the understanding that more precise analyses may be used to establish a venting pressure limit. These analyses, in general, could consider containment integrity structural tests, purge valve operability, and leaktightness of gaskets and seals. Currently, the staff is reviewing the applicant's/ licensee's submittals of PGPs for the plant specific implementation of the EPGs.
3.
In its letter of August 18, 1982, on the Grand Gulf Station, one o'f the lead BWR Mark IIIs, the ACRS stated, "MP&L has proposed to include in the Grand Gulf Emergency Procedures a provision for venting the containment in the unlikely event of buildup of pressures above the design basis. The NRC Staff has not completed its review of this proposal. The ACRS wishes to be advised when the NRC~ Staff has reached a position on this matter and to have an opportunity to comment generically or specifically." The ACRS~had an essentially identical paragraph in its letter of July 17, 1984, on the River Bend Station. What is the status of the NRC Staff's review of the final or interim basis containment venting EPGs for these and other Mark III reactors. What are the NRC Staff's plans and schedule for ACRS review?
Response
The licensees for both the Grand Gulf Station and the River Bend Station, in their submittals of the PGPs, addressed the issue of containment venting by referencing the BWR Owners Group generic EPGs.
The OL applicant for Perry made an identical reference. The OL applicant for Clinton took a different approach by providing detailed analyses and justifications for containment venting. The staff reviewad these analyses and justifications and found them to be accept.ble in Supplement 5 to the Clinton SER.
. As indicated in the above responses to Question 2, the issue of containment venting will be generically addressed in Revision 4 to the EPGs. Once the Owners Group 1:as submitted Revision 4 to the EPGs, the staff will be in a better position to schedule completion of its review and arratige an appropriate time for ACRS consideration.
4.1 What is the technical and philosophical basis for the SER on Radioactivity Release Guidance issued by the Staff on November 23, 19837
Response
If an accident produces containment conditions beyond design bases, vent to prevent a catastrophic failure of the ccntainment.
For accidents releasing activity, implement emergency planning if anticipated dose rates indicate it is necessary.
4.2 What review and approval process did this SER receive?
Response
The November, 1983 memorandum was reviewed and approved primarily within NRR.
5.
What is the status of the NRC Staff's consideration of containment venting EPGs for Mark I and Mark II reactors, for ice-condenser s, and for large dry containments? Please provide and describe the technical and philosophical rationale, as it currently exists.
Response
The concept of containment venting has been evolving over the last several years and the optimum approach has not yet been achieved. The most detailed guidance on containment venting EPGs for Mark I, Mark II and Mark III reactors will be addressed in Revision 4 to the BWR Owners Group EPGs and in the November 12, 1985 submittal from the Hydrogen Control Owners Group. Containment venting for ice-condenser and large dry containment has not been explicitly addressed.
The rationale for containment venting in Rev 2 and Rev 3 to the EPGs was not to vent unless catastrophic containment failure was inminent; then, to vent regardless of the activity in the containment. The idea was that a controlled release was better than an uncontrolled, unisolatable release. The major debate centered on the appropriate containment pressure for venting with the concerns being rupture
{
pressure and limit for operability of isolation valves.
t
9 Since the approval of Rev 3 to the EPGs, new concerns about operability-of ADS valves and hydrogen control have been raised.
In addition, severe accident work has demonstrated the desirability of venting through the suppression pool to facilitate scrubbing. All of these considerations are included in the draft Rev 4 to the EPGs which the BWR Owners Group has discussed with the staff.
6.
In a letter dated November 12, 1985, to the NRC from the Mark III Containment Hydrogen Control Owners Group (HCOG), venting is proposed under some conditions, without specification of the offsite radioactive release rate. With regard to this proposal:
(a) What is the technical basis and safety philosophy for such a procedure and what release rates will be considered.
Response
Containment venting is proposed to provide additional protection to assure long term containment structural integrity for accidents i
more severe than desion basis events. Thus, venting assures that the suppression pool is maintained to continue its heat sink and fission product scrubbing functions. The staff believes that containment venting, regardless of offsite release, should be taken only as a last resort to save the containment structure.
