ML19253A773
| ML19253A773 | |
| Person / Time | |
|---|---|
| Issue date: | 08/13/1979 |
| From: | Ross D NRC - TMI-2 BULLETINS & ORDERS TASK FORCE |
| To: | Reed C COMMONWEALTH EDISON CO. |
| Shared Package | |
| ML19253A774 | List: |
| References | |
| NUDOCS 7909110226 | |
| Download: ML19253A773 (6) | |
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v AUG13 ISM Mr. Cordell Reed, Chairman Westinghouse Owner's 3roup Commonwealth Edison Company P. O. Box 767 One First National Plaza Chicago, Illinois 60690
Dear Mr. Reed:
SUBJECT:
REQUEST FOR ADDITIONAL INFORMATION REGARDING WCAP-9600 Before the staff can ccmplete its review of the report WCAP-9600, "Small Break Analysis for Westinghouse NSSS Systems," additional information is required. The required information, which is related to Michaelson's concerns, non-condensible heat transfer models, audit calculations, and guidelines for operational procedures is identified in the enclosure.
This information was discussed previously with your representatives at our July 18, 1979 meeting regarding procedures and during our telephone conversation regarding analysis on July 27, 1979.
In order to expedite our review, we request that you furnish the requested infcrmation in a timely manner. Please provide, within seven days of receipt of this letter, your schedule for responding to the information requests contained in the enclosure.
If you have any questions about the contents of this letter, please con-tact Patrick O'Reilly, ;301) 492-7745, the Bulletins & Orders Task Force Project Manager for Westinghouse-designed plants.
Sincerely, N
D. F. Ross, Jr., Director Bulletins & Orders Task Force
Enclosure:
Request for Additional Information Re. WCAP-9600 c.;.
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Enclosure RE0 VEST FOR ADDITIONAL INFORMATION REGARDING WCAP-9600 A.
Michelson's Concerns - (Item numbers in this section correspond to the item numbers.used in Annex 1 to the enclosure to the staff's June 4,1979 letter, D. F. Ross to T. M. Anderson.)
3.
Pressure Boundary Damage The conclusion should show that pressure loadings are less than design basis loadings. A general conclusier, that damage will not occur is not sufficient. Revise your response accordingly.
7.
HPSI/LPSI Pioing/ Operation The response states "for most plants".
Revise your response to provide information for all plants.
B.
Treatment of Non-condensible Gases 1.
Discuss the applicability and application of the Roshenow Correlation.
(In deriving the non-condensible heat transfer mcdeiz. the assumption was made that this correlation predicts the liquid film conduction only.)
This discussion should address the verification of the model, namely, the predictability of the nodel versus the non-condensible gas concen-tration/ prototypic conditions and geometry.
2.
Discuss the introduction of accumulator nitrogen for the case of a small pipe break larger than 2 inches in diameter.
3.
Discuss how the reactor is brought to a cold shutdown condition following a small break LOCA in the primary system in which non-condensible gas accumulates in bends in the steam generator U-tubes.
C.
Audit Calculat' ions 1.
Considering the analysis of a 4.0-inch diameter pipe break in a 4-loop PWR, provide the results of an assessment of the impact on the transient of allowing SI and accumulator injection into the broken loop node upstream of the break. Discuss how the system response would change under the above assumption for the 0.5-inch and 1.0-inch diameter pipe breaks.
2.
For the analysis of a 4.0-inch diameter pipe break in a 4-loop PWR, plots of certain steam generator parameters were provided for the broken loop.
Provide plots of the same parameters for the steam generator in the intact loop.
3.
For the analysis of a 0.5-inch diameter pipe break in a 4-loop PWR, provide results of an assessment of numerical instability of the core volumetric heat rate incut.
Include in this assessment the impact on reactor trip, reactor coolant system pressure, and steam generator water level.
Provide the results of an assessment of the same behavior for the 1.0-inch and 4.0-inch diameter breaks.
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D.
Guidelines for Ocerators 6 0 '" -
1.
We believe that the Westinghouse (W) proposal for termination of high pressure injection (HPI) has merit.
