ML13162A589
| ML13162A589 | |
| Person / Time | |
|---|---|
| Site: | FitzPatrick  |
| Issue date: | 05/16/2013 |
| From: | NRC/OIS/IRSD |
| To: | Entergy Nuclear Operations |
| References | |
| FOIA/PA-2013-0010 | |
| Download: ML13162A589 (34) | |
Text
Appendix A MARK I PLANT-SPECIFIC ENHANCED VENTING CAPABILITY REGULATORY ANALYSIS FOR JAMES A.
FITZPATRICK NUCLEAR POWER PLANT
TABLE OF CONTENTS 1.0 STATEMENT OF THE PROBLEM A-i 2.0 OBJECTIVES.......................................
A-2 3.0 ALTERNATIVE RESOLUTIONS A-2 3.1 Alternative (i).......................................
A-2 3.2 Alternative (ii)
A-3 3.3 Alternative (iii)
A-4 4.0 CONSEQUENCES A-4 4.1 Costs and Benefits of Alternative Resolutions.......
A-4 4.1.1 Alternative (i)
A-4 4.1.2 Alternative (ii)
A-5 4.1.2.1 Value: Risk Reduction Estimates.......
A-5 4.1.2.2 Impacts: Cost Estimates...............
A-5 4.1.2.3 Value-Impact Ratio.....................
A-7 4.1.3 Alternative (iii)
A-7 4.1.3.1 Value: Risk Reduction Estimates.......
A-7 4.1.3.2 Impacts: Cost Estimates...............
A-7 4.1.3.3 Value-Impact Ratio.....................
A-8 4.2 Impacts on Other Requirements.....................
A-12 4.3 Constraints I
A-12 5.0 DECISION RATIONALE A-12 5.1 Commission's Safety Goal............................
A-12 6.0 IMPLEMENTATION A-12 6.1 Schedule for Implementation.........................
A-12
7.0 REFERENCES
A-14 ATTACHMENT 1 TO APPENDIX A -
BACKFIT RULE ANALYSIS.........
A-15
Mark I Plant-Specific Enhanced Venting Capability Regulatory Analysis 1.0 STATEMENT OF THE PROBLEM In SECY-89-017 dated January 23, 1989 (Reference 1), the staff presented its findings concerning the Mark I Containment Performance Improvement (CPI) program to the Commission.
One of the improvement that the staff recommended was the installation of hardened vent capability.
The Commission concurred with the staff's position and directed the staff to proceed with the imposition of a hardened vent capability for each boiling water reactor (BWR) with a Mark I containment where a plant-specific backfit analysis supports such a backfit.
The General Electric Company has designed and constructed several BWR configurations with three basic containment designs designated as Mark I, Mark II, and Mark III.
Probabilistic Risk Assessment (PRA) studies have been performed for a number of BWRs with Mark I containments.
Although these PRA studies do not show the BWR Mark I plants to be risk outliers as a class relative to other plant designs, they do suggest that the Mark I containment could be challenged by a large scale core melt accident, primarily due to its smaller size.
However, estimates of the probability of containment failure under such conditions are based on calculations of complex accident conditions that contain significant uncertainty.
Draft NUREG-1150 (Reference 2) evaluated the dominant accident sequences for five plants, one of which was a BWR Mark I.
The dominant accident sequences were identified as station blackout (SBO),
which includes the loss of all AC and DC power; and anticipated transient without scram (ATWS).
This list would have included the loss of long-term decay heat removal (TW) except that, for the particular plant being reviewed, the likelihood of this sequence was considered to be greatly reduced because of assumed successful venting of the containment.
While the TW sequence was not considered in NUREG-1150 to be a dominant sequence for the plant reviewed, it can be a significant contributor to overall plant risk for Mark I plants in general.
(The June 1989 version of draft NUREG-1150 reported similar results for the Peach Bottom Atomic Power Station as were reported in the February 1987 edition.)
All BWRs with Mark I containments have a capability to vent the containment with various size lines.
The largest lines usually are associated with the vent and purge system used to inert and deinert containment.
Venting of containment as an accident mitigative action is permitted in the Emergency Operating Procedures (EOPs).
In part, the existing vent path uses sheetmetal ductwork from the containment isolation valves through the standby gas treatment system (SGTS) to the plant stack.
The sheetmetal ductwork is usually designed for low A-i
pressure and is expected to fail under severe accident pressures.
Failure of the ductwork would introduce the containment atmosphere to the reactor building.
This could result in harsh environmental conditions that would complicate operator accident recovery actions within the reactor building and could cause failure of equipment within the reactor building.
The hard pipe vent would be designed to withstand severe accident pressures, and, thus, would not fail during a TW event thereby alleviating the harsh environmental concerns in the reactor building.
This regulatory analysis studied the costs and benefits of installing a hardened vent capability at BWRs with Mark I containments.
2.0 OBJECTIVES The staff objective is to reduce the overall risk in BWR Mark I plants by pursuing a balanced approach using accident prevention and accident mitigation.
Most recent PRA studies indicate that TW is an important contributor to BWR Mark I risk.
The balanced approach includes (1) accident prevention - those features or measures that should reduce the likelihood of an accident occurring or measures that the operating staff can use to control the course of an accident and return the plant to a controlled, safe state, and (2) accident mitigation -
those features or measures that can reduce the magnitude of radioactive releases to the environment during an accident.
Although the staff considered the quantification aspects of both accident prevention and mitigation, this regulatory analysis only quantified the preventive aspects.
The proposed hardened vent capability would provide enhanced plant capabilities and procedures concerning both accident prevention and mitigation.
3.0 ALTERNATIVE RESOLUTIONS Plant modifications to the containment venting capability are being proposed to reduce the probability of or to mitigate the conse-quences of a severe core melt accident.
The proposed modification consists of installation of a hard pipe from the existing wetwell ventilation penetration, bypassing the ductwork to the standby gas treatment system, and going to the plant stack.
The ventilation penetration is the 18-to 24-inch penetration normally used as part of the vent and purge system for deinerting the containment.
For the proposed modifications, the new components need not be safety-grade or safety-related.
However, no failure of the modified system or non-safety-related component is to adversely affect any safety-related structure, system, or component required for coping with design-basis accidents.
3.1 Alternative (i)
This alternative is the no-action option, that is, to leave the existing venting capability unaltered.
