ML18078A406

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Forwards Comments in the Form of Redraft of Commission Paper Re Proposed Fed Register Notice Abnormal Occurrence Event, Loss of Containment Integrity W/Encl Draft Notice of Issuance
ML18078A406
Person / Time
Site: Salem, Millstone  
Issue date: 11/11/1978
From: Harold Denton
Office of Nuclear Reactor Regulation
To: Haller N
NRC OFFICE OF MANAGEMENT AND PROGRAM ANALYSIS (MPA)
References
TAC-42588, NUDOCS 7811220107
Download: ML18078A406 (26)
v • d • e


Text

....

Ntiv ~ 1.1978

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.NRC PD OEisenhut WRusse.11.

. MEMORANDUM.FOR:. Norman-M. lia.1ier, Director

. Office of Manager:iant & Prograrns.l\\nalysis

  • VStell o
  • . BGrimes SUBJECT;.
  • : HDenton

.. ECase H. R. Denton~- Di rector "

JMi ll er Office of riuclear Reactor.R&aulation.

GZech:

\\'O' MConne~

. *PROPOSED ABNORMAL GCCURREHCE* - LOSS OF cmffArnMEHT DDavis IMTEGRIT.Y *

. PCheck Gla inas*

  • .: VN()onan
  • . Youi" memorandum of September 11 ~ 1978~- on the same subject requested GKni ghton NRR comment by September 14, 1978.

On Friday, September: 8~ 1978s u RClark a similar event at Salem.Unit No. 1 was reported.

NRR recommends. that.FPagano this event be reported as an Atn10.m1al Occu.rrenceo ** *our comments; in the ASchwencer

  • form of a complet~::.! redraft of the Commission Paper~ are enclosecia DZiemann
  • . Tipp_ol ito

~n light of these two events; and the *genaric *imµl icati ons for operatinf~Rei.d

.. reactors; NRR is taking~ ac.tion* to review the entire. question.of puruing JMcGough...

containment' during operation -on an 11rgentbasi s because tt!ese ir:ifHict' MMlynczak_ ~-,

  • safety. { i.<Sq the' loss cf containin*.:nt isolation and degraded ECC~ *

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performance);...

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Two additional crnnmants concernJng* your September 11!>.1978 r:;mor*andur.f, ~ftl?t:d-S--4~

are required:

1

  • The. MRR position regarding purging through large diameter va 1 ves as..

stated_in Contairnnent Systems Branch Position BTP 6-4 is appliC.able to new. plants (i.. e., CP. and OL reviewsL

2. Specific* cal cu! at ions were not perfonuecf becaiise they we rt~ not needed, rather than for any considerat'ion *of-.cost.

.. 7 811 2 2 () l 01 cc: c.- V. Smiti1, Di rec:tor NMSS S:. Levine,, Di rector~ RES Jh"igi!!aHSigned by. *

  • M. ft ~entmi.

Marold R. Dent.on, Oh~ector.. _,

Office. of Nuclear Reactor Regulation J. G. Davis! Acting Director!< IE R..

B~ Minoguej) Director. SD H. K. Shapar, Executive Legal Director*

S~ H. Hanauer, Technical Advisor, EfJO J..

NRC FORM 318 (9-76) NRCM 0240 U. s. GOVERNMENT PRINTING 'OFFICE: U178 -

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DEisenhut BGrimes WRussell HDenton

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. MEMOR:AflDUM F()R:

N~an M.* Hai ier, Oirecto.r '.

~~!~~~r FROM:

Off_!~* of rtianagement.&*_~rograms.* ~nalysis MConner H. R. 'Btnton, Di rector *. *.-

DDavi s

  • **Office °'\\Nuclear Reactor Regulati~n

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SUBJECT:

PROPOSED ABNORMAL OCCURRENCE - LOSS OF CONTAINMENT.

VNoonan

  • INTEGRITY \\

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FPagario_

Your memorandum of Sep""'en1ber 11\\1978 on the same subJ" Pct rPouested

  • ASchwencer

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DZi emann N~R canment by _September 14, 1978,.. On friday, September 8, 1918, a

  • TI 01 ito

. "a similarevent atSalemUnit No. l\\\\!'JaS reported.