In all likelihood, the pressure criterion (greater than 2000 psig and increasing) and steam generator level criterion would be' particularly useful to the operator. However, we continue to believe that some measure of subcooling is important to the guidelines.
0 For example, hot leg temperature measurements of 586 F or less would provide 50 F subccoling (or more) consistent with the W criterion for 0
pressure. Please reconsider, for completeness, your proposal.
In addition, you should provide (not necessarily in the guidelines) interpretation regarding the time interval over which the increasing trend in pressurizer level or pressure is important.
Annex 1 to this Enclosure is provided for your infomation. Annex 1 is a memorandum documenting the results of a comparison which we made of the two sets of HPI temination criteria.
2.
Identify the conditions under which HPI injection would be terminated for plants which do not have high head (above 1600 psig) safety injection pumps in view of the proposed 2000 psig termination criterion.
3.
Using the Westinghouse HPI temination criteria, HPI flow cannot be terminated unless primary system pressure is above 2000 psig. Under the current guidelines, for small breaks for which the break flow balances the HPI flow at a lower pressure, HPI flow could never be terminated and tre primary system could never be depressurized. Provide procedural guidelines for the long term depressurizaton of the primary system, considering the need for the possible throttling of the HPI injection.
4.
If the operator teminates HPI when conditions pemit, he must also reset reactor trip or the ECCS will not be re-initiated automatically if conditions require it. The operator should be able to rely on automatic actions whenever possible (i.e., the generic guidelines should not place an additional burden on him).
In this regard, revise the guidelines to include instructions for the operator to reinstate the automatic circuitry when conditions require.
5.
On Figure 1: Define the tem " Safeguards" in a footnote to the figure to include the auxiliary feedwater system.
6.
Item 1(a) on page A-2,tates, "If the plant is in a condition for which a reactor trip is warranted and an auto reactor trip has not yet occurred, manually trip the reactor." Revise the guidelines to include clarification about when a manual reactor trip is " warranted" to offer the operator a more definitive course of action.
7.
Item 1 (b) on page A-2 states, "If the plant is in a condition for which safety injection is warranted and an auto safety injection has not yet occurred, manually initiate safety injection." Revise the guidelines to include clarification about when manual safety injection is " warranted" to offer the operator a more definitive course of action.
3.
Page A-5, Item 4, requires the operator to go to the steam line break procedures if the steam line pressure is lower in one steam generator than in the others. Justify that this condition would not also occur for a large break, particularly for one at the pump suction.
Describe how the operator would distinguish a pump suction break from a steam line break.
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9.
Revise Items a) and b) on page A-7 to specify the expected pressure and water level so that the operatory may have a more definitive basis for a course of action.
- 10. On page A-10 " Subsequent Actions" should be re-structured for time considerations. For example, the note on page A-ll instructs the operator to check CST level, yet it is not until page A-14 that the operator is told to trip all reaci'r coolant pumps.
- 11. Clarify the meaning of " unaffected steam generators" on page A-11.
Specify in the guideline how the "affected" steam generator is identified to offer the operator a more definitive course of action.
- 12. Justify the statement that the reactor coolant system pressure will stabilize between 2000 psig and the safety valve pressure if safety injection is reinstated as discussed on page A-12.
13.
Clarify the tenn " standby mode" used in step B on page A-12.
- 14. Discuss the basis for selecting 1250 psig for tripping the reactor coolant pumps.
15.
Item F on page A-13 requires that the operato" maintain a subcooled condition in the primary system during a controlled cooldown. Specify in the guideline how the operator is to determine that the system is sufficiently subcooled.
- 16. Page A-13 indicates that the operator is to stop low head safety injection pumps if RCS pressure is above the shut-off head.
Revise the procedure to incorporate some margin of protection against ECCS damage at the shut-off head in the procedure.
If deadheading is allowed prior to stopping pumps, submit operating data to support continued pump perfonnance.
17.
Item 5 on page A-14 deals with stopping the reactor coolant pumps and cantinuously monitoring the condition for stopping the pumps.
Identi fy in the guideline the conditions for which the pumps would be restarted if the reactor system pressure increases above 1250 psig plus the pressure indication inaccuracy.
18.
Provide the basis for the pressure setting required for the steam generators (200 psig below the safety valve setting) required in the " caution" at the bottom of page A-15.
