ML19327A663

Discusses View on Purging Re Plant Containment Isolation Valves

ML19327A663
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	08/11/1989
From:	Thadani A Office of Nuclear Reactor Regulation
To:	Miraglia F Office of Nuclear Reactor Regulation
Shared Package
ML19327A642	List: ML19327A641 ML19327A643 ML19327A644 ML19327A647 ML19327A651 ML19327A652 ML19327A656 ML19327A657 ML19327A658 ML19327A660 ML19327A661 ML19327A662 ML19327A663 ML19327A664 ML19327A665 ML19327A666 ML19327A667 ML19327A668 ML19327A669 ML19327A670 ML19327A671 ML19327A672 ML19327A673 ML19327A693 ML19327B570 ML19327B588 ML19327B595 ML19327B596 ML19327B598 ML19327B599
References
TAC-73427, NUDOCS 8909140124
Download: ML19327A663 (2)

Text

L i

g f

. c (,

• p ucy

),% V, a l, O l *' E Q a

• g UNITED sT ATss

[

g n

NUCLEAR REGULATORY COMMISSION /Issc d.t 5 A " M g f'

\\}v ;)

h*

YU' R.e} 4 l'

n, n fl0TE T0: Frank J. Miraglia, Associate D re tor for Inspection and Technical Assessment NRR FROM:

Ashok Thadani, Director Division of Systems Technology, NRR l

SUBJECT:

DPV CONCERNING CONTAINMENT ISOLAION VALVES AT ZION l

In your note to me dated July 27, 1969 regarding the above subject you asked i

for infonnation regarding the technical rationale for time to fuel damage from the onset of a LOCA in tie Appendex K analysis. Specifically: (1)the l

temperature and pressure effects experienced by fuel early in a LOCA eventi and, (2) why entry into DNBR does not result in fuel failure. Wayne Hodges' note to me.datee August 10,1989, (Enclosure 1) addressed these issues.

l t

With regard to (1) above, analysis indicates that there is potential for fuel pin rupture during the LOCA blowdown ( 7 seconds) for very high power pins.

However, for fuel pin powers that exist for current designs no blowdown rupture is predicted. Thus, fuel pin rupture during blowdown is not a problem for existing designs but should be checked for future designs.

i With regard to (2) above, the main contributors to " fuel cladding rupture" are f

While high pressure across cladding and high clac' ding) temperature.significantly reduces j

entry into departure from nucleate boiling (DNB the heat transfer resulting in rapid cladding temperature rise, the heat transfer is not zero and the temperature rise is not instantaneous. Thus, it is not physically possible for the cladding to instantaneously rupture upon entry into DNBR because of LOCA conditions. Experimental data confirms this conclusion.

I The fuel criteria described in Chapter 4 of the Standard Review Plan SRP) l could be interpreted to apply to LOCA analyses,in the absense of staf I

practice. However, staff practice has never to our knowledge been to assume fuel failure upon inception of DNB for LOCA analyses. Perhaps, the SRP i

should be revised to more clearly describe staff practice, but I do not believe the effort to be worth the cost in staff resources.

Based upon these analyses and discussions with several staff experts, I do not believe that rupture of high burnup fuel pins during the blowdown transient to be credible for existing fuel designs. However, it is appropriate to verify that blowdown rupture does not occur for future designs.

j You also requested cossnents regarding the applicability of Reg Guides, SRP's and BTP's cited in the reviews of the Zion amendment. Jack Kudrick, SPLB, and

}

Ted Quay, PD31, looked into this (See Enclosures 2 and 3, respectively).

t 0

i l

2 Regarding Reg Guides, SRP"s and BTP's cited in the subject DPV, the major reference within the DPV is BTP CSB 6-4 This BTP is referenced in SRP Section 6.2.4, Containment Isolation Section. The focus of the DPV only adcresses the BTP, however, to present a complete picture of the staff's position SRP 6.2.4 and how BTP CSB 6-4 is referenced need be considered. In particular SRP 6.2.4 states that for lines which provide an open path from the containment to the environs eg., the containment purge and vent lines, l

isolation valve closure times "on the order of" 5 seconds or less may be necessary. Note that the intent must be taken as a goal but does not preclude closure times greater than 5 seconds, j

Subsection n of SRP 6.2.4 is relevant to the DPV regarding dose analysis.

Subsection n states:

(

...regarding the size of the purge system used during nonnal plant operation and the justification by acceptable dose consequence analysis, may be waived if the ap>11 cant consnits to limit the use of the purge system to less than 90 tours per year while the plant is in the startup, power, hot standby and hot shutdown modes of operations."

, provides discussion on Reg Guides and the SRP regarding the subject DPV's contentions on the release of fission products to the l

containment and subsequently to the environment through open purge valves.

The bottom line of this discussion is that although the staff has used the l

• instantaneous" source term in accidents such as LOCA, its use was to ensure that containment isolation features incorporated either fast acting valves i

or features that would ensure containment integrity was not compromised during operation (e.g., dual doors on personnel locks). This simplified approach was never intended to be applied to purge valves except for those valves that were i

extremely slow closing (e.g., 2 minutes). No opening in containment during operations could be justified using the simplified instantaneous source term assumption. Specifically, no purge / vent system design could be found acceptable and without such systems, plant operations would be extremely restricted. Although the SRP specifies 5 seconds, the staff acce)ted closure times up to 15 seconds based on informal discussions we had with lesearch on their severe accident analyses. We were told that even for closure times up to 2D seconds that no substantial releases would occur.

The above discussion more properly reflects the staff view on purging. It does not indicate that the staff curing the development of the S P believed that the consequences of purging at the time cf a LOCA would result in the impact asserted in the DPV.

W

<W Asht k Thadani, Director Div'sion of Systems Technology

Enclosures:

1.

Note from W. dodges on DPY, dated August 10, 1989 2.

Note from J. Kudrick on DPV, d w ed August 8, 1989 3.

Note from T. Quay on DPV, dated August 10, 1989

-.- -.