A-2
The existing venting capability vents the containment through the existing ductwork from the suppression pool to the SGTS.
The ductwork design pressure is usually a few psid or less (Reference 3).
Consequently, venting under severe accident conditions could cause failure of the ductwork and a direct release into the reactor building.
The discharge of high-temperature gases over an extended period of time may pose a threat to the availability or performance of safety-related equipment.
The discharge of hydrogen could result in hydrogen burns (or detonations) inside the reactor building.
Electrical cables, motor operators on valves, relays, and control room components may fail under these environmental conditions.
Adverse environmental conditions would complicate entry into the reactor building.
Calculations from a venting study during an anticipated transient without scram (ATWS) indicate a severe environment would be present in the reactor building during venting operations (Reference 4).
If systems that are needed to terminate the accident need repair, this environment (high temperature and radiation) could hamper recovery efforts by preventing personnel from entering into the reactor building.
3.2 Alternative (ii)
This alternative would involve the installation of a hardened venting capability from the containment wetwell to the plant stack.
The proposed venting improvement would provide a wetwell path to the plant stack capable of withstanding the anticipated environmental conditions of a severe accident.
This proposed modification would include the installation of bard pipe from the outlet of an existing wetwell vent outboard containment isolation valve to the base of the plant stack.
This pipe would be routed through a new isolation valve that would bypass the existing ductwork and the SGTS.
The hard pipe to the stack could contain a rupture disk to prevent inadvertent operation and release of radioactivity.
The emergency procedures would need to be modified to provide appropriate instructions for the operator.
This alternative would mitigate the consequences of severe accidents by reducing the likelihood of core melt from the TW sequence.
All releases through the vent would pass through the suppression pool, and the particulates would be scrubbed.
During a loss of long-term decay heat removal accident, this alter-native would prevent failure of the vent path inside the reactor building and would result in an elevated release.
The elevated release could reduce the offsite consequences.
Since the vent path should not fail inside of the reactor building, personnel could repair equipment and perform other plant recovery activities in the reactor building.
Furthermore, there would be no harsh environmental conditions to degrade or fail other equipment.
There is the possibility of inadvertent operation of the vent that would release some radioactive material without any holdup time or filtration.
This alternative would not affect the releases of radioactive A-3
material for those sequences where the drywell fails, such as from corium attack, once the drywell shell has failed.
3.3 Alternative (iii)
This alternative would involve alternative (ii) plus the instal-lation of an external filter system.
The proposed venting improvement includes the hard pipe vent discussed in alternative (ii) plus the installation of an external filter system, such as the Filtra system or the Multi Venturi Scrubbing System (MVSS).
This external filter would be installed outside of the existing facilities.
A single external filter unit could be constructed to service multiple containments with proper isolation valves.
Both the Filtra and the MVSS systems do not rely on AC power to perform their intended functions.
Similar to alternative (ii), the emergency procedures would need to be modified to provide appropriate instructions for the operator.
This alternative would mitigate the consequences of a severe accident and could reduce the likelihood of core melt if the operator transfers suction of the injection pumps from the suppression pool to an alternate source of water, such as the condensate storage tank, before venting containment.
With the external filter, the amount of particulate removal of the external filter would not be sensitive to the conditions in the suppression pool.
No significant additional risk reduction was estimated to result from an external filter system in addition to the suppression pool scrubbing.
Since all particulate releases through the hardened vent (alternative ii) are scrubbed, the external filter will only provide minimal additional scrubbing.
The external filter provides no additional benefit in core melt prevention although it would provide filtration and some holdup time for inadvertent operation of the vent.
Similar to alternative (ii),
this alternative would not affect the releases of radioactive material for those sequences where the drywell fails, such as from corium attack, once the drywell shell has failed.
4.0 CONSEOUENCES 4.1 Costs and Benefits of Alternative Resolutions The staff used available PRAs to estimate the incremental benefit of the three alternatives discussed in the following paragraphs.
The only accident sequence that is being considered for this analysis is the TW.
This is considered to be conservative since the alternatives could have a beneficial but small effect on other sequences (Reference 5).
The staff estimated the change in the CDF, but not the total CDF from internal events (Reference 6).
4.1.1 Alternative (i)
This alternative would be to take no action.
Since it is expected that the ductwork would fail if the containment were vented at high A-4
pressure, this approach would not only jeopardize personnel, but also the ability to regain control of the facility during the accident.
Furthermore, based on a generic regulatory analysis (Reference 1) the Commission instructed the staff to require hardened vent capability for plants for which it could be shown to be cost effective.
Therefore, based on the discussion below the no-action alternative is not recommended.
4.1.2 Alternative (ii) 4.1.2.1 Value: Risk Reduction Estimates For those accident scenarios where containment failure results in core degradation and a severe accident, the approach using a hard pipe vent path could reduce or delay core degradation.
This is estimated to reduce the total core damage frequency per reactor year by 4.5E-5.
Corresponding to a release of 1.46E6 man-rem, this represents a risk reduction in man-rem per reactor year of 65.5.
4.1.2.2 Impacts: Cost Estimates The estimated cost for installation of the hard pipe vent path is 0.68 million dollars (Reference 7).
The averted cost associated with prevention and mitigation of an accident can be discussed as five separate costs:
replacement power, cleanup, onsite occupational health impacts, offsite health impacts, and onsite property damage.
To estimate the costs of averting plant damage and cleanup, the reduction in accident frequency was multiplied by the discounted costs of onsite property.
The following equations from NUREG/CR-3568 (Reference 8) were used to make this calculation:
V* = NdFU U = (C/m) [ (e'r' 1 )/r1J Il-e-rC(f't(*))J (l-eIm) where: (cited values are from Table 2)
V value of avoided onsite property damage ($)
N number of affected facilities - I dF reduction in accident frequency - 4.5E-5 /RY U
present value of onsite property damage ($)
C cleanup and repair costs = $1.0 billion t(f) - years remaining until end of plant life = 25 t(i)
- years before reactor begins operation -
0 r
- discount rate = 10%
m period of time over which damage costs are paid out (recovery period in years) -
10 Using these values, the present value of avoided onsite property damage is estimated to be $261,105.
A-5
Replacement power costs can be estimated using NUREG/CR-4012 (Reference 9), which lists the replacement power costs for each nuclear power reactor by season.