NRR recommends ~h~t-RR~~d..

. *this event be *reported _a~ qn ~Atil}Ol'Tlla'\\_ ~cc~rrence. Our_ comments, in the JMcGough form of.a_ complete r~dratt or t_h~ Comn11 ssrnn Paper, :_are.enc:;losed.

  • MMlynczak

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In light of these ui~ everi-ts, and _the 9~i{eric implication.s for operating re.actors,. NRR is*tak.ing action.to*revievi 't;;he entirt:; question of,purg)ng.

cpntai nment during operation on _an urgent -b\\asis beca_use these '.impact_

s:fety (i.e., th~ l_oss of cont~iriment":i*s.ol_a~on and* 4egraded ECCS p... rfonnance).

_. \\

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Two additional cdnments concerning your September 11'~ 1978 memorandum

.are.required:

  • . '.:. * \\.._ * *

. : \\:.

r.. The NRR pos i t1 on *regarding purgi rig 'through farg\\.. diameter valves as
  • st11tetj ~n_Conta~nment Systems Branch,Pos~tion BTP\\_6-4 is applicable to new plants. ( l.e., CP and OL revie~s) *.
  • 2. *Specifi.c cal cul a'tfons \\*iere' not performed because they\\e~e not needed; rat)1er ~han for any considerati.on of cost... \\

.. cc:

C. V. Smith's-Di rector NMSS

  • S. Levine, Director, RES

- Harold R. Denton~* Di rector

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  • Office of Nuc 1 ear Reactor Regul a,ti on.

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HRDenton I./.

J. G. Davis, Acting Director~ IE R. B. Minogue, Di rector, SD H.K. Shapar, Executive Legal.Director

s. H. Hanauer, Technical Advisor, EDO J *. Foucha rd*, Oi rector; PA o~~f DOR~~~

DOR:DIR NRR

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NRC FORM 318 (9*76) NRCM 0240 UI s. GOVERNMENT PRINTING_OF_FICE1 19715- ~21S*IS24

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Dockets(i~*50-272 NRG PDR DEisenhut WTRussell VStello 50-336)

JMiller GZech FOR:

f.1. l'laller $ Di rector BGrimes Marrngc-ment & Pn:i~wru.1s Ana.1ysi s

~L Re DcJton, Director Office 01 Nuclear Reactor Regl~iation MCo.nnor DDa vis PCneck Glainas GKnighton VNoonan RClark FPagano

SUBJECT:

PROPOSED f\\.B 'ORMfU. OCGlJR~ENC[

INTEGRITY

- LDSS OF CmffP,FJf.JUJT ASchwencer DZiemann Tippolito Your memorandum of September 11 3 -g7g, on tl1e same sutijcct r9qu.;:,;sted RReid JMcGough NRR comment by September H~ 1978 Late in the: day on Friday,

~eptember 8,, 19?3,_a_ s~mi1ar ~v~nt\\t Salcm_Un~t No. 1 *,ms report1~d.

NRR reccr."Timends that. t:h1 s event oe 1 n foded rn "Ghe PD,,

O;!r comnerrts ~

in t!1e fon;1 of a red1a'ft, tsf the Cm:1miss*inn Paper are t.mc1osed.

In *light of thGse t:~w events, ani:l the 9e:*eric imp1icv.tions for operatin~J reactors, NRR. is taki r.g act*i on to revi ei*1 ~1~ entire questfon of rurgi !liJ containment during op8ration on an urgf:nt b sis~

Two adtlitional CDl!lffil~nt~; concerning your Septfa £H:r' n, 1978 meraorandum are required:

1. The HRR position upon purging thi"OUqh large."iameter valves as stated in Contairm10nt Systems Branch PositiOt) "TP 6-4 is app1icab1e to nc1i"t plants (i.e..,, CP and Ol r~viev-;s).
2.

Spec*i fie cal c1.fi atfons ~:ere not performed bec<mse *;H:y vK:l"e not needed rather than for a!ly consideration of cost.

