GB2526507A - Emergency roofing and barrier system - Google Patents

Abstract

This invention is designed to isolate and contain systems that are at risk from explosion or subsequent damage arising from an explosion, fire, hazard, or other calamity. Preferably, it acts as a preventative system in nuclear reactors to reduce the risk of damage, but the Emergency Roofing and Barrier System can also be used after an explosion or damage has occurred to bring the situation under control and to facilitate the system being made safe. In one basic embodiment, the system comprises a two-piece cap for a nuclear reactor vessel which, under normal operating conditions, allows the circulation of coolant between the two-pieces through vents in the cap. However, in the event of an explosion, the pressure within the reactor forces the two pieces together, thereby closing the vents and sealing the reactor vessel. Alternatively, it could be used as a barrier system to contain the spread of fires or explosions in mining and other hazardous situations.

Description

Emergency Roofing and Barrier System

Background of the invention

This invention (Emergency Roofing and Barrier System or ERBS) came about as a result of personally investigating how the disaster at the nuclear powcr plant Fukashima in Japan could be averted in the future. It scems to mc that the present design of fission nuclear reactors leaves them vulnerable to damage of their reactor roofs.

My design is intended to allow for the automatic containment of the reactor coolant should a breach in the roof appear. Ideally the ERBS should be in position before a disaster happens but it may be possible to help with containing any such disaster after the event through the ERBS.

Problem this Patent Solves Should the roof a nuclear fission reactor suffer damage because of the intense heat and pressure inside the reactor such a breach may rapidly spread out of control. This invention is designed to remedy this specific problem but not limited to it.

The main reason for the rapid loss of the system's integrity is that the reactor coolant is lost to the atmosphere.

The ERBS would act automatically to remedy this situation without human intervention although by incorporating electronic switches within the ERBS the shutdown of the whole reactor could be initiated through a failsafe system.

Similar disasters historically seem to illustrate that human reaction times are not as effective as having automatic systems in place. The system is intended as a preventative system but in the event of a disaster that has already occurred may be applied to remedy that situation as far as possible.

Access to a nuclear reactor after an explosion in the reactor is difficult and so having this ERBS in place would avoid and alleviate many problems of access and repair.

What this invention does.

The Emergency Roofing System or ERBS allows the coolant to circulate the reactor vessel without obstruction until there is a sudden loss of pressure.

The responsiveness of the ERBS could depend upon the weight of the constituent parts /pieces/flanges (afterwards herein called pieces). However it may be that the pressure inside the reactor would cause almost immediate closure without regard to the ERBS' weight.

The pieces incorporate vents which automatically close when the pressure inside the reactor forces the pieces upwards against a neighbouring unvented flange. The shape and size of these vents may be designed and used to delay or hasten that closure time. It may even be possible to allow these pieces to close consecutively.

Key Features of the Invention Schematic Diagram 5 shows the basic arrangement for the ERBS. It is a cap made in 2 or more pieces that are the shame cross sectional shape as the reactor vessel it is sealing.

While the cap is fitted during a disaster it will need the vents to be kept open to allow the coolant to escape. This could be achieved by fixing some pins that can be removed when the cap has been successfully sited and attached to the reactor. This arrangement could also allow for thc closing of the cap in stages depcnding upon the particular circumstances of a reactor breach.

I have allowed for a situation where the cap of the reactor may not be completely destroyed and the cap should have sufficient clearance so that the vent flanges do not touch the top of the reactor vessel when they are raised.

By keeping a cavity between the two vessels the overall size of the nuclear reactor will increase but this is to be balanced against the benefit of providing more protection against impact damage. Any object that impacts the top to the reactor would need to crush or penetrate the reactor vessel lid as far as and through the ERBS cap to create a reactor breach.

Therefore the probability of this occurring is reduced.

The ERBS cap can be made of more than two pieces provided more venting positions.

However this is likely to reduce the pressure that the ERBS can withstand.

The system is better suited to a preventative system placed in position prior to a disaster so two conditions are considered separately below.

Using the ERRS Re fore a Disaster This is the best use for my invention and it may be possible to modify existing reactors by placing an ERBS as shown in Schematic Diagram 4.

The ideal system would be for new reactors to be built as in Schematic Diagram 2.

However perhaps a reservoir of modifier (or coolant for pumping) placed under the reactor should also be used to enhance the efficiency of the overall safety measures. This pumping arrangement could be automatically set to cut in if the temperature rises beyond a pre-set limit.

