ML20206B273
| ML20206B273 | |
| Person / Time | |
|---|---|
| Issue date: | 09/07/1988 |
| From: | Advisory Committee on Reactor Safeguards |
| To: | Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-2596, NUDOCS 8811150396 | |
| Download: ML20206B273 (17) | |
Text
- CERTIFIED COPY DATE ISSUED: Sept. 7,1988 g- '
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SUMMARY
/ MINUTES If1 PROVED LIGHT WATER REACTORS SUBCOMMITTEE <
MEETING, AUGUST 9, 1988 i
i The Improved Light Water Reactors Subcomittee met on August 9,1988, 8:40 a.m., Room 1046, l'/17 H Street NW., Washington, D.C.
L The ACRS members present were: Charles J. Wylie, Subcomittee Chairman, Carlyle Michelson, and Chester P. Siess. The Cognizant ACRS Staff Member was Herman Aldertran, i
The purpose of the meeting was to review Chapters 2,3, 4 and 5 of the
- EPRI Advanced Light Water Reactors Document, Notice of this meeting was published in the Federal Register on Tuesday, July 26, 1988. ,
I Chairman Wylie called upon Mr. Charles Miller as the opening speaker.
J Charles Miller, Project Dire.ctor for Standardization Projects fol Advanced Light Water Reuctor Mr. Miller noted the staff would discuss their review of Chapters 2, 3, 3
and 4 of the EPRI requirements document. Mr. Miller introduced Mr. l l William Long who has been named as Project Manager for the EPRI Project.
- Mr. Miller then turned the meeting over to Mr. Paul Leech, who was the
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MINUTES / LIGHT WATER REACTORS 2
, SUBCOMMITTEE MTGo AUGUST 9,
. 1988 EPRI Proiect Manager until ? 7 cent retirement. Mr. Leech was re-tained in a consulting capacity.
Mr. Paul Leech, Consultant Mr. Leech said he wosid give a brief introduction fcr each chapter and then Mr. Sugnet of EPRI will discuss key items of each chapter. Then the staff would summarize its review of the chapter.
Mr. Miller noted that the Utility Requirements Document (URD) is a comprehensive statement of utility industry requirements for use in designing and constructing an entire ALWR power plant, either BWR or PWR, in sizes up to 1359 MWe. However, it is not intended to be a complete compendium of specifications needed to design a plant. Many details are lacking that will have to be provided later for specific
- designs. The staff, therefore, has considered the utility requirements at the level of detail presented in order to identify any actual or potential conflicts with regulatory requirements, but not to determine their complete adequacy with respect to the NRC requirements. The NRC Standard Review plan is used, to the extent possible as guidance for the staff review.
l Tnere were several questions regarding whether the EPRI document is approved or certified at the conclusion of the review, and does the EPRI f document represent a requirement for advanced light water recctors.
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._' MfNUTES/ LIGHT WATER REACTORS 3 l SUBCOMMITTEE MTGe AUGUST 9,
'1988 Mr. Sugnet responded that EPRI has undertaken this work on behalf of the electric utilities primarily to provide a high-level design specifica-tion for future procurement of reactors. It is important to the poten-tial purchaser of such a plant that he knows that the design require-ments are acceptable to fulfill the minimum regulatory requirements in
, order for him to specify that design in his purclosing process to a potential supplier.
He noted that they feel that it is important that this document be reviewed and be signed off to the point of saying that what is there is acceptable as far as meeting the regulatory requirements.
1 Mr. Michelson pointed out that the EPRI document is a guidar e document.
The real review and approval process is as each individual project applies.
Mr. Leech ncted that Chapter 2 was straight-forward as far as the staff review. Chapter 2 covers the utility requirements for main extraction of steam, feedwater and condensate, chemical addition, condensate makeup purification and auxiliary steam systems.
Mr. Sugnet listed some of the improvements in Chapter 2.
o Feedwater heating system simplified o Adjustable speed electric-driven main feed pumps o Condensate polishing system nas been simplified o Single-stage moisture separator / reheater in the deaerator feed
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.. MINUTES / LIGHT WATER REACTORS 4
. SUBCOMMITTEE MTGo AUGUST 9 1988 tank o Valving improvements 4
Mr. Michelson pointed out that the question of reactor vessel overfill, l A-l'/, becomes particularly critical if you are going to use electric i
driven feedwater. If electric driven feedwater pumps are used, you have !
to be careful that it doesn't become the mechanism for overfill. :
t Chapter 3 - Mr. Leech r
Mr. Leech noted that Chapter 3 for PWR's covers the Reactor Coolant System, Steam Generator System, Chemical and Volume Control System, ;
i Boron Recycle System and Process Sampling. In the case of BWR's, Reactor Coolant System, Reactor Water Cleanup System, and process
, sampling are covered. This chapter includes six generic safety issues and one regulatory optiomization proposal.