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'j V. Smith, Di rector N1lSS Li:~vi ne, Di rector 11 RES Harold H. Denton, Office* of Nuclear Reactor G. Davis~ Acting Director, IE i3 4 Mi nocme, Director, SD K..Shaoa r,,. Ei'~ecut i ve leqa l t:H rector H. Hanauer~ Technical ;'l,dvisor~ EDO

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9 UNITED'STATES NUCLEAR RF.GULATORY COMMISSION WASHINGTON, D. C. 20555 November ll, 1978 MEMORANDUM FOR:

Nonnan M. Haller, Director FROM:

SUBJECT:

Office of Management & Programs Analysis H. R. Denton, Director Office of Nuclear Reactor Regulation PROPOSED ABNORMAL OCCURRENCE - LOSS OF CONTAINMENT INTEGRITY Your memorandum of September 11, 1978, on the same subject requested NRR canment by September 14, 1978.

On Friday, September 8, 1978, a a similar event at Salem Unit No. 1 was reported.

NRR recanmends that this event be reported as an Abnonnal Occurrence. Our canments, in the fonn of a canplete redraft of the Commission Paper, are enclosed.

In light of these two events, and the generic implications for operating reactors, NRR is taking action to review the entire question of purging containment during operation on an urgent basis because these impact safety (i.e., the loss of containment isolation and degraded ECCS perfonnance}.

Two additional canments concerning your September 11, 1978 memorandum are required:

1. The NRR position regarding purging through large diameter valves as stated in Contairment Systems Branch Position BTP 6-4 is applicable to new plants (i.e., CP and OL reviews}.
2. Specific calculations were not perfonned because they were not needed, rather than for any consideration of cost.

cc:

C. V. Smith, Director NMSS S. Levine, Director, RES

/r#7 t12.L Harold R. Denton, Director Office of Nuclear Reactor Regulation J. G. Davis, Acting Director, IE R. B. Minogue, Director, SD H. K. Shapar, Executive Legal Director S. H. Hanauer, Technical Advisor, EDO J. Fouchard, Director, PA

Contact:

.W~ T~ Russell, NRR 492~8256 *...

._,*~**.".":_ 3

FOR:

FROM:

SUBJECT:

PURPOSE:

DISCUSSION:

The Commissioners Lee V. Gossi ck Executive Director for Operations ABNORMAL OCCWRRENCE RECOMMENDATION - LOSS OF CONTAINMENT INTEGRITY DRAFT Approval of an abnonnal occurrence detennination.

Enclosure l is a proposed detennination of an abnonnal occurrence involving a loss of containment integrity while purging at Millstone Unit No. 2 and Salem Unit No. l.

Example II.B.2 of the Abnonnal Occurrence policy statement notes that a major degradation of primary contairment boun~, should be considered an abnonnal occurrence.

No press release was issued by the NRC.

The licensee for Millstone Unit No. 2 issued a press release on July 25, 1978.

The licensee for Salem Unit No. l did not issue a press release.

Following approval, the Office of Congressional Affairs will notify the Congressional Committees of the intent to publish the Federal Register Notice.

COORDINATION:

The Offices of Nuclear Reactor Regulation, Nuclear Materials Safety and Safeguards, Nuclear Regulatory Research, Inspection and Enforcement, Standards

Contact:

J. L. Crooks, MPA 492-7735 **

I I i; SCHEDULING:

Enclosure:

DRAFT Development and Public Affairs concur. The Executive Legal Director has no legal objection.

Staff review was ccxnpleted in October 1978.

Publication should be made by November 3, 1978.

Lee V. Gossi ck Executive Director for Operations Proposed Federal Register Notice Note:

Commissioner's ccxnments should be provided directly to the Office of the Secretary by close-of-business ____ _

-j

NUCLEAR REGULATORY COMMISSION ABNORMAL OCCURRENCE EVENT LOSS OF CONTAINMENT INTEGRITY Section 208 of the Energy Reorganization Act of 1974, as amended, requires the NRC to disseminate information on abnormal occurrences (i.e., unscheduled incidents or events which the Commission determines are significant fran the standpoint of public health and safety).

The following incidents were determined to be abnormal occurrences using the criteria published in the FEDERAL REGISTER on February 24, 1977 (42 FR 10950).