If in the case of a meltdown of the fuel rods a modifier that will combine with the fuel can be found then a reservoir of this modify directly under the reactor would be beneficial.

The ERBS is like an additional layer olproiection bul avoids the dillicully ola second jackel around the reactor core preventing coolant circulation. However the ERBS should not be seen as a complete solution in itself or as a system that can be used to reset the reactor after a disaster. I envisage its use as a containment device to bring the failure under control and limit damage.

Using the ERRS Before a Disaster This is the worst case scenarios. If the ERBS is successfully placed in situ above the reactor and the containment is or is not complete then by allowing one or more of the vents to remain partly open could allow for coolant to be pumped around a damaged reactor core (see Schematic Diagram # 11). The fitting of such an access point on the vent flange to allow pumping may not be possible due to the large pressure from the reactor. A strengthen opening on the lid of the cap may be better for access point(s) to pump coolant into and out of the reactor.

The main difficultly in placing the ERBS after a disaster and there has been damage to a reactor roof is that the more of the roof that is lost the more difficult it may be to fix the ERBS to the remains of that reactor.

Depending upon the reliability of those new connections it may be necessary or desirable to allow at least one vent opening to either release pressure or allow for the pumping of coolant around the reactor core.

Other Features of the Invention The EBBS pieces/flanges are fitted with a retaining flange core (see Schematic Diagram # 5) to prevent that piece being forced upward and losing its seal.

The sealing flange (see Schematic Diagram # 7) also has a flange cuff to stop that piece falling onto the reactor while being placed or otherwise.

I have allowed for the possibility of attaching a pumping system to the ERBS (see Schematic Diagram # 13). By incorporating one or more box shapes like inverted sump(s) the inlet and outlet paths of the pumped coolant are free for usc. The dashed line shown in Schematic Diagram # 13 at the bottom of the sump may vary in the amount and size of holes to allow a path for the pumped coolant.

This access pumping point might also be used for other purposes. For instance if a foam were invented that was useful or even for concrete so that when the reactor was cold it could be decommissioned.

Brief Introduction to Patent Drawings

The drawings are shown schematic and not to scale as the dimensions of reactor vessel will vary. A complete ERBS cap is only shown in Schematic Diagram # 5 and only in outline.

The ERBS cap can bc modified to allow different fixing mcthods and so only its csscntial elements are illustrated.

Schematic Diagram # 6 shows how hot coolant is allowed to escape when the ERBS system is open. This is very useful for fitting the ERBS device as it avoids the rector pressure tending to force the ERBS cap off its mountings.

The choice of mountings will very much depend upon the amount of damage to the reactor.

So the ERBS system would need modification to allow the best means of fixing it to the reactor. Even incorporating more than one such fixing method seems prudent.

Schematic Diagram # 7 shows how hot coolant is prevented from escape when the ERBS system is closed.

Schematic Diagram # 8 shows one possibility of how the ERBS system can be kept closed.

The behaviour of materials within the reactor means that wiring may melt, springs and moving parts become fused in the absence of coolant. Therefore the only moving part in Schematic Diagram # 8 is a hinged stop that is held in position by the lower retainer while the cap is being placed into position or the cap is allowed to stay in the open position. As the hinged stop moves into position and the cap is raised it aligns with the top retainer than prevents the hinged stop from allowing the cap to fall.

Details of Drawings The other drawings show suggested means of fixing the ERBS and some means of attaching a pumping line or system to the device or cap.

Schematic Diagrams #2 and 3 show how a new reactor design can be built incorporating the ERB S. Schematic Diagram # 4 shows a possible way of modifying existing fusion reactors to incorporate the ERBS and improve safety.

Schematic Diagram # 9 shows the ERBS placement for a damaged reactor if there it can be attached to existing flanges. This may not be possible at Fukashima as I at first anticipated although one of the four reactors may be intact enough to proceed as in this method.

Schematic Diagram # 10 shows a suggested solution if the reactor has lost most of the body of the reactor vessel. Ideally the bracing structure could be dropped into position or bolted together by robots (the Fukashima plant has robots for this purpose), If the cap could be pre-assembled with the ERBS fixed to it this would be an advantage. In severe and worst case scenarios like this complete sealing may not be possible. However if coolant can be pumped onto the reactor then filling any gaps between the wall of the reactor and the ERBS could then be undertaken. Perhaps a short term fix would be to pour a ring of concrete over such a gap on top of metal form work to prevent the concrete falling down such a gap if it exists.