Mr. Sugnet pointed out some requirements that he thought were improve-ments over current generation plants: 1 i-1 4
- o Reduced hot leg temperature (PWR) 600 Degrees F. It improved thermal margin and is a increase in steam generator integrity. l o The size of the pressurizer has been increased. This gives a better transient performance and allows e'imination of the ;
i power operated relief valve based on the slow responding f t
system with a larger pressurizer. l i !
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., . MINUTES / LIGHT WATER REACTORS 5-SVBCOMMITTEE MTG, AUGUST 9, 1988 o The sacondary side inventory on the steam generator has been increased, r
n The redctor coolant pump seals have been improved over the current seals as far as their integrity and their ability to withstand loss of seal injection and cooling.
o Pressure relief under low temperature conditions is provided using the DHR system relief valve.
in response to a question about what kind of relief valves on the pressurizer, Mr. Sugnet replied that the pressurizer has a code safety ,
valve. L l
Mr. Sugnet noted that the chemical volume control system has been completely disconnected from all safety functions and is a near-safety system.
Mr. Sugnet pointed out that the boric acid concentration has been limited to two and a half weight per cent to get away from any problems with respect to boric acid crystallization and high concentration boric acid. f r
Mr. Sugnet stated that for BWR's internal recirculation pumps are used.
This completely eliminates the recirculation piping. It gives an !
improved ability for performance and control of the plant, and reduces ,
1 the LOCA vulnerability overall. He noted that the design calls for ,
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,- MfNUTES/ LIGHT WATER REACTORS 6 SUBCOMM1TTEE MTb AllGUST 9, 1988 improved main steam isolation valves and a higher capacity water cleanup :
system.
Mr. Leech noted that the reviewers didn't have any problem with the discussion of instrumentation and controls as presented in Chapter 3.
He noted that the details to complete the review will be in Chapter 10.
Consequently, the final review won't be until the details are supplied [
in Chapter 10.
2 The staff pointed cut the need for protection of non-critical components ,
to the extent that their failure will not degrade Class 1-E power supplies. EPRI responded to the staff that they are going to add to their requirements to take care of that.
i Mr. Leech noted that in response to staff comments, EPRI agreed to add a 4
paragraph that says that boric acid corrosion resistant bolting must be i i
used for closure bolting on systems which contain boroted water during j normal operation. l i
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- Mr. Michelson point out the wording should be changed to include any .
closure of a pressure boundary worse leakage would be jeopardizing the bolting if it is a bolted closure ought to be included, i l Mr. Leech pointed out that the EPRI requirements take great pains to i ,
i make maintenance easier than in past plants. It will also minimize i
radiation exposure. ;
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MINUTES / LIGHT WATER REACTORS 7 SUBCOMMITTEE MTG. AUGUST 9, 1988
- Mr. Wylie asked if the EPRI requirements specify that the reactor ,
systems ird plant to be designed to take pool load rejection and run back to house load, or are yot saying trip?
Mr. Sugent responded that they are specifyin3 that the systems be capable of handling load rejection from an intermediate pcwer. He said he believes it is 50 percent for pressurized water reactors and 40 percent for boiling water reactors. This is without trip. This is intended to avoid loss of the reactor in a power ascension situation, but we are not specifying the capability to have full load rejection without reactor trip.
Mr. Wylie asked if they are specifying the bypass to the condenser cdpacity? How much is that?
Mr. Chapin replied in round numbers, it is about 50 percent.
Mr. Sugnet pointed out that the pressurizer will have power operated valves but they will not have a relief function.
Mr. Leech noted that EPRI will add a sentence stating that low tempera-ture overpressure protection will be provideo by the residual heat removal pressure relief system.
The ACRS cembers, staff and EPRI discussed the need for independent seal cooling during station blackout. The staff position was that if EPRI can denonstrate the seal will survive conditions like station blackout
., MINUTES / LIGHT WATER REACTORS 8
"'; SUBCOMMITTEE MTG 0 AUGUST 9
' 1988 it would be accepted otherwise an independent cooling system should be e
installed.
EPRI believes the seal characteristics will be satisfactory and all against the more complicated system. They stated that can provide a seal that will meet all the requirements.
This is an open item at this time.
Mr. Michelson asked what is the startup feedwater system?
Mr. Surgnet answered that in this plant it is intended that if the
- normal feedwa+er system fails, there be a non-safety startup feedwater system which will be used for the startup function. It will also be available to be used as the first line of backup. In addition to that
! there will be a safety grade emergency feedwater system.
., Mr. Wylie asked if EPRI has considered the problems which have been 4
associated with the reactor uncovered such as with the head off, such as loss of decay heat removal, and what could be done to improve that
- situation?
l Mr. Chapin replied that this is a major concern and is addressed in Chapter 5.
