ML17320A974

Forwards First Round Questions on Exxon Methodology Rept for PTSPWR2.Rept Lacks Specific Details Re Biases in Initial Conditions & Boundary Conditions

ML17320A974
Person / Time
Site:	Cook, 05000000
Issue date:	03/05/1984
From:	Abramson P, Wei T ARGONNE NATIONAL LABORATORY
To:	Guttmann J Office of Nuclear Reactor Regulation
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ML17320A970	List: ML17320A971 ML17320A972 ML17320A973 ML17320A974
References
CON-FIN-A-2311 NUDOCS 8404040326
Download: ML17320A974 (9)

Text

A'RCONNE NATIONAL ABQRATORY 9700 Scvr4 Ass AvENUE,ARcp~ liNois 60439 Q~~ 312972- 4868 March 5, 1984 Mr. Jack Guttmann Reactor Systems Branch Division of Systems Integration Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555

Subject:

FIN A2311 Task I Exxon PTSPWR2 Code Review

Dear Mr. Guttmann:

We have completed the review of the recent draft of the reissue of the Exxon methddology report, XN-74-5(P) Rev. 2, Suppl. 2, which Exxon intends to use as documentation of its conservative usage of .the Chapter 15 transient analysis code PTSPWR2. This draft has not altered our conclusions conveyed to you in the letter of January 25, 1984, summarizing the review of the original report. The report is still too general for an evaluation of the conserva-ti sms Exxon claims to employ through appropriate usage of the input to guaran-tee conservative results. It lacks specific details regarding biases in initial conditions, boundary conditions and those internal parameters which have to be input for each class of transients.

We have prepared a list of questions and comments on the section in the report (Section 4.0) which describes the evaluation of specific transients.

This may be of help to Exxon in preparing a document which involves more specifics rather than generalities.

If, you or your colleagues have any questions regarding this review, please contact us.

Yours sincer T. Y. C.

Li 9 ht Water' eactor y stems Anal y si s Reactor Analysis and Safety Division 8404040326 8403ih PDR, ADQCK ." 050003l6 Abramson, Manage PDR P Light Water Reactor Systems Analysis Reactor Analysis and Safety Division PBA:TYCW:kr Enclosure U S. DEwlnuExT of ExERQ, T4< Lhi~msiTv of C4icaco 4 R(QXXE Uhih EA(iTIFC ANACiATIAX

Mr. J. Guttmann March 5, 1984 cc: R. Mattson, Director, Division of Systems Integration, NRC/NRR B. Sheron, Chief, Reactor Systems Branch, NRC/NRR R. W. Houston, Assistant Director for Reactor Safety, NRC/NRR S. M. Boyd, NRC/NRR J. Carter, NRC/NRR B. L. Grenier, NRC/NRR W. Jensen, NRC/NRR N. Lauben, NRC/NRR L. W. Deitrich, RAS R. Avery, RAS LWR Systems Analysis Section RAS Files: 8M627, A15

First Round Ouestions: Exxon Methodolo Re ort for PTSPWR2, XN-74-5(P), Rev. 2, -Su . 2 1;0 $ 4.1.1 Feedwater Malfunctions Leadin to Increased Heat Removal and Excess Load Transients "Conservatism in the ENC analyses is assessed on the basis that PTSPWR2 is conservative relative to the FSAR with respect to primary side cooldown. Where this is not possible, due to .lack of FSAR information, the PTSPWR2 power increases are compared to FSAR power increases." This is the only place where conserva-ti sms are mentioned and its only implication is that Exxon is justifying the results on the basis of comparison to prior vendor FSAR analysis. Contrary to the stated purpose of this report the

'onservatisms in the methodology are not mentioned at all. What is required is information regarding the Exxon specific conservatisms used in the Exxon specific methodology to obtain conservative results with the Exxon Code PTSPWR2.

(a) What conservatisms in the methodology are used? List the specific biases in:

Initial Boundary Conditions Conditions Internal Parameters Power Spray Heat Transfer Coefficients Pressure Pumps Pressurizer Constants Temperature Reactivity Coefficients Level Flow Setpoints This list is not entirely comprehensive and is provided for illustrative purposes.