- 19. On page A-16, provide a reference in the guidelines for the criteria and procedure for adjusting sumo pH.
- 20. On page A-20, Step 2, the " Caution" statement should provide guidance as to the proper course of action if one ECCS pumo is not receiving flow (or a reference to the proper procedure should be added).
21. Page A-21 requires continued cperaticn of the ccntainment spray system for plants which utilize cnly this system for icng-term sump energy removal following a LOCA.
Include criteria in the guideline for eventually tenninating cperatien of this system.
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- 22. On page A-32, Step 2, revise the guideline to reflect the failure conditions being postulated.
- 23. RCS temperature criteria are not specified in the generic emergency procedural guidelines.
Include RCS temperature criteria to offer the operator a more complete basis for a course of action (core exit thennoccuples, for example).
- 24. The generic procedural guidelines for long-tenn depressurization should include the option for the oparator to use the nonnal residual heat removal (RHR) system piping for cooldown from a loss-of-coolant accident (hot leg suction), particularly since some small breaks may not discharge sufficient water to the sump. The guidelines should address such criteria as maximum allowed RHR temperature / pressure and signs of insufficient RHR pump suction.
25.
Some plants have loop isolation valves. Any role which these valves may have regarding operator use for mitigation during a LOCA should be addressed in the guidelines and the recomended action justified.
- 26. Provide results of a detailed analysis of the thermal-mechanical conditions in the pressure vessel.
In particular, address brittle fracture during recovery from small LOCA events with extended loss of feedwater.
Indicate what the vessel beltline response would be in tenns of vessel integrity limits. These results may be provided as a temperature-time history.
Include in the generic guidelines instructions to the operator on the proper course of action and criteria to use to preclude brittle fracture (ncte operators are trained to adhere to tech specs).
- 27. Revise the generic guidelines to provide the following guidance to the ope ntor:
a.
the caution that pressurizer level alone may not be a good indication of primary system inventory.
b.
Appropriate action (or provide a reference) to take if auxiliary feedwater flow cannot be obtained for small breaks.
Appropriate action to take in the event large amounts of non-cendensible c.
gas are released to the primary system.
d.
Instructions on the use of pressurizer heaters during a small break LOCA.
e.
Guidance on the use of alternate channels and indications to confirm specified key parameters.
f.
The proper course of action for leaking steam cenerators if LCCA occurs.
g.
Guidance on the initiation and maintenance of natural circulation and how to recognize a loss of this mode of core cooling under emergency conditier.:
h.
Guidance to the operators regarding the accumulators (i.e., isolation )
during very small break LOCAs.
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28.
Discuss the interaction among the following:
The Westinghouse Owner's Group - Working Group on Procedures a.
b.
The individual utilities, and, The various Westinghouse plant simulators located throughout the c.
- country, d.
The Westinghouse Interdisciplinary Task Force, and, e.
The Westinghouse safety analysts.
29.
If a utility-operator were to take exception to the Westinghouse recomendaticr for emergency operational procedures, would Westinghouse be informed about such exception? Does Westinghouse review typical plant emergency operational procedures to determine whether their recommendations have been incorporated properly? If not, explain why this is not done.
30.
In addition to the Westinghouse ecormiendations for operational procedures regarding Small Break LOCA, we wish to review certain other guidelines for operators.
Provide a schedule for submitting the following Westinghouse recommendations for operational procedures to the staff for review:
a.
Extended Loss of All Feedwater; b.
Steam Generator Tube Leak;
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c.
Natural Circulation; d.
Loss of Secondary Coolant; and, e.
- 31. Page 6.1-2 indicates that plants incorporating different designs for the safety injection and auxiliary feedwater systems will require " adaption" of the generic guidelines to those design differences. Also, this page states that additional generic guidelines are being prepared for 3-loop and 2-loop NSSS designs. Provide more definitive guidance on those particular paragraphs in the generic procedures which must be revised, and by which licensees.
- 32. The generic guidelines are supported analytically by WCAP-9600.
Provide more definitive guidance on the applicability of WCAP-g600 for reference by licensees in the fom of a table of key parameters used as input to these calculations.
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