Appendix A (Example II.B.2) of the Policy Statement notes that a major degradation of *** primary containment 0..

bouncrry, can be considered an abnormal occurrence.

The following description of the events also contains the remedial actions taken.

Date and Place - On July 26, 1978, the Northeast Nuclear Energy Company {NNECO) reported to the NRC an event at Millstone Unit No. 2, a pressurized water nuclear plant located in New London County, Connecticut.

On September 8, 1978, the Public Service Electric and Gas Company (PSE&G) reported a similar event at Salem Unit No. 1, a pressurized water nuclear plant located in Salem County, New Jersey.

. I

7590-01 2 -

Nature and Probable Consequences At nuclear power plants two of many safety features are the containment systems and the emergency core cooling systems.

The containment systems._ m~IJ,D.~ a-p._ss'"°'

a large~structure or vessel surrounding the reactor and primary coolant wi..'~ *~

system areas~ designed to be a leak tight enclosure to limit accidental releases of radioactivity to the envjronment. The emergency core cooling airio~ual "1 systems (ECCS) are designed to~supply noolant to mi ti gate the consequences of postulated events where the nonnal coolant is lost, that is, loss of coolant accidents (LOCAs).

To maintain the temperature, humidity, pressure and the radioactivity levels, within specified limits, the containment enclosures are designed with purging systems which can add fresh air and exhaust the containment atmosphere.

To provide for containment integrity, each purge inlet and outlet line penetrating the containment has two redundant i sol at ion val ~es,

..f.o pt:~""".~"'

~

as do the other contai1111ent penetrations.

Thes~ valves, which are efteR Jur5,..ac.ci(>

in the open condition during operation, are~to automatically close in very short time period, if a plant condition occurs requiring their closure.

At many of the operating nuclear power plants, the normal containment

\\.W.O\\'(. ~

purge systems use large lines - ranging fran two feet totfive aRs eRe ~

Ral fl"feet in diameter.

7590-01 flRA.fl In May 1976, Commonwealth Edison Company reported that they had ceased the practice of purging containment during operation at Zion Station after having detennined that a safety analysis had not been perfonned to assess the affect of purge valve closure time upon ECCS perfonnance.

Preliminary calculations by Commonweal th Edi son Company indicated that contaillllent pressure would fall below that assumed for the design basis loss of coolant.accident and that the existing analysis was therefore not conservative.

The NRC review of this event concluded that the effect of purging upon ECCS performance was generic to many operating reactors. However, the significance of this event for public health and safety was determined to be minor when evaluated on more realistic -Nsi'!, i.e., automatic valve closure times on the order of 5 to 10 seconds, with peak pressures in contai1111ent being reached on the order of 1-2 minutes.

This item was therefore given relatively low priority for re~lution.

The events reported at Millstone Unit No. 2 and Salem Unit 1 involved loss of the automatic valve closure capability for these valves. Such loss of closure capability significantly degraded both the contai1111ent and the ECCS capability for limited time periods, while the units were operating at power, should they have been necessary to respond to design basis events.

DRAFT

\\

7590-01 DRAFT:

I Based on our assessment of these events, the NRC believes that tighte~ controls are warranted on purging and venting operations to assure contairrnent integrity at these two and other nuclear power plants.

The reported events were:

Millstone Unit No. 2 Event - During a review of operating procedures on June 25, 1978, the licensee discovered that since May l, 1978, intennittent contairrnent purge operations had been conducted at the plant with the isolation signals to the redundant containment isolation valves in the purge inlet and outlet (48 inch butterfly valves) manually overridden and inoperable. The isolation signals, which are required to automatically close the purge valves for containment integrity if a plant condition requiring closing then occurs, were manually overridden to allow purging of contairrnent with a 11 high radiation 11 signal present.

The manual override circuitry, designed by Bechtel (the plant's architect/engineer), not only defeated the 11 high radi ation 11 actuation signal to close these valves, but also bypassed all other isolation signals to these valves. The operator had no indication that this condition existed. To manually override a safety actuation signal, the operator cycles the valve control switch to the closed position and then to the open position. This action energizes a relay which

7509-01 DRAFT overrides the safety signal and allows manual operation independent of any safety ~ctuation signal. This circuitry is designed in this manner to pennit re-opening of certain valves after an accident to allow manual operation of safety equipment.