(b) If Exxon methodology is to replicate vendor methodology as described in the FSARs then Exxon should list vendor assump-tions, ascertain comprehensiveness and justify the 1

applicability of vendor assumptions to the Exxon models in PTSPWR2.

2.0 $ 4.1.2 Secondar Safet or Relief Yalve 0 enin'mall Steam Line Break)

"Conservatism of the PTSPWR2 analysis is verified by comparing the ENC calculated cooldown against FSAR results for comparable conditions."

Same comment/question as in 1.0.

3.0 $ 4.1.3 Lar e Steam Line Breaks (a) "In view of these factors, it is important to establish acceptability of the FSAR analysis prior to making compari-sons of PTSPWR2 results for system response to the FSAR results."

Does Exxon intend to use prior FSAR results for justifying the conservatisms in its analysis7 If so, they will need to demonstrate a comprehensive understanding of the limitations of the FSAR analysis itself.

(b) "The basis for conservatism has been to compare PTSPWR2 results for core power, pressure and temperature to FSAR results for comparable conditions."

What are the conservatisms used in, the methodology to gen-erate these PTSPWR2 results? I

4.0 $ 4.2.1 Loss of External Load, Turbine Tri, Loss of Condenser Vacuum and Steam Pressure Re ulator Failure Events (a) "and other applicable conservatisms detailed in Tables 3.3 and 3.4."

What are these other applicable conservatisms? Tables 3.3 and 3.4 are so general, cover both heatups and cooldowns, and do not give details.

(b) "ENC uses an isentropic pressurizer model (Reference 1) in PTSPWR2 to conservatively bound pressurizer pressure re-sponse to the primary coolant expansion that characterizes this event."

How does Exxon select its input data to make an isentropic model of the non equilibrium pressurizer model described in the reference? This is an example of internal model para-meters which have to be selected by input. Another example is the initial core heat transfer coefficient. Exxon should make a list of these internal parameters and indicate how values are chosen for each class of transients.

5.0 g4.2.3 Loss of Normal Feedwater "PTSPWR2 has been applied to examine or confirm the short term

( 1-2 min.) consequences of the loss of normal feedwater flow event."

The conservatisms have not been specified at all. This section only confirms that PTSPWR2 is used for this event. Same question as (1.0).

e 6.0 g4.2.4 Feedwater Pi e Break How is Exxon going to address the overpressure consequences of the feedwater line break?

7.0 $ 4.3.1 Flow Coastdown "The flow coastdown is developed to be consistent with the FSAR or applicable plant coastdown data."

Same question as (1.0).

8.0 g4.3.2 Seized Pum Rotor "along with conservative FSAR trip delays and trip uncertainties as detailed in Table 3.3."

This is too general. Same comment(question as in (1.0) and (4.0a).

9.0 $ 4.4.1 Uncontrolled Control Rod Bank Withdrawal from a Subcritical or Low Power Condition "Conservatism in PTSPWR2 analyses is assured by using conserva-tively low doppler feedback and conservative scram characteris-ties AN What does conservatively low mean? Same question as in (1.0).

e 10.0 g4.4.2 Uncontrolled Control Rod Bank Withdrawal at Power (a) "To ensure conservatism in the PTSPWR2 analyses, it is important to avoid overestimating primary to secondary heat transfer since this would lead to larger hot-to-cold leg temperature differences, high sensed AT power and premature reactor trip."

How is the overestimate avoided? Same comment/questi.on as in (1.0).

(b) "It is also important not to underestimate transport and instrumentation delays."

How are the input biases selected?

11.0 g4.4.3 Control Rod Miso eration "A conservatively bounding large EOC negative moderator temper-ature coefficient is used to not underestimate the maximum return to power."

What other. biases are applied? Same comment/question as (1.0).

12.0 $ 4.6.1 Inadvertent 0 enin of a Pressurizer Relief or Safet Valve "Pressurizer inventory is maximized to give the highest rate of depressurization."

What about the other initial conditions? Same question as (1-0).

13.0 g4.6.2 Steam Generator Tube Ru ture Event "Adverse consequences of this event do not generally threaten DNB =because of reactor scram on either the low pressurizer pressure trip or the thermal margin trip."

This event is considered for reasons of dose rate consequen-ces. I f PTSP WR2 is used for thi s event, what bi ases are appl i ed to maximize the releases?

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