Revision of the ORE assessment for the Port-Interfacing Systems Garching – 25th April 2006 Comment...

Revision of the ORE assessment for the Port-Interfacing Systems Garching – 25th April 2006

Comment on the main received Comment on the main received commentscomments

EFDA Task TW4 TSS SEA2.1 AEFDA Task TW4 TSS SEA2.1 A

Revision of the ORE assessment for the Port-Interfacing Revision of the ORE assessment for the Port-Interfacing systems (WBS 5.0)systems (WBS 5.0)

M. T. Porfiri, A. NatalizioM. T. Porfiri, A. Natalizio

EFDA Garching 25 April 2006EFDA Garching 25 April 2006

ENTE PER LE NUOVE TECNOLOGIE, L'ENERGIA E L'AMBIENTEAssociazione ENEA-EURATOM sulla Fusione

FUSION UNIT


Comments received

1. ITER (Design Integration - S. Chiocchio)2. ITER (Diagnostics - C. Walker)3. ITER (ECRH team – G. Saibene)4. ITER (Remote handling - A. Tesini)5. EFDA (Safety - V. Massaut)


Comment: Some of the conclusions in the summary are based onthe assumption that we consider the replacement of single window on the plug installed in the port. As far as I know this is not a requirement.If this requirement still exist in some of our document we need to remove it, because, beside the larger dose:1) in many design options there is no isolation valve inside thewindow; 2) the total unavailability time of the machine would be longer then maintaining the window in the hot cell.3) it would be very difficult to carry this operation inside theconnecting duct.Answer: in the report this choice is described together with the option of in situ replacement to have the comparison

Design Integration team comments (1)


Comment: For the electron cyclotron plug we considered a different scenario:

in case of a failure of one window (not compromising the integrity of the vacuum boundary) the transmission line would be blocked (insulation valve closed and gyrotron shut off) and the operation of the system would be continued at reduced performance until the next scheduled maintenance.

Answer: the isolation of the single failed window is foreseen in the description of ECRH maintenance

Design integration team comments (2)


Comment: The window and whole plug replacement dose uptake may be the same. However, full plug removal estimate should be repeated to accurately reflect plug lip seal cutting, cask operations time, time spent inside the Hot Cell. The time required for taking the plug to the HC and back may be so long that the project may decide to do repair work in situ.

Answer: the most controversial argument in this report.Discussion is still open. The evaluation of the two different scenarios with the complete and correct estimation of the ORE and, at the same time, of the availability evaluation of the machine can give us a correct picture.

Remote handling team comments (1)


Comment: The in-situ vs. plug-to the-HC argument may become irrelevant if the assumptions on window replacement frequency are different from the ones assumed in the study

Answer: after the maintenance procedure discussion and failure rate acceptance this point must be clarified. It is not possible to skip a priori



Comment: “It is clear from this study that even removing a single window, in-situ, has a higher worker dose burden than replacing the entire launcher. Moreover, on average, it may be necessary to remove several windows, before it is possible to access the failed window. In such situations the worker dose would be even higher. Therefore, it can be concluded that, from a worker dose perspective, when a primary window has failed, the entire launcher should be removed and the window replaced inside the hot cell.” This is correct in principle; however the dose uptake alone should not be used to conclude that the whole plug would be better moved to the HC for windows replacement (unless the window is broken and leaking) due to the complexities of dealing with the plug using RH.

Answer: the comparison between the two practices helps in the decision.



Comment: The TBM replacement dose uptake should also take into account the hands-on work which takes place in the green zones of the HC. This is still the reference, with men standing behind the TBM plug, while docked to the HC wall. However, it has recently been suggested that the TBM would better be worked on by putting the entire TBM plug inside the HC red zone, thus removing the issue of workers’ dose (in this phase at least)

Answer: It can be taken into account in the future. The preparation of the zone for the cask access remain for the RH will remain in place.



Safety team comments (1)General comments:-in general this report is very extended and comprehensive, and should allow to improve the various input data (work effort, persons involved, time, dose rate) through easy access to the different sets of data;-nevertheless, the wording should be used with prudence, as such a document can be referenced for safety analysis and licensing;- at different places it seems to be mentioned that the ALARA process has little significance or low importance, although it is its application to the specific topic which could be taken with care; not the principle in itself.Answer: it should be clear that not the ALARA principle has littlesignificance, but it is when there is the lack of detailed information


Safety team comments (2)

Comment: page 5, last par. “while ALARA optimization has little significance, in the context of such early estimates“ : I am not sure that even at this level the ALARA optimisation should have little significance ! It is at pre-design levels for instance that big savings in dose commitments can be gained (e.g. by reducing the number of equipments, etc.)Answer: As said before the lack of details implies that the approachcould be accepted but the ORE values are not absolute. Theyare only indication that, in the specific case, the dose exists and must be accounted for. What is important is the relative value,because the approach is similar for all the systems.



Comment: - The dose rate used in 2.3.2. when the bio-shield blocks are in place, is it based on a typical attenuation factor from the bio-shield (incl. its thickness) ?

