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1 NUCLEAR REGULATORY COMMISSION WASHINGTON, D. C. 20666 z
%......o AUG 2 51978 MEMORANDUM FOR:
E. J. Brunner,' Chief, RO& SB, RI F. J. Long, Chief, RO&NSB, RII G. Fiorelli, Chief, RO&NSB, RIII G. L. Madsen, Chief, RO&NSB, RIV J. L. Crews, Chief, RO&NSB, RV FROM:
R. W. Woodruff, Acting Assistant Director for Technical Programs, IE
SUBJECT:
INSPECTION OF LICENSEE RESPONSE TO IEB-78-03 PER MC 92703 To complete our action on IE Bulletin No. 78-03, " Potential Explosive Gas Mixture Accumulations Associated With BWR Offgas System Operations,"
we have searched the applicable Inspection Report Files for the required re'gional inspection of licensee response per IE Manual Chapter 92703. Out of a total of 25 operating BWR facilities whose licensees were required to take action in response to the Bulletin, we found the corresponding followup regional inspection close-out reported for eight facilities. We need to establish satisfactory close-out at each facility before we can determine the need for further action.
Pertinent background information regarding the stimulus of our interest in determining the need for further action is given by the GA0 report on offgas explosions dated August 4,1978. A copy of the report and a copy of the transmittal to the Comission is enciesed for your information.
In view of the above considerations, we request a status report on the inspection close-out of IEB-78-03 for the operating BWRs within your purview. This should include those closed-out identified as to facility and Inspection Report Number.
Those not yet closed-out should be identified.as to scheduled completion.
Your response is needed as soon as possible.
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Roger W. Woodruff, Acting A sistant Director for Technical Programs Division of Reactor Operations Inspection CONTACT:
C. J. DeBevec, TP 49-28180 8301100053 821207 f,
nth 2545 PDR
Multiple Addressees 2
AU$ 2 51978
Enclosures:
1.
Memo, Abston to Hendrie, et al, dtd 8-14-78 2.
Report, Comptroller General to Chairman Tom Bevill dtd 8-4-78 cc: w/ encl.
N. C. Moseley, IE E. L. Jordan,. IE J. H. Sniezek, IE i
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NUCLEAR REGULATORY COMMisslON WASHINGTON. D. C. 20555
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. s, AUG 141978 MEMORAN00M FOR: Chairman Hendrie Commissioner Gilinsky
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Commissioner Kennedy Comissioner Bradford l
Comissioner Ahearne FROM:
- 0. Gene Abston, Acting Director d'
Office of Inspector and Auditor
SUBJECT:
GAOFINALREPORTTOTHEHONORABLETOMBEh!L*LONOFF-GAS EXPLOSIONS In accordance with our August 24, 1975 memorandum concerning coordination of GAO activities within NRC, the subject report is being sent for your informa tion.
It should be noted that a recommendation directed to the Chairman, NRC',
is contained on page 8 of this letter report.
As you know, Section 236 of.the Legislative Reorganization Act of 1970 requires the Chairman to sJbmit a W/itten statement on actions taken on GAO recommendations to the House and Senate Committees on Government Operations not later than 60 days after the date of the report and to the House and Senate Committees on Appropriations with the NRC's first request for appropriations made more than 60 days af ter the date of the report.
This response on NRC's actions will be coordinated and drafted by EDO.
Should you have any views or comments on 'the subject report, we will be happy to pass them on to GA0.
Enclosure:
Cy subj rpt dtd 8/4/78 cc: Q. Gossick, w/ encl.
S. Chilk, w/ encl.
J. Kelley, w/ encl.
C. Kamerer, w/ enc 1.
K. Pedersen, w/ encl.
J. Fouchard, w/ encl.
H. Shapar, w/ encl.
J. Davis, w/ enc 1.
C. Smith, w/ encl.
R. Minogue, w/ encl.
S. Levine, w/ encl.
H. Denton, w/ encl.
Contact:
Fred Herr OIA, 27051 i
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3-164105 AUGUST 4,1978 The Honorable Tom Bevill Chairman, Subcommittee on Public Works Committee on Appropriations House of Representatives
Dear Mr. Chairman:
In a June 21, 1978, letter you asked us to look into those gas explosions 1/ which have occurred at boiling water nuclear powerplants and to assess the acticns of the Nuclear Regulatory Commission in connection with these explosions.
On Dece=ber 13, 1977, a gas explosion at the Millstone i
nuclear powerplant in Connecticut became widely publici:ed.