Using this information for only Mark I reactors averaged over the four years of projected data and escalated by six percent for 1989 dollars, the generic replacement power cost is $400,666 per day.
(The plant-specific replacement power cost is shown in Table 3.
NUREG-1109 (Reference 10) used a generic cost of $500,000 per day and compares favorably with NUREG/CR-4012.)
The change in public health risk associated with the installation of the proposed hardened vent system is expressed as total man-rem of avoided exposure.
The following equations from NUREG/CR-3568 were used to make this calculation:
vp. ý NT (Dp x R) where:
VPH
- value of public health risk avoided for net-benefit method ($)
N
- number of affected reactors -
1 T
= average remaining lifetime of affected facilities (years) = 25 DP avoided public dose per reactor-year (man-rem/RY) 65.5 R
= monetary equivalent of unit dose ($/man-rem)
= $1000 Using these values, the avoided public health exposure of 1.638 million dollars is obtained for FitzPatrick.
Considering a possible 20-year operating life extension, the value of avoided public health exposure is 2.948 million dollars.
The occupational health risk avoided because of the installation of the proposed hardened vent system is expressed as man-rem of avoided exposure.
The following equations from NUREG/CR-3568 were used to make this calculation:
Vom NT(DO x R) where; Vou = value of occupational health risk due to accidents avoided ($)
N number of affected reactors (reactors) = 1 T
= average remaining lifetime of affected facilities (years)=25 DOA
= avoided occupational dose per reactor year (Man-Rem/Reactor-Year)
R
= monetary value of unit dose ($/Man-Rem)=$1000/Man-rem A-6
There are two types of occupational exposure related to accidents, immediate and long-term.
The first occurs at the time of the accident and during the immediate management of the emergency.
The second is a long-term exposure, presumably at significantly lower individual rates, associated with the cleanup and refurbishment of the damaged facility.
The best estimate of the immediate occupational exposure as specified in NUREG/CR-3568 is 1000 man-rem.
The best estimate of the long-term occupational exposure as specified in NUREG/CR-3568 is 20,000 man-rem.
This results in occupational exposure of 21,000 man-rem.
The multiplication of 21,000 man-rem by the reduction in
- CDF, 4.5E-5 per reactor year, produces the avoided occupational dose per reactor year, DO.
Using these values, the present value of avoided occupational health exposure was calculated to be $23,625, approximately one to two percent of the public health risk, and is not considered to be a significant contributor.
Therefore, the occupational health exposures will not be considered further.
4.1.2.3 Value-Impact Ratio The value-impact ratio, not including the costs of onsite accident avoidance, is 2408 man-rem averted per million dollars.
If the savings to industry from accident avoidance (cleanup and repair of onsite damages and replacement power) were included, the overall value-impact ratio would be -15366 man-rem averted per million dollars.
Considering a likely 20-year operating life extension, the overall value-impact ratio would be -17609 man-rem averted per million dollars.
4.1.3 Alternative (iii 4.1.3.1 Value: Risk Reduction Estimates This alternative would provide minor additional particulate scrubbing for the hard vent.
However, because all particulate releases will have been scrubbed by the suppression pool, the improvement over alternative (ii) could be minimal.
4.1.3.2 Impacts: Cost Estimates External filters were estimated to cost $10 million to $50 million for the Filtra design and about $5 million for the Multi-Venturi Scrubber System design.
Using the same equations given in alternative (ii), the present value of the estimated avoided onsite damage to property is
$261,105.
Similarly, the estimated replacement power cost is
$201 million per year.
Thus, the estimated avoided damage to onsite property and the replacement power is
$786,578.
A-7
The present value of the change in the estimated public health risk associated with the installation of the hard vent and the external filter is $1.638 million.
4.1.3.3 Value-Impact Ratio The overall value-impact ratio of this alternative is in terms of man-rem averted per million dollars.
If the savings to industry from accident avoidance (cleanup and repair of onsite damages and replacement power) were included, the overall value-impact ratio would be 335 man-rem averted per million dollars.
This is calculated from the value in Column G of Table 2 divided by the installation cost in Column H of Table 2 and added 5 million dollars for the MVSS design minus the value in Column N of Table 2.
This alternative is not recommended because it does not provide substantial additional safety benefit over alternative (ii) and is not cost effective.
A-8
Table I - Cost Benefits of Alternatives (i)-(iii)
(man-rem averted per million dollars)
Alternative (i) do nothing 0
Alternative (ii)
- hard pipe venting for the remaining life
-15366 with 20-year life extension
-17609 Alternative (iii)
- hard pipe venting 335
+ MVSS external filter A-9
n hill I -hlalifi bAuls IV or ftqaw4 lVoee4l pdiib1 1t for fittpilrick 161 II I) ii ~
f t
IN) (it 111 (11 it) m1 1) 2 stlat a) Iwos of tseiatiu If
'Strip' kiss An-itn An-to 111111t Mul i
............................ Y~1,11 I &RCaowercil Oeratim 1 mlt-A sila EN factor lw por It 5ae, Cosh~ lipat 4 he VIA Ynlij lip)
For.4 1 1 I/ ullsp No. Ploti list lseipee fi l IM1aaa4 Itt1OR I ISSlit IflIu 1111241 i f la)il 1151 1611 1 it per Isj lapI for Uff11 I.....
I fitfileruct 113 2 71 y I3,102 450
.1mm 1.35
,40114 is's 2101.1 0.11 49 171.1,101 11,1131,511 I7T1.'i5 1101,791Sti 9191,55 15
- SO
- 2 2 itparll IMl 05 931W4 05 1.3315294 1.491146 i5.5 l2lli
.1 US 9)35 1201,711 12,911,035 11?,03
,10,711,590 U$I,31,
-1111 D isfolmt fill; 1O 1
khlysil bit-) l-Ii-*Il list -1 11:13 11 Suit: 115A Onri33m, 1111W ld tIV 31 Swism Nwu~a fro LI. %,n, Mllu ktir It.
