 aMEC SURGED up the top-tier index yesterday after investors were told that nuclear energy still "remains an area of significant potential" for the engineer, despite the ongoing events in Japan.  Rising as high as 1,151p during the session, the group - whose nuclear services division contributed nearly 10 per cent of sales last year - eventually closed 17p ahead at 1,128p, halting a seven-day losing streak in which it shed nearly 10 per cent of its share price. Helping it upwards was Investec's decision to initiate coverage with a "buy" rating, describing amec as "undervalued and well positioned for growth".  "Our focus is on the strong balance sheet," said the broker's analysts. "The pace of acquisitions appears to be increasing and the pipeline has strengthened, a situation we believe will continue."  although admitting the tragedy in Japan "will once again highlight the risks associated with nuclear and may slow developments both in the UK and other geographies", they added that nuclear still "offers material potential" and argued that it does not have a feasible alternative in this country.  They also noted that "concerns over nuclear could also improve the opportunities in the renewables and bioprocess arena, another strong growth area [for amec], with the accessible market estimated by management to be growing at 8 to 10 per cent per annum."  The broker examined two other oil services groups as well, but only gave Hunting - which increased 15.5p to 751.5p - and Wood Group - 14p better off at 633p - "hold" ratings because of their current valuation.  Overall, the FTSE 100 climbed 22.02 points to 5,718.13, maintaining its recovery from its recent bad run, although at the bell it was still 110.54 points lower than at the start of the week. Sentiment was helped by the Libyan government's decision to call a ceasefire, which halted the rise of oil prices, and the decision by G7 finance ministers to help steady the yen.  National Grid took the top spot, powering up 24.5p to 577p despite market voices disagreeing on Ofgem's report on the regulatory body's new price review regime. angelos anastasiou, an analyst at Investec, said it "confirmed a number of the negatives previously indicated", and kept the utility group's "sell" rating.  However, Killik's head of equities Jonathan Jackson described it as good news for both National Grid and Scottish &amp; Southern Energy, which increased 29p to 1,234p, and said the report was "more positive than the consultation document published at the end of last year".  ON THE FTSE 250, Jupiter Fund Management slid to the bottom of the index, slipping 20.3p to 298p after the release of its final results. The group's revenue failed to meet expectations, despite growing over 25 per cent last year, and the numbers failed to move Peel Hunt's Stuart Duncan from his "hold" recommendation, with the analyst citing its "premium valuation".  also updating the market was Berkeley, which was lifted 36p to 1,040p following its interim management statement, helped by its positive comments on its full-year earnings.  None of the other housebuilders looked as strong, however, as the Council of Mortgage Lenders' latest figures showed lending last month had failed to see a significant increase. Barratt Developments crept back 0.6p to 102.8p and Bovis Homes stayed steady at 442.5p, despite Deutsche Bank choosing them among its top picks in the sector in which it sees "over 25 per cent upside ... even without a housing market recovery".  Go-ahead was driven up 55p to 1,384p after the transport group said that, together with the French company Keolis, it would continue to run the Southeastern rail franchise until March 2014.  Meanwhile, SDL edged back 0.5p to 669p despite Jefferies International taking a positive first look at the software group. The broker's analysts clearly liked what they saw as they gave it a "buy" rating and told investors to "expect consolidation to continue" in the sector. Saying it was "now a market- leading player in its area of specialism within the wider Enterprise Content Management space", they added that they expected to "increasingly see SDL as an attractively placed sector asset".  THERE WaS a spurt of 38.25p to 161.75p for Gulf Keystone on the alternative Investment Market after the oil exploer issued a statement that "substantial smoke and/or the oil flare" could be seen coming from its Shaikan-2 well in Kurdistan, indicating "that a significant flow has been encountered".  Meanwhile, assetCo - which runs London's fire engines - announced that des 