Frcxn May 1 to July 25, 1978 (about 2,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br />), the containment of Millstone 2 was purged to reduce radioactivity levels, for interim periods ranging frcxn 5 minutes to 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br />, with a purge occurring for approximately 9% (180 hours0.00208 days <br />0.05 hours <br />2.97619e-4 weeks <br />6.849e-5 months <br /> total) of the total time period. For each purge, the levels of radioactivity released to the environment were monitored and were within Technical Speci fi ca ti on requirements.

However, the Technical Specifications and Regulations (GDC 56) both require contaiment isolation valves in lines that open directly to contairrnent atmosphere to be capable of automatic closure during purging or other operation or such lines must be acceptable on some other defined basis to mitigate the potential consequences of postulated design basis accidents.

r Salem Unit No. l Event - On September 8, 1978, the staff was advised that, as a matter of routine, Salem Unit l has been "venting" the containment through the contai1111ent ventilation system valves to reduce pressure. In certain instances, this venting has occurred with the containment "high particulate" radiation monitor isolation signal overridden to the purge valves and pressure-vacuum relief vent valves. Override of the containment isolation signal was acccxnplished by resetting the train A and B reset buttons. Under these circumstances, six valves in the containment vent and purge systems could be opened with a high particulate isolation signal present. This override was perfonned after verifying that the actual contai1111ent particulate levels were acceptable for venting.

The licensee, after further investigation of this practice, determined that the reset of the particulate alarm also bypasses the containment isolation signal to the purge valves and the vent valves and therefore, these valves would not have automatically closed in the event of a safety injection (ECCS) signal.

-590-01 DRAFT The licensee has modified its procedures to preclude venting of the containment through the purge valves when the containment "high particulate" alarm exists.

Nature and Probable Consequences - Purging does not occur continually at the facilities.

As mentioned earlier, purging normally occurs with all isolation signals operative. Containment high radiation would result in rapid isolation well within the design basis assumptions and the conse-quences would be as "realistically" evaluated in the staff Environmental Impact Statement.

In the unlikely event of a postulated design basis loss of coolant accident (LOCA) while purging with these containment penetrations open and their isolation signals inoperative the contain-ment boundary would be degraded and the emergency core cooling system (ECCS) performance would also be degraded due to the reduced (a few psi) containment backpressure.

The low containment backpressure would result in a calculated reduction in core reflood rate and heat removal capability and would lead to calculated higher fuel cladding temperatures.

It is unlikely that operator action could be taken in time to close the valves to prevent degraded ECCS performance since (1) in approxi-mately one to two minutes, blowdown would be complete and peak contain-ment pressure would be reached, and (2) there would be no indication to the operator that the isolation signals D R A F T

I~

7590-01 had been bypassed.

The only means the operator would have had to identify the valve status would be the valve position indication. Even if the operator were to take manual action, it is questionable whether the valves would be able to close against the blowdown flow rate through the penetrations.

Cause or Causes - The events resulted due to procedural inadequacies and design deficiencies. While the containment atmospheres were properly sampled and the purging (venting) discharges were within regulatory requirements, the procedures did not adequately address the operability of the purge valves and the limitations on overriding the closure signal.

The requirements for valve operability were not discussed, and the related Technical Specifications were not referenced in the procedures.

Design deficiencies contributed to the event as the override condition bypassed other safety signals and is not annunciated.

Action Taken to Prevent Recurrence Licensees Northeast Nuclear Energy Company (NNECO) - The immediate corrective action taken by NNECO, at Millstone Unit No. 2, was to close, deenergize and remove from service (tag out) the containment purge valves.

~590-01 Future NNECO actions include the development of procedure revisions and submission of proposed changes to the Millstone Unit No. 2 Technical Specifications. These changes would allow somewhat higher containment radiation monitor setpoints, still based on remaining well within allowable effluent release limits, which will pennit the flexibility of containment purging over a wide range of nonnal containment conditions without overriding the "high radiation" signal.