- tIM, ts I.E. W~illi,
- kt*lIu s la a ig trhIe Wiiaw of hArdea Iests is 0 lull I aclsra 1Sw ill Wesit ltoter W0211, hill Sdeptir 1, 11111
'lesW11iiu of Iliff 01*1w~tl
,i 11 Sovure:
Iditalatim [Dill Ir" uwaud Inn 1.1 Part). to U1. blip, filed laebm r 1,191,
't~ceeueg leopee" to kurct: ettir 111-1141110 to le1itltotim iiofte Vi ew i 11* eeVt' 11 WOns: USK MI/CH 51, 11Ate W~eill 119, pips3tIM l
LN321.1), 3i3 III The msur is (t gim bs, illst rfelt( mis MIf of unartin will 0111e
- 1) Tih flotor is bkullts, m1, eift the utwo idwtfsti w~ ath itettrs is irickits, till), Mifth w paiju 0 ~ ~ jjs aIN Cio ue tieutllienolv rfersacttlo.
Its pitp, if saste Ititl lest w-re 55i9 MWte fri (At Strip Awler divie 4 1111 OWNit howi IV hles WINu kit I to ain' ft OF tesill Alltutlses.
III littalto sAf t it Colo if) iolunaotil thi atilwth clsts IM III ithe ifl Cost s.aiu u
Iherejlinte pFVpWe jliulictiuu etteeil tIke 111111mvie Criteriael W q SieI iopold.
III IN f vim f avoiddlo vtt priety ##p III
- v~Iai if pata hiti rul Faw "m (V *t4eIl t~ lwIII Ma rt.Ii e inl Waitl ruu*I w. idlest 811idM III 11
Table 3 - Estimated Replacement Power Costs (in dollars per day)
Reactor Name FitzPatrick Year MWe Licensed 816 1975 Est. Cost 1985$
$444,650 Est. Cost Est. Cost 1989$
(per year)
$551,366
$201,248,590 Notes: l:NUREG/CR-4012 (Table S.1) provides replacement power costs for all plants on per plant/season basis for 1987-1991.
2:The inflation rate used is 6 percent/year, and the discount rate used is 10 percent/year.
A-11
4.2 Impacts on Other Regpirements There are six programs related to severe accidents: Individual Plant Examination (IPE),
Containment Performance Improvement (the topic of this regulatory analysis), Improved Plant Operations, Severe Accident Research Program, External Events, and Accident Management.
Each of the five programs related to Containment Performance Improvement (CPI) will be discussed briefly in Item 3 of Attachment 1, Backfit Rule Analysis.
4.3 Constraints The plant-specific imposition of a hardened vent is constrained by the guidelines of U.S. NRC Manual Chapter 0514, "NRC Program for Management of Plant-Specific Backfitting of Nuclear Power Plants",
which is based on the backfit rule (10 CFR 50.109), as published by the Commission on September 20, 1985, and the provisions of ID CFR 50 Appendix 0, 10 CFR 50.54(f), and 10 CFR 2.204.
No other constraints have been identified that affect this program.
5.0 DECISION RATIONALE The evaluation of the CPI program included deterministic and probabilistic analyses.
Calculations to estimate the CDF and the consequences of the TW sequence were performed using information available from the NUREG-1150 program and from existing PRAs.
The best estimate of the contribution of TW to the total plant CDF expressed in events per reactor year for FitzPatrick is 4.5E-5.
Implementation of the proposed hardened venting capability will cause TW to be a minor contributor to the total CDF and will significantly reduce the total risk to the health and safety to the public.
5.1 Commission's Safety Goal On August 4, 1986, the Commission published in the Federal Register a policy statement on "Safety Goals for the Operations of Nuclear Power Plants" (51 FR 28044).
This policy statement focuses on the risks to the public from nuclear power plant operation and establishes goals that broadly define an acceptable level of radiological risk.
The discussion in the Regulatory Analysis of SECY 89-017 addressed the CPI program recommendation in light of these goals.
6.0 IMPLEMENTATION 6.1 Schedule for Implementation The licensee may reconsider its position on the installation of the hardened vent under the provisions of 10 CFR 50.59.
Without the licensee's commitment, the staff intends to pursue an order after 30 days of its receipt of this analysis, requiring this backfit under A-12
the provision of 10 CFR 50.109.
Within 60 days after issuance of the backfit order, the licensee will be required to submit to the NRC a schedule for implementing any necessary equipment and procedural modifications to meet the performance goals and to provide adequate defense-in-depth.
All plant modifications are to be installed, procedures (including the decision making process for venting) revised, and operators trained not later than January 1993.
Other schedules were considered; however, the staff believes the proposed implementation of the hard pipe vent capability can be largely performed with minimum interfacing with containment and engineered safety feature systems and thus with the plant online.
Therefore, the licensee can install the proposed modification without unnecessary financial burden for plant shutdown.
The schedule allows reasonable time for the implementation of necessary hardware to achieve a reduction in the risk from TW.
Shorter or less flexible schedules would be unnecessarily burdensome.
A-13
7.0 REFERENCES
- 1.
SECY-89-017, "Mark I Containment Performance Improvement Program," January 23, 1989.
- 2.
NUREG-1150, (Draft), "Reactor Risk Reference Document,"
February 1987.
- 3.
NUREG/CR-5225, "An Overview of Boiling Water Reactor Mark I Containment Venting Risk Implications," October 1988.
- 4.
Harring, R.M.,
"Containment Venting as a Mitigation Technique for BWR Mark I Plant ATWS,"
1986 Reactor Water Safety Meeting.
Gaithersburg. Maryland, October 1986.
- 5.
NUREG/CR-5225, Addendum 1, "An Overview of Boiling Water Reactor Mark I Containment Venting Risk Implications, An Evaluation of Potential Mark I Containment Improvements," June 1939.
- 6.
- Sheron, B.W.,
Memorandum to Thadani, A.C.,
"Reduction in Risk from the Addition of Hardened Vents in BWR Mark I Reactors,"
October 19, 1989.
- 7.
Letter From John C.
Brons (New York Power Authority) to U.S.
- NRC, October 27,
- 1989, "James A. FitzPatrick Nuclear Power Plant Response to Generic Letter 89-16, Installation of a Hardened Vent."
- 8.
NUREG/CR-3568, "A Handbook for Value-Impact Assessment,"
December 1983.
- 9.
NUREG/CR-4012, "Replacement Energy Costs for Nuclear Electricity-Generating Units in the United States: 1987-1991," January 1987.
- 10.