Also, enclosed for information and purposes is the summary of the December 18, 1985 meeting with the HC0G and the staff regarding the proposed Combustible Gas Control Emergency Procedure Guidelines.
)
(b) What are the scenarios during which such procedures might be used and what are the estimated frequencies for these scenarios.
Response
Venting the primary containment irrespective of the offsite radioactivity release rate would only be considered to restore and maintain the primary containment hydrogen concentration below the Hydrogen Deflagration Overpressure Limit.
These procedures might be used during the following postulated accidents: [given that protracted core uncovery exists to produce the hydrogen].
(1) Failure of the Hydrogen Ignition System; (2) High primary containment steam concentrations which prevent hydrogen combustion, (3) Failure of the hydrogen analyzers.
No estimates of frequencies relating to these scenarios have been made.
I 5-(c)
In the event that these procedures would be used, who would be involved in the decision to use them and who would have the authority to order the use of these procedures.
Response
The staff believes that licensee's implementation of these guidelines should be consistent with the implementation of the I
overall Emergency Procedure Guidelines. Thus, given conditions requiring venting, the operators should be able to vent without additional approval.
(d) To what degree are the use of such procedures influenced by differences in containment design.
Response
Principally, these procedures are influenced b:- the differences of the ultimate containment capability as related to the Hydrogen Deflagration Overpressure Limit. Also, the vent paths chosen will be dependent on the plant specific design features to assure that adequate performance can be achieved.
(e) What is the status of the NRC Staff's review of (a), (b), (c).and (d) above? To what extent has the use of relatively inexpensive filters, such as are being considered by the French, been considered by either the Owners Group or the NRC Staff.
Response
The status of all of the above is still under staff review; refer I
to the Enclosed meeting sumary. Design backfits have not been considered by either the HC0G or the NRC staff for the purpose of the EPG's.
7.
The HC0G letter of November 12, 1985, also proposed other situations i
as trigger points for venting-related actions. What criteria or analyses will the Staff use in arriving at a judgment concerning their acceptability?
Response
Currently, the staff has concluded that venting the containment at non-threatening hydrogen concentrations is not appropriate.
Unnecessary venting may jeopardize containment integrity by opening and closing the vent system, thereby decreasing the overall reliability of the containment isolation valves. The above
. consideration would also be applicable to the backup containment hydrogen purge system. But for the situation where the primary-containment hydrogen concentration reaches the Hydrogen Deflagration Temperature limit, venting is required only if the offsite radioactivity release rate is expected to remain below the offsite release rate which requires an alert. The staff is requiring HCOG to demonstrate whether or not the operator has sufficient and timely information to determine the conditions where releases are expected to remain below the offsite alert level.
l l
i l
l l
L
t MEMORANDUM FOR:
R. F. Fraley, Executive Director for ACRS FROM:
s Victor Stello, Jr.
\\'
for Operations Acting Executive Director N
SUBJECT:
xRESPONSE TO ACRS QUESTIONS ON CONTAINMENT VENTING Your February'21, 1986, memorandum requested the NRC staff to provide
\\
responses to seven qu'estions proposed by Dr. Okrent as background for the
\\
March 12, 1986 meeting'o the subcommittee on Safety Philosophy, Technology and Criteria.
Enclosed a're the responses to these questions.
\\
'\\,
N Victor Stello, Jr.
\\ Acting Executive Director N
for Operations
\\
Enclosures:
\\
As stated
\\
\\
cc w/ enclosures
~
E. Rossi T. Rehm J. Sniezek R. Minogue J. Heltemes G. Cunningham R. W. Houston D. Vassallo G. Hulman J. Collins
't W
,l
( N01'D
'x y y>o
't %ed
.r
. 3 3
- See previous concurrence
- DBL: AD *
- D: DBL *
- s D:DFHT D: R D:
RR EDO 0FC :0BL:RSB L...__.:.........__
.____:_.._........:............:....._______:.1 NAME :MWH00GES:jh :GLAINAS
- RBERNERO
- WRU$5
- D T
- HDE ON
- VSTELLO V 86
- 3/A /86 3/ /86 DATE :
3/ 6 /86
- 3/ 7/86
- 3/10/86
- 2
/ff6x 3/t /
/~
\\\\
OFFICIAL RECORD COPY
~
MEMORANDUM FOR:
R. F. Fraley, Executive Director for ACRS FROM:
Victor Stello, Acting Executive Director for Operations
SUBJECT:
RESPONSE TO ACRS QUESTIONS ON CONTAINMENT VENTING Your February 21, 1986, memorandum requested the NRC staff to provide responses to seven questions proposed by Dr. Okrent as background for the March 12, 1986 meeting of the subcomittee on Safety Philosophy, Technology and Criteria.