An employee a.t Millstone was injured and slightly contaminated with radioactive gases, a building was damaged extensively, and the powerplant was shut down for 10 days.
In our view, the explosion at Millstone, as well as other gas explosions might have been prevented if the Commission had acted decisively and aggressively to require itcensees to take certain precautions.
However, only recently has the Commission initiated actions which should =inimize the possibility of these explosions.
We believe these actions, when implemented, will minimi:e the chances of explosions, but under the Commission's present plans these measures will not be implemented for at least 1 year.
Because the measures are available, we believe the Cc.n-mission should accelerate the process for requiring and imple-menting the actions aimed at minimizing gas explosions at nu-clear powerplants.
1/In the nuclear industry jargon, they are referred to as
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ff-gas explosions.
o EMC-75-99 (30140)
n 3-164105 As you requested, we-did not obtain the Commission's formal comments on this. report.
However, we met with Com-mission officials and received informal. comments wh'ich have been incorporated into the report.
The rest of this report discusses the details of gas ex-plosions which led us to the above conclu: ion.
WHAT ARI GAS EXPLOSIONS AND TEEI A SAZ ARDS ?
Gas explosions are potential hazards only,to the 25 boil-ing water power reactors now licensed to operate in the United States.
In a boiling water reactor, nuclear fuel
- converts water to steam to drive electric generating turbines.
The steam then condenses and returns to the reactor to be reheated.
As it creates steam, the reactor also produces gas which cannot be condensed.
Some of the gas is -radioactive.
An off-gas system is designed to remove this gas f rom the steam.
Through a delaying and filtering process, the radioactivity is reduced and then released to.the environment.
-The off-gas system consists of equipment located away from the reactor building, which separates the gas from the steam, and piping to carry the gas to a release stack.
The stack usually houses fans and filters.
The delay time designed into the o f f-gas system is impor-tant because most of the radioactive gas loses its radioactive properties rapidly.
Very small radioactive particles carried oy the gas are collected by the system filters.
After teing delayed and filtered, the remaining gas, containing a limited amount of radiation, is diluted with air and released to the environment through the stack.
The amount of radiation that can be released is limited by Federal regulations.
At present, 20 of the 25 operating boiling water reactors use a new off-gas system which releases much less radiation than the older system. 1/
Although the new syste= is not re-quired by the Commission, nearly,all of the remaining boiling water reactor licensees, according to the Commission, are com-mitted to installing the system soon to meet new radiation standards.
1/The older system is designed to release about 20 percent of
-. the amoun t allowable by the Commission regulations.
The newer j
system, releases less than 1 percent of the allowable amount.
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B-164105 Over the past several years, about 50 gas explosions have been reported at nuclear powerplants.
According to the Com-mission, none of the explosions resulted in offsite releases of radioactivity which exceeded _the limits specified in the rederal regulations.
But in some cases, these explosions have caused property damage and injuries to workers.
Explosions occur both internally and externally to the system.
In internal explosions, gases contained within the system are ignited.
Internal explosions are not, viewed by the Commission as a problem because the systems 'are designed to withstand these explosions.
Neither. personal 1njury nor property damage is known to have resulted from an internal explosion.
External explosions are generally caused by equipment failure which permits gas leakage.
They can follow an in-ternal explosion which damages or weakens a part of the sys-tem.
The failure of equipment or an internal explosion may permit combustible hydrogen, oxygen, and radioactive gas to escape from the contained system.
If the gas escapes into a closed area, the buildup of hydrogen in the presence of an ignition source could result in an explosion.
The severity and consequences of a gas explosion depend on whether the explosion is internal or external.
Of the approximately 50 explosions reported, 5 were exte:nal and all of these resulted ir. physical damage or personal injury.
The following table shows the consequences of the fi'in external explosions.
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s Iteactor facility Date of and location explosion Probable cause (no_te a)
Damage Dresden 2 4/1973 Welding are from welders working Two workers received 8
Horris, Illinois near an off-gas system filter.
minor burns.
Cooper 11/1975 Improperly installed valve in a One worker received Ilrownville, drain area allowed gas to escape.
major burns and five Hebraska The gas was ignited by a spark others received minor from an air sampler..
radiation exposure, i
Cooper 1/1976 Ice blocked the top of system's Oft-gas building de-Ilrownville, release stack, backing up gas molished,.no injuries Nebraska in the off-gas building.