' ' ' '. , g, MINUTES / LIGHT WATER REACTORS 9
... SUBCOMMITTEE MTG, AUGUST 9, 1988 Mr. llvech mentioned.the discussions of whether three valves in series are necessary to control MSI leakage.- EPIR's position is that two valves are adequate.
I Dr. Siess asked about the generic issues hat are not yet in the resolu-tiori process. Mr. Sugnet said they started a list in the early 80's.
Any issues that were listed have been dealt with, either by being shown l not to apply or by being put into a list to resolve.
- Dr. Siess asked what was done with the issues that had no resolution in sight. .
l Mr. Sugnet said these were put in the list of 70 that they are address-ing point by point in the requirements document. !
e Dr. Siess asked how many new generic issues have been added to the list? f l
Mr. Sugnet said as of July 1986 there were about 770 in the list, i
Mr. Wylie asked about the installed piping to facilitate changing the oil in the pumps. He noted that it wasn't clear as to whether there is ;
a valve there, or whether there is a disconnect. He noted t. hat if the '
I pipe is permanently installed, you could have a broken pipe and pump oil to the containment.
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'[ MINUTES / LIGHT WATER. REACTORS 10 SUBCOMM TTEE MTGo AUGUST 9,
. / ,' 1988 Mr. Nicols said there would be an isolation valve close to the pump.
The oil soerce will be in containment. The line to the pump will be normally enipty. It is meant as a maintenance convenience.
Mr. Michelson asked about thermal insulation for the reactor coolant ,
system. He noted that fiber glass insulation is used. He asked about guidance about how much of the insulation would end in the sump during a LOCA and how big the sump screens would have to be to avoid blockage, d
Mr. Nichols replied that the requirements document states that insu- ;
lation design shall assure that sump bicckage is precluded.
Mr. Michelson cautioned the staff to carefully review the use of fibrous insulation. He noted the pumps to circulate the water will have to be looked at very carefully because no screen will stop the fiber from t
- going through. He asked if the staff is sctisfied that there is no problem with fiber glass? Mr. Leech replied that he doubted that the staff has looked into it that closely.
Chap %r 4 d
Mr. Leech noted that Chapter 4 for both BWR's and PWR's addresses the l reactor pressure vessel, nozzles and safe ends, reactor internals, in vessel portions of fluid systems, nuclear fuel, control rods, control l rod drive systems, and special tools for maintenance, inspection and '
testing. !
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- MINUTES / LIGHT WATER REACTORS 11 SUBCOMMITTEE MTG. AUGUST 9,
- 1988 Mr. Sugnet asked Mr. Phil Kofik of MPR to discuss the issues of Chapter 4 He noted the requirements state that there shall be 15 percent thermal margin added to any full design for an ALWR which goes on and above any other margin that you add for uncertainties in instrumentation and uncertainties in calculation methodology.
The core design is designed to avoid power excursions having a negative power coefficient at all times and under all conditions.
Both PWR and BWR control rod lifetimes are significantly longer than current designs.
The fuel is designed to ensure high cechanical integrity and higher burnup than are currently delivered.
For the BWR the burnup expected will be 45,000 n,egawatt days per ton, and for the PWR 55,000 megawatt days per ton.
The reactor vessel will be designed for a 60 year lifetime. The reactor vessel will be built with a ring forged center section which encompasses the entire core section without either longitudinal or circumferential welds. This elin.inated a lot of the uncertainty that has arisen over the years with welding, i.e., the radiation behavior c f the welded reactor vessel shell section. This also eliminates the need for in-specting those welds.
MfNUTES/ LIGHT WATER REACTORS 12 SUBCOMMITTEE MTG. AUGUST 9,
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- 1988 The BWR has several unique features. It uses internal pumps. This also enhances the exposure resistance of the BWR vessel because it now has raore water in the annual space outside of the fuel in order to attenuate neutron radiation.
The BWR 4150 has fine motion control rod drive mechanisms. These are ;
drhe mechanism which in addition to having a hydraulic scram capability I 11sn ho e positioning capability by a lead screw motor mechanism, which ,
-Miically provides very controlled fine motion stepping of the control rod as it ( !s up into the case.
Mr. Leech discussed the draft sdfety evaluation of Chapter 4.
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He noted the concept of cefense in depth as shown by:
o two separate barrier against release of fission products o pretsure boundary integrity o nagative power coefficient o freedom f.om power oscillation o reactivity control reliability o shutdown margin o criticality margin Mr. Leech called upon Mr. George Swink of the Reactor Systems Branch to discuss power oscillation. Mr. Swink noted:
o It is irrportant that the fuel safety limits are protected by
.' MINUTES / LIGHT WATER REACTORS 13 SU200KMITTEE MTG. AUGUST 9
" 1988 design o The center line fuel melt criteria must be preserved by the design of the plant o The oscillations are possible but the staff feels that a stronger statement should be made that all attempts be made to prevent unstable operation by design o Even within the excluded region the staff would like to take dll possible attempts to mSintain stability o EPP.I talked about a 15 percent margin to stability and the staff believes this margin should be on top of calculation uncertainties, o EPRI has talked about reduced feedwater temperature. The possibility o' making the plant more unstable must be j considered if the feedwater temperature is reduced.
