ML20098H172

Provides Replies & Comments to Util Re Tech Spec Limiting Condition for Operation 4.1.9 in Advance of 840823 Meeting W/Util in Arlington,Tx

ML20098H172
Person / Time
Site:	Fort Saint Vrain
Issue date:	08/21/1984
From:	Ball S OAK RIDGE NATIONAL LABORATORY
To:	Wagner P NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION IV)
Shared Package
ML20098H170	List: ML20098H172
References
TAC-52634, NUDOCS 8409120069
Download: ML20098H172 (2)

Text

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OAK RIDGE NATIONAL LABORATORY post omcE sox v CAN RIDGE. TENNESSEE 37831 orERaTEo av wmN MNETTA ENER0v SYSTEMS. NC.

August 21, 1984 Mr. Philip Wagner, Project Manager U. S. Nuclear Regulatory Commission Region IV 611 Ryan Plaza Drive, Suite 1000 Arlington, Texas 70611 Doar Mr. Wagner:  ;

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Subject:

Initial Response to PSC Letter on LCO 4.1.9 (P-84223, dated j August 14, 1984)

I expect that a lot of the questions and differences between the ORNL and PSC views can be resolved at the August 23 meeting at Region IV in Arlingtoni however, I thought it might be useful to write down my replies and comments in advance. The itam numbers correspond to those in the attachment to P-84223.

1. Our understanding of LCO 4.1.9 is that it limits the core conditions such that the region outlet thermocouples can be relied upon i to give an adequate astimate of maximum core temperatures. If any region flows were stagnated or reversed, the outlet temperature measurements l would not be able to indicate the status of the region fuel temperaturac.

The name of the LCO implies that it provides operating restrictions to limit " core temperatura rise", which is misleading. ORNL comments about "nonconservative-features" are covered in item 3.

2. Our comment that the current approach is " overly conservative" stems from the fact that, according to our calculations with the ORECA code, region flow stagnation is almost impossible to achieve under normal operating conditions. Hence the extra restrictions put on the operation by LCO 4.1.9 appear to be unnecessary. From a safety standpoint, we sculd have no complaints about the current LCO.

It is also our impression that the proposed ORNL scheme would be easier to implement (which is PSC's problem) and enforce (which is NRC's problem), so we would leave that evaluation to others.

PSC notes th - the current scheme minimizes the number of orifice adjustments required in going from low to high power, and that this is desirable. It appears to us that a scheme such as in ORNL's proposal, which starts out going for equal cutlet temperatures at very low powers, would require simpler, if not fewer, mani pul ati ons. In any case, from our experienca with sticking drives, it would seem beneficial to operate them occasionally to keep them limber.

3. Our comments about non-conservative features cf tne current LCC 4.1.9 had to do wi th the " hole" in LCO 4.1.7 between TK950F and on-scale on Fig. 4.1.7-1. PSC's proposed fix in their item 0 would cura that crablem. Cur other concern was that since P5C's stagnat;cn analysis was 8409120069 840906 PDR ADOCK 05000267 P PDR

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'Mr. Philip' Wagner 2' August 21, 1984 done:for steady-state equilibrium cases only, it doesn't necessarily

. fellow that it-would be conservativ'e for transients, especially those

\ involving rapid power and flow reductions from full power.

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Our subsequent analyses of-representative shutdowns using ORECA have

-indicated that this would not be a problem, however.

4. The=1ow-flow measurement situation will hopefully be clarified at

!the meeting. From what we have observed, however, it is difficult to tell what the "real" low-range flow is. The plant data logger appears to have several estimates,. and PSC's HISTORY code has an elaborate echeme_for estimating it. Sometimes these estimates vary widely, and sometimes.they are all quite different from " heat balance" estimates of the_ flow. We assume that the plant operators use panel readouts of the low-range d/p cells, which should.give them good estimates. However, f .from the data we obtained, these readings don't necessarily make it to L :- :the DAS,lwhich we understand is what PSC uses to determine if they are h approaching or violating a tech spec limit. A good flow estimate is p important in that :it is a primary parameter in both the old and proposed j"

vsrsions of.LCO 4.1.9. Additionally, estimates of core power in the low range are also subject to. considerable % of reading error. We believe

that an:" official" estimate of core-power during shutdowns should include calculated afterheat.

5. In addition to commenting on the relative merits of the proposed approaches, (which we cover above),JPSC states that ORNL's proposed test to' observe. flow redistributions is unacceptable because stagnation would Loccur'long before it could be detected.- This is contrary by an enormous margin.to what our ORECA code calculations indicate, and is a very important point.to pursue. If PSC has observed such behavior on FSV,

-then-the fidelity of ORECA and GAT's RECA code (which generally " agrees" with'ORECA) is in question. These codes have been used extensively in NRC safety evaluations, and if indeed there is such a discrepancy, some verification tests would be advisable.

Yours truly, S. J. Ball, Manager HTGR Safety Studies for NRC

'cc: -J. C. Cleveland R. B. Foulds DAE/RES R. M. Harrington R. Ireland NRC/RIV

'T. S. Kress

A. P. Malinauskas D. L. Moses

-Frank Novachek PSC (3)

G. L. Plumlee,-III NRC/FSV P. M. Williams -NRC/NRR

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