The to people.
gas was ignited by electrical equipment.
Is r unsw ick 2 1/1976 Ilecause of equipment failure, Minor damage to equip-Southport, North excessive moisture accumulated ment, no injuries to Carolina in a filter.
It froze and people.
blocked gas flow.
Increased pressure drained loop seal al-lowing gas to escape.
Hillstone 1 12/1977 I'irst explosion caused by One worker suffered a Waterford, welding arc.
I.oop seals were concussion, multiple Connecticut defeated allowing gas to es-abrasions, and was cape into base of stack.
Ig-slightly contaminated.
nited by electrical equipment.
,0uilding sustained
,' major damage.
a/The probable cause is determined and documented by the Commission, or its predecessor, the Atomic Energy Commission.
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B-164105.
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At the Millstone-plant, an internal explosion weakened the system and resulted in a much more severe external explo-sion.
The internal explosion weakened seals -in the system.and allowed the hydrogen gas to escape.
The explosien was ignited by heat from a welding arc.
Attempts to replace all the seals in the system were un ~
successful.
As a result, combustible gas escaped into an un-ventilated area at the base of the stack.
According to the Commission, the probable ignition source of the second explo-sion, which occurred about 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> af ter the fi r,s t explosion, was a spark f cm an electrical switch.
The second' explosion blev a metal door fecm the stack base into a warehouse about 200 feet away.
The impact of the door bent a 12-inch structural beam approximately 8 inches.
The blast also removed two 2,000 pound shield plugs f r em the floor of the stack base and did extensive damage to the ceiling.
WEAT RAS THE COMMISSION DONE TO ELIMINATE OR REDUCE THE CHANCE OF GAS EXPLOSIONS?
The Commission and its predecessor, the Atomic Energy Ccamission, were aware of gas explosions as early as 1971 when the first one wa s repor ted.
S ince tha t time, abcut 49 more explccions have been reported.
In a 197 4 report entitled " Review of Explosions in Boiling Water Reactor Off-Gas Systems," the Atcmic Energy Commission discussed the causes of six explosions and the actions that could be taken to prevent future explosions.
The report stated that because of the diverse causes of the explosions, they would continue at frecuent intervals unless system =cdifica-tions were made to minimite ignition sources.
The report did not call for corrective actions to be recuired at all boiling water reactors.
However, since 1974 the Ccmmission has re-quired all boiling water reacters in the design or construction stage to improve the integrity of seals in the off-gas system.
The General Electric Company, the prime vendor of boiling water reactor off-gas syste=s, as early as 1973 sent ecmmuni-cations to all boiling water reactor owners emphasizing the potential hazard of the gas explosions and identifying opera-ting and engineering actions wnich.might be used to prevent them.
In 1976 the General Electric Cc=pany recommended, among other things, that reactor owners (1) label pipes and ecuip-ment containing detonable mixtures of gas, (2) provide for adecuate ventilation to prevent buildup of detonable mixtures, 5
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and-(3); assure the-integrity of all-seals.. Commission officials ;
could not.tell us how man ~y reactor owners may age taken these actions.
s In the past, the Acomic' Energy.Cemmission and the Commis-sion' requested reactor'osners'who-had reported ext'ernal exO' 1
plosions to take steps aimed at: preventing a fimilar:1txploripn y at the same powerplant.
For $ example, an explosi'ch occurradritt a
the Cooper nuclear powerplant in early 19 7 6, 'shich completti.'y
's dumolianed a 3 2-f oo t,.by 48-foo t metal. buildine.
Immed ia te!.y beforeihe'explosionoccurred,';1a'n'tipersonnMikhad. entered'the g to perform their duties < but(noticed 'an g
huildinf and an abnormal ruding of' air' monitoring equioment.
Tr.ere employeesvacatedthebuilding,whichexpidded[shortlythure-[)
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During cleanup, aNpartially melted pbce of ice was ', l, A, found and it-was postulated that the' ice had forted,at the tod '
'of the stack the gas to backup in therstacf building.through which the; gas 'is released
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Ignit' ion was p:
ably caused 'by a s, park f rom one of the electricaY deVicis 'in ~ i N"
4 the buildin.gi, 4 f.
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/js The T:mmis_sion requestedithe cwner of the Coooer cower-1^}
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r plant to. heat and insulate.*.he Mpper.10-f oot se.ction o'f che, i
' stack pspd to prevent a no tnir, i'c e bd i'1'd um.