NUREG-1109, "Regulatory/Backfit Analysis for the Resolution of Unresolved Safety Issue A-44, Station Blackout," June 1988.
- 11.
SECY-88-147, "Integration Plan for Closure of Severe Accident Issues," May 25, 1988.
- 12.
Memorandum from S. J.
Chilk to V. Stello, "SECY-89-017 - Mark I Containment Performance Improvement Program," July 11, 1989.
A-14
ATTACHMENT 1 TO APPENDIX A BACKFIT RULE ANALYSIS Analysis and Determination That the Recommended Hard Pipe Vent Capability for Containment Performance Improvement Complies with the Backfit Rule 10 CFR 50.109 The Commission's regulations establish requirements for the design and testing of containment and containment cooling systems (10 CFR 50, Appendix A, General Design Criteria 50, 52, 53, 54, 55, 56, and
- 57) with respect to design basis accident conditions.
As evidenced by the accident at TMI Unit 2, accidents could progress beyond design basis considerations and result in a severe accident.
Such an accident could challenge the integrity of containment.
Existing regulations do not explicitly require that nuclear power plant containments be designed to withstand severe accident conditions.
The staff and our consultants studied this issue as part of the severe accident program for the General Electric Company boiling water reactors (BWRs) with Mark I containments.
BWRs with Mark I containments were reviewed first because of the perceived susceptibility of the Mark I containments to failure based, in part, on the small containment volume of the Mark I containment design.
Both deterministic and probabilistic analyses were performed to evaluate the loss of long-term decay heat removal (TW) in challenging containment integrity and potential failure modes affecting the likelihood of core melt, reactor vessel failure, containment failure, and risk to the public health and safety.
The risk analysis shows that the risks from plants with Mark I containments are generally similar to the risks from plants with containments of other types.
In addition, the hardened pipe vent capability is not needed to provide adequate protection of the public health and safety.
- Rather, the proposed plant improvement will provide substantial cost-effective enhancement to Mark I plant safety.
The estimated benefit from implementing the proposed hard pipe vent is a reduction in the frequency of core melt caused by TW and the associated reduction in risk of offsite radioactive releases.
The estimated risk reduction in terms of man-rem is 1638 and supports the conclusion of the Commission that implementation of the proposed improvement provides a substantial improvement in the level of protection of the public health and safety.
The estimated cost to the licensee to implement the proposed safety enhancement is 0.68 million dollars. This cost would be primarily for the licensee to 1) assess the plant's capability, 2) install equipment to provide additional pressure relieving capability, 3) revise the emergency operating procedures, and 4) provide operator training concerning mitigating the TW sequence.
The estimated value-impact ratio, not including accident avoidance A-15
costs, in terms of man-rems averted per million dollars is 2408.
If the net cost, which includes the cost savings from accident avoidance (i.e.
cleanup and repair of onsite damages and replacement power following an accident),
was included, the estimated overall value-impact in terms of man-rems averted per million dollars would be -
15366.
If 20 years of life extension were included, the estimated overall value-impact in terms of man-rems averted per million. dollars would be -17609.
These values support proceeding with the proposed hard pipe vent capability improvement.
Although the preceding quantitative value-impact analysis was one of the factors considered in evaluating the proposed improvements, other factors were considered as a part in the decision-making process.
PRA studies performed for this issue have shown that the loss of long-term decay heat removal (TW) events can be a significant contributor to core melt frequency.
With consideration of the conditional containment failure probability, TW events can provide an important contribution to reactor risk.
Although there are licensing requirements and guidance for providing a containment and support systems to contain any release of material from the reactor vessel, containment integrity may be significantly challenged under severe accident conditions.
In general, active systems required for reactor and containment heat removal are unavailable during the TW event.
Therefore, the offsite risk is higher from a TW event than it is from many other types of accidents.
The containment integrity is primarily challenged by over-pressure for the TW events.
Under certain conditions, failure of the containment can also initiate core degradation.
The estimated frequency of core melt from TW events is directly proportional to the frequency of the initiating events.
The estimate of the TW frequency for FitzPatrick was partly based on information provided in draft NUREG-1150, "Severe Accident Risks: An Assessment for Five US Nuclear Power Plants," for the Peach Bottom Atomic Power Station, Unit 2, and other available PRAs.
This is assumed to be a realistic estimate of the core melt frequency when compliance with 10 CFR 50.63, the Station Blackout Rule, has been achieved.
The factors discussed in the previous paragraphs support the determination that the additional defense-in-depth provided by the ability to cope with a TW event would substantially increase the overall protection of the public health and safety. Also, this increased protection will justify the direct and indirect costs of implementation.
Analysis of 10 CFR 50.109(c) Factors (1)
Statement of the specific objectives that the backfit is designed to achieve The objective of the proposed hard-pipe vent capability is to A-16
reduce the risk from TW events by reducing the likelihood of core melt and to mitigate releases given a TW or other similar events leading to core melt.
(2)
General description of the activity required by the licensee or aDplicant in order to gomnplete the backfit To comply with the proposed improvement in containment venting, the licensee will be required to:
Evaluate the actual capability of the existing containment vent system to withstand the anticipated containment temperatures and pressures without failing any portion of the vent path to the plant stack.
Evaluate the actual capability of the existing containment vent isolation valves to be opened and closed under anticipated containment pressures and vent flow rates during severe accidents involving TW sequences.
Determine the necessary plant modifications to ensure a hard-pipe vent path will be available under TW events, develop a schedule for plant modification, and submit the schedule to the NRC within 60 days from the issuance of the backfit order.
Complete the necessary modifications by January, 1993.
The licensee will be required to have the decision making process, the procedures and training to cope with and recover from a TW severe accident.
These procedures should conform to the Emergency Procedure Guidelines of the Boiling Water Reactor Owner's Group.
(3)
The potential safety iMuact of changes in Rlant or operational comDlexitv. including the relationship to proposed and existing requlatorv reauirements The hardened vent capability to cope with the TW event should not add to plant or operational complexity, because the vent is normally closed and not operated during normal power operation.
Although this system does add some additional hardware to the plant, it is a simple system.
The containment performance improvement (CPI) program is related to implementation of the Commission's Severe Accident Policy Statement as defined in SECY-88-147 (Reference 11).
In SECY-88-147 the staff described the various programs underway related to closure of severe accident issues.
