ML19347E089
| ML19347E089 | |
| Person / Time | |
|---|---|
| Issue date: | 01/20/1981 |
| From: | Catton I Advisory Committee on Reactor Safeguards |
| To: | Boehnert P Advisory Committee on Reactor Safeguards |
| References | |
| ACRS-CT-1314, NUDOCS 8104150428 | |
| Download: ML19347E089 (4) | |
Text
~ /8/I RELEIVED 20 Januaq 1981 ADVISORY COMMin(( og DCW sutGUARUS. U.S N R.C.
TO:
Paul Boehnert JAN 2 61981 Ay h
FROM-Ivan Catton
,1011,14 j,2,3,4 i Nucle Dyne Passive Contain ent System Sl'BJ :
COPY 10: M. Plesset The Passive Containnent System (PCS) concept developed by Nucle Dyne Engineering Corporation (NEC) is described as being a unique contaiment structure which replaces the present LWR reactor building and portions of the auxiliary building as well as having passive engineered safety systems and ecuipment to aupent the convectional active safety systens and The primary equi;nent and serving as a containnent suppression system.
containment system is envisioned to be a series of freestanding evacuated steel cells which enclose the reactor coolant system and passive The steel cells are to serve as a leak engineered safety equipment.
tight pressure boundary protecting against release of radioactivity to the environment.
NEC has published and presented a number of papers describing their system The design and its advantages since obtaining a patent in October 1976.
As questions arise the design has been a noving target since the patent.
For example, the containment free volume for a four loop is changed.
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PWR has increased from 59,000 ft to 250,000 ft. A passive auxiliary A series of Water filled quench tanks feedwater system has been added.
Thedelugetank[rs have replaced the single large water filled well.
The were redesigned to use vertical vents instead of rupture disks.
primary reactor containment was changed to enclose the reactor coolant Plate cooling coils are to be used for the rejection of heat All these nodifications system.
radiated by the reactor coolant piping and equipment.
l i to the original design concept have been made with little or no ana ys s.
d the PCS is requires utilization of complex physical processes an without detailed analysis one cannot be sure that risk to the public The design is based more on intuition is reduced by its implementation.
than sound engineering.
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s The passive engin:er d stfety systems ara essentially the follodng.
Provides core flood water following depressurization Refill System The refill system of the primary systen to 1000 psia.
Ihe water is operates on steam rather than nitrogen.
injected into the primary system hot and cold legs through check valves.
Acts as a suppression pool during the early stages of Deluge System It a 1DCA and later as a low pressure flooding system.
During replaces the reactor building spray system.
nonnal operation it acts as a suppression pool for It is the pressurizer and steam generators.
connected to the refill tanks by a number of check valves.
A passive suppression pool following a 1DCA and certain Quench System other accidents involving steam and feedwater systems.
It also acts as a source of emergency feedwater following It operates on secondary side steam that is a1DRL controlled by e check valve.
A heat mb;mger inside the primary containment connected Post Accident heat exchanger in the cooling pond designed to "hstem Y
t operate by natural circulation.
Some of the more significant technical Concerns about the PCS are many.
problens are as follows.
- 1) The space available is inadequate for installation and maintenance of major reactor coolant system components.
interconnecting the various systems
- 2) The large number of check valvet, and the primary system may increase the probability of a high risk acciden
- 3) The primary reactor containment design pressure may be too low for la The pressure suppression calculation does not appear to have breaks.
accounted for vent clearing.
- 4) Quench and deluge systems may not survive their mission as steam Deep submergence leads to large clearing loads.
suppression pools.
Steam bubble collapse in subcooled water may cause damage.
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- 5) The passive heat removal systen depends on natural circulation within the primary containment, within the loop connecting the primary 1
At 1% decay containment to the cooling pond and within the cooling pond.
heat the system nust reject 30W. Obtaining sufficient heat transfer surface area with the PCS will be difficult and may not be achievable.
- 6) Use of freestanding steel cells results in significant structural design problems because the cells nust be free to expand under various thermal loads yet nust be attached to the surrounding concrete structure to carry tensile loads at support points for major reactor coolant system camponents.
- 7) Class 9 Accidents may be more difficult to contain because the small reactor cavity will lead to deeper core debris beds and enhanced chance of dryout and base mat penetration.
- 8) Limited flow areas may lead to counter current flow limitations and accompanying lack of system performance.
- 9) The system is not passive with all the valves and controls needed for its performnce.
They may
- 10) Shrouds in the quench tank are there for no good reason.
interfere with its operation.
No
- 11) The auxiliary feed system operates by natural circulation.
calculations have been carried out to establish its pcrfonnance limits or s.hether it will operate stably.
In spite of the above list, the PCS has the possibility of yielding some At present, however, the lack of analysis makes all proposed benefits.
benefits highly speculative.
Significant changes in the concept will be needed to resolve structural and spatial problems. Analysis for a full spectrun of accidents will be necessary with attention to the SBIDCA as well as Class 9 Accidents. As of this time little or no A substantial effort will be needed.
analysis has been carried out.
The capital cost will probably be significantly greater than a conventional A comparative risk assessment is needed to determine where AR.
weaknesses and strengths lie relative to a typical AR containment.
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To end on e positive noto, some of the positive tspects cra highlighted.
The auxiliary feedwater system using the quench tanks could be e ustful Under total loss of power (AC and DC) it could lengthen contribution.
the available time for corrective action. A properly designed passive heat removal system could be an asset for Class 9 Accident mitigation.
Re: roving post accident sensible heat without phase change could add to Isolation of the steam generator with a proble the margin of safety.
is good. How it will be done is not clear. Finally, steam generator relief valves exhausting into a suppression pool decrease the chance of a steam generator tube rupture allowing a path for primary coolant to get to the atrosphere.
In conclusion, the PCS is too premature for consideration as an alternative A substantial effort will be needed to present PkR containment systems.Its not clear the NEC has the talent to make the PCA a viable design.The highly speculative nature and possibly or the resources to do this.
high cost of the design make it relatively uninteresting for further consideration.
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