Schematic Diagram # 12 shows two suggestions for attaching a pumping system.

Arrangement # 3 is potentially the most uncertain due to the internal pressure of the reactor being unknown. When the cap is open for Arrangement # 3 then the only way the reactor coolant can escape is through the pump connections. However it may be useful so I have included it.

Examples Uses of the Emergency Roofing System The invention is mainly restricted to nuclear reactors as they have explosive substances that need isolating rapidly.

Perhaps in mines where there are explosive gases this system could be arranged vertically to isolate sections of the mine but allow pumping of air throughout the mine shafts. These barriers Duld need to placed with an arrangement of pairs of access doors to the side of them to allow people to move freely. These doors would be set so that they could not open together but only one at a time. The force of the gas exploding would determine the calculation for the weight of the caps that would need to be used. If this was successful in operation it could prevent the collapse of the tunnel away from the explosion. It may also be necessary for such a system of ERBS to guard against explosions from both directions.

The design here already seems possible of fulfilling these needs of protection from two directions and for critical systems with explosive substances.

The consideration of using this system in mines has produced an alteration to the ERBS as shown in Schematic Diagram # 14 (with two arrangements) in the Emergency Barrier System (EBS). The term roofing is now inappropriate as the system would be positioned vertically within a horizontal mine shaft. The EBS would be more effective if the openings were restricted to a piped ventilation system(s). The Barrier Flange could cover most of the area of the mine shaft cross section apart from the entry and exit door.

A separate parallel system including an EBS may be needed in mines to allow for mined ore to be transported. A load of mined ore could be transported with a double door system integrated into it to isolate any fire or explosion.

It may be possible to incorporate the ERBS in fusion or other reactor design however the risk of radiation from a disaster would be lower in that case.

Key to Schematic Diagram #2 ]tem# Ncte I Clearanceshouldbeallowed betweenReactor.Roofandfuflyextended * Emergency Roofing Device.

* 2 Standard Reactor Vessel ________ ___________________________________ C) * 3 New Inneriacketwith EmergencyRoofingSystern 4 spossib:1ethatdamagetotIeieactorroofrnaybepreventedfro*mbeirig catastrophicand complete by the Emergency RoofingSystem (ERS).

To minirnisethe riskof furtherdamage the roof dearance, as shown, is desirable Key to Schematic Diagram # 3 item it Note 2 New1nnerJacietwithEmergencyRoofinSystem 3 Concrete/Metal Outer Conta inment Vessel Key to Schen atic Diagram # 4 Item if Note I EmergencyFooflngSystern(ERS 2 Standard Reactor Vessel 3 Detail of possble installation ofEmergency Roofingsystem (ERS) in existing reactorvessels 4 If reactorvessel is constructed with weidingthe serni-sphericM top to the cyiindricaibodythen it maybe possibieto separath them again and piacethe ERS on piaceif the flanges are present this is even better Key to Schematic Diagram: #5 Item# Note 1 Two Piece Cap -Emergency RooflngSystem (ERS) 2 One piece shown in cross section butflange like and circular in plan section.

3 Three piece Cap-Emergency Roofing System (ERS) 4 There is no reason whythe ERS cannot be made with more than 2 pieces.

Howeverthefewerthe number of piecesthe more it Will withstand pressure.

The holes in each piece are not shown hereforbut elsewherefor*clarity.

The control ofthe size ofthevent holes by design wHibe significant.

The retainingflanges are also shown better elsewhere Key to Schematic Diagram #6 item# Note I Solid flange (at ieastwherevents In neighbowingflangewi:H be sealed when ______________ systemsdosed) 2 Verthoe(s).

3 Retainingf1angetoretanCOOlantwithinthereactOr..

4 Solid flange if anotherpiece isbuilt intothe design of the system Key to Schematic Diagram #7 ftem# Note 1 Flange Cuff 2 Solid flange (at leastwhere vents in neighbouringfiangewiil be sealedwhen _______________ system isdosed) 3 flange Collar 4 SeathngFiange.

ElangeSleeve 6 Vent Flange 7 Venthole(s) 8 Solid flange if another piece k built into the design of the system.

