ML19332A992

Discusses Response to ACRS Re Reactor Coolant Pump Trip & HPI Termination Criteria.Agrees W/Comments by Accrs W/Exception of Two Items

ML19332A992
Person / Time
Issue date:	09/03/1980
From:	Zech G Office of Nuclear Reactor Regulation
To:	Fraley R Advisory Committee on Reactor Safeguards
References
ACRS-GENERAL, NUDOCS 8009190416
Download: ML19332A992 (2)

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NUCLEAR REGUgTORY CoMMisslON wasmuct k o. c. asss

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G-E MEMORANDUM FOR:

R. F. Fraley, Executive Director 3 sis Advisory Comittee on Reactor Safeguards

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'FROM:

G. G. Zech, Technical Assistant C..

Technical Support Branch, NRR jj

SUBJECT:

STAFF RESPONSE TO ACRS COMENTS ON ~HE RCP TRIP AND HPI TERMINATION CRITERIA

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By letter dated July 16, 1980, from M. S. Plesset to J. F. Ahearne, the

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ACRS fomarded comments regarding the present reactor coolant pump e~"

(RCP) trip and high ' pressure injection (HPI) termination criteria. With

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respect to this letter, the staff is in agreement with the comments

!! =f-expressed by the ACRS with the exception of the two items addressed below.

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With respect to RCP trip requirements, the letter states, "We believe

'~5:I:1 that reactor coolant pump trip upon primary depressurization is an E" i acceptable procedure, but we see no urgency at this time for installation

+I H of automatic pump trip."

In its evaluation of the need for tripping the

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RCPs during.a LOCA situation (NUREG-0623), the staff recommended that automatic RCP trip'should be installed and operational by December 31, 1981.

This recommendation was modified in the May 1980 version of the E.

TMI Action Plan (NUREG-0660) to provide for continued study of criteria

'"H for early RCP trip.

Implementation of automatic circuitry i.o perfonn

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this function will be delayed pending the results of LOFT Test L3-6.

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As part of the continued study, all holders of approved ECC models have j~'

been renuested to analyze LOFT Test L3-6, presently scheduled to

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be conducted prior to the end of this calendar year. The capability of the industry models to correctly predict the experimental behavior of this test wi11 have a strong input on the staff's determination of when and how the RCPs should be tripped. The present schedule calls for completion of the study by, February 15, 1981; submission of proposed design modifications (if required) by July 1,1981; and implementation of modifications (if

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required) by March 1,1981.

m With respect to the adequacy of the HPI termination criteria, we agree that

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the~ procedural requirements are intended to prevent-a recurrence of the TMI-2

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situation; however, it should be noted that subsequent to the referenced North Anna 1 event of September 26,.1979, these procedt.<al requirements EOs were tempered by reconsideration of the need to maintain HPI flow for 20 minutes, rf

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This change recognized the wisdom of allowing the properly trained operator some flexibility in terminating HPI flow once suitable subcooling margin became

~i evident. Also, I&E Bulletin.30-18 has been recently issued pertaining to the referenced Westinghouse 10'CFR 50.55(e) deficiency report. Responses to this Bulletin will be reviewed to determine the need for further procedural modifications on ECCS operation.

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G. Zech, T. hnical Assistant i

Technical Support Branch a

Office of Nuclaar Reactor Regulation

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, D, UNITED STATES NUCLEAR REGULATORY COMMISSION g

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WASMGTON D. C. 20555

,O July 16,1980 Honorable John F. Ahearne Chai man

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U. S. Nuclear Regulatory Commission Washington, D.C.

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SUBJECT:

ADDITIONAL ACRS COMMENTS ON THE RCP TRIP AND H?I *ERMINATION CRITERIA

Dear Dr. Ahearne:

In your letter of April 1,1980, ycu requested that we clarify cur concerns with the present reactor coolan: pump (RC?) trip and the high pressure injection (HPI) termination criterion.

Ycu also indicated in a memorancum to P.

Fraley on February 22, 1980 :nat you would wele:me cur cements on NUREG-0623, " Generic Assessment of Delayed Reactor Coolant Pump Trip During Small Break Loss-of-Coolant Accidents in Pressurized Wa er Reactors."

Tqe present requirements for RCP tri: and HP! termination have deveicoed from the lessons learned frem the Three Mile Island accident and from the extensive number of small break LOCA calculations su:sequently carried cut.

Tnere are twc distinct requirements in the I3E Sulle: ins issued, as referenced belew, wnich can be cens1dered separately.

The first concerns the directive wnich recuires promot shutdown of all reactor c clant pumps in PWRs follcwig a cecressurization transient which initiates safety injection.

The second is the requirement that the safety injection system continue to be o:erated until a soecified degree of subecoling is attainec in the primary system.

The :remp: reactor coolant pum: tri: mandated by the Bulletins followec analyses by the vendors of nuclear steam sue:ly systems which seemed :: show

-hat there was a "windcw" of break si:es anc ;:um: trip delay times which woujd lead to calculated peak. cladding temperatures in excess of the 2200 ?

Iicensing limit.

Tnese same metneds of analysis indicated that with prgpt

um ~ tric. the peak cladding temoeratures would remain below 2200 F.