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Mr. Leech pninted out that power assisted machines will be placed on the reactor pressure vessel closure head remotely controlled so that they can disconnect and remove vessel steel nuts. This would reduce the critical path refueling time and reduce the exposure of workers.
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! The feedwater spargers will be designed with top exit holes to aim the feedwater radically inward. This will prevent the reactor coolant from j flowing backward into feedwater spargers, prevent temperature cycling and help prevent water hanmers, i
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MINUTES / LIGHT WATER REACTORS 14
. SUBCOMMITTEE MTG. AUGUST 9 1988 Mr. Leech observed that on the basis of current industry experience, staff notes there has been a substantial improvement in full retrieability.
The staff took exception to EPRI's statement that there are no failure modes of the RPS power supplies that would result in a non fail safe
-failure 'of scram pilot solenoids. EPRI reiterated their belief that this can be done.
Mr. Leech noted the requirement that appropriate analysis be performed to demonstrate adequacy of the RPV for natural circulation cooldown by the reactor from full power. The staff has raised the question of whether the RPV would be able to withstand most of the cooldowns. The question is how many events will have to be considered. Mr. Kusik said 5 to 10 would be a reasonable number.
Chapter 5, Engineered Safety Systems, - Mr. Sugnet Mr. Sugnet noted Cha;;ter 5 has a introduction which contains a number of sections that EPRI refers to as policy statements. This is the first time in the EPRI document that the idea of policy statements is used.
He stated that the first thing we've tried to do is to accomplish design requirements to produce a plant that is accident resistant. This is accomplished by increasing design margins in selected areas. The best available materials will be used. The aim is to produce a plant that
, '. MIf.UTES/ LIGHT WATER REACTORS 15 SUBCOMM1TTEE MTG AUGUST 9, 1988 has more capability, slower response to transients and more time avail-able for operator.
In Chapter 5 are listed systems to prevent an accident from progressing ;
to a point of core damage. He defined core damage as exceeding 2200 F '
in the core. !
e TF ; a r. Gree categories of design basis accidents. .
i o Licensing' design basis !
o Risk Evaluation basis o Performance evaluation basis The Licensing Design Basis are the same as those that have been tradi-I tionally called licensing design basis events in regulatory review.
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- The risk evaluation basis considers core damage events. These will use probabilistic risk assessment type methods.
f The performance evaluation basis would include things like the ability I on a best estimate basis to sustain a plant for eight hours in a station i
l blackout condition.
l l Mr. Sugnet stated that EPRI plans to write a policy statement on source term issues. This will include:
o Deletion of spray additives in containment spray systems
.. WINUTES/ LIGHT WATER REACTORS 16 SUBCOMMITTEE MTG. AUGUST 9,
. 1988 o Deletion of charcoal in filtration trains o_ Credit for radionuclide scrubbing in reactor suppression pools o The use of a' finite time from the time of initiation of the event until the release of fission products in close calculations o Containment leakage as a function of containment pressure The policy statement on severe accident protection has three key ele-ments:
- 1. Design to meet the applicable regulatory requirements.
- 2. Emphasize core damage prevention. A high level target for damage frequency of ten to the minus fifth per reactor year has been set.
- 3. Analysis of severe accident sequences to show that the design as developed through these requirements contain sufficient margin.
Mr. Sargent said the ALWR requirements have specified the ability to accommodate oxidation of the equivalent of seventy five percent of the active fuel cladding and to keep the average hydrogen concentration in the containment below thirteen percent to avoid concerns about detainability, given this amount of hydrogen being generated. The requirements document calls for the assurance of a good natural circu-lation mixing of the containment to avoid packeting of hydrogen at higher concentrations. The use of hydrogen control systems, is called for, if its necessary to meet these requirements.
o MINUTES / LIGHT WATER REACTORS 17 SUBCOMMITTEE MTG, AUGUST 9 1988 Mr. Sargnet noted that EPRI has a well established position against containment venting. He said that the containment is designed by definition to be a last defense against release of radioactivity against events that probably were not foreseen. The idea of intentially putting a break in that barrier is the wrong way to go.
The meeting was adjourned at 5:25 p.m.
NOTE: A transcript of the meeting is available at the NRC Public Document Room, 1717 H St. NW., Washington, D.C. or can be purchased from Heritage Reporting Corporation, 1220 L Street.
NW., Washington, D.C. 20005, Telephone (202) 628-4888.
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