Public Service Electric and Gas Company {PSE&G) - The immediate corrective action taken by PSE&G at Salem Unit No. l, was to cease venting when orerride of contairment isolation signals is involved.

In addition, PSE&G initiated design changes such that the containment ventilation isolation valves will not be prevented from automatic closure by a safety injection signal should any of the containment radiation monitor alanns be overridden.

NRC - In addition to reviewing the licensees' corrective actions for these events the NRC staff is reviewing the generic implications for other facilities.

DRAFT l.

.590-01 All operating reactor licensees, whose Technical Specifications do not prohibit purging during operation will be requested, to commit to cease pur~ing during operation or to provide a basis why purging during operation should be permitted. The staff basis for allowing

~"I" ~T" c..loi*,.."> \\J~\\._J limited purging'Y'during operation will require a demonstration of the

. I capability of these valves to close under postulated accident conditions and a 90-hour per year Technical Specification limitation upon purging

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during operation. The staff basis for allowing unlimited purging during operation will require; (1) demonstration of the capability of the valves to close under postulated accident conditions, (2) an evaluation demonstrating acceptability of the impact of purging during operation upon ECCS performance (i.e., containment backpressure), (3) containment purge and isolation instrumentation, and control circuit designs which conform to IEEE Standard 279-1971, and (4) an evaluation demonstrating acceptability of the radiological consequences of the design basis loss of coolant accident initiated during purge operations.

~

All licensees will be requested to review~safety-actuation signal circuit designs which incorporate a manual override feature to insure (1) that override of a single safety actuation signal does not bypass other safety actuation signals and (2) that the use of the manual override feature is appropriately annunciated. Licensees will be required to report the results of their review and their corrective actions for any non-conforming override circuits.

DRAR

.590-01 11 In addition, all licensees will be advised of the necessity for proper management controls for the use of manual override of safety signals during non-emergency conditions.

IE will, through their inspection program, assure *that licensees have initiated appropriate follow-up action.

DRA*FT FOR THE NUCLEAR REGULATORY COMMISSION Dated at Washington, D.C., this day of October 1978.

Samuel J. Chilk Secretary for the Commission

\\

MEMORANDUM FOR:

FROM:

SUBJECT:

UNITED STATES NUCLEAR REGULATORY COMMISSION

\\

WASHINGTON, D. C. 20555 SEP 1. 1 1978

/Ji. R. Denton, Director, NRR C. V. Smith, Director, NMSS S. Levine, Director, RES J. G. Davis, Acting Director, IE R. B. Minogue, Director, SD H. K. Shapar, E~cutive Legal Director S. H. Hanauer2/Technical Advisor, EDO J. Fouchard 'Uirector, PA Norma~~ller, Director Offiie.-uf Management & Program Analysis

--w_i9f~tD ABNORMAL OCCURRENCE - LOSS OF CONTAINMENT

_,.>f ffTEGRITY Enclbsed is a Commission paper with a proposed Federal Register Notice in regard to the subject above.

The event is under.consideration as an abnormal occurrence since it appears to satisfy Example II.B.2 of the abnormai occurrence policy statement; i.e., procedural deficiencies which result tn 1 oss of pl ant capability to perform essential safety functions such that a potential release of radioactivity in excess of 10 CFR Part 100 guidelines could result from a postulated transient or accident. This particular event involved an unanticipated bypassing of the automatic containment isolation signals to the containment

  • purge valves during containment purging with the plant at power.

This type event was previously noted to have possible generic implications to certain plants in late 1975.

At that time the NRC staff decided to not permit purging during power operation through large diameter butterfly valves and to require a separate system for purging at power.

At that time generic safety concerns were noted regarding the capability of the large purge valves to close against LOCA steam flow, the effects of low backpressure on ECCS performance, and purge valve seal leakage.

However, due to the availability of the automatic isolation feature, the low probability of simultaneous failures, and other considerations, the item was

. then not considered high priority.

The occurrence of this event and the identification of apparent design deficiencies now seems to warrant priority treatment of the safety concerns previously identified.