Included among these was the CPI program.
Other programs described in SECY-88-147 are related to the CPI program as the following discussion indicates.
Individual Plant Examination (IPE)
The IPE involves the formulation of an integrated and A-17
systematic approach to an examination of each nuclear power plant in operation or under construction for possible significant plant-specific risk contributors that might be missed without a systematic search.
Supplement 1 to Generic Letter 88-20 requested that Mark I licensees include in their IPEs the proposed plant improvements identified in SECY 017, other than the hardened vent, namely operation of the enhanced automatic depressurization system, and alternative low-pressure water supply for injection into the reactor vessel and for containment sprays. The examination will carefully examine containment performance in striking a balance between accident prevention and consequence mitigation.
The IPE program may require three to four years until the last plant has performed the IPE.
Improved Plant Operations (IPO)
The IPO includes consideration of continued improvements in the following areas: Systematic Assessment of Licensee Performance (SALP) program; regular reviews by senior NRC staff managers to identify and evaluate those plants that may not be meeting NRC and industry standards of operating performance; diagnostic team inspections; improved plant Technical Specifications; improved operating procedures; expansion of the Emergency Operating Procedures (EOPs) to include guidance on severe accident management strategies; industry's programs to reduce transient and other challenges to engineered safety feature systems; feedback from the IPE program of experience and improvements in operational areas, such as maintenance and training; and continued research to evaluate the sensitivity of risk to human errors, and the effectiveness of operational reliability methods to help identify potential problems early and prevent their occurrence.
The IPO is related to the CPI program's recommendation since we recommend improved procedures and operator training to use the proposed hard vent system.
Severe Accident Research Program (SARP)
The SARP was begun after the Three Mile Island, Unit 2, (TMI-
- 2) accident in March 1979 to provide the Commission and the NRC staff with the technical data and analytical methodology needed to address severe accident issues.
This program has provided input to the NUREG-1150 program and to the CPI program.
Additional research is being carried out to evaluate the need for and feasibility of core debris controls.
Research will also confirm and quantify the benefits of having water in the containment to either scrub fission products or to prevent or delay shell melt by core debris.
Accident Management A-18
The accident management program addresses certain preparatory and recovery measures that plant operating and technical staff can perform to prevent or significantly mitigate the consequences of a severe accident.
This program includes the following measures to be performed by the plant staff: 1) prevent core damage,
- 2) terminate the progress of core damage if it begins and retain the core within the reactor vessel, 3) failing that, maintain containment integrity as long as possible, and 4) minimize the consequences of offsite releases.
The plant enhancement recommended by the CPI program would provide the accident management program with additional capability to achieve their goals by providing improved hardware with which to deal with a severe accident.
The procedures for using the vent should be re-examined under the Accident Management program.
(4)
Whether.the backfit is interim or final and. if interim. the Justification for imposing the backfit on an interim basis The proposed hardened-vent capability is not an interim measure.
(5)
Potential change in the risk to the public from the accidental offsite release of radioactive material Implementation of the proposed hardened-vent capability is expected to result in an estimated risk reduction to the public of 1638 man-rem over the remaining plant life.
(6)
Potential impact on radioloaical exposure of facility employees Although the reduction in occupational exposure caused by reduced CDF and associated post-accident cleanup and repair activities has not been quantified, it could be substantial if the hardened vent prevents contamination of the reactor building.
The estimated total occupational exposure for installation of the hardened-vent path should be negligible.
No increase in occupational exposure is expected from operation and maintenance of the hardened-vent system.
In fact, if the vent is ever used, it should decrease the risk to employees because of the reduced potential for vent path failure and the resulting reactor building contamination.
(7)
Installation and continuing costs associated with the backfit.
including the cost of facility downtime or the cost of construction delay Because the plant can be operating during most of the installation, there are no significant costs associated with construction delays.
With the exception of connections to the existing piping the hardened-vent path can be installed with the plant operating and the work completed during normal plant outages without an adverse A-19
impact on the outage schedule. Thus, there are no costs associated with additional plant downtime.
The estimated cost of the hardened vent system is 0.68 million dollars.
(8)
The estimated burden on the NRC associated with the backfit and the availability of such resources With an estimated expenditure of 200 man-hours for review of the submittals, the estimated total cost for NRC review of industry submittals is $17,000.
The staff will concentrate on the review of design criteria and the method to incorporate the venting into emergency operating procedures.
(9)
Consideration of important gualitative factors bearing on the need for the backfit at the Rarticular facility The installation of the hardened vent will provide greater flexibility in managing accidents other than the TW events, and will provide defense in depth.
(10)
Statement affirming aRprovriate interoffice coordination related to the Rro~osed backfit and the Dlan for implementation The licensee may reconsider its position on the installation of the hardened vent under the provisions of 10 CFR 50.59.
Without the licensee's commitment, the staff intends to pursue an order after 30 days, requiring this backfit under the provision of 10 CFR 50.109.
The proposed backfit was developed as a cooperative effort between the Offices of Nuclear Regulatory Research (RES) and Nuclear Reactor Regulation (NRR) with consultation with the Office of General Counsel.
The implementation is being handled within the NRR.
The staff considered implementation schedules consistent with the guidelines provided by the Commission (Reference 12).
Within 60 days after issuance of the backfit order, the licensee is to provide to the NRC a schedule for implementing any equipment and procedural modifications necessary to meet the performance goals and to provide adequate defense-in-depth.
All plant modifications are to be installed, procedures revised, and operators trained not later than January 1993.
(11)
Basis for reauiring or Dermitting implementation on a particular schedule Although other schedules were considered, the staff believes the proposed implementation of the hard pipe vent capability can be performed with minimum interfacing with containment and engineered safety feature systems and either with the plant online or during a A-20
normal refueling outage.
Therefore, the staff believes the schedule is achievable without incurring unnecessary financial burden on the licensee for plant shutdown.
The schedule allows reasonable time for the implementation of necessary hardware to reduce the risk from TW and allows appropriate coordination with IPE program.
Shorter or less flexible schedules would be unnecessarily burdensome.
(12)
Schedule for staff actions involved in implementation and verification of imDlementation of the backfit. as appropriate The proposed backfit is to be installed under 10 CFR 50.59 for most of plants and, thus, will require minimal staff effort.