9 Tight fit -NO gaptlils is just a schematic diagram The protruding partofthe flange fits perfectly and aisothe flange coliarso that the vents are sealed when thp ressureforces the insideflange/piece upwards..

Key to Schematic Diagram # 8 kem# Note I FiangeCuff 2 Hinged Stop 3 TopretainertohouseHingedStopvhencapisdosedinhigherposWon 4 FIangeSIee'e Vent hoie() 6 FiangeCoflar 7 Sofid flar geif ancther piece is built intothe design ofthe system.

8 Lo:verRetainer-tohousehinged sto pwhen cap is open linlowerposition Key to Schernafic Diagram # 9 item# Note I Estimated loss of top of reactor.

2 Standard Reactor Vessel -a 3 Emergency RoofingSystem (ERS) lowered over damaged reactor and secured by _________________ remainingflanges 4 The flanges to the reactorvessei andthe ERS can have a betterfit ft theyare madeto lie flush to each other but radiation and heat may impairthiswork2 S This solution isnotguaranteedto completely seal of the reactorvessel cornpletelybutshouid allowfora much reduced loss of coolant and aiiowfor remedial workto advance more speedily.. . Key to Schematic Diagram # 1:0 tterr. Note I Estimated loss of top of reactor if more severe and flanges not present.

2 Standard Reactor Vessel 3 Fix. ERSto body of reactor is more problematic. Here the flanges of the ERS ________________ are turned_down to ailowwelding or othei_fixing,.

4 Another alternative is to provide some bracing so that the fixing of the support for the ERS does not require an exact fit to the diarneterof the reactorn the first instance at east..

lithe outer concrete retair ingstructure is still present then some addlilonal support biocksbetween the reactorvessel andthe concret:mayhe.lp ________________ strengthen the structurefurther.

6 Anotherpossible rroblem isthat the diameter of the reactormay not be exactly thesame as priortothe accident andtFe ER Smayhaveto be con structed a little undersize.

7 if a steel ringor blocks can be welded onto the innersideofthe reactorthen thiswffl help position the ERSand preventitfaliingwhile beingfixed into ______________________ position Key to Schematic [.iagram # 11 item# Note I Flange Cuff 2 Flange couar 3 Seaflng Flange 4 Flange Sleeve Vent Flange 6 Vent hole(s) 7 Possible site for pumpflneconneclion 8 Tightflt-NO gap thi:s isjust a schematkdiagram 9 Due to the large internal pressurethen restrictingand arrestingthe upward mcvernent ofthe vent fla nge to provide a pump connection point seems a less effective option than plactngthe connection point as shown.

If a new reactoris built wfth the E Sthen theconnectionpoint(s)can be built ________________ intothejacketiowerdownthanthe cap.

* Key to Schematic Diagram # 12 item #. Note I Flangecuff 2 Flange Collar * 3 SealingFlange * 4 Possible siteforpumplineconnection Flange Sleeve 6 Ven.. Flange * 7 Vent hole(s) 8 Tight fit-NO gap this is] ust a schematic diagram 9 Arrangement 315 stro.ngerthan arrangement 2 as it can be cast:fl one piece _________________ ea$ily.

A fourth arrangementwould beto isolatethe region aroundthe pumping connector in aria ngement3 by casting an inverted sump around it.

* Seeschern.aticdiag.rarn#13 Key to Schematic Diagram # 13 item 4* Note 1 Flange Cuff 2 flange Collar 3 SeaiingFiange 4 Possible site for pump iineconnecfion -a VentElange 6 Vent hole(s) 7 These are not holes butshow the line ofthe ca.p behindthis"sump'Ylhesump would be open alongthisdashed line to allowthe pump to circulate coolant, S Tightfit-NO gap this isjüst a schematic dagrarn 9 Afou.rth arrangementwouidbetokoiatetheregion aroundthepuming connector in arrangement 3 by casti ng an inverted sump (shape) around it.

See schematicdiagrarn#13 Key to Schematic Diagram # 14 [tem# Note 1. ClosurePiri 2 Opening I 3 Opening2 4 Opening3 S Opening4 6 Flanges widened to create more force to close barrier.

7 Opening5added 8 Barder Flange 9 NO gap irtended-drawLngisschematic Distanced can bewidened to create a largerarea forthe flangesto catch the force ofan expiosion.Theywin then act like sails beingforced to ciosethevalve _________________ system. Closure Pin closes system if it moves an either direction.