Contact:

P. Bobe/J. Crooks, MPA 492-7735

\\r' *

.. 2 -

SEP 1 l 1978 In order to save funds, we understand specific calculations have not been made by NRR for the Millstone Unit 2 event to support the statements regarding degraded ECCS performance, fuel failure, and releases exceeding 10 CFR Part 100.

Previous similar calculations and extrapolated model performance were used to predict the consequences.

Per L. V. Gossick's memorandum to you dated August 23, 1977, MPA will set up an informal briefing with the Commission within 3 days after staff determination.

The proposed attendees are IE, NRR and MPA.

It is suggested that NRR take the lead at the briefing.

Your review, comments and written (or telephone) concurrence are requested by close-of-business Thursday, September 14, 1978.

If you have questions or wish to discuss details, please contact J. Crooks or P. Bobe of my office at 492-7735.

frV~vvvvvi Norman M. Haller, Director

~

(.:___ Office of Man.agement & Program Ana 1 ys i s

Enclosure:

Commission Paper cc w/encl:

L. V. Gossick, EDO D. Eisenhut, NRR (2)

E. Jordan, IE (2)

R. Fonner, ELD G. Gower, IE G. Beveridge, NMSS H. Scott, RES R. E. Alexander, SD.

M. Taylor, RES W. T. Russell, NRR R. D. Smith, NMSS R. Gramann, NMSS

~*-------

~-~--------...~-*****--~---!

FOR:

FROM:

SUBJECT:

PURPOSE:

DISCUSSION:

ORA FT The Commissioners Lee V. Gossick Executive Director for Operations ABNORMAL OCCURRENCE RECOMMENDATION - LOSS OF CONTAINMENT INTEGRITY Approval of an abnormal occurrence determination. is a proposed determination of an abnormal occurrence involving a loss of containment integrity while purging at Millstone Unit No. 2.

Example II.B.2 of the abnormal occurrence policy statement notes that a procedural deficiency which results in a loss of plant capability to perform essential safety functions, such that a potential release of radioactivity in excess of 10 CFR Part 100 guideltnes could result from a postulated transient or accident, can be considered an abnormal occurrence.

No press release was issued by the NRC.

The licensee issued a press release on July 25, 1978.

Following approval, the Office of Congressional

  • Affairs will notify the Congressional Committees of the intent to publish the Federal Register Notice.

COORDINATION:

The Offices of Nuclear Reactor Regulation, Nuclear Materials Safety and Safeguards, Nuclear Regulatory Research, Inspection and Enforcement, Standards

Contact:

J. L. Crooks, MPA 492-7735

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SCHEDULING:

Enclosure:

Development and Public Affairs concur.

The Executive Legal Director has no legal objections.

Staff review was completed in mid-September, 1978.

Publication should be made by October 3, 1978.

Lee V. Gossick Executive Director for Operations Proposed Federal

. Register Notice Note:

Commissioner's comments should be provided directly to the Office of the Secretary by close-of-business

7590-01 DRAFT e

NUCLEAR REGULATORY COMMISSION ABNORMAL OCCURRENCE EVENT LOSS OF CONTAINMENT INTEGRITY Section 208 of the Energy Reorganization Act of 1974, as amended, requires the NRC to disseminate information on abnormal occurrences (i.e., unscheduled incidents or events which the Commission determines are significant from the standpoint of public health and safety).

The following incident was determined to be an abnormal occurrence using the criteria published in the FEDERAL REGISTER on February 24, 1977 (42 FR 10950).

Appendix A (Example II.B.2) of the Policy Statement notes that a procedural deficiency which results in a loss of plant capability to perform essential safety functions, such that a potential release of radioactivity in excess of 10 CFR Part 100 guidelines could result from a postulated transient or accident, can be considered an abnormal occurrence.

The following description of the event also contains the remedial actions taken.

Date and Place - On July 25, 1978, the Northeast Nuclear Energy Company (NNECO) reported to the NRC an event at Millstone Unit No. 2, a pressurized water nuclear plant located in New London County, Conn*ecti cut.