F am 'nd a i ticMng andpipingchangeswhichmayMveprevented,the'e@fostonYvere'
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M so made'.
However, the Corr <nission did ne t,readire 'any othe rf plant cwnet's to assess and edere'et gas buildups in stack areas. I
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.Tne M.111 stone explosion is another exammie o f en'elccmmis-2
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sion's action in recpen'se 'ev,/in e'xternal explcsion.
In 9.is f
i case, the Commissiobeequiri:hthe owner te imp:ove seal,ihteg- ~
city,. Identify and label pipes,,and improve' mtilation.,Th'it cost aheut $10,000 and was cocpleted.ia.less than 1% dayr,a Agairi,,the Commission requited the$e' correcticas 'enly at P.ill j- '7 stone ant ldid-not apply them to 'other plants'.
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The first' action. Ma ken by the Ccmmissic.r. that waq directst z
at all operaj 'ig bollhg1 water teactor 'ovneis was to isrue~e bulle tin orc Febr uaiy -5:, 19.78,.
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3-164105
--describe actions to prevent accumulation of explosive t
gas, and describe monitoring equipment that will warn of the accumulation and disposal of such accumulations;
--describe procedures for' assuring seal int 1grity; and
--review operating and emergency procedures to-respond properly to gas explosions.
All owners have responded, and the Commission has begun its review of the responses.
The Commission's review will first involve inspecting each reactor to verify t,the information in the response.
Then the Commis3 ion will determine what addi-tional steps, if any, are needed to assure that every reactor owner has taken or will take actions to minimize the possibil-ity of external explosions.
Commission of ficials told us that this inspection and review will take about 6 months, and that another 6 months will be given to the reactor owners to comply.
CONCLUSIONS Since 1971 about 50 gas explosions have been reported at boiling water reactors.
These explosions have caused degrada-tion and failure of off-gas systems, radiation exposure and other injuries to personnel, physical damage to facilities, and lost revenues during reactor shutdowns for repair.
The Commission and its predecessor, the Atomic Energy Commission, have known about the problem, its ha:ards, and
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actions which would minimize the eroblem for some time.
The Commission has required some action on plants under design and construction, however, no action has been taken on opera-ting plants except on an after-the-fact, case-by-case basis.
Measures to eliminate or reduce explosions, seen as ventilat-ing closed areas, have been known for years by both industry and the Commission.
In most cases, these measures appear to be relatively simple and are not as time-consuming as one might believe.
At the Millstone factitty, for example, the total cost was about 510,000, and the work could have been co=-
pleted during a normal shutdown A direct cause of the Mill-stone explosion was lack of ventilation in a closed area.
The explosion at Millstone may not have occurred if the stack ares had been ventilated.
Although the Commission has f ailed to act promptly, we believe the recent actions, when !=plemented, will minimize the chances of gas explosions.
However, according to the Com-miss ton's present plans, it will take up to a total of 1 year s'
before corrective actions are implemented at all facilities.
These corrective actions inc.lude such measures as prov. ding 7
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B-164105
~ ventilation in closed' areas where gas may accumulate, assuring seal integrity, and protection of piping from ignition sources.
In the past, corrective actions have been taken at individual powerplants in relatively short time frames; therefore, the Commission should accelerate its process and promptly require all powerplants to take those measures necessary to provide a greater margin of safety.
In commenting on this report, the Commission stated that its efforts are timely and disagrees with accelerating the actions.
Commission officials said that off-gas systems are not reactor-safety related and therefore present no danger to the public.
However, the Commission did recognize that injuries to plant workers, property damage, and lost revenues due to reactor shutdown can occur.
Further, although Commission of-ficials recognize that gas explosions are an occupational safety issue that could be considered the responsibility of the Occu-pational Safety and Health Administration, the Commission be-lieves it should be the lead agency on this problem because the Commission has the experience and expertise needed to deal with the problem.
RECOMMEMDATICN GAO recommends the Chairman, Nuclear Regulatory Commission:
--Accelerate the process for requiring and implementing the actions aimed at minimizing gas explosions at nuclear powerplants.
These actions should include
/entilation of closed areas where explosive gas may accumulate, assuring seal integrity, and protection of piping from ignition sources.
As arranged with your office, unless you publicly announce its contents earlier, we plan no further distribution of this report until 7 days from the date of the report.
At that time we will send copies to interested parties and make copies avail-able to others upon request.
Sin
- / yours, JW
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Comptroller General of the United States 8
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