Answer: “With the bio-shield blocks in place we used a dose rate of 5 Sv/h for work performed inside the port cell. Clearly, these are notional values……”The criteria adopted when the dose rate is not reported in the “Nuclear data analysis”, is to have a dose rate higher than in

the gallery (1 Sv/h – design value), and lower than in the port

interspace. If better values exist we can implement them.



Comment: - - Page 16, first 2 lines: “Moreover, we have not taken into account contributions from radiation fields produced by activated or contaminated equipment located inside these spaces.”. It should be good to define them, at least in a next step, and e.g. for ONE typical example, to see if this has a significant influence or not (sort of sensitivity analysis). Even if the dose rate is only very roughly known. The effects of ACP should also be taken into account in this (future) analysis.

Answer: Good suggestion…. for the future, it should be clear!



Comment: - On page 21, par.3.2., an indicative estimate is probably good, but with which degree of conservatism ? “The quantity of design and maintenance information available for the electron cyclotron heating and current drive system has not improved significantly from the time the last detailed assessment was performed in 2002 [SAN02]. The most significant changes in the design are: 1) the elimination of one of the four upper launchers, and 2) the elimination of the cryostat port cover. Although the level of information is insufficient to produce a credible estimate, a detailed, systematic approach has been used, in the current study, which should provide, at the very least, a good indicative estimate.”Answer: It is hard to evaluate the degree of conservatism, but an attempt can be made.



Comment: - For NBI (Appendix C, pages 126 and 127) are the gamma dose rate indicated on the figures not coming only from the activated components in the NBI launcher, and not taking into account the gamma dose rate coming from the Torus ?Answer: In the design took as a reference all the maintenance was in the mezzanine floor. The radiation from the VV was absent


ECRH team comments (1)

Comment: Proposal to extract the entire port plug to replace failed windows, instead of doing it with the port plug in place.This proposal does not consider the very large impact such a measure would have on machine availability and operations. It therefore seems to go against the ALARA principle because it is unreasonable. It also raises questions about the available hot-cell capacity. It could further be remarked that diagnostic design is considering options to be able to replace diagostic components in the port plug without having to extract the entire port plug to be able to ensure less impact on operationsAnswer: As said before the two options must be evaluated and compared to have the better choice



Comment: The design of diagnostic systems is not at all sufficiently advanced to be able to accurately predict what maintenance will be required. The estimates in the report are therefore as good as any that can be made with the limited information available.However, of the 105 separate diagnostic installations a significant number will not require access or maintenance in the port cell. If the estimate for a representative diagnostic installation is appropriate, multiplying it by 105 will be an overestimation

Answer: If the number of the diagnostics not requiring maintenance is known, it is possible to scale the work effort and the consequent dose.



Comment: The new reference design data are often recalled in the comments (number of ECRH ports, radiation field in the upper port and so on).

Answer: The design options and parameter referred to the last reference release are not included in the report because wehad them (November 2006) when the work was almost completed (January 2006).



Comment: we foresee in-situ replacement

Answer: Summary of Estimated Work Effort for Window Replacement

The calculation is performed for in situ replacement condition. The isolation valve of a single line helps in the operation at a reducedpower, but the maintenance can be foreseen if this type of operation is not satisfactorily.

Step Description

Work Effort Equatorial level

(p-h)

Work Effort Equatorial level

(p-h)

1 Clear Port Cell 392.85 170.45

2 Remove Bio-Shield Block 70.25 70.25

3 Clear Port Interspace 218.30 107.10

4 Remove and Reinstall Primary Window 103.50 103.50

5 Reinstall Port-Interspace Components 249.50 125.50

6 Reinstall Bioshield Blocks 65.85 65.85

7 Reinstall Port-Cell Components 512.85 218.45

Total 1,613.10 861.10



“As the actual maintenance requirements were not well established it was assumed that, those diagnostics requiring Class II maintenance would be maintained once every 4 years. ” Comment: what is Class II? An explanation, or a reference to a document where this is explained would help) Answer: RH class is defined as follows:- Class 1: those components that require scheduled remote maintenance or replacement.- Class 2: those components that do not require scheduled but are likely to require unscheduled or very infrequent remote maintenance.- Class 3: those components not expected to require remote maintenance during the life time of ITER.


ECRH team comments (4) One of the main comments of the ECRH team is relating to the evaluation of the work effort, normally considered too high.To discuss better this topic the evalution of the elementary works it is fundamental.Work-Effort Estimates for Launcher Replacement Minor Activity 1.2.1 (Remove Section of Vacuum Pump Line 1) is here reported.

ELEMENTARY ACTIVITY NOTES WE (p-h)

make visual inspection 0.25

set-up work platform to proper height above head level 4.00

set-up temporary supports for PVL1 1.00

transport tools to work location by trolley 0.20

make first cut small pipe <5 cm dia. 1.50

make second cut small pipe <5 cm dia. 1.50

transport section of line to temporary storage by trolley 0.20

transport tools back to tool room 0.00

remove temporary supports 1.00

remove work platform 0.00

TOTAL 9.65

Revision of the ORE assessment for the Port-Interfacing Systems Garching – 25th April 2006 Comment...

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