7590-01 Nature and Probable Consequences - During a procedure review, the licensee discovered on July 25, 1978 that since May l, 19J8 intermittent containment purging operations had been conducted at the plant with the isolation signals to both redundant containment isolation valves (48 inch butterfly valves) in the purge inlet and exhaust penetrations bypassed.

The isolation signals which are required for containment integrity were bypassed to allow a purging operation to proceed.

The bypass circuitry, designed by Bechtel (the plant's architect/engineer), not only defeated the high radiation signal to these valves, but all other isolation signals to these valves as well.

The circuitry is designed for permitting 'post.,.

accident' operation of certain safety equipment.

Purging of the containment at this and some other plants is currently permitted on a periodic basi.s in order to reduce the airborne radiological activity levels within the containment.

The duration of the purging periods at Millstone Unit No. 2 during May l, 1978 to July 25, 1978 (about 2000 hours0.0231 days <br />0.556 hours <br />0.00331 weeks <br />7.61e-4 months <br />) extended from 5 minutes to 31 hours3.587963e-4 days <br />0.00861 hours <br />5.125661e-5 weeks <br />1.17955e-5 months <br />, with the fatal purging occurring for approximately 9% (180 hours0.00208 days <br />0.05 hours <br />2.97619e-4 weeks <br />6.849e-5 months <br /> total) of that time.

For each purging, the levels of radioactivity released to the environment were monitored and were within technical specification requirements; however, the containment

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7590-01

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isolation valves are required to 'be automatically isolable during the purging operations to mitigate the consequences of postulated design basis accidents.

The NRC staff estimates that, in the event of a postulated design basis loss of coolant accident (LOCA) while these containment penetrations were open, the emergency core coolant system (ECCS) performance would have been degraded due to the reduced containment backpressure.

The resultant reduction in core reflood rate and heat removal capability would lead to higher fuel cladding temperatures, virtually assuring significant perforation of the fuel cladding.

The resulant release of the fission gas inventory from the fuel, in combination with the excessive containment leakage, would lead to off-site doses well above 10 CFR Part 100 guidelines.

In this event, if a postulated design basts LOCA, a low probability event, had occurred during one of the purging periods, it is unlikely that adequate operator action could have been taken in time since (a) in approximately one to two minutes, blowdown is complete and peak containment pressure is reached, and (b) there was no indication to the operator that the isolation signals had been bypassed.

The only means the operator would have had to identify the valve status is the valve position indication; and even if the J

fl 7590-01

.. operator were to take manual action, it is questionable whether the valves would have been able to close against the blowdown flow rate through the penetrations.

Cause or Causes - The event resulted due to procedural inadequacies and possible design deficiencies.

While the containment atmosphere was properly sampled and the discharges were within regulatory require-ments, the procedures did not adequately address the operability of the purge valves.

The requirements for valve operability were not discussed and the related technical specifications were not referenced in the procedures.

Design deficiencies contributed to the event as the bypass condition is not annunciated nor is manual reset available.

Action Taken to Prevent Recurrence Licensee - The immediate corrective action taken was to close, de-energize and tag the purge valves to prevent them being opened.

The licensee is currently purging through a smaller line, which has proper isolation capability.

The licensee is making procedure changes which will prevent overriding the purge valves open while the reactor is critical.

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S a-4 ~1111*s*9t*t*o~,---~~~~~

' Future actions include the development of proposed changes to the plant Technical Specification to allow higher containment radiation monitor gaseous and particulate setpoints which will permit normal containment purging.

In addttion, the licensee will review the need for.the isolation signal bypass and develop revised procedures for containment purging.

NRC - In addition to reviewing the licensees corrective actions for this event, the NRC is reviewing any generic implications at other facilities.

The NRC will request that other facilities look for similar procedural or design deficiencies.

In addition, NRC may require each licensee to:

(1) demonstrate by testing that the purge isolation valves can close against the dynamic forces of a LOCA, and (2) perform leakage tests of the purge isolation valves after each purging operation.

In lieu of these requirements, a commitment to keep the purge systems closed during normal plant operation would be acceptable.

for the Nuclear Regulatory Commission Samuel J~ Chi1k Secretary of the Commission Dated at Washington, D.C. this day of September 1978.

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