Tne HRC Staff prepared a useful critique in NUREG-0623 cf these vendor calcu-

• ations and, _ wnile this reper clearly presented the deficiencies in the analytical metneds used, tne report agreec witn :ne vendors' conclusions.

The sn:r.-:erm action by the Staff tnerefere was ne requirement of prompt tri: of

ne reac:cr coolant pumps; as a long-term action :he Staff rec mmended Sna:

li:ensees rescse anc submit design cnanges na sill assure aute.:atic tri: of al* reac:Or coelan: pum:s.

We ce not, a: this time, disagree er:f re?7 w -h

.he Staff's requiremen of

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ne analytical limi:stions u:en wr, en : remet :ri: is based we believe tha:

ne em:hasis on immediacy c#

he tr :' anc n eventual aut:mati: tri Tay nc

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Recen: experMen-a cata' qas :u: deu : On the axis ence c# :ne "wincew' which is the : asis l$ 3031 a

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.Honora'ble John F. Ahearre July'16,1980 for requiring prompt pump trip.

Additional experimental data will become available befote-the end of the year.

The prompt trip has been carried i

out in four transients since the Sulletins have appeared.

In none of these t

was there a.:LOCA in' the primary system; all of these transients arose from disturbances. on' the secondary side.

No significant plant damage ensued in these transients. and there was no harm to plant personnel or to the public.

There has been complaint, however, tha: without reactor c clant pump flow the operator loses reactor pressurizer centrol since, in 'many PWRs, pressurizer

spray flow depends on coolant pumo flow.

Further, natural circulation must also be established to remove decay heat.

It must be said that the Staff's hope to develop a clear distinction between depressurization from a. small break on the primary side and depressurization from a sec ndary side transient seems quite optimistic.

We believe that reactor coolant pump trip upon rimary depressurization is an acceotable procedure, but we see no urgency a: this time for installation of automatic pump trip.

With regard to primary pressure control, we believe that it is desirable to provide pressurizer spray flow which is independent of main coolant pump flow.

The present set of requirements for HPI termination criteria is based upon achieving a specified degree of subcooling in the primary coolant system along with, in some cases, a specified water level in the pressurizer and steam - generators.

These requirements are intended to prevent a recurrence of the TMI-2 situation in which HPI ficw was terminated while still necessary; these requirements, however, do not accress the conditions in whicn HPI should ba terfainated when not required.

We are concerned that relatively frecuent system transients which activate HPI might progress to liquid disenarge through safety val ces or PORVs, valve failure under liquid flow, and a resultant small break LCCA.

It should also be pointed out that Westinghouse I

has recently reported a.significant ceficiency under 10 CFR 50.55(e) for a number of reactors with high head centrifugal charging / safety injection

umes.

Failure to -step these pum:s promptly when high pressures are reached could result in pump failure from icw flow - a common mode failure of the l

redundant HPI pumps.

Changes in ocerational procedures may also affect the des 4gn limits of Other : mponents.

These interactions need to :e carefully i

revi ewed.

We note that a numoer of plant transients that have Occurred in the pas ' year have been affected by the NRC approved HPI termination and RCP tri: criteria.

These include l events, as referenced belcw, a: 'icrth Anna, Unit 1, Sec: ember 25, 1979; Prairie Island, -Unit 1,.00:::er 2,1979; and ANO, Uni: 2, January 29.. 1980.- Some changes have been made in criteria in res:ense c tnese events.

We believe that aantinuec Staff attenti:n in this area is recuired.

Sincerely,

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,j hencrable John

- *hearne 3-July 18,1980 4

Referenc' l.

U.S. Nuclear Regulatory' Commission Office of Inspection and Enforcement, "I&E Sulletin 79-05A," April 5, 1979.

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U.S.- Nuclear Regulatory Commission, Office of Inspection and Enforcement, "I&E Bullctin 79-06A," April 14, 1979.

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U.S. Nuclear Regulatory Commission, Office of Inspection and Enforcement, "I&E Bulletin 79-063," April 14,1979.

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U. S. Nuclear Regulatory Commiss';on, Office of Inspection and Enforcement,

"I&E Sulletin 79-05C and 79-06C,* acly 26, 1979.

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NUREG-0623, " Generic Assessment of Deiayed Reactor Coolant Pump Trip During Small Break Less-of-Coolant Accidents in Pressurized Water Reactors," November 1979.

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5.

Letter, C. M. Stallings, VEPCO, to J. P. O'Reilly, NRC, Submitting Licensee Event Report for Septemoer 25, 1979 North Anna Number 1 Cooldown Incident (Oc:ober 9,1979).

7.

Letter, L. O. Mayer, NSP, to J. G. Keppler, NRC, Submitting Licensee Event Report for October 2,1979 Steam Generator Tube Rupture Inci-dent (Oc:cber 16,1979).

'J.S. Nuclear Re tlatory Commission ?reliminary Notification cf Event or 3.

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'Jnusual Occurrence, PNO-IV-80-05, January 30, 1980.

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Letter, D. C. Trimble, AP&L, to R. W. Reid, NRC, Submitting Startup Report, S 'olemen: 2 for ANO<"-i* 2, Maren 6, 1980.

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