Therefore, timely staff review will be expected.
However, for those plants that choose not to implement the modifications under 10 CFR 50.59, more staff time and efforts will be involved.
(13) iMportance of the proDos2d backfit considered in light of other safety-related activities underway at the affected The proposed backfit should not directly involve any other safety-related activities that may be underway at the affected facility.
(14) statement of the consideration of the Droposed vlant-sDecific backfit as a potential generic backfit Initially, the staff proposed the installation of hardened vent as a generic backfit.
The Commission directed the staff to implement it as a plant-specific backfit considering the plant differences in risk reduction and benefits to be gained from a generic backfit.
A-21
improvement (CPI) program is related to implementation of the Commission's Severe Accident Policy Statement as defined in SECY-88-147 (Reference 11).
In SECY-88-147 the staff described the various programs underway related to closure of severe accident issues.
Included among these was the CPI program.
Other programs described in SECY-88-147 are related to the CPI program as the following discussion indicates.
Individual Plant Examination (IPE)
The IPE involves the formulation of an integrated and systematic approach to an examination of each nuclear power plant in operation or under construction for possible significant plant-specific risk contributors that might be missed without a systematic search.
Supplement I to Generic Letter 88-20 requested that Mark I licensees include in their IPEs the proposed plant improvements identified in SECY-89-017, other than the hardened vent, namely operation of the enhanced automatic depressurization system, and alternative low-pressure water supply for injection into the reactor vessel and for containment sprays. The examination will carefully examine containment performance in striking a balance between accident prevention and consequence mitigation.
The IPE program may require three to four years until the last plant has performed the IPE.
Improved Plant Operations (IPO)
The IPO includes consideration of continued improvements in the following areas; Systematic Assessment of Licensee Performance (SALP) program; regular reviews by senior NRC staff managers to identify and evaluate those plants that may not be meeting NRC and industry standards of operating performance; diagnostic team inspections; improved plant Technical specifications; improved operating procedures; expansion of the Emergency Operating Procedures (EOPs) to include guidance on severe accident management strategies; industry's programs to reduce transient and other challenges to engineered safety feature systems; feedback from the IPE program of experience and improvements in operational areas, such as maintenance and training; and continued research to evaluate the sensitivity of risk to human errors, and the effectiveness of operational reliability methods to help identify potential problems early and prevent their occurrence.
The IPO is related to the CPI program's recommendation since we recommend improved procedures and operator training to use the proposed hard vent system.
Severe Accident Research Program (SARP)
A-18
The SARP was begun after the Three Mile Island, Unit 2, (TMI-2) accident in March 1979 to provide the Commission and the NRC staff with the technical data and analytical methodology needed to address severe accident issues.
This program has provided input to the NUREG-1150 program and to the CPI program.
Additional research is being carried out to evaluate the need for and feasibility of core debris controls.
Research will also confirm and quantify the benefits of having water in the containment to either scrub fission products or to prevent or delay shell melt by core debris.
Accident Management The accident management program addresses certain preparatory and recovery measures that plant operating and technical staff can perform to prevent or significantly mitigate the consequences of a severe accident.
This program includes the following measures to be performed by the plant staff: 1) prevent core damage,
- 2) terminate the progress of core damage if it begins and retain the core within the reactor vessel, 3) failing that, maintain containment integrity as long as possible, and 4) minimize the consequences of offsite releases.
The plant enhancement recommended by the CPI program would provide the accident management program with additional capability to achieve their goals by providing improved hardware with which to deal with a severe accident.
The procedures for using the vent should be re-examined under the Accident Management program.
(4)
Whether the backfit is interim or final and. if interim, the justification for imposing the backfit on an interim basis The proposed hardened-vent capability is not an interim measure.
(5)
Potential change in the risk to the public from the accidental offsite release of radioactive material Implementation of the proposed hardened-vent capability is expected to result in an estimated risk reduction to the public of 738 man-rem over the remaining plant life.
(6)
Potential impact on radiological exposure of facility employees Although the reduction in occupational exposure caused by reduced CDF and associated post-accident cleanup and repair activities A-19
has not been quantified, it could be substantial if the hardened vent prevents contamination of the reactor building.
The estimated total occupational exposure for installation of the hardened-vent path should be negligible.
No increase in occupational exposure is expected from operation and maintenance of the hardened-vent system.
In fact, if the vent -is ever used, it should decrease the risk to employees because of the reduced potential for vent path failure and the resulting reactor building contamination.
(7)
Installation and continuing costs Associated with the backfit.
including the cost of facility downtime or the cosj of construction delay Because the plant can be operating during installation, there are no costs associated with construction delays.
The hardened-vent path can be installed with the plant operating or during normal plant outages. Thus, there are no costs associated with additional plant downtime.
The estimated cost of the hardened vent system is 1.1 million dollars.
(8)
The estimated burden on the NRC associated with the backfit and the availability of such resources With an estimated expenditure of 200 man-hours for review of the submittals, the estimated total cost for NRC review of industry submittals is
$17,000.
The staff will concentrate on the review of design criteria and the method to incorporate the venting into emergency operating procedures.
(9)
Consideration of important gualitative factors bearing on the need for the backfit at the Particular facility The installation of the hardened vent will provide greater flexibility in managing accidents other than the TW events, and will provide defense in depth.
(10) Stateent affirmino apropriate interoffice coordination related to the proposed backfit and the Rlan for implementation The licensee may reconsider its position on the installation of the hardened vent under the provisions of 10 CFR 50.59.
Without the licensee's commitment, the staff intends to pursue an order after 30 days, requiring this backfit under the provision of 10 CFR 50.109.
The proposed backfit was developed as a cooperative effort between the Offices of Nuclear Regulatory Research (RES) and Nuclear Reactor Regulation (NRR) with consultation with the A-2 0
Office of General Counsel.
The implementation is being handled within the NRR.
The staff considered implementation schedules consistent with the guidelines provided by the Commission (Reference 12).
Within 60 days after issuance of the backfit order, the licensee is to provide to the NRC a schedule for implementing any equipment and procedural modifications necessary to meet the performance goals and to provide adequate defense-in-depth.
All plant modifications are to be installed, procedures revised, and operators trained not later than January 1993.