Enclosed are the responses to these questions.
Victor Stello, Acting Executive Director for Operations
Enclosures:
As stated cc w/ enclosures:
E. Rossi T. Rehm J. Sniezek R. Minogue J. Heltemes G. Cunningham R. W. Houston D. Vassallo G. Hulman J. Collins
- SEE ORIGINAL C0flCURREI 6HEET F_0R SIGflATURE OFC
- DBL:RSB
- DBL:AD j 'c ' D:DB D:DFHT DD:NRR
- D:NRR EDO
....:$WH0DGES:jh:dLAINAS NAME :
- RBERNE
- WRUS L
- DEISENHUT
- HDENTON
- VSTELLO DATE :
3/ /86
- 3/ /86
- 3/10/86 3/ /8 3/ /86
- 3/ /86 3/ /86 0FFICIAL RECORD COPY
MEMORANDUM FOR:
R. F. Fraley, Executive Director for ACRS FROM:
Victor Stello, Acting Executive Director for Operations
SUBJECT:
RESPONSE T0'ACRS QUESTIONS ON CONTAINMENT VENTING Your February 21, 1986, memorandum requested the NRC staff to provide responses to seven questions proposed by Dr. Okrent as background for the March 12, 1986 meeting of the subcommittee on Safety Philosophy, Technology and Criteria. The questions all deal with containment venting. We believe that the enclosed responses should be helpful.
The subject of containment venting is complicated and, as can be seen from our responses, not all of our concerns have been completely resolved. We welcome ACRS comments and advice. However, please keep in mind that containmenc venting guidance is evolutionary and our review is not complete..
Victor Stello, Acting Executive Director for Operations
Enclosures:
As stated ccw/ enclosures:
E. Rossi T. Rehm J. Sniezek R. Minogue J. Heltemes G. Cunningham l
R. W. Houston D. Vassollo G. Hulman
. Collins
'YAH OFC : DBL:RSB
- DB AD
- D: DBL
- D:DFHT DD:NRR
- D:NRR EDO NAME :MWHODGES:jh :GL S
- RBERNERO
- WRUSSELL
- DEISENHUT
- HDENTON
- VSTELLO DATE : 3/(p/86 3/'/86
- 3/ /86
- 3/ /86
- 3/ /86 3/ /86 3/ /86,
1 0FFICIAL RECORD COPY
p=
+*gg># #f0 e'
09jo UNITED STATES g
8 NUCLEAR REGULATORY COMMISSION g
- a wAsHWGTON. D. C. 205S5
\\...../
EDO PRINCIPAL CORRESPONDENCE CONTROL FROM:
DUE: 03/11/86 EDO CONTROL: 001460 DOC DT: 02/21/86 R.
F._FRALEY FINAI. REPl.Y:
ACRS TO:
STELLO FOR SIGNATURE OF:
OREEN SFCY NO:
l EXECUTIVE DIRECTOR l
DESC:
ROUTING:
CONTAINMENT VENTING GilIDELINE STELLO i
ROE l
DATE: 02/25/86 REHM l
ASSIGNED TO: NRR CONTACT: DENTON___
SNIFZEK~
MINOGUE HELTFMES SPECIAL INSTRUCTIONS OR REMARKS:
GCUNNINGHAM NRR RECEIVED: 02/25/86 ACTION:
"q1.00LN-?BERNERD :
NRR ROUTING:
D ON/EISENHUT HOSSBURG/ TOMS L
Ok l
.