(11) Basis for re~airing or Rermitting implementation on a particular schedule Although other schedules were considered, the staff believes the proposed implementation of the hard pipe vent capability can be performed with minimum interfacing with containment and engineered safety feature systems and either with the plant online or during a normal refueling outage.
Therefore, the staff believes the schedule is achievable without incurring unnecessary financial burden on the licensee for plant shutdown.
The schedule allows reasonable time for the implementation of necessary hardware to reduce the ris)k from TW and allows appropriate coordination with IPE program.
Shorter or less flexible schedules would be unnecessarily burdensome.
(12) Schedule for staff actions involved in imnlementation and verification of implementation of the backfit, as a~pronriate The proposed backfit is to be installed under 10 CFR 50.59 for most of plants and, thus, will require minimal staff effort.
Therefore, timely staff review will be expected.
However, for those plants that choose not to implement the modifications under 10 CFR 50.59, more staff time and efforts will be involved.
(13)
Importance of the proposed backfit considered in lietht of other safety-related Activities underway at the affected facility The proposed backfit should not directly involve any other safety-related activities that may be underway at the affected facility.
(14) Statement of the consideration of the proposed plant-specific backfit as a potential generic backfit Initially, the staff proposed the installation of hardened vent as a generic backfit.
The Commission directed the staff to implement it as a plant-specific backfit considering the plant differences in risk reduction and benefits to be gained from a A-21
generic backfit.
A-22
Apoendix B RESPONSE TO COMMENTS IN NYPA LETTER (JPN-99-70)
DATED OCTOBER 27, vqe9 Generii C:nee'ts:
- 1.
T.e letter questions the 's~ecial treatsent" of the hardened vent ano i:n:tts it should be put in the IFE crocess like the other recotmended Mark I improvements.
Response: The hardened vent is not being treated specially, but is bein-
- ursued in a manner similar to any other "backfit" and consistent with NPC rules and procedures.
The IPE process is not a vehicle to make regulatory requirements, and it would be improper to use it as such.
The decision to pursue the requirement for a hardened vent was approved by the Commission, if supported by a technical basis and established procedures and rules are iollowed.
- 2.
The letter notes that the cost-benefit analyses in SECY-99-017 are generic and not applicable to FitzPatrick.
The low population of the site is hi;hliqhted as a major 4actor in invalidating the analyses.
Response: The analyses followed standard practice in attempting to evaluate known plant-specific differences.
- Further, the site population and the cost estimate provided by NYPA are used In the current analysis.
Specific comments:
- 3.
On page 4, the next-to-last paragraph contains the statementt "These low risks were achieved Ein the Peach Bottom NURES-1150 analyses).,.
without dependence on a hardened vent.0 Response: This statement is in error.
The NURES-1150 analyses assumed that venting through an existing hardened vent was successful.
The technical analyses supporting SECY-99-017 used the Peach Bottos results, but had to rebaselint the results by removing the assumption of successful venting through a hardened path to provide a baseline for benteit analyses.
- 4.
On page 4, the last paragraph contains the Statement that NURES-3150 identified drywell shell failure as the maoor containment failure code for Mark I plants, yet the hardened vent is ineffective in preventing B-1
this failure mode.
"Consequently, the hardened vent...
is inconsistent with the ori;inal purpose of the Program.,
Pesponse:
The CF orvgrim looked at all modes of containment failure, as well as the prevention of severe accidents.
The hardened vert is attractive because it both prevents and mitigates some core jejt accidents. Although resolution of the liner melt issue wail not occur for some time, the importance of this issue :s great>v red.,ced,f the probability o0 core melt is reduced.
- 5.
The basis for the cost-benefit equations are questioned on page 6 and 7.
Response
We believe this equation is correct, but solutions oust be correctly interpreted.
If the denominator is zero, the solution is indeterminate, but we would know that this means that any benefit gained has no associated net cost.
This mould be a favorable result.
The regulatory analysis does not blindly make use of this equation.
Individual values of installation cost, averted exposure, averted onsite costs, and sensitivity studies are displayed both separately and in various combinations to provide as complete a picture as possible.
In addition, other factors enter the equation besides the cost-benefit ratio.
For example, the backfit rule requires that the benefit of a backfit must be significant in addition to the baCkfit being cost-effective.
- 6.
The need to calculate the present worth of health effects is proposed.
Response: Although the draft Electric Power Research Institute (EPRI) report is not available to us and therefore we can not respond to it, the NRC policy is to not discount health effects.
Discounting radiation induced health effects raises ethical and moral questions.
Furthermore, the concept of present worth was derived for economic entities with long lives and based on the fungibility of money.
Neither of these concepts completely applies to human health effects.
Illustrative of the difficulties in discounting health effects is the assessment of the doem effects from radioactive waste over long periods.
Discounting would lead to the anomalous conclusion that there is little or no present value in averting future doses.
- 7.
Page B Indicates that venting can have both benefits and detriments and that the net risk should be used.
In addition, exposure to persons installing the vent should be used.
Responsat We agree that venting has both negative and positive risk 6-2
aspects.
The baci*. t is designed to reduce the risk potential from an existing procedure by ensuring that venting, ii performed, will be performed properly.
The staf! did consider occupational exposure, but concluded that it wouJd be negligible since most of the modifications would be external to the containment.
S.
P30e ý questions the benefit of the hardened vent for ATWS seouences.
Response: No benefit was given for prevention of ATWS sequences in the regulatory analysis.
- 9.
Page :0 discusses the interaction oi various imoroveoents and essert3illy indicates that the benefit of the improvements depends on other improvements.
Response: We strongly agree that the improvements overlap and interact in a complex manner.
That is the reason we considered all improvements together and performed a sensitivity study on the-benefit of the other improvements, given the existence of a hardened vent.
The sensitivity of the benefit of a vent, given the other improvements was not explicitly performed, but would not impact the conclusions since the primary benefit of venting is prevention of the TW sequence for which ADS is assumed to f(inction and water is available to the vessel.
- 10.
Page 11 discusses alternative ways to reduce risk from the TM
- sequence, Responsei Improving existing procedures and hardware for venting appears to be the least costly method of preventing a TW sequence and has other benefits. However, the stai4 would bte willing to evaluate alternative &van% that a licensee may propose to meet the intent of this backfit.
9-3
Outside of Scope
Outside